Programmable Logic Controllers (PLC) & Distributed Control Systems (DCS)

The AD5758 is a single-channel, voltage and current output digital-to-analog converter (DAC) that operates with a power supply range from −33 V (minimum) on AVSS to +33 V (maximum) on AVDD1 with a maximum operating voltage between the two rails of 60 V. On-chip dynamic power control (DPC) minimizes package power dissipation, which is achieved by regulating the supply voltage (V_DPC+) to the VI_OUT output driver circuitry from 5 V to 27 V using a buck dc-to-dc converter, optimized for minimum on-chip power dissipation. The C_HART pin enables a HART^® signal to be coupled onto the current output.

The device uses a versatile 4-wire serial peripheral interface (SPI) that operates at clock rates of up to 50 MHz and is compatible with standard SPI, QSPI^™, MICROWIRE^™, DSP, and microcontroller interface standards. The interface also features an optional SPI cyclic redundancy check (CRC) and a watchdog timer (WDT). The AD5758 offers improved diagnostic features from its predecessors, such as an integrated 12-bit diagnostic analog-to-digital converter (ADC). Additional robustness is provided by the inclusion of a line protector on the VI_OUT, +V_SENSE, and −V_SENSE pins. When used with its companion power management unit (PMU)/isolator (ADP1031), the AD5758 is capable of enabling customers to develop an eight channel to channel isolated analog output module with less than 2 W power dissipation, while meeting CISPR 11 Class B.

Product Highlights

1. DPC, using an integrated buck dc-to-dc converter for thermal management. When used with the ADP1031, the AD5758 enables eight channel to channel isolated outputs at <2 W dissipated power.
2. Range of advanced diagnostic features, including an integrated ADC for high reliability.
3. Highly robust with output protection from miswire events (±38 V).
4. HART compliant.

Applications

• Process control
• Actuator control
• Channel isolated analog outputs
• Programmable logic controller (PLC) and distributed control systems (DCS) applications
• HART network connectivity

The ADP1031 is a high performance, isolated micropower management unit (PMU) that combines an isolated flyback dc-to-dc regulator, an inverting dc-to-dc regulator, and a buck dc-to-dc regulator, providing three isolated power rails. Additionally, the ADP1031 contains four, high speed, serial peripheral interface (SPI) isolation channels and three general-purpose isolators for channel to channel applications where low power dissipation and small solution size is required.

Operating over an input voltage range of +4.5 V to +60 V, the ADP1031 generates isolated output voltages of +6 V to +28 V (adjustable version) or+ 21 V and +24 V (fixed versions) for V_OUT1, factory programmable voltages of +5.15 V, +5.0 V, or +3.3 V for V_OUT2, and an adjustable output voltages of −24 V to −5 V for V_OUT3.

By default, the ADP1031 flyback regulator operates at a 250 kHz switching frequency and the buck and inverting regulators operate at 125 kHz. All three regulators are phase shifted relative to each other to reduce electromagnetic interference (EMI). The ADP1031 can be driven by an external oscillator in the range of 350 kHz to 750 kHz to ease noise filtering in sensitive applications.

The digital isolators integrated in the ADP1031 use Analog Devices, Inc., iCoupler^® chip scale transformer technology, optimized for low power and low radiated emissions.

The ADP1031 is available in a 9 mm × 7 mm, 41-lead LFCSP and is rated for a −40°C to +125°C operating junction temperature range.

Applications

• Industrial automation and process control
• Instrumentation and data acquisition systems
• Data and power isolation

The AD7124-4 is a low power, low noise, completely integrated analog front end for high precision measurement applications. The device contains a low noise, 24-bit Σ-Δ analog-to-digital converter (ADC), and can be configured to have 4 differential inputs or 7 single-ended or pseudo differential inputs. The onchip low gain stage ensures that signals of small amplitude can be interfaced directly to the ADC.

One of the major advantages of the AD7124-4 is that it gives the user the flexibility to employ one of three integrated power modes. The current consumption, range of output data rates, and rms noise can be tailored with the power mode selected. The device also offers a multitude of filter options, ensuring that the user has the highest degree of flexibility.

The AD7124-4 can achieve simultaneous 50 Hz and 60 Hz rejection when operating at an output data rate of 25 SPS (single cycle settling), with rejection in excess of 80 dB achieved at lower output data rates.

The AD7124-4 establishes the highest degree of signal chain integration. The device contains a precision, low noise, low drift internal band gap reference, and also accepts an external differential reference, which can be internally buffered. Other key integrated features include programmable low drift excitation current sources, burnout currents, and a bias voltage generator, which sets the common-mode voltage of a channel to AV_DD/2. The low-side power switch enables the user to power down bridge sensors between conversions, ensuring the absolute minimal power consumption of the system. The device also allows the user the option of operating with either an internal clock or an external clock.

The integrated channel sequencer allows several channels to be enabled simultaneously, and the AD7124-4 sequentially converts on each enabled channel, simplifying communication with the device. As many as 16 channels can be enabled at any time; a channel being defined as an analog input or a diagnostic such as a power supply check or a reference check. This unique feature allows diagnostics to be interleaved with conversions.

The AD7124-4 also supports per channel configuration. The device allows eight configurations or setups. Each configuration consists of gain, filter type, output data rate, buffering, and reference source. The user can assign any of these setups on a channel by channel basis.

The AD7124-4 also has extensive diagnostic functionality integrated as part of its comprehensive feature set. These diagnostics include a cyclic redundancy check (CRC), signal chain checks, and serial interface checks, which lead to a more robust solution. These diagnostics reduce the need for external components to implement diagnostics, resulting in reduced board space needs, reduced design cycle times, and cost savings. The failure modes effects and diagnostic analysis (FMEDA) of a typical application has shown a safe failure fraction (SFF) greater than 90% according to IEC 61508.

The device operates with a single analog power supply from 2.7 V to 3.6 V or a dual 1.8 V power supply. The digital supply has a range of 1.65 V to 3.6 V. It is specified for a temperature range of −40°C to +105°C. The AD7124-4 is housed in a 32-lead LFCSP package or a 24-lead TSSOP package.

Applications

• Temperature measurement 
• Pressure measurement 
• Industrial process control 
• Instrumentation Smart transmitters
• Smart transmitters

The AD7124-8 is a low power, low noise, completely integrated analog front end for high precision measurement applications. The AD7124-8 W grade is AEC-Q100 qualified for automotive applications. The device contains a low noise, 24-bit Σ-Δ analog-to-digital converter (ADC), and can be configured to have 8 differential inputs or 15 single-ended or pseudo differential inputs. The on-chip low gain stage ensures that signals of small amplitude can be interfaced directly to the ADC.

One of the major advantages of the AD7124-8 is that it gives the user the flexibility to employ one of three integrated power modes. The current consumption, range of output data rates, and rms noise can be tailored with the power mode selected. The device also offers a multitude of filter options, ensuring that the user has the highest degree of flexibility.

The AD7124-8 can achieve simultaneous 50 Hz and 60 Hz rejection when operating at an output data rate of 25 SPS (single cycle settling), with rejection in excess of 80 dB achieved at lower output data rates.

The AD7124-8 establishes the highest degree of signal chain integration. The device contains a precision, low noise, low drift internal band gap reference and accepts an external differential reference, which can be internally buffered. Other key integrated features include programmable low drift excitation current sources, burnout currents, and a bias voltage generator, which sets the common-mode voltage of a channel to AV_DD/2. The low-side power switch enables the user to power down bridge sensors between conversions, ensuring the absolute minimal power consumption of the system. The device also allows the user the option of operating with either an internal clock or an external clock.

The integrated channel sequencer allows several channels to be enabled simultaneously, and the AD7124-8 sequentially converts on each enabled channel, simplifying communication with the device. As many as 16 channels can be enabled at any time, a channel being defined as an analog input or a diagnostic such as a power supply check or a reference check. This unique feature allows diagnostics to be interleaved with conversions. The AD7124-8 also supports per channel configuration. The device allows eight configurations or setups. Each configuration consists of gain, filter type, output data rate, buffering, and reference source. The user can assign any of these setups on a channel by channel basis.

The AD7124-8 also has extensive diagnostic functionality integrated as part of its comprehensive feature set. These diagnostics include a cyclic redundancy check (CRC), signal chain checks, and serial interface checks, which lead to a more robust solution. These diagnostics reduce the need for external components to implement diagnostics, resulting in reduced board space needs, reduced design cycle times, and cost savings. The failure modes effects and diagnostic analysis (FMEDA) of a typical application has shown a safe failure fraction (SFF) greater than 90% according to IEC 61508.

