Resistive Temperature Detectors (RTDs)

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.

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 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 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 a flexible, 4-channel, low power thermocouple measurement circuit with an overall power consumption of less than 8 mW. The circuit has a multiplexed front end, followed by an instrumentation amplifier that performs cold junction compensation (0°C to 50°C) and converts the thermocouple output to a voltage with a precise scale factor of 5 mV/°C. The error is less than 2°C, over a measurement range of −25°C to +400°C, and is primarily due to the thermocouple nonlinearity. A nonlinearity correction algorithm reduces the error to less than 0.5°C over a 900°C measurement range. Noise free resolution is less than 0.1°C.

The signal is then digitized by a 24-bit Σ-Δ ADC, and the digital value is provided on an SPI serial interface. With the PMOD form factor for rapid prototyping, the design requires minimal PC board area and is ideal for applications that require precise thermocouple temperature measurements.

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 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 onchip low gain stage ensures that signals of small amplitude can be interfaced directly to the ADC.

One of the major advantages of the AD7124-8 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.

Note that, throughout this data sheet, multifunction pins, such as DOUT/RDY, are referred to either by the entire pin name or by a single function of the pin, for example, RDY, when only that function is relevant.

Applications

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

The AD8221 is a gain programmable, high performance instrumentation amplifier that delivers the industry’s highest CMRR over frequency in its class. The CMRR of instrumentation amplifiers on the market today falls off at 200 Hz. In contrast, the AD8221 maintains a minimum CMRR of 80 dB to 10 kHz for all grades at G = 1. High CMRR over frequency allows the AD8221 to reject wideband interference and line harmonics, greatly simplifying filter requirements. Possible applications include precision data acquisition, biomedical analysis, and aerospace instrumentation.

Low voltage offset, low offset drift, low gain drift, high gain accuracy, and high CMRR make this part an excellent choice in applications that demand the best dc performance possible, such as bridge signal conditioning.

Programmable gain affords the user design flexibility. A single resistor sets the gain from 1 to 1000. The AD8221 operates on both single and dual supplies and is well suited for applications where ±10 V input voltages are encountered.

The AD8221 is available in a low cost 8-lead SOIC and 8-lead MSOP, both of which offer the industry’s best performance. The MSOP requires half the board space of the SOIC, making it ideal for multichannel or space-constrained applications.

Performance is specified over the entire industrial temperature range of −40°C to +85°C for all grades. Furthermore, the AD8221 is operational from −40°C to +125°C*.

Applications

• Weigh scales
• Industrial process controls
• Bridge amplifiers
• Precision data acquisition systems
• Medical instrumentation
• Strain gages
• Transducer interfaces

The AD8226 is a low cost, wide supply range instrumentation amplifier that requires only one external resistor to set any gain between 1 and 1000.

The AD8226 is designed to work with a variety of signal voltages. A wide input range and rail-to-rail output allow the signal to make full use of the supply rails. Because the input range also includes the ability to go below the negative supply, small signals near ground can be amplified without requiring dual supplies. The AD8226 operates on supplies ranging from ±1.35 V to ±18 V for dual supplies and 2.2 V to 36 V for single supply.

The robust AD8226 inputs are designed to connect to real-world sensors. In addition to its wide operating range, the AD8226 can handle voltages beyond the rails. For example, with a ±5 V supply, the part is guaranteed to withstand ±35 V at the input with no damage. Minimum as well as maximum input bias currents are specified to facilitate open wire detection.

The AD8226 is perfect for multichannel, space-constrained industrial applications. Unlike other low cost, low power instrumentation amplifiers, the AD8226 is designed with a minimum gain of 1 and can easily handle ±10 V signals. With its MSOP package and 125°C temperature rating, the AD8226 thrives in tightly packed, zero airflow designs.

The AD8226 is available in 8-lead MSOP and SOIC packages, and is fully specified for −40°C to +125°C operation.

