Field Instruments

The ADuCM362/ADuCM363 is a fully integrated, 3.9 kSPS, 24-bit data acquisition system that incorporates dual, high performance, multichannel sigma-delta (Σ-Δ) analog-to-digital converters (ADCs), a 32-bit ARM Cortex™-M3 processor, and Flash/EE memory on a single chip. The ADuCM362/ ADuCM363 are designed for direct interfacing to external precision sensors in both wired and battery-powered applications. The ADuCM363 contains all the features of the ADuCM362, except that only one 24-bit Σ-Δ ADC (ADC1) is available.

The ADuCM362/ADuCM363 contain an on-chip 32 kHz oscillator and an internal 16 MHz high frequency oscillator. The high frequency oscillator is routed through a programmable clock divider from which the operating frequency of the processor core clock is generated. The maximum core clock speed is 16 MHz; this speed is not limited by operating voltage or temperature.

The microcontroller core is a low power ARM Cortex-M3 processor, a 32-bit RISC machine that offers up to 20 MIPS peak performance. The Cortex-M3 processor incorporates a flexible, 11-channel DMA controller that supports all wired communica-tion peripherals (both SPIs, both UARTs, and I²C). Also integrated on chip are up to 256 kB of nonvolatile Flash/EE memory and 24 kB of SRAM.

The analog subsystem consists of dual ADCs, each connected to a flexible input mux. Both ADCs can operate in fully differential and single-ended modes. Other on-chip ADC features include dual programmable excitation current sources, diagnostic current sources, and a bias voltage generator of AVDD_REG/2 (900 mV) to set the common-mode voltage of an input channel. A low-side internal ground switch is provided to allow power-down of an external circuit (for example, a bridge circuit) between conversions. Optional input buffers are provided for the analog inputs and the external reference inputs. These buffers can be enabled for all PGA gain settings.

The ADCs contain two parallel filters: a sinc3 or sinc4 filter in parallel with a sinc2 filter. The sinc3 or sinc4 filter is used for precision measurements. The sinc2 filter is used for fast measure-ments and for the detection of step changes in the input signal.

The devices contain a low noise, low drift internal band gap reference, but they can be configured to accept one or two external reference sources in ratiometric measurement config-urations. An option to buffer the external reference inputs is provided on chip. A single-channel buffered voltage output DAC is also provided on chip.

The ADuCM362/ADuCM363 integrate a range of on-chip peripherals, which can be configured under microcontroller software control as required in the application. The peripherals include two UARTs, I²C, and dual SPI serial I/O communication controllers; a 19-pin GPIO port; two general-purpose timers; a wake-up timer; and a system watchdog timer. A 16-bit PWM controller with six output channels is also provided.

The ADuCM362/ADuCM363 are specifically designed to operate in battery-powered applications where low power operation is critical. The microcontroller core can be configured in a normal operating mode that consumes 290 μA/MHz (including flash/SRAM IDD). An overall system current consumption of 1 mA can be achieved with both ADCs on (input buffers off), PGA gain of 4, one SPI port on, and all timers on.

The ADuCM362/ADuCM363 can be configured in a number of low power operating modes under direct program control, including a hibernate mode (internal wake-up timer active) that consumes only 4 μA. In hibernate mode, peripherals, such as external interrupts or the internal wake-up timer, can wake up the devices. This mode allows the devices to operate with ultralow power while still responding to asynchronous external or periodic events.

On-chip factory firmware supports in-circuit serial download via a serial wire interface (2-pin JTAG system) and UART; non-intrusive emulation is also supported via the serial wire interface. These features are incorporated into a low cost QuickStart™ Development System that supports this precision analog micro-controller family.

The devices operate from an external 1.8 V to 3.6 V voltage supply and are specified over an industrial temperature range of −40°C to +125°C.

Applications

• Industrial automation and process control
• Intelligent precision sensing systems
• 4 mA to 20 mA loop-powered smart sensor systems
• Medical devices, patient monitoring

The AD5700/AD5700-1 are single-chip solutions, designed and specified to operate as a HART^® FSK half-duplex modem, complying with the HART physical layer requirements. The AD5700/AD5700-1 integrate all of the necessary filtering, signal detection, modulating, demodulating and signal generation functions, thus requiring few external components. The 0.5% precision internal oscillator on the AD5700-1 greatly reduces the board space requirements, making it ideal for line-powered applications in both master and slave configurations. The maximum supply current consumption is 115µA, making theAD5700/AD5700-1 an optimal choice for low power loop-powered applications. Transmit waveforms are phase continuous 1200 Hz and 2200 Hz sinusoids. The AD5700/AD5700-1 contain accurate carrier detect circuitry and use a standard UART interface.

Applications

• Field transmitters
• HART multiplexers
• PLC and DCS analog I/O modules
• HART network connectivity

The ADuM1440/ADuM1441/ADuM1442/ADuM1445/ADuM1446/ADuM1447 are micropower, 4-channel digital isolators based on the Analog Devices, Inc., iCoupler^® technology. Combining high speed, complementary metal oxide semiconductor (CMOS) and monolithic air core transformer technologies, these isolation components provide outstanding performance characteristics superior to the alternatives, such as optocoupler devices. As shown in Figure 3 in the data sheet, in standard operating mode, when EN_x = 0 (internal refresh enabled), the current per channel is less than 10 μA. When EN_x = 1 (internal refresh disabled), the current per channel drops to less than 1 μA.