The device operates with a single analog power supply from 2.7 V to 3.6 V or a dual 1.8 V power supply. The digital supply has a range of 1.65 V to 3.6 V. It is specified for a temperature range of −40°C to +125°C. The AD7124-8 is housed in a 32-lead LFCSP package.

APPLICATIONS

• Temperature measurement
• Pressure measurement
• Industrial process control
• Instrumentation
• Smart transmitters

The fido5100 and fido5200 (REM switch) are programmable IEEE 802.3 10 Mbps/100 Mbps Ethernet Internet Protocol Version 6 (IPv6) and Internet Protocol Version 4 (IPv4) switches that support virtually any Layer 2 or Layer 3 protocol. The switches are personalized to support the desired protocol by firmware that is downloaded from a host processor.

The firmware is contained in the real-time Ethernet multiprotocol (REM) switch driver and is downloaded at power-up. The REM switch can be ready for network data operation in less than 4 ms to support fast startup and quick connect type network functionality. The REM switch devices have the same signal assignments as defined in this data sheet.

The fido5100 supports the following protocols: PROFINET real time (RT) and isochronous real time (IRT), EtherNet/IP with and without device level ring (DLR), Modbus TCP, and POWERLINK.

The fido5200 supports the following protocols: EtherCAT and all protocols defined for the fido5100.

The REM switch is intended for use with a host processor. Network operation is handled using the functions and services provided in the REM switch driver. The host processor can implement any protocol stack by integrating it with the REM switch driver. An example application is shown in Figure 11 in the data sheet.

The REM switches are available in a 144-ball chip scale package ball grid array (CSP_BGA) package.

APPLICATIONS

• Industrial automation
  • Process control
  • Managed Ethernet switch

The fido5100 and fido5200 (REM switch) are programmable IEEE 802.3 10 Mbps/100 Mbps Ethernet Internet Protocol Version 6 (IPv6) and Internet Protocol Version 4 (IPv4) switches that support virtually any Layer 2 or Layer 3 protocol. The switches are personalized to support the desired protocol by firmware that is downloaded from a host processor.

The firmware is contained in the real-time Ethernet multiprotocol (REM) switch driver and is downloaded at power-up. The REM switch can be ready for network data operation in less than 4 ms to support fast startup and quick connect type network functionality. The REM switch devices have the same signal assignments as defined in this data sheet.

The fido5100 supports the following protocols: PROFINET real time (RT) and isochronous real time (IRT), EtherNet/IP with and without device level ring (DLR), Modbus TCP, and POWERLINK.

The fido5200 supports the following protocols: EtherCAT and all protocols defined for the fido5100.

The REM switch is intended for use with a host processor. Network operation is handled using the functions and services provided in the REM switch driver. The host processor can implement any protocol stack by integrating it with the REM switch driver. An example application is shown in Figure 11 in the data sheet.

The REM switches are available in a 144-ball chip scale package ball grid array (CSP_BGA) package.

APPLICATIONS

• Industrial automation
  • Process control
  • Managed Ethernet switch

The circuit shown in Figure 1 is a full-featured, flexible, and programmable analog output solution that uses only two analog devices. It meets programmable logic controller (PLC) and distributed control system (DCS) applications Most of the requirements. AD5660-1 is a low power consumption (2.8 mW @ 5 V), rail-to-rail output, 16-bit nanoDAC^® , AD5750-1 is an industrial current/voltage output driver. The combination of the two can provide all typical current and Voltage output range, 16-bit resolution and no missing codes, 0.05% linearity and less than 0.1% output error. The circuit also has some important features that support industrial applications, such as on-chip output fault detection, CRC check to prevent packet errors (PEC), and flexible power-on options, etc., making it very suitable for building robust industrial control systems. In mass production, it can maintain consistent performance without external precision resistors or calibration procedures, so it is an ideal choice for PLC or DCS modules.

The circuit, shown in Figure 1, is a complete analog front end for digitizing ±10 V industrial level signals with a 16-bit differential input PulSAR^® ADC. The circuit provides a high impedance instrumentation amplifier input with high CMR, level shifting, attenuation, and differential conversion, with only two analog components. Because of the high level of integration, the circuit saves printed circuit board space and offers a cost effective solution for a popular industrial application.

Signal levels of up to ±10 V are typical in process control and industrial automation systems. With smaller signal inputs from sensors such as thermocouples and load cells, large common-mode voltage swings are often encountered. This requires a flexible analog input that handles both large and small differential signals with high common-mode rejection and also has a high impedance input.

Attenuation and level shifting are necessary to process industrial level signals with modern low voltage ADCs. In addition, fully differential input ADCs offer the advantages of good common-mode rejection, reduction in second-order distortion products, and simplified dc trim algorithms. Industrial signals, therefore, need further conditioning to properly interface with differential input ADCs.

The circuit in Figure 1 is a complete and highly integrated analog front end industrial level signal conditioner that uses only two active components to drive an AD7687 differential input 16-bit PulSAR ADC: the AD8295 precision in-amp (with two on-chip auxiliary op amps) and the AD8275 level translator/ADC driver. An ADR431 low noise 2.5V XFET^® reference supplies the voltage reference for the ADC.

The AD8295 is a precision instrumentation amplifier with two uncommitted on-chip signal processing amplifiers and two precisely matched 20 kΩ resistors in a small 4 mm × 4 mm package.

The AD8275 is a G = 0.2 difference amplifier that can be used to attenuate ±10 V industrial signals, and the attenuated signal can be easily interfaced to a single supply low voltage ADC. The AD8275 performs the attenuation and level shifting function in the circuit, maintaining good CMR without any need for external components.

The AD7687 is a 16-bit, successive approximation ADC that operates from a single power supply between 2.3 V and 5.5 V. It has a differential input for good CMR and also offers the ease of use associated with SAR ADCs.

The circuit shown in Figure 1 is a completely isolated 12-bit, 300 kSPS RTD temperature measuring system that uses only three active devices. The system processes the output of a Pt100 RTD and includes an innovative circuit for lead-wire compensation using a standard 3-wire connection. The circuit operates on a single 3.3 V supply. The total error after room temperature calibration is less than ±0.24% FSR for a ±10°C change in temperature, making it ideal for a wide variety of industrial temperature measurements.

The small footprint of the circuit makes this combination an industry-leading solution for temperature measurements where accuracy, cost, and size play a critical role. Both data and power are isolated, thereby making the circuit robust to high voltages and also ground-loop interference often encountered in harsh industrial environments.

The novel circuit for 3-wire RTD lead wire compensation was developed by Hristo Ivanov Gigov, Associate Professor and PhD, and Stanimir Krasimirov Stankov, Engineer and PhD Student, Department of Electronic Engineering and Microelectronics, Technical University of Varna, Varna, Bulgaria.

The circuit shown in Figure 1 provides a unique power saving solution for a digital-to-analog converter (DAC)-based, 4 mA to 20 mA output circuit. To provide sufficient headroom for typical resistive loads between 10 Ω and 1000 Ω, traditional 4 mA to 20 mA output driver stages must operate on at least 20 V (plus some additional headroom) to provide a sufficient voltage to drive high value resistive loads. For low value resistive loads, however, the fixed value, high voltage supply results in significant internal power dissipation that can affect DAC accuracy and require additional heat sinking.

The AD5755 quad 16-bit DAC has four independent high efficiency, internal dc-to-dc converters that drive the four output stages at a dynamically adjusted boost voltage based on sensing the actual output voltage of the 4 mA to 20 mA driver. The boost circuit maintains several volts of headroom on the output stage, regardless of the load resistance, thereby reducing the maximum internal power dissipation by a factor of approximately 4× for a 24 mA output current into a 10 Ω load.

The internal dc-to-dc converters require an external 5 V supply and can draw significant currents when the DAC outputs full-scale slew. A high efficiency external dc-to-dc converter circuit based on the ADP2300 is driven from the 15 V and supplies this voltage. The ADP2300 has excellent transient response to large current steps up to 800 mA and ensures proper operation of the boost converters as well as eliminating the need for a separate 5 V supply.

The entire circuit operates on ±15 V supplies that allow the DAC to provide voltage outputs that cover the industrial signal level range of up to ±10 V in addition to the 4 mA to 20 mA outputs. This combination of parts is a low cost, power efficient solution that minimizes the number of external components required and that ensures 16-bit performance for varying load conditions.

