Бортовая система зарядки

The ADuM4138 is a single-channel gate driver optimized for driving insulated gate bipolar transistors (IGBTs). Analog Devices, Inc., iCoupler^® technology provides isolation between the input signal and the output gate drive.

The Analog Devices chip scale transformers also provide isolated communication of control information between the high voltage and low voltage domains of the chip. Information on the status of the chip can be read back from the dedicated outputs.

The ADuM4138 includes an isolated flyback controller, allowing simple secondary voltage generation.

Overcurrent detection is integrated in the ADuM4138 to protect the IGBT in case of desaturation and/or overcurrent events. The overcurrent detection is coupled with a high speed, two-level turn off function in case of faults.

The ADuM4138 provides a Miller clamp control signal for a metal-oxide semiconductor field effect transistor (MOSFET) to provide IGBT turn off, with a single rail supply when the Miller clamp voltage threshold drops below 2 V (typical) above GND₂. Operation with unipolar secondary supplies is possible with or without the Miller clamp operation.

A low gate voltage detection circuit can trigger a fault if the gate voltage does not rise above the internal threshold within the time allowed after turn on (12.8 µs typical). The low voltage detection circuit detects IGBT device failures that exhibit gate shorts or other causes of weak drive.

Two temperature sensor pins, TS1 and TS2, allow isolated monitoring of system temperatures at the IGBTs. The secondary undervoltage lockout (UVLO) is set to 11.2 V (typical) in accordance with common IGBT threshold levels.

A serial peripheral interface (SPI) bus on the primary side of the device provides in field programming of temperature sensing diode gains and offsets to the ADuM4138. Values are stored on an electrically erasable programmable read-only memory (EEPROM) located on the secondary side of the device. In addition, programming is available for specific V_DD2 voltages, temperature sensing reporting frequencies, and overcurrent blanking times.

The ADuM4138 provides isolated fault reporting for overcurrent events, remote temperature overheating events, UVLO, thermal shutdown (TSD), and desaturation detection.

Applications

• MOSFET and IGBT gate drivers
• Photovoltaic (PV) inverters
• Motor drives
• Power supplies

The ADuM4120/ADuM4120-1 are 2 A isolated, single-channel drivers that employ Analog Devices, Inc., iCoupler^® technology to provide precision isolation. The ADuM4120/ADuM4120-1 provide 5 kV rms isolation in the 6-lead wide body SOIC package with increased creepage. Combining high speed CMOS and monolithic transformer technology, these isolation components provide outstanding performance characteristics, such as the combination of pulse transformers and gate drivers.

The ADuM4120/ADuM4120-1 operate with input supplies ranging from 2.5 V to 6.5 V, providing compatibility with lower voltage systems. In comparison to gate drivers employing high voltage level translation methodologies, the ADuM4120/ ADuM4120-1 offer the benefit of true, galvanic isolation between the input and the output.

Options exist for models with and without an input glitch filter. The glitch filter helps reduce the chance of noise on the input pin triggering an output.

As a result, the ADuM4120/ADuM4120-1 provide reliable control over the switching characteristics of insulated gate bipolar transistor (IGBT)/metal-oxide semiconductor field effect transistor (MOSFET) configurations over a wide range of switching voltages.

Applications

• Switching power supplies 
• IGBT/MOSFET gate drivers
• Industrial inverters 
• Gallium nitride (GaN)/silicon carbide (SiC) power devices

AD8418 - это обеспечивающий высокое разрешение высоковольтный усилитель для измерения тока в токовом шунте. Он обладает номинальным коэффициентом усиления 20 В/В и максимальной погрешностью усиления ±0.15% во всем рабочем температурном диапазоне. Буферизированное выходное напряжение может подаваться непосредственно, без применения дополнительных внешних компонентов, на любой типичный аналого-цифровой преобразователь. AD8418 поддерживает превосходное ослабление входного синфазного сигнала в диапазоне от −2 В до +70 В. Компонент предназначен для измерения двунаправленных токов через шунтирующий резистор разнообразных областях промышленности и автомобильной техники, включая управление электрическими двигателями, контроль состояния аккумуляторных батарей и управление соленоидами.