The ADuM1440/ADuM1441/ADuM1442/ADuM1445/ADuM1446/ADuM1447 family of quad 2.5 kV digital isolation devices are packaged in a small 16-lead QSOP and 20-lead SSOP, freeing almost 70% of board space compared to isolators packages in wide body SOIC packages.

The devices withstand high isolation voltages and meet regulatory requirements, such as UL and CSA standards. In addition to the space savings, the ADuM1440/ADuM1441/ADuM1442/ADuM1445/ADuM1446/ADuM1447 operate with supplies as low as 2.25 V.

Despite the low power consumption, all models of the ADuM1440/ADuM1441/ADuM1442/ADuM1445/ADuM1446/ADuM1447 provide low, pulse width distortion at <8 ns. In addition, every model has an input glitch filter to protect against extraneous noise disturbances.

APPLICATIONS

• General-purpose, low power multichannel isolation
• 1 MHz, low power peripheral interface (SPI)
• 4 mA to 20 mA loop process controls

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 ADP2360 is a high efficiency, high input voltage, discontinuous conduction mode (DCM) synchronous, step-down, dc-to-dc switching regulator. The ADP2360 operates with a wide input voltage range from 4.5 V to 60 V and can source up to 50 mA continuous output current, making it ideal for regulating power from a variety of voltage sources in space-constrained applications. The ADP2360 is available with an adjustable output (0.8 V to V_IN) or in 3.3 V and 5.0 V factory-programmable fixed output voltage models.

The ADP2360 uses a single-pulse PFM architecture with adjustable I_PEAK control to minimize the input and output ripple. The adjustable I_PEAK current limit allows the ADP2360 to optimize the efficiency for the application operating conditions and minimize the compatible inductor size.

The ADP2360 further offers a power-good (PG) pin to indicate when the output voltage is good. Other key features include 100% duty cycle operation, precision enable control, external soft start control, undervoltage lockout, and thermal shutdown.

The ADP2360 requires no external compensation and the solution for the fixed output voltage options requires a minimum of three external components. The ADP2360 is available in a 3 mm × 3 mm, 8-lead LFCSP package with an operating junction temperature range from −40°C to +125°C.

Applications

• 4 mA to 20 mA loop powered systems
• HART modems
• Building automation
• Distributed power systems
• Industrial control supplies
• Other high V_IN, low I_OUT systems

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.

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 shown in Figure 1 combines the  AD5755-1 (quad channel voltage and current output DAC with dynamic power control) and the AD5700-1 HART modem, to give a completely isolated multiplexed HART^®1 analog output solution. Power can be provided either from the transformer isolated power circuit provided on the board (±13 V and +5.2 V outputs, dependent on the load current) or from external power supplies connected to terminal blocks. This circuit is suitable for use in programmable logic controllers (PLCs) and distributed control system (DCS) modules that require multiple HART-compatible 4 mA to 20 mA current outputs, along with unipolar or bipolar voltage outputs. External transient protection circuitry is also included, which is important for applications located in harsh industrial environments.

The AD5755-1 DAC is software configurable and allows the user to easily program the required output ranges and dc-to-dc converter settings used for dynamic power control. It allows access to all of the internal control registers, including the slew rate control register, which is important for applications using HART communication.

The AD5700-1 is the lowest power and smallest footprint HART-compliant IC modem in the industry. It operates as a HART frequency shift keying (FSK) half-duplex modem and integrates all of the necessary signal detection, modulating, demodulating, and signal generation functions. It contains a 0.5% precision internal oscillator, thus reducing board space requirements and cost. The AD5700-1 uses a standard UART interface.

Digital isolation is provided using the quad and dual channel ADuM3481/ADuM3210 digital isolator components based on Analog Devices, Inc., iCoupler^® technology. The use of iCoupler technology reduces the need for the additional external components often required in solutions based on optoisolators. An external transformer is used to transfer power across the isolation barrier.

The ADG759 provides multiplexing capability, enabling HART communication, across the four analog output channels. The ADG759 switches one of four differential inputs to a common differential output as determined by the 2-bit binary address lines A0 and A1. When disabled, all channels are switched off. Bypass links are included to provide the flexibility to bypass the multiplexer.

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

The circuit shown in Figure 1 is an isolated smart industrial field instrument that interfaces to many types of analog sensors such as temperature (Pt100, Pt1000, and thermocouple) or bridge pressure sensors. The instrument communicates via a 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. The HART interface allows features such as remote calibration, fault interrogation, and transmission of process variables, which are necessary in applications such as temperature and pressure control.

The circuit uses the AD7124-4, an ultralow power, precision 24-bit, Σ-Δ analog-to-digital converter (ADC), which includes all the features needed for temperature and pressure systems. The circuit also includes the AD5421, a 16-bit, 4 mA to 20 mA, loop powered digital-to-analog converter (DAC); the AD5700, the industry’s lowest power and smallest footprint HART-compliant IC modem; the ADuM1441, which provides ultralow power serial peripheral interface (SPI) isolation; the ADG5433 CMOS switch; and the ADP162 low power, 3.3 V regulator in the isolated power circuitry.

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.