This circuit provides a complete, fully isolated, analog output channel suitable for programmable logic controllers (PLCs) and distributed control system (DCS) modules that require standard 4 mA to 20 mA HART^®1-compatible current outputs and unipolar or bipolar output voltage ranges. It provides a flexible building block for channel-to-channel isolated PLC/DCS output modules or any other industrial application that requires a fully isolated analog output. The circuit also includes external protection on the analog output terminals.

The AD5422 16-bit digital-to-analog converter (DAC) is software configurable and provides all the necessary current and voltage outputs.

The AD5700-1, the industry’s lowest power and smallest footprint HART-compliant IC modem, is used in conjunction with the AD5422 to form a complete HART-compatible 4 mA to 20 mA solution. The AD5700-1 includes a precision internal oscillator that provides additional space savings, especially in channel-to-channel isolated applications.

PLC/DCS solutions must be isolated from the local system controller to protect against ground loops and to ensure robustness against external events. Traditional solutions use discrete ICs for both power and digital isolation. When multichannel isolation is needed, the cost and space of providing discrete power solutions becomes a big disadvantage. Solutions based on optoisolators typically have reasonable output regulation but require additional external components, thereby increasing board area. Power modules are often bulky and can provide poor output regulation. The circuit in Figure 1 uses the ADuM347x family of isolators and power regulation circuitry along with associated feedback isolation. External transformers are used to transfer power across the isolation barrier.

The ADuM3482 provides the UART signal isolation for the AD5700-1.

The ADP2441, 36 V step-down dc-to-dc regulator, accepts an industrial standard 24 V supply, with wide tolerance on the input voltage. It steps this down to 5 V to power all controller side circuitry. The circuit also includes standard external protection on the 24 V supply terminals, as well as protection against dc overvoltage of +36 V down to −28 V.

¹ HART is a registered trademark of the HART Communication Foundation.

The circuit in Figure 1 provides 16-bit fully isolated ±10 V and 4 mA-to-20 mA outputs suitable for programmable logic controllers (PLCs) and distributed control systems (DCSs).

The circuit uses digital isolation, as well as PWM-controlled power regulation circuitry along with associated feedback isolation. External transformers are used to transfer power across the isolation barrier, and the entire circuit operates on a single +5 V supply located on the primary side. This solution is superior to isolated power modules, which are often bulky and may provide poor output regulation.

Digital isolators are superior to opto-isolators especially when multichannel isolation is needed. The integrated design isolates the circuit from the local system controller to protect against ground loops and also to ensure robustness against external events often encountered in harsh industrial environments.

The circuit shown in Figure 1 uses the AD5700, the industry’s lowest power and smallest footprint HART¹-compliant IC modem and the AD5420, a 16-bit current-output DAC, to form a complete HART-compatible 4 mA to 20 mA solution.

For additional space savings, the AD5700-1 offers a 0.5% precision internal oscillator.

This circuit adheres to the HART physical layer specifications as defined by the HART Communication Foundation, for example, the analog rate of change and noise during silence specifications.

For many years, 4 mA to 20 mA communication has been used in process control instrumentation. This communication method is reliable and robust, and offers high immunity to environmental interference over long communication distances. A limitation, however, is that only 1-way communication of one process variable at a time is possible.

The development of the highway addressable remote transducer (HART) standard provided highly capable 2-way digital communication, simultaneously with the 4 mA to 20 mA analog signaling used by traditional instrumentation equipment. This allows for features such as remote calibration, fault interrogation, and transmission of additional process variables. Put simply, HART is a digital two-way communication in which a 1 mA peak-to-peak frequency-shift-keyed (FSK) signal is modulated on top of the 4 mA to 20 mA analog current signal.

The circuit shown in Figure 1 is a multichannel, flexible, analog output solution with only two analog components and meets most requirements for multichannel I/O cards, programmable logic controllers (PLCs), and distributed control systems (DCSs) applications. The AD5686R quad, 16-bit nanoDAC+ with rail-to-rail buffered outputs combined with four of the AD5750-2 industrial current/voltage output drivers provide all the typical output current and voltage ranges with 16-bit resolution, no missing codes, 0.05% linearity, and less than 0.1% output error.

An ultralow drift (2 ppm/°C typical), 2.5 V voltage reference with high drive capability (up to ±5 mA) is integrated in the AD5686R and provides the reference voltage for both the AD5686R and the AD5750-2. This guarantees low noise, high accuracy, and low temperature drift for the circuit.

The ADuM1301 and ADuM5400 provide 2500 V rms isolation both on power, and all the necessary signals between the analog signal chain and the host controller.

For multichannel I/O card applications that need more than 4 channels, several AD5686Rs can be connected in a daisy chain, and no additional external digital I/O circuits are required. This minimizes the cost, especially for high channel count isolated applications.

The circuit also contains key features for industrial applications, such as on-chip output fault detection, packet error checking (PEC) by the CRC, flexible power-up options, and ESD protection (4 kV for the AD5686R, human body model and 3 kV for the AD5750-2, human body model), making it an ideal choice for robust industrial control systems. No external precision resistors or calibration routines are needed to maintain consistent performance in mass production, thereby making it ideal for PLC or DCS modules.

The circuit shown in Figure 1 is a flexible current transmitter that converts the differential voltage output from a pressure sensor to a 4 mA-to-20 mA current output.

The circuit is optimized for a wide variety of bridge-based voltage or current driven pressure sensors, utilizes only five active devices, and has a total unadjusted error of less than 1%. The power supply voltage can range from 7 V to 36 V depending on the component and sensor driver configuration.

The input of the circuit is protected for ESD and voltages beyond the supply rail, making it ideal for industrial applications.

The circuit shown in Figure 1 is a completely isolated 4-channel temperature measurement circuit optimized for performance, input flexibility, robustness, and low cost. It supports all types of thermocouples with cold junction compensation and any type of RTD (resistance temperature detector) with resistances up to 4 kΩ for 2-, 3-, or 4-wire connection configurations.

The RTD excitation current are is programmable for optimum noise and linearity performance.

RTD measurements achieve 0.1°C accuracy (typical), and Type-K thermocouple measurements achieve 0.05°C typical accuracy because of the 16-bit ADT7310 digital temperature sensor used for cold-junction compensation. The circuit uses a four-channel AD7193 24-bit sigma-delta ADC with on-chip PGA for high accuracy and low noise.

Input transient and overvoltage protection are provided by low leakage transient voltage suppressors (TVS) and Schottky diodes. The SPI-compatible digital inputs and outputs are isolated (2500 V rms), and the circuit is operated on a fully isolated power supply.

The circuit shown in Figure 1 uses the AD5700, the industry’s lowest power and smallest footprint HART^®1-compliant IC modem, and the AD5422, a 16-bit current output and voltage output DAC, to form a complete HART-compatible 4 mA to 20 mA solution. The use of the OP184 in the circuit allows the I_OUT and V_OUT pins to be shorted together, thus reducing the number of screw connections required in programmable logic control (PLC) module applications. For additional space savings, the AD5700-1 offers a 0.5% precision internal oscillator.

Application Note AN-1065 describes a manner in which the AD5420 I_OUT DAC can be configured for HART communication compliance. AN-1065 outlines how the AD5700 HART modem output can be attenuated and ac coupled into the AD5420 via the CAP2 pin. The same is true of the AD5422. However, if the application involves a particularly harsh environment, an alternative circuit configuration can be used which offers better power supply rejection characteristics. This alternative circuit requires the use of the external R_SET resistor and involves coupling the HART signal into the R_SET pin of the AD5420 or AD5422. The CN-0270 describes this solution for the AD5420, typical of line-powered transmitter applications. The current circuit note is relevant to the AD5422, which, unlike the AD5420, offers both a voltage and a current output pin, and so is particularly useful in PLC/distributed control system (DCS) applications. The AD5422 is available in both 40-lead LFCSP and 24-lead TSSOP packages and the relevance of this, to the circuit characteristics, is examined in the Circuit Description section.

This circuit adheres to the HART physical layer specifications as defined by the HART Communication Foundation, for example, the output noise during silence and the analog rate of change specifications.

For many years, 4 mA to 20 mA communication has been used in process control instrumentation. This communication method is reliable and robust, and offers high immunity to environmental interference over long communication distances. A limitation, however, is that only 1-way communication of one process variable at a time is possible.