AD8418 обеспечивает революционные характеристики точности при работе в диапазоне температур от −40°C до +125°C. Он основан на архитектуре с нулевым дрейфом, которая позволяет достичь типичного дрейфа напряжения смещения не хуже 0.1 мкВ/°C в диапазоне рабочих температур и синфазных напряжений. AD8418 полностью испытан на соответствие требованиям автомобильной промышленности и содержит фильтры электромагнитных помех, а также патентованную схему для поддержания высокой точности выходного сигнала при синфазных напряжениях с широтно-импульсной модуляцией (ШИМ) на входе. Типичное входное напряжение смещения компонента составляет ±200 мкВ. AD8418 выпускается в 8-выводных корпусах MSOP и SOIC.

Области применения

• Измерение тока в цепи высокого напряжения
  • Управление двигателями
  • Управление соленоидами
  • Управление питанием
• Измерение тока в цепи низкого напряжения
• Диагностические средства зашиты

Области применения

This amplifier has ultralow offset, drift, and bias current. The AD8628/AD8629/AD8630 are wide bandwidth auto-zero amplifiers featuring rail-to-rail input and output swing and low noise. Operation is fully specified from 2.7 V to 5 V single supply (±1.35 V to ±2.5 V dual supply).

The AD8628/AD8629/AD8630 provide benefits previously found only in expensive auto-zeroing or chopper-stabilized amplifiers. Using Analog Devices, Inc., topology, these zero-drift amplifiers combine low cost with high accuracy and low noise. No external capacitor is required. In addition, the AD8628/ AD8629/AD8630 greatly reduce the digital switching noise found in most chopper-stabilized amplifiers.

With an offset voltage of only 1 μV, drift of less than 0.005 μV/°C, and noise of only 0.5 μV p-p (0.1 Hz to 10 Hz), the AD8628/AD8629/AD8630 are suited for applications where error sources cannot be tolerated. Position and pressure sensors, medical equipment, and strain gage amplifiers benefit greatly from nearly zero drift over their operating  temperature range. Many systems can take advantage of the rail-to-rail input and output swings provided by the AD8628/AD8629/AD8630 to reduce input biasing complexity and maximize SNR.

The AD8628/AD8629/AD8630 are specified for the extended industrial temperature range (−40°C to +125°C). The AD8628 is available in tiny 5-lead TSOT, 5-lead SOT-23, and 8-lead narrow SOIC plastic packages. The AD8629 is available in the standard 8-lead narrow SOIC and MSOP plastic packages. The AD8630 quad amplifier is available in 14-lead narrow SOIC and 14-lead TSSOP plastic packages. See the Ordering Guide section for automotive grades.

Applications

• Automotive sensors
• Pressure and position sensors
• Strain gage amplifiers
• Medical instrumentation
• Thermocouple amplifiers
• Precision current sensing
• Photodiode amplifiers

The LT3757/LT3757A are wide input range, current mode, DC/DC controllers which are capable of generating either positive or negative output voltages. They can be configured as either a boost, flyback, SEPIC or inverting converter. The LT3757/LT3757A drive a low side external N-channel power MOSFET from an internal regulated 7.2V supply. The fixed frequency, current-mode architecture results in stable operation over a wide range of supply and output voltages.

The operating frequency of LT3757/LT3757A can be set with an external resistor over a 100kHz to 1MHz range, and can be synchronized to an external clock using the SYNC pin. A low minimum operating supply voltage of 2.9V, and a low shutdown quiescent current of less than 1µA, make the LT3757/LT3757A ideally suited for battery-operated systems.

The LT3757/LT3757A feature soft-start and frequency foldback functions to limit inductor current during startup and output short-circuit. The LT3757A has improved load transient performance compared to the LT3757.

Applications

• Automotive and Industrial Boost, Flyback, SEPIC and Inverting Converters
• Telecom Power Supplies
• Portable Electronic Equipment

The LT8301 is a micropower isolated flyback converter. By sampling the isolated output voltage directly from the primary-side flyback waveform, the part requires no third winding or opto-isolator for regulation. The output voltage is programmed with a single external resistor. Internal compensation and soft-start further reduce external component count. Boundary mode operation provides a small magnetic solution with excellent load regulation. Low ripple Burst Mode operation maintains high efficiency at light load while minimizing the output voltage ripple. A 1.2A, 65V DMOS power switch is integrated along with all high voltage circuitry and control logic into a 5-lead ThinSOT^™ package.