For a device with a similar package and performance as the AD8226 but with gain settable from 5 to 1000, consider using the AD8227.

Applications

Industrial process controls

Bridge amplifiers

Medical instrumentation

Portable data acquisition

Multichannel systems

The AD8422 is a high precision, low power, low noise, rail-to-rail instrumentation amplifier that delivers the best performance per unit microampere in the industry. The AD8422 processes signals with ultralow distortion performance that is load independent over its full output range.

The AD8422 is the third generation development of the industry standard AD620. The AD8422 employs new process technologies and design techniques to achieve higher dynamic range and lower errors than its predecessors, while consuming less than one-third of the power. The AD8422 uses the high performance pinout introduced by the AD8221.

Very low bias current makes the AD8422 error-free with high source impedance, allowing multiple sensors to be multiplexed to the inputs. Low voltage noise and low current noise make the AD8422 an ideal choice for measuring a Wheatstone bridge.

The wide input range and rail-to-rail output of the AD8422 bring all of the benefits of a high performance in-amp to single-supply applications. Whether using high or low supply voltages, the power savings make the AD8422 an excellent choice for high channel count or power sensitive applications.

The AD8422 uses robust input protection that ensures reliability without sacrificing noise performance. The AD8422 has high ESD immunity, and the inputs are protected from continuous voltages up to 40 V from the opposite supply rail.

A single resistor sets the gain from 1 to 1000. The reference pin can be used to apply a precise offset to the output voltage.

The AD8422 is specified from −40°C to +85°C for the 8-lead MSOP and the 8-lead SOIC_N and from −40°C to +125°C for the 8-lead LFCSP.

APPLICATIONS

• Medical instrumentation
• Industrial process controls
• Strain gages
• Transducer interfaces
• Precision data acquisition systems
• Channel-isolated systems
• Portable instrumentation

The LTC2986 measures a wide variety of temperature sensors and digitally outputs the result, in °C or °F, with 0.1°C accuracy and 0.001°C resolution. The LTC2986 can measure the temperature of virtually all standard (Type B, E, J, K, N, S, R, T) or custom thermocouples, automatically compensate for cold junction temperatures and linearize the results. The device can also measure temperature with standard 2-, 3-, or 4-wire RTDs, thermistors, and diodes. The LTC2986 includes excitation current sources and fault detection circuitry appropriate for each type of temperature sensor.

The LTC2986/LTC2986-1 are 10-channel software and pin-compatible versions of the 20-channel LTC2983/LTC2984. Additional features include special modes that enable easy protection in universal multi-sensor applications, custom tables for generic ADC readings, and direct temperature readout from active analog temperature sensors. The LTC2986-1 is the EEPROM version of the LTC2986.

Applications

• Direct Thermocouple Measurements
• Direct RTD Measurements
• Direct Thermistor Measurements
• Custom Sensor Applications

The ADuC7060/ADuC7061 are fully integrated, 8 kSPS, 24-bit data acquisition systems incorporating high performance multi-channel sigma-delta (Σ-Δ) analog-to-digital converters (ADCs), 16-bit/ 32-bit ARM7TDMI^® MCU, and Flash/EE memory on a single chip.

The ADCs consists of a 5-channel primary ADC and up to an 8-channel auxiliary ADC. The ADCs operate in single-ended or differential input modes. A single channel buffered voltage output DAC is available on-chip. The DAC output range is programmable to one of two voltage ranges.

The devices operate from an on-chip oscillator and a PLL gene-rating an internal high frequency clock up to 10.24 MHz. The microcontroller core is an ARM7TDMI, 16-bit/32-bit RISC machine offering up to 10 MIPS peak performance. 4 kB of SRAM and 32 kB of nonvolatile Flash/EE memory are provided on-chip. The ARM7TDMI core views all memory and registers as a single linear array.