The development of the highway addressable remote transducer (HART) standard provided highly capable 2-way digital communication, simultaneously with the 4 mA to 20 mA analog signaling used by traditional instrumentation equipment. This allows for features such as remote calibration, fault interrogation, and transmission of additional process variables. Put simply, HART is a digital two-way communication in which a 1 mA peak-to-peak, frequency-shift-keyed (FSK) signal is modulated on top of the 4 mA to 20 mA analog current signal.

The circuit shown in Figure 1 is a completely isolated 12-bit, 300 kSPS data acquisition system utilizing only three active devices.

The system processes ±10 V input signals using a single 3.3 V supply. The total error after room temperature calibration is less than ±0.1% FSR over a ±10°C temperature change, making it ideal for a wide variety of industrial measurements.

The small footprint of the circuit makes this combination an industry-leading solution for data acquisition systems where the accuracy, speed, cost, and size play a critical role. Both data and power are isolated, thereby making the circuit robust to high voltages and also ground-loop interference often encountered in harsh industrial environments.

The circuit in Figure 1 is a complete single-supply,16-bit buffered voltage output DAC that maintains ±1 LSB integral and differential nonlinearity by utilizing a CMOS DAC followed by an innovative amplifier that has no crossover distortion.

The circuit eliminates the crossover nonlinearity associated with most rail-to-rail op amps that can be as high as 4 or 5 LSBs for a 16-bit system.

This industry-leading solution is ideal for industrial process control and instrumentation applications where a compact, single-supply, low cost, and highly linear 16-bit buffered voltage source is required.

Total power dissipation for the three active devices is less than 25 mW typical when operating on a single 6 V supply.

The circuit shown in Figure 1 is a completely isolated 12-bit, 300 kSPS data acquisition system utilizing only three active devices.

The system processes 4 mA to 20 mA input signals using a single 3.3 V supply. The total error after room temperature calibration is ±0.06% FSR over a ±10°C temperature change, making it ideal for a wide variety of industrial measurements.

The small footprint of the circuit makes this combination an industry-leading solution for 4 mA to 20 mA data acquisition systems where the accuracy, speed, cost, and size play a critical role. Both data and power are isolated, thereby making the circuit robust to high voltages and also ground-loop interference often encountered in harsh industrial environments.

The circuit shown in Figure 1 provides a complete, fully isolated, highly flexible, quad channel analog input system suitable for programmable logic controllers (PLCs) and distributed control system (DCS) applications that require multiple voltage inputs and HART-compatible, 4 mA to 20 mA current inputs.

The analog input circuit is designed for group isolated industrial analog inputs and can support voltage and current input ranges including ±5 V, ±10 V, 0 V to +5 V, 0 V to +10 V, +4 mA to +20 mA, and 0 mA to +20 mA.

The circuit is powered from a standard 24 V bus supply and generates an isolated 5 V system supply voltage.

In power line measurement and protection systems, there is a requirement to simultaneously sample large numbers of current and voltage channels of multiphase power distribution and transmission networks. In these applications, the channel count can vary from as few as six channels to greater than 64 channels. The AD7606 8-channel data acquisition system (DAS) with 16-bit bipolar simultaneously sampling SAR ADCs with on-chip overvoltage protection greatly simplifies signal condi-tioning circuitry and reduces the overall parts count, board real estate, and cost of the measurement and protection board. Even with its high level of integration, each AD7606 requires only nine low value ceramic decoupling capacitors.

In measurement and protection systems, simultaneous sampling capability is needed to maintain the phase information between the current and voltage channels on multiphase power line networks. The wide dynamic range capability of the AD7606 makes it ideal for capturing both under voltage/current and over voltage/current conditions. The input voltage range is pin-programmable for either ±5 V or ±10 V.

This circuit note describes details of the recommended PC board layout for applications using multiple AD7606 devices. The layout is optimized for channel-to-channel matching and part-to-part matching and will help reduce the complexity of calibration routines in high channel count systems. The circuit provides the ability to use the AD7606 2.5 V internal reference when channel-to-channel matching is important or an external ADR421 precision high accuracy (B grade: ±1 mV max), low drift (B grade: 3 ppm/°C max), low noise (1.75 μV p-p, typical, 0.1 Hz to 10 Hz) reference for high channel applications that require excellent absolute accuracy. The low noise and the stability and accuracy characteristics of the ADR421 make it ideal for high precision conversion applications. The combination of the two devices yields a level of integration, channel density, and accuracy that is unsurpassed in the industry.

With single-ended signaling, one wire from the signal source is routed throughout the system to the data acquisition interface. The voltage measured is the difference between the signal and the ground. Unfortunately, “ground” can be a different level in different places because the ground impedance can never be zero. This can lead to errors when using single-ended inputs, especially where the signal trace is long and grounds currents contain large digital transients. Single-ended signal runs are sensitive to noise pickup because they act as an antenna, picking up electrical activity. With single-ended inputs there is no way of distinguishing between the signal and the interfering noise. Most of the ground and noise problems are solved by differential signaling.

With differential signaling, two signal wires run from the signal source to the data acquisition interface. This can solve both of the problems caused by single-ended connections. Noise between the sending and receiving ground planes acts as a common-mode signal and is, therefore, greatly attenuated. The use of twisted pair wire causes noise pickup to appear as a common-mode signal, which is also greatly attenuated at the receiver. Another advantage of differential transmission is that the differential signal has twice the amplitude of the equivalent single-ended signal, therefore giving greater noise immunity.

Here we describe a differential driver that can be adapted to either a voltage or current output DAC. The driver is based on the dual AD8042 op amp configured as a cross-coupled differential driver. The AD8042 has a rail-to-rail output stage that operates within 30 mV of either rail and an input stage that can operate 200 mV below the negative supply (ground in this circuit) and within 1 V of the positive supply. In addition, the AD8042 has 160 MHz bandwidth and fast settling time, making it an ideal choice for the output driver.

The voltage output DAC is the 12-bit AD5620, a member of the nanoDAC^® family. The DAC contains an on-chip 5 ppm/°C reference and is available in an 8-lead SOT-23 or MSOP package. The current output DAC is the 12-bit AD5443, which is available in a 10-lead MSOP package.

The two circuits represent a cost effective, low power, and small board area solution for generating differential signals from industrial CMOS DACs. Both circuits operate on a single +5 V supply.

Data acquisition systems with wide dynamic range often need some method for adjusting the input signal level to the analog-to-digital converter (ADC). In order to get the most from an ADC, the maximum input signal should match its full-scale voltage. This is achieved by implementing a programmable gain amplifier circuit.

This circuit provides a programmable gain function using a quad SPST switch (ADG1611) and a resistor-programmable instrumentation amplifier (AD620).

The gain values are set by controlling the external gain setting resistor value, R_G, with the four SPST switches, which are connected to four precision resistors.

Low switch on resistance is critical in this application, and the ADG1611 has the industry’s lowest R_ON (1 Ω typical) and is available in the smallest package, a 16-lead, 4 mm × 4 mm LFCSP.

The combination of the industry-standard low cost AD620 and the ADG1611 quad switch yields unmatched performance in this circuit and provides all the benefits of a precision instrumentation amplifier, along with the programmable gain feature.

Achieving true 16-bit performance with a voltage output DAC requires selecting not only the correct DAC but also the correct complementary supporting components. This circuit provides a low risk solution for precision 16-bit digital-to-analog conversion using the AD5542A/AD5541A voltage output DAC with the ADR421 voltage reference and the AD8675 ultralow offset op amp used as the voltage reference buffer.

The reference buffer is critical to the design because the input impedance at the DAC reference input is heavily code- dependent and will lead to linearity errors if the DAC reference is not adequately buffered. With a high open-loop gain of 120 dB, the AD8675 has been proven and tested to meet the settling time, offset voltage, and low impedance drive capability required by this circuit application.

The precision, low offset OP1177 can be used as an optional output buffer if needed.

This combination of parts provides industry-leading 16-bit integral nonlinearity (INL) of ±1 LSB and differential nonlinearity (DNL) of ±1 LSB with guaranteed monotonicity, as well as low power, small PCB area, and cost effectiveness.

The circuit shown in Figure 1 is a complete thermocouple system based on the AD7793 24-bit sigma-delta (Σ-Δ) analog-to-digital converter (ADC). The AD7793 is a low power, low noise, complete analog front end for high precision measurement applications. The device includes a programmable gain amplifier (PGA), an internal reference, an internal clock, and excitation currents, thereby greatly simplifying the thermocouple system design.