The LT8301 operates from an input voltage range of 2.7V to 42V and can deliver up to 6W of isolated output power. The high level of integration and the use of boundary and low ripple burst modes result in a simple to use, low component count, and high efficiency application solution for isolated power delivery.

Applications

• Isolated Telecom, Automotive, Industrial, Medical Power Supplies
• Isolated Auxiliary/Housekeeping Power Supplies

The LTC4380 low quiescent current surge stopper protects loads from high voltage transients. Overvoltage protection is provided by clamping the gate voltage of an external N-channel MOSFET to limit the output voltage to a safe value during overvoltage events such as load dump in automobiles. Fixed gate clamp voltages are selectable for 12V and 24V/28V systems. For systems of any voltage up to 72V, use the adjustable gate clamp versions. Overcurrent protection is also provided.

An internal multiplier generates a TMR pin current proportional to V_DS and I_D, so that operating time in both overcurrent and overvoltage conditions is limited in accordance with MOSFET stress.

The GATE pin can drive back-to-back MOSFETs for reverse input protection, eliminating the voltage drop and dissipation of a Schottky diode solution. A low 8µA operating current permits use in always-on and battery powered applications. An accurate ON pin comparator monitors the input supply for undervoltage (UV) conditions and also serves as a shutdown input, reducing the quiescent current to 6µA.

Applications

• Automotive/Avionic/Industrial Surge Protection
• Hot Swap, Live Insertion
• High Side Switch for Battery Powered Systems
• Automotive Load Dump Protection

ADuM140E - это четырехканальный цифровой изолятор, построенный на базе технологии iCoupler^® компании Analog Devices. Благодаря сочетанию технологий изготовления быстродействующих КМОП транзисторов и монолитных трансформаторов с воздушным сердечником эти компоненты обеспечивают отличные характеристики, превосходящие характеристики альтернативных решений, например, на базе оптопар и других интегрированных устройств сопряжения. Максимальная задержка распространения составляет 13 нс, а искажение длительности импульса — менее 3 нс. Компоненты обеспечивают межканальное согласование временных характеристик в пределах 3 нс.

Компоненты серии ADuM140E имеют независимые каналы данных и выпускаются в конфигурациях с различным направлением каналов и выдерживаемым напряжением 3.0 кВ, ср.кв. или 3.75 кВ, ср.кв. Они работают с напряжением питания на любой из сторон канала в диапазоне от 1.8 В до 5 В, обеспечивая совместимость с низковольтными системами и позволяя осуществлять преобразование уровней при передаче данных через изоляционный барьер.

Области применения

ADuM141E - это четырехканальный цифровой изолятор, построенный на базе технологии iCoupler^® компании Analog Devices. Благодаря сочетанию технологий изготовления быстродействующих КМОП транзисторов и монолитных трансформаторов с воздушным сердечником эти компоненты обеспечивают отличные характеристики, превосходящие характеристики альтернативных решений, например, на базе оптопар и других интегрированных устройств сопряжения. Максимальная задержка распространения составляет 13 нс, а искажение длительности импульса — менее 3 нс. Компоненты обеспечивают межканальное согласование временных характеристик в пределах 3 нс.

Компоненты серии ADuM141E имеют независимые каналы данных и выпускаются в конфигурациях с различным направлением каналов и выдерживаемым напряжением 3.0 кВ, ср.кв. или 3.75 кВ, ср.кв. Они работают с напряжением питания на любой из сторон канала в диапазоне от 1.8 В до 5 В, обеспечивая совместимость с низковольтными системами и позволяя осуществлять преобразование уровней при передаче данных через изоляционный барьер.

В отличие от других альтернатив оптопарам компонент гарантирует корректное постоянное напряжение на выходе при статическом состоянии входного логического сигнала. Он имеет два различных варианта поддержания отказоустойчивости, в которых выходы переходят в предопределенное состояние при отсутствии напряжения питания на входной стороне или при отключенных входах. ADuM140E1/ADuM141E1/ADuM142E1 совместим по выводам с ADuM1400/ADuM1401/ADuM1402.

Области применения

The circuit shown in Figure 1 is a complete thermopile-based gas sensor using the nondispersive infrared (NDIR) principle. This circuit is optimized for CO₂ sensing, but can also accurately measure the concentration of a large number of gases by using thermopiles with different optical filters.