The ADuC7060/ADuC7061 contain four timers. Timer 1 is wake-up timer with the ability to bring the part out of power saving mode. Timer 2 may be configured as a watchdog timer. A 16-bit PWM with six output channels is also provided.

The ADuC7060/ADuC7061 contain an advanced interrupt controller. The vectored interrupt controller (VIC) allows every interrupt to be assigned a priority level. It also supports nested interrupts to a maximum level of eight per IRQ and FIQ. When IRQ and FIQ interrupt sources are combined, a total of 16 nested interrupt levels are supported. On-chip factory firmware supports in-circuit serial download via the UART serial interface ports and nonintrusive emulation via the JTAG interface.

The parts operate from 2.375 V to 2.625 V 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-based smart sensors

The LT6650 is a micropower, low voltage 400mV reference. Operating with supplies from 1.4V up to 18V, the device draws only 5.6µA typical, making it ideal for low voltage systems as well as handheld instruments and industrial control systems. With only two resistors the internal buffer amplifier can scale the 400mV reference to any desired value up to the supply voltage.

The reference is post package-trimmed to increase the output accuracy. The output can sink and source 200µA over temperature. Quiescent power dissipation is 28µW. Stability is ensured with any output capacitor of 1µF or higher.

The LT6650 is the lowest voltage series reference available in the 5-lead SOT-23 package.

Applications

• Battery-Operated Systems
• Handheld Instruments
• Industrial Control Systems
• Data Acquisition Systems
• Negative Voltage References

The LT6654 is a family of small precision voltage references that offers high accuracy, low noise, low drift, low dropout and low power. The LT6654 operates from voltages up to 36V and is fully specified from –55°C to 125°C. A buffered output ensures ±10mA of output drive with low output impedance and precise load regulation. These features, in combination, make the LT6654 ideal for portable equipment, industrial sensing and control, and automotive applications.

The LT6654 was designed with advanced manufacturing techniques and curvature compensation to provide 10ppm/°C temperature drift and 0.05% initial accuracy. Low thermal hysteresis ensures high accuracy and 1.6ppm_P-P noise minimizes measurement uncertainty. Since the LT6654 can also sink current, it can operate as a low power negative voltage reference with the same precision as a positive reference.

The LT6654 references are offered in 6-lead SOT-23 package and an 8-lead LS8 package. The LS8 is a 5mm × 5mm surface mount hermetic package that provides outstanding stability.

Applications

• Automotive Control and Monitoring
• High Temperature Industrial
• High Resolution Data Acquisition Systems
• Instrumentation and Process Control
• Precision Regulators
• Medical Equipment

The LT6656 is a tiny precision voltage reference that draws less than 1μA of supply current and can operate with a supply voltage within 10mV of the output voltage. The LT6656 offers an initial accuracy of 0.05% and temperature drift of 10ppm/°C. The combined low power and precision characteristics are ideal for portable and battery powered instrumentation.

The LT6656 can supply up to 5mA of output drive with 65ppm/mA of load regulation, allowing it to be used as the supply voltage and the reference input to a low power ADC. The LT6656 can accept a supply voltage up to 18V and withstand the reversal of the input connections.

The LT6656 output is stable with 1μF or larger output capacitance and operates with a wide range of output capacitor ESR.

This reference is fully specified for operation from –40°C to 85°C, and is functional over the extreme temperature range of –55°C to 125°C. Low hysteresis and a consistent temperature drift are obtained through advanced design, processing and packaging techniques.

The LT6656 is offered in the 6-lead SOT-23, (2mm × 2mm) DFN, and 8-lead LS8 Packages. The LS8 is a 5mm × 5mm surface mount hermetic package that provides outstanding stability.

APPLICATIONS

• Precision A/D and D/A Converters
• Portable Gas Monitors
• Battery- or Solar-Powered Systems
• Precision Regulators
• Low Voltage Signal Processing
• Micropower Remote Sensing

The LT6657 is a precision voltage reference that combines robust operating characteristics with extremely low