The AD7793 consumes only 500 μA maximum, making it suitable for any low power application, such as smart transmitters where the complete transmitter must consume less than 4 mA. The AD7793 has a power-down option. In this mode, the complete ADC, along with its auxiliary functions, is powered down so that the part consumes 1 μA maximum.

Because the AD7793 provides an integrated solution for thermocouple design, it interfaces directly to the thermocouple. For the cold junction compensation, a thermistor along with a precision resistor is used. These are the only external components required for the cold junction measurement other than some simple RC filters for EMC considerations.

In most systems, there are trade-offs between performance and low power. The focus of this circuit design is to explore a few of these trade-offs and still achieve low power (8 mW typical) and high performance in a 16-bit, 100 kSPS data acquisition system.

This circuit uses the AD7988-1, a low power (350 μA) PulSAR^® analog-to-digital converter (ADC), driven directly from the ADA4841-1 high performance, low voltage, low power op amp. This amplifier was chosen for its excellent dynamic performance and its ability to operate with a single-supply voltage and to provide a rail-to-rail output. In addition, the input common-mode voltage range includes the negative rail.

The AD7988-1 ADC requires an external voltage reference between 2.4 V and 5.1 V. In this application, the voltage reference chosen was the ADR4525 precision 2.5 V reference.

The circuit shown in Figure 1 is a flexible signal conditioning circuit for processing signals of wide dynamic range, varying from several mV p-p to 20 V p-p. The circuit provides the necessary conditioning and level shifting and achieves the dynamic range using the internal programmable gain amplifier (PGA) of the high resolution analog-to-digital converter (ADC).

A ±10 V full-scale signal is very typical in process control and industrial automation applications; however, in some situations, the signal can be as small as several mV. Attenuation and level shifting is necessary to process a ±10 V signal with modern low voltage ADCs. However, amplification is needed for small signals to make use of the dynamic range of the ADC. Therefore, a circuit with a programmable gain function is desirable when the input signal varies over a wide range.

In addition, small signals may have large common-mode voltage swings; therefore, high common-mode rejection (CMR) is required. In some applications, where the source impedance is large, high impedance is also necessary for the analog front-end input circuit.

The circuit shown in Figure 1 solves all of these challenges and provides programmable gain, high CMR, and high input impedance. The input signal passes through the 4-channel ADG1409 multiplexer into the AD8226 low cost, wide input range instrumentation amplifier. The AD8226 offers high CMR up to 80 dB and very high input impedance (800 MΩ differential mode and 400 MΩ common mode). A wide input range and rail-to-rail output allow the AD8226 to make full use of the supply rails.

The AD8475 is a fully differential, attenuating amplifier with integrated precision gain resistors. It provides precision attenuation (G = 0.4 or G = 0.8), common-mode level shifting, and single-ended-to-differential conversion. The AD8475 is an easy to use, fully integrated precision gain block, designed to process signal levels up to ±10 V on a single supply. Therefore, the AD8475 is suitable for attenuating signals from the AD8226 up to 20 V p-p, while maintaining high CMR and offering a differential output to drive the differential input ADC.

The AD7192 is a 24-bit sigma-delta (Σ-Δ) ADC with an internal PGA. The on-chip, low noise gain stage (G = 1, 8, 16, 32, 64, or 128) means that signals of large and small amplitude can be interfaced directly to the ADC.

With the combination of the previous parts, the circuit offers very good performance and easy configuration for signals with varying amplitudes. The circuit can be used in industrial automation, process control, instrumentation, and medical equipment applications.

The circuit shown in Figure 1 provides a precision 16-bit, low drift bipolar voltage output of ±2.5 V and operates on a single +10 V to +15 V supply. The unipolar voltage outputs of the AD5668 octal denseDAC are amplified and level shifted by the AD8638 auto-zero op amps. The maximum drift contribution of the AD8638 is only 0.06 ppm/°C. The external REF192 reference ensures a maximum drift of 5 ppm/°C (E grade) and provides a low impedance pseudo ground for the AD8638 level gain and shifting circuit.

The circuit offers an efficient solution to a problem often encountered in systems with a single +12 V supply rail. Proper printed circuit board (PCB) layout and grounding techniques ensure that the ADP2300 switching regulator does not degrade the overall performance of the circuit.

The circuit in Figure 1 is a 4 mA-to-20 mA current loop transmitter for communication between a process control system and its actuator. Besides being cost effective, this circuit offers the industry’s low power solution. The 4 mA-to-20 mA current loop has been used extensively in programmable logic controllers (PLCs) and distributed control systems (DCS’s), with digital or analog inputs and outputs. Current loop interfaces are usually preferred because they offer the most cost effective approach to long distance noise immune data transmission. The combination of the low power AD8657 dual op amp, AD5641DAC, and ADR02 reference allows more power budget for higher power devices, such as microcontrollers and digital isolators. The circuit output is 0 mA to 20 mA of current, and it operates on a single supply from 8 V to 18 V. The 4 mA to 20 mA range is usually mapped to represent the input control range from the DAC or micro-controller, while the output current range of 0 mA to 4 mA is often used to diagnose fault conditions.

The 14-bit, 5 V AD5641 requires 75 μA typical supply current. The AD8657 is a rail-to-rail input/output dual op amp and is one of the lowest power amplifiers currently available in the industry (22 μA per amplifier over the full supply voltage and input common-mode range) with high operating voltage of up to 18 V. The ADR02 ultracompact precision 5 V voltage reference requires only 650 μA. Together, these three devices consume a typical supply current of 747 μA.

The circuit has a 12-pin Pmod^™ digital interface (Digilent specification).

Cost sensitive, high channel count applications that require wide dynamic range can effectively use the AD7607 8-channel integrated data acquisition system (DAS) with on-chip 14-bit SAR ADCs to achieve greater than 80 dB dynamic range.

A typical application for the DAS is in power-line measurement and protection equipment, where large numbers of current and voltage channels of multiphase distribution and transmission networks must be sampled simultaneously.

Many low voltage power-line measurement and protection systems do not require full 16-bit ADC resolution (such as provided by the AD7606 DAS); however, they still require more than 80 dB dynamic range to capture the under- and over- voltage/current conditions. Simultaneous sampling is also needed to maintain the phase information between the current and voltage channels on a multiphase power line.

The AD7607 8-Channel DAS with 14-Bit, bipolar input, simultaneous sampling SAR ADC has 84 dB signal-to-noise ratio (SNR) to meet the requirements for these types of low voltage protection and measurement systems. The circuit shown in Figure 1 also uses an external ADR421 precision, low drift, low noise reference for high channel count applications that require absolute accuracy performance.

The circuit shown in Figure 1 provides a programmable 18-bit voltage with an output range −10 V to +10 V, ±0.5 LSB integral nonlinearity, ±0.5 LSB differential nonlinearity, and low noise.

The digital input to the circuit is serial and is compatible with standard SPI, QSPI, MICROWIRE^®, and DSP interface standards. For high accuracy applications, the circuit offers high precision, as well as low noise—this is ensured by the combination of the AD5781, ADR445 and AD8676 precision components.

The reference buffer is critical to the design because the input impedance at the DAC reference input is heavily code dependent and will lead to linearity errors if the DAC reference is not adequately buffered. With a high open-loop gain of 120 dB, the AD8676 has been proven and tested to meet the settling time, offset voltage, and low impedance drive capability required by this circuit application. The AD5781 is characterized and factory calibrated using the AD8676 dual op amp to buffer its voltage reference inputs, further enhancing confidence in partnering the components.

This combination of parts provides industry-leading 18-bit integral nonlinearity (INL) of ±0.5 LSB and differential nonlinearity (DNL) of ±0.5 LSB, with guaranteed monotonicity, as well as low power, small PCB area, and cost effectiveness.

This circuit, shown in Figure 1, is a flexible sensor signal conditioning block, with low noise, relatively high gain, and the ability to dynamically change the gain in response to input level changes without affecting performance, while still maintaining a wide dynamic range. Existing sigma-delta technology can provide the dynamic range needed for many applications, but only at the expense of low update rates. This circuit presents an alternative approach that uses the AD7985 16-bit, 2.5 MSPS PulSAR^® successive-approximation ADC, combined with an autoranging AD8253 iCMOS^® programmable gain instrumentation amplifier (PGA) front end. With gain that changes automatically based on analog input value, it uses oversampling and digital processing to increase the dynamic range of the system to more than 125 dB.