The printed circuit board (PCB) is designed in an Arduino shield form factor and interfaces to the EVAL-ADICUP360 Arduino-compatible platform board. The signal conditioning is implemented with the AD8629 and the ADA4528-1 low noise amplifiers and the ADuCM360 precision analog microcontroller, which contains programmable gain amplifiers, dual 24-bit Σ-Δ analog-to-digital converters (ADCs), and an ARM Cortex-M3 processor.

The circuit shown in Figure 1 is a complete high performance resolver-to-digital (RDC) circuit that accurately measures angular position and velocity in automotive, avionics, and critical industrial applications where high reliability is required over a wide temperature range.

The circuit has an innovative resolver rotor driver circuit that has two modes of operation: high performance and low power. In the high performance state, the system operates on a single 12 V supply and can supply 6.4 V rms (18 V p-p) to the resolver. In the low power state, the system operates on a single 6 V supply and can supply 3.2 V rms (9.2 V p-p) to the resolver, with less than 100 mA of current consumption. Active filtering is provided in both the driver and receiver to minimize the effects of quantization noise.

The maximum tracking rate of the RDC is 3125 rps in the 10-bit mode (resolution = 21 arc min) and 156.25 rps in the 16-bit mode (resolution = 19.8 arc sec).

This circuit provides precision data conversion using the AD5542 voltage output DAC together with the ADR421BRZ voltage reference and the AD8628 auto-zero op amp as the reference buffer. The AD8628 reference buffer provide benefits previously found only in expensive auto-zeroing or chopper-stabilized amplifiers. Using Analog Devices, Inc., circuit topology, these zero-drift amplifiers combine low cost with high accuracy and low noise. No external capacitor is required, and the digital switching noise associated with most chopper-stabilized amplifiers is greatly reduced, thereby making this the optimum choice for reference buffering.

This circuit provides precision, low power, voltage output, digital-to-analog conversion. The AD5542 can be operated in either the buffered or unbuffered mode. The application and its requirements on settling time, input impedance, noise, etc., determine which mode of operation is best. The selection of the output buffer amplifier can be tailored to suit either dc precision or fast settling time. Where the DAC is required to drive a load less than 60 kΩ, an output buffer will be required. The output impedance of the DAC is constant and code independent, but to minimize gain errors the input impedance of the output amplifier should be as high as possible. The output amplifier should also have a 3 dB bandwidth of 1 MHz or greater. The output amplifier adds another time constant to the system, thereby increasing the settling time of the final output.

A higher 3 dB amplifier bandwidth results in a faster effective settling time of the combined DAC and amplifier. All devices in the circuit can be powered from a single +5 V supply. The input voltage range of the ADR421 reference is 4.5 V to 18 V.

This circuit is a weigh scale system, which uses the AD7190, an ultralow noise, low drift, 24-bit Σ-Δ ADC with internal PGA. The AD7190 simplifies the weigh scale design because most of the system building blocks are included on the chip.

The AD7190 maintains good performance over the complete output data rate range, from 4.7 Hz to 4.8 kHz, which allows it to be used in weigh scale systems that operate at low speeds along with higher speed weigh scale systems, such as hopper scales.

Figure 1. Weigh Scale System Using the AD7190 (Simplified Schematic: All Connections Not Shown)

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).

Looking for true 16-bit level set performance in a small package and ultralow power? This circuit provides a low power, small footprint solution for precision 16-bit digital-to-analog conversion using the AD5542A/ AD5541A voltage output DAC with the ADR421BRZ voltage reference and the 20 μA AD8657 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 AD8657 has been proven and tested to meet the settling time, offset voltage, and low impedance drive capability required by this circuit application.

The combination of parts shown in Figure 1 minimizes PC board area, as well as power dissipation. The AD5542A is available in a 3 mm × 3 mm, 16-lead LFCSP or 16-lead TSSOP package. The AD5541A is available in 3 mm × 3 mm, 10-lead LFCSP or 10-lead MSOP.

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 monitors current in systems with high positive common-mode dc voltages of up to +500 V with less than 0.2% error. The load current passes through a shunt resistor, which is external to the circuit. The shunt resistor value is chosen so that the shunt voltage is approximately 500 mV at maximum load current.

The AD8212 accurately amplifies a small differential input voltage in the presence of large positive common-mode voltages greater than 500 V when used in conjunction with an external PNP transistor.

Galvanic isolation is provided by the ADuM5402 quad channel isolator. This is not only for protection but to isolate the downstream circuitry from the high common-mode voltage. In addition to isolating the output data, the ADuM5402 digital isolator can also supply isolated +3.3 V for the circuit.

The measurement result from the AD7171 is provided as a digital code utilizing a simple 2-wire, SPI-compatible serial interface.

This combination of parts provides an accurate high voltage positive rail current sense solution with a small component count, low cost, and low power.

High-side current monitors are likely to encounter overvoltage conditions from transients or when the monitoring circuits are connected, disconnected, or powered down. This circuit, shown in Figure 1, uses the overvoltage protected ADA4096-2 op amp connected as a difference amplifier to monitor the high-side current. The ADA4096-2 has input overvoltage protection, without phase reversal or latch-up, for voltages of 32 V higher than and lower than the supply rails.

The circuit is powered by the ADP3336 adjustable low dropout 500 mA linear regulator, which can also be used to supply power to other parts of the system, if desired. Its input voltage can range from 5.2 V to 12 V when set for a 5 V output. To save power, the current sensing circuit can be powered down by removing power to the ADP3336; however, the power source, such as a solar panel, can still operate.

This applies voltage to the inputs of the unpowered ADA4096-2; however, no latch-up or damage occurs for input voltages up to 32 V. If slower throughput rates are required, the AD7920 can also be powered down between samples. The AD7920 draws a maximum of 5 μW when powered down and 15 mW when powered up. The ADA4096-2 requires only 120 μA under operational conditions. When operating at 5 V, this is only 0.6 mW. The ADP3336 draws only 1 μA in the shutdown mode.

This circuit uses the ADuC7060 or the ADuC7061 precision analog microcontroller in an accurate thermocouple temperature monitoring application. The ADuC7060/ ADuC7061 integrate dual 24-bit sigma-delta (Σ-Δ) analog-to-digital converters (ADCs), dual programmable current sources, a 14-bit digital-to-analog converter (DAC), and a 1.2 V internal reference, as well as an ARM7 core, 32 kB flash, 4 kB SRAM, and various digital peripherals such as UART, timers, serial peripheral interface (SPI), and I2C interfaces.

In the circuit, the ADuC7060/ ADuC7061 are connected to a thermocouple and a 100 Ω platinum resistance temperature detector (RTD). The RTD is used for cold junction compensation. As an extra option, the ADT7311 digital temperature sensor can be used to measure the cold junction temperature instead of the RTD.

In the source code, an ADC sampling rate of 4 Hz was chosen. When the ADC input programmable gain amplifier (PGA) is configured for a gain of 32, the noise-free code resolution of the ADuC7060/ ADuC7061 is greater than 18 bits.

The single edge nibble transmission (SENT) interface to the host is implemented by using a timer to control a digital output pin. This digital output pin is then level shifted externally to 5 V using an external NPN transistor. An EMC filter is provided on the SENT output circuit as recommended in Section 6.3.1 of the SENT protocol (SAE J2716 Standard). The data is measured as falling edge to falling edge, and the duration of each pulse is related to the number of system clock ticks. The system clock rate is determined by measuring the SYNC pulse. The SYNC pulse is transmitted at the start of every packet. More details are provided in the SENT Interface section.

The circuit in Figure 1 is a completely isolated, robust, industrial, 4-channel data acquisition system that provides 16-bit, noise free code resolution and an automatic channel switching rate of up to 42 kSPS. The channel to channel crosstalk at 42 kSPS switching is less than 15 ppm FS (less than −90 dB) because of the unique selection of fast settling components in the multiplexed signal chain.

The circuit acquires and digitizes standard industrial signal levels of ±5 V, ±10 V, 0 V to 10 V, and 0 mA to 20 mA. The input buffers also provide overvoltage protection, thereby eliminating the leakage errors associated with conventional Schottky diode protection circuits.

Applications for the circuit include process control (PLC/DCS modules), battery testing, scientific multichannel instrumentation, and chromatography.

Figure 1. Functional Block Diagram of 4-Channel Data Acquisition System (Simplified Schematic: All Connections and Decoupling Not Shown)  

The circuit shown in Figure 1 is a high performance, resolver-to-digital converter (RDC) circuit that accurately measures angular position and velocity in automotive, avionics, and critical industrial applications where high reliability is required over a wide temperature range. The AD8397 high current driver can supply 310 mA into a 32 Ω load and eliminates the requirement for discrete push-pull buffer solutions.