The circuits shown in Figure 1 demonstrate proven and tested electromagnetic compatibility (EMC) compliant solutions for three protection levels for popular RS-485 communication ports using the ADM3485E transceiver. Each solution was tested and characterized to ensure that the dynamic interaction between the transceiver and the protection circuit components functions correctly together to protect against the electrostatic discharge (ESD), electrical fast transients (EFT), and surge immunity specified in IEC 61000-4-2, IEC 61000-4-4, and IEC 61000-4-5, respectively. The circuits offer proven protection for RS-485 interfaces using the ADM3485E to the ESD, EFT, and surge levels often encountered in harsh environments.

The circuit shown in Figure 1 is a complete smart industrial, loop powered field instrument with 4 mA to 20 mA analog output and a highway addressable remote transducer (HART^®) interface. HART is a digital 2-way communication in which a 1 mA peak-to-peak frequency-shift-keyed (FSK) signal is modulated on top of the standard 4 mA to 20 mA analog current signal. This allows features such as remote calibration, fault interrogation, and transmission of process variables, which are necessary in applications such as temperature and pressure control.

This circuit has been compliance tested, verified, and registered by the HART Communication Foundation (HCF). This successful registration provides circuit designers with a high level of confidence using one or all of the components in the circuit.

The circuit uses the ADuCM360, an ultralow power, precision analog microcontroller, the AD5421, a 16-bit, 4 mA to 20 mA, loop powered digital-to-analog converter (DAC), and the AD5700, the industry’s lowest power and smallest footprint HART compliant IC modem.

The circuit, shown in Figure 1, is a 16-bit, ultra stable, low noise, precision, bipolar (±10 V) voltage source requiring a minimum number of precision external components.

Maximum integral nonlinearity (INL) is ±0.5 LSB, and maximum differential nonlinearity (DNL) is ±0.5 LSB for the AD5760 voltage output DAC (B-grade).

The complete system has less than 0.1 LSB peak-to-peak noise and drift measured over a 100 second interval. The circuit is ideal for medical instrumentation, test and measurement, and industrial control applications where precision low drift voltage sources are required.

The circuit shown in Figure 1 provides two, 16-bit, fully isolated, universal analog input channels suitable for programmable logic controllers (PLCs) and distributed control system (DCS) modules. Both channels are software programmable and support a number of voltage, current ranges, thermocouple, and RTD types, as shown in Figure 1.

The evaluation board contains two different fully isolated universal input channels, one with a 4-pin terminal block (CH2), and one with a 6-pin terminal block (CH1).

For the 4-terminal block channel (CH2), the voltage, current, thermocouple, and RTD inputs all share the same 4 terminals, thus minimizing the number of terminal pins required. For the 6-pin terminal block channel (CH1), the voltage and current inputs share a set of 3 terminals, and the thermocouple and RTD inputs share another set of 3 terminals; this configuration requires more terminals but has a lower part count and component cost. Figure 2 shows a photo of the printed circuit board (PCB), and Figure 3 shows a more detailed schematic of the circuit.

The circuit shown in Figure 1 is an ultralow, power data acquisition system using the AD7091R 12-bit, 1 MSPS SAR ADC and an AD8031 op amp driver with a total circuit power dissipation of less than 5 mW on a single 3 V supply.

The low power consumption and small package size of the selected components makes this combination an industryleading solution for portable battery-operated systems where power dissipation, cost, and size play a critical role.

The AD7091R requires typically only 350 μA of supply current on the V_DD pin at 3 V, which is significantly lower than any competitive ADC offering currently available in the market. This translates to ~1 mW typical power dissipation.

The AD8031 requires only 800 μA of supply current, that results in 2.4 mW typical power dissipation at 3 V supply, making the total power dissipation of the system less than 5 mW when sampling at 1 MSPS with a 10 kHz analog input signal.

The circuit shown in Figure 1 provides a programmable 20-bit voltage with an output range −10 V to +10 V, ±1 LSB integral nonlinearity, ±1 LSB differential nonlinearity, and low noise.

The digital input to the circuit is serial and is compatible with standard SPI, QSPI^™, MICROWIRE^®, and DSP interface standards. For high accuracy applications, the circuit offers high precision, as well as low noise, and this is ensured by the combination of the AD5791, AD8675, and AD8676 precision components.

The reference buffer is critical to the design because the input impedance at the DAC reference input is heavily code dependent and will lead to linearity errors if the DAC reference is not adequately buffered. With a high open-loop gain of 120 dB, the AD8676 has been proven and tested to meet the settling time, offset voltage, and low impedance drive capability required by this circuit application. The AD5791 is characterized and factory calibrated using the AD8676 dual op amp to buffer its voltage reference inputs, further enhancing confidence in partnering the components.

This combination of parts provides industry-leading 20-bit integral nonlinearity (INL) of ±1 LSB and differential nonlinearity (DNL) of ±1 LSB, with guaranteed monotonicity, as well as low power, small PCB area, and cost effectiveness.

Standard single-ended industrial signal levels of ±5 V, ±10 V, and 0 V to +10 V are not directly compatible with the differential input ranges of modern high performance 16-bit or 18-bit single-supply SAR ADCs. A suitable interface drive circuit is required to attenuate, level shift, and convert the industrial signal into a differential one with the correct amplitude and common-mode voltage that match the input requirements of the ADC.

Whereas suitable interface circuits can be designed using resistor networks and dual op amps, errors in the ratio matching of the resistors, and between the amplifiers, produce errors at the final output. Achieving the required output phase matching and settling time can be a challenge, especially at low power levels.

The circuit shown in Figure 1 uses the AD8475 differential funnel amplifier to perform attenuation, level shifting, and conversion to differential without the need for any external components. The ac and dc performances are compatible with those of the 18-bit, 1 MSPS AD7982 PulSAR^® ADC and other 16- and 18-bit members of the family, which have sampling rates up to 4 MSPS.

The AD8475 is a fully differential attenuating amplifier with integrated precision thin film gain setting resistors. It provides precision attenuation (by 0.4× or 0.8×), common-mode level shifting, and single-ended-to-differential conversion along with input overvoltage protection. Power dissipation on a single 5 V supply is only 15 mW. The 18-bit, 1 MSPS AD7982 consumes only 7 mW, which is 30× lower than competitive ADCs. The total power dissipated by the combination is only 22 mW.

The circuit shown in Figure 1 provides a full function, flexible, programmable analog output solution that meets most requirements for programmable logic controller (PLC) and distributed control system (DCS) applications. The AD5662 low power (0.75 mW @ 5 V), rail-to-rail output, 16-bit nanoDAC^® converter and the AD5750 industrial current/voltage output driver are well matched with respect to input and output voltage ranges, as well as reference voltage requirements. The ADR444 low drift (3 ppm/°C maximum for B-grade ), high initial accuracy (0.04% maximum for B-grade), and low noise (1.8 μV p-p typical, 0.1 Hz to 10 Hz) provides the reference voltage for both the AD5750 and AD5662 and guarantees ultralow noise, high accuracy, and low temperature drift for the circuit. This circuit provides all the typical voltage and current output ranges with 16-bit resolution and no missing codes, 0.05% linearity, and less than 0.2% total output error.

The circuit also contains key features for industrial applications, such as on-chip output fault detection and protection (short circuit, undervoltage output, open circuit current output, and overtemperature), CRC checking to prevent packet error (PEC), and flexible power-up options, making it an ideal choice for robust industrial control systems. No external precision resistors or calibration routines are needed to maintain consistent performance in mass production, thereby making it ideal for PLC or DCS modules.

The circuit, shown in Figure 1, provides a full function, high voltage (up to 44 V), flexible, programmable analog output solution that meets most requirements for programmable logic controller (PLC) and distributed control system (DCS) applications.

The AD5662 low power (0.75 mW typical @ 5 V), rail-to-rail output, 16-bit nanoDAC^® device and the AD5751 industrial current/voltage output driver are well matched with respect to input and output voltage ranges, as well as reference voltage requirements.

The ADR444, with low drift (3 ppm/℃ maximum for B grade), high initial accuracy (0.04% maximum for B grade), and low noise (1.8 μV p-p typical, 0.1 Hz to 10 Hz), provides the reference voltage for both the AD5751 and AD5662 and guarantees ultralow noise, high accuracy, and low temperature drift for the circuit. This circuit provides all the typical voltage and current output ranges with 16-bit resolution and no missing codes, 0.05% linearity, and less than 0.2% total output error.