Common applications of RDCs are in automotive and industrial markets to provide motor shaft position and/or velocity feedback.

Figure 1. High Current Buffer Using the AD8397 for the AD2S1210 RDC Excitation Signal Output (Simplified Schematic: Decoupling and All Connections Not Shown)  

The circuit shown in Figure 1 is an isolated, flyback power supply that uses a linear isolated error amplifier to supply the feedback signal from the secondary side to the primary side. Unlike optocoupler-based solutions, which have a nonlinear transfer function that changes over time and temperature, the linear transfer function of the isolated amplifier is stable and minimizes offset and gain errors when transferring the feedback signal across the isolation barrier.

The entire circuit operates from 5 V to 24 V, allowing it to be used with standard industrial and automotive power supplies. The output capability of the circuit is up to 1 A with a 5 V input and 5 V output configuration.

This solution can be adapted for use in applications where higher dc input voltages are used to create lower voltage isolated supplies with good efficiency and a small form factor. Examples include 10 W to 20 W telecommunication and server power supplies, where power efficiency and printed circuit board (PCB) density are important, and −48 V supplies are common.

The circuit in Figure 1 is a complete, low power signal conditioner for a bridge type sensor and includes a temperature compensation channel. This circuit is ideal for a variety of industrial pressure sensors and load cells that operate with drive voltages of between 5 V and 15 V.

The circuit can process full-scale signals from approximately 10 mV to 1 V, using the internal programmable gain amplifier (PGA) of the 24-bit, sigma-delta (Σ-Δ) ADC, making it suitable for a wide variety of pressure sensors.

The entire circuit uses only three ICs and requires only 1 mA (excluding the bridge current). A ratiometric technique ensures that the accuracy and stability of the system does not depend on a voltage reference.

The circuit shown in Figure 1 is a completely self-contained, microprocessor controlled, highly accurate conductivity measurement system ideal for measuring the ionic content of liquids, water quality analysis, industrial quality control, and chemical analysis.

A carefully selected combination of precision signal conditioning components yields an accuracy of better than 0.3% over a conductivity range of 0.1 μS to 10 S (10 MΩ to 0.1 Ω) with no calibration requirements.

Automatic detection is provided for either 100 Ω or 1000 Ω platinum (Pt) resistance temperature devices (RTDs), allowing the conductivity measurement to be referenced to room temperature.

The system accommodates 2- or 4-wire conductivity cells, and 2-, 3-, or 4-wire RTDs for added accuracy and flexibility.

The circuit generates a precise ac excitation voltage with minimum dc offset to avoid a damaging polarization voltage on the conductivity electrodes. The amplitude and frequency of the ac excitation is user-programmable.

An innovative synchronous sampling technique converts the peak-to-peak amplitude of the excitation voltage and current to a dc value for accuracy and ease in processing using the dual, 24-bit Σ-Δ ADC contained within the precision analog microcontroller.

The intuitive user interface is an LCD display and an encoder push button. The circuit can communicate with a PC using an RS-485 interface if desired, and operates on a single 4 V to 7 V supply.

The circuit shown in Figure 1 is a cost effective, isolated, multi- channel 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, 2.0 MSPS precision 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 2 MSPS in turbo mode, and 1.5 MSPS in normal mode. The channel switching logic is synchronous to the ADC conversions, and the maximum channel switching rate is 1.5 MHz. A single channel can be sampled at up to 2 MSPS with 18-bit resolution in turbo mode. Channel switching rates up to 750 kHz also provide 18-bit performance.

The circuit shown in Figure 1 measures indoor air quality by using a metal-oxide sensor to detect gases composed of volatile organic compounds. The sensor is composed of a heating resistor and a sensing resistor. When the sense resistor is heated, its value changes as a function of the concentrations of different gases.

The circuit uses a 12-bit, current output digital-to-analog converter (DAC) for precision control of the heater current, and the flexible software allows the heater to operate in one of the following four modes: constant current, constant voltage, constant resistance, and constant temperature.

The circuit is able measure a wide range of sense resistance values by using a software-selectable, five range resistor divider. The board also includes a temperature and humidity sensor that is used for compensating the gas concentration value.