The ADuM1301 and ADuM5401 provide all the necessary signal isolation between the microcontroller and the analog signal chain. The ADuM5401 also provides isolated 5 V power. The circuit also contains key features for industrial applications, such as on-chip output fault detection, CRC checking to prevent packet error (PEC), and flexible power-up options, making it an ideal choice for robust industrial control systems. No external precision resistors or calibration routines are needed to maintain consistent performance in mass production, thereby making it ideal for PLC or DCS modules.

The circuit shown in Figure 1 provides a fully programmable universal analog front end (AFE) for process control applications. The following inputs are supported: 2-, 3-, and 4- wire RTD configurations, thermocouple inputs with cold junction compensation, unipolar and bipolar input voltages, and 4 mA-to-20 mA inputs.

Today, many analog input modules use wire links (jumpers) to configure the customer input requirements. This requires time, knowledge, and manual intervention to configure and reconfigure the input. This circuit provides a software controllable switch to configure the modes along with a constant current source to excite the RTD. The circuit is also reconfigurable to set common-mode voltages for the thermocouple configuration. A differential amplifier is used to condition the analog input voltage range to the Σ-Δ ADC. The circuit provides industry-leading performance and cost.

Because of the voltage gain provided by the AD8676 and AD8275, the design is particularly suitable for small signal inputs, all types of RTDs, or thermocouples.

The AD7193 is a 24-bit Σ-Δ ADC that can be configured to have four differential inputs or eight pseudo differential inputs. The ADuM1400 and ADuM1401 provide all the necessary signal isolation between the microcontroller and the ADC. The circuit also includes standard external protection and is compliant with the IEC 61000 specifications.

Signal levels in industrial process control systems generally fall into one of the following categories: single-ended current (4 mA-to-20 mA), single-ended, differential voltage (0 V to 5V, 0 V to 10 V, ±5 V, ±10 V), or small signal inputs from sensors such as thermocouples or load cells. Large common-mode voltage swings are also typical, especially for small signal differential inputs; therefore good common-mode rejection is an important specification in the analog signal processing system.

The analog front-end circuit shown in Figure 1 is optimized for high precision and high common-mode rejection ratio (CMRR) when processing these types of industrial-level signals.

The circuit level shifts and attenuates the signals so they are compatible with the input range requirements of most modern single-supply SAR ADCs, such as the AD7685 high performance 16-bit 250 kSPS PulSAR^® ADC.

With an 18 V p-p input signal, the circuit achieves approximately 105 dB common-mode rejection (CMR) at 100 Hz and 80 dB CMR at 5 kHz.

High precision, high input impedance, and high CMR are provided by the AD8226 instrumentation amplifier. For high precision applications, a high input impedance is required to minimize system gain errors and also to achieve good CMR. The AD8226 gain is resistor-programmable from 1 to 1000.

A resistive level shifter/attenuator stage directly on the input would inevitably degrade CMR performance due to the mismatch between the resistors. The AD8226 provides the excellent CMR required for both small signal and large signal inputs. The AD8275 level shifter/attenuator/driver performs the attenuation and level shifting function in the circuit, without any need for external components.

Traditionally, sigma-delta ADCs have been used in high resolution measurement systems because signal bandwidths are quite low, and the sigma-delta architecture provides excellent noise performance at low update rates. However, there is an increased trend for higher update rates, especially in multichannel systems, to allow faster per-channel update, or for increased channel density. In such cases a high performance SAR ADC is a good alternative. The circuit shown in Figure 1 uses the AD7685 250 kSPS 16 bit ADC, with the AD8226 high performance in-amp, and the AD8275 attenuator/level shifter amplifier implemented as a complete system solution without the need for any external components.

The circuit, shown in Figure 1, is a 20-bit, linear, low noise, precision, unipolar (+10 V) voltage source with a minimum amount of external components. The AD5790 DAC is a 20-bit, unbuffered voltage output DAC that operates from a bipolar supply of up to 33 V. The AD5790 accepts a positive reference input range of 5 V to VDD − 2.5 V, and a negative reference input range of VSS + 2.5 V to 0 V. Both reference inputs are buffered on the chip, and external buffers are not required. The AD5790 offers a relative accuracy specification of ±2 LSB maximum, and operation is guaranteed monotonic with a −1 to +2 LSB maximum DNL specification.

The AD8675 precision op amp has low offset voltage (75 μV maximum) and low noise (2.8 nV/√Hz typical) and is an optimum output buffer for the AD5790. The AD5790 has two internal matched 6.8 kΩ feedforward and feedback resistors, which can either be connected to the AD8675 op amp to provide a 10 V offset voltage for a ±10 V output swing, or connected in parallel to provide bias current cancellation. In this example, a unipolar +10 V output is demonstrated, and the resistors are used for bias current cancellation. The internal resistor connection is controlled by setting a bit in the AD5790 control register (see AD5790 data sheet).

The digital input to the circuit is serial and is compatible with standard SPI, QSPI, MICROWIRE^®, and DSP interface standards. For high accuracy applications, the compact circuit offers high precision, as well as low noise—this is ensured by the combination of the AD5790 and AD8675 precision components.

The circuit shown in Figure 1 is an 18-bit linear, low noise, precision bipolar (±10 V) voltage source with a minimum amount of external components. The AD5780 DAC is an 18-bit, unbuffered voltage output DAC operating from a bipolar supply of up to 33 V. The AD5780 accepts a positive reference input range of 5 V to VDD − 2.5 V, and a negative reference input range of VSS + 2.5 V to 0 V. Both reference inputs are buffered on the chip, and external buffers are not required. The AD5780 offers a relative accuracy specification of ±1 LSB maximum, and operation is guaranteed monotonic, with a ±1 LSB maximum DNL specification.

The AD8675 precision op amp has low offset voltage (75 μV maximum), low noise (2.8 nV/√Hz typical), and is an optimum output buffer for the AD5780. The AD5780 has two internal matched feedforward and feedback resistors, which are connected to the AD8675 op amp and provide the 10 V offset voltage. This allows an output voltage swing of ±10 V with a single external 10 V reference.

The digital input to the circuit is serial and is compatible with standard SPI, QSPI, MICROWIRE^®, and DSP interface standards. For high accuracy applications, the compact circuit offers high precision, as well as low noise—this is ensured by the combination of the AD5780, ADR445, and AD8675 precision components.

This combination of parts provides industry-leading 18-bit integral nonlinearity (INL) of ±1 LSB and differential nonlinearity (DNL) of ±0.75 LSB, with guaranteed monotonicity, as well as low power, small PCB area, and cost effectiveness in an LFCSP package.

This circuit, shown in Figure 1, provides galvanic isolation for high speed, high accuracy, simultaneous sampling analog-todigital conversion applications. The 16-bit AD7685 PulSAR ADC is versatile and allows monitoring of multiple channels through daisy chaining. An input circuit based on the AD8615 op amp level shifts, attenuates, and buffers a ±10 V industrial signal to match the input requirements of the ADC. The flexible circuit includes a precision ADR391 reference and two quadchannel ADuM1402 digital isolators to provide a compact and cost effective solution to a popular industrial data acquisition application.

The circuit shown in Figure 1 is a cost effective, highly integrated 16-bit, 250 kSPS, 8-channel data acquisition system that can digitize ±10 V industrial level signals. The circuit also provides 2500 V rms isolation between the measurement circuit and the host controller, and the entire circuit is powered from a single isolated PWM controlled 5 V supply.

The circuit shown in Figure 1 is a cost effective, low power, multichannel data acquisition system that is compatible with standard industrial signal levels. The components are specifically selected to optimize settling time between samples, providing 18-bit performance at channel switching rates up to approximately 750 kHz.

The circuit can process eight gain-independent channels and is compatible with both single-ended and differential input signals.

The analog front end includes a multiplexer, programmable gain instrumentation amplifier (PGIA); precision analog-to-digital converter (ADC) driver for performing the single-ended to differential conversion; and an 18-bit, 1 MSPS PulSAR^® ADC for sampling the signal on the active channel. Gain configurations of 0.4, 0.8, 1.6, and 3.2 are available.

The maximum sample rate of the system is 1 MSPS. The channel switching logic is synchronous to the ADC conversions, and the maximum channel switching rate is 1 MHz. A single channel can be sampled at up to 1 MSPS with 18-bit resolution. Channel switching rates up to 750 kHz also provide 18-bit performance. The system also features low power consumption, consuming only 240 mW at the maximum ADC throughput rate of 1 MSPS.

It is important to provide fast and high resolution conversion information when sampling industrial level signals. Traditionally, the highest resolution analog-to-digital converters (ADCs) available at sampling rates up to 500 kSPS were 14 bit to 18 bit. The circuit shown in Figure 1 is a single-supply system optimized for sampling industrial level signals with a 24-bit, 250 kSPS sigma- delta (Σ-Δ) ADC. Each of the two differential or four pseudodifferential channels can be scanned at a rate up to 50 kSPS with 17.2 bits of noise-free code resolution.

This circuit solves the problem of acquiring and digitizing the standard industrial signal levels of ±5 V, ±10 V, and 0 V to 10 V with precision ADCs having low supply voltages by using an innovative differential amplifier with internal laser trimmed resistors to perform the attenuation and level shifting. Applications for the circuit include process controls (PLC/DCS modules), medical, and scientific multichannel instrumentation and chromatography.

The circuit shown in Figure 1 is a high performance industrial signal level multichannel data acquisition circuit that has been optimized for fast channel-to-channel switching. It can process 16-channels of single-ended inputs or 8-channels of differential inputs with up to 18-bit resolution.

A single channel can be sampled at up to 1.33 MSPS with 18-bit resolution. A channel-to-channel switching rate of 250 kHz between all input channels provides 16-bit performance.

The signal processing circuit combined with a simple 4-bit up-down binary counter provides a simple and cost effective way to realize channel-to-channel switching without an FPGA, CPLD, or high speed processor. The counter can be programmed to count up or count down for sequentially sampling multiple channels, or can be loaded with a fixed binary word for sampling a single channel.

This circuit is an ideal solution for a multichannel data acquisition card for many industrial applications including process control, and power line monitoring.

The circuit shown in Figure 1 is a highly integrated 16-bit, 1 MSPS, multiplexed 8-channel flexible data acquisition system (DAS) with a programmable gain instrumentation amplifier (PGIA) capable of handling the full range of industrial signal levels.

A single +5 V supply powers the circuit, and a high efficiency, low ripple boost converter generates the ±15 V that allows processing differential input signals up to ±24.576 V with ±2 LSB INL (maximum), and ±0.5 LSB DNL (typical). For high accuracy applications, this compact and cost-effective circuit offers high precision, as well as low noise.

The successive approximation register (SAR)-based data acquisition system includes true high impedance differential input buffers; therefore, there is no need for additional buffering, as is usually required to reduce kickback in capacitive digital-toanalog converter (DAC)-based SAR analog-to-digital converters (ADCs). In addition, the circuit has high common-mode rejection, eliminating the need for external instrumentation amplifiers, which are typically required in applications where common-mode signals are present.

The ADAS3022 is a complete 16-bit, 1 MSPS data acquisition system that integrates an 8-channel, low leakage multiplexer; a programmable gain instrumentation amplifier stage with a high common-mode rejection; a precision low drift 4.096 V reference; a reference buffer; and a high performance, no latency, 16-bit SAR ADC. The ADAS3022 reduces its power at the end of each conversion cycle; therefore, the operating currents and power scale linearly with throughput make it ideal for the low sampling rates in battery-powered applications.

The ADAS3022 has eight inputs and a COM input that can be configured as eight single-ended channels, eight channels with a common reference, four differential channels, or various combinations of single-ended and differential channels.

In the circuit shown in Figure 1, the reference is supplied by the ADR434 low noise reference buffered by an AD8031 op amp. The AD8031 is ideally suited as a reference buffer because of its ability to drive dynamic loads with fast recovery.

The ADP1613 is a dc-to-dc boost converter with an integrated power switch and provides the ADAS3022 high voltage ±15 V supplies required for the on-chip input multiplexer and the programmable gain instrumentation amplifier without compromising the performance of the ADAS3022.

This circuit offers high precision, as well as low noise, which is ensured by the combination of the ADAS3022, ADP1613, ADR434, and AD8031 precision components.

The circuit shown in Figure 1 is an integrated thermocouple measurement system based on the AD7124-4/AD7124-8 low power, low noise, 24-bit, Σ-Δ analog-to-digital converter (ADC), optimized for high precision measurement applications. Thermocouple measurements using this system show an overall system accuracy of ±1°C over a measurement temperature range of −50°C to +200°C . Typical noise free code resolution of the system is approximately 15 bits.

The AD7124-4 can be configured for 4 differential or 7 pseudo differential input channels, while the AD7124-8 can be configured for 8 differential or 15 pseudo differential channels. The on-chip low noise programmable gain array (PGA) ensures that signals of small amplitude can be interfaced directly to the ADC.

The AD7124-4/AD7124-8 establishes the highest degree of signal chain integration, which includes programmable low drift excitation current sources, bias voltage generator, and internal reference. Therefore, the design of a thermocouple system is simplified when the AD7124-4/AD7124-8 is used because most of the required system building blocks are included on-chip.

The AD7124-4/AD7124-8 gives the user the flexibility to employ one of three integrated power modes, where the current consumption, range of output data rates, and rms noise are tailored with the power mode selected. The current consumed by the AD7124-4/AD7124-8 is only 255 μA in low power mode and 930 μA in full power mode. The power options make the device suitable for non-power critical applications, such as input/output modules, and also for low power applications, such as loop-powered smart transmitters where the complete transmitter must consume less than 4 mA.

The device also has a power-down option. In power-down mode, the complete ADC along with its auxiliary functions are powered down so that the device consumes 1 μA typical. The AD7124-4/AD7124-8 also has extensive diagnostic functionality integrated as part of its comprehensive feature set.

The circuit shown in Figure 1 is an integrated 2-wire, 3-wire, or 4-wire resistance temperature detector (RTD) system based on the AD7124-4/AD7124-8 low power, low noise, 24-bit Σ-Δ analog-to-digital converter (ADC) optimized for high precision measurement applications.

This circuit note uses a Class B Pt100 RTD sensor with an accuracy of ±0.3°C at 0°C but it can support other classes such as Class A, Class AA, 1/3 DIN, or 1/10 DIN that are higher accuracy RTDs. This circuit also has provision for Pt1000 RTDs that are useful in low power applications.

The AD7124-4/AD7124-8 can achieve high resolution, low nonlinearity, and low noise performance as well as high 50 Hz and 60 Hz rejection, suitable for industrial RTD systems. The typical peak to peak resolution of the system is 0.0043°C (17.9 bits) for full power mode, sinc4 filter selected, at an output data rate of 50 SPS, and 0.0092°C (16.8 bits) for low power mode, post filter selected, at an output data rate of 25 SPS. These settings show that the system accuracy is significantly better than the sensor accuracy.

The AD7124-4/AD7124-8 integrate several important system building blocks required to support RTD measurements. Functions, including programmable excitation current sources and a programmable gain amplifier (PGA), excite and gain the RTD, respectively, which allows direct interfacing with the sensor and simplifies the design while reducing cost and power consumption.

Several options of the on-chip digital filtering and three integrated power modes, where the current consumption, range of output data rates, settling time, and rms noise are optimized, provide application flexibility. The current consumed in low power mode is only 255 μA and in full power mode is 930 μA. In power-down mode, the complete ADC along with its auxiliary functions are powered down so that the AD7124-4/AD7124-8 consume 1 μA typical. The power options make the AD7124-4/AD7124-8 suitable for nonpower critical applications, such as input modules, and also for low power applications, such as loop-powered smart transmitters where the complete transmitter must consume less than 4 mA.

The AD7124-4/AD7124-8 also have extensive diagnostic functionality integrated as part of its comprehensive feature set. This functionality can be used to check that the voltage level on the analog pins are within the specified operating range. These devices also include a cyclic redundancy check (CRC) on the serial peripheral interface (SPI) bus and signal chain checks, which leads to a more robust solution. These diagnostics reduce the need for external components to implement diagnostics, resulting in a smaller solution size, reduced design cycle times, and cost savings.

The circuit shown in Figure 1 provides a dual-channel, channel-to-channel isolated, thermocouple or RTD input suitable for programmable logic controllers (PLC) and distributed control systems (DCS). The highly integrated design utilizes a low power, 24-bit, Σ-Δ analog-to-digital converter (ADC) with a rich analog and digital feature set that requires no additional signal conditioning ICs.

Each channel can accept either a thermocouple or a RTD input. The entire circuit is powered from a standard 24 V bus supply. Each channel measures only 27 mm × 50 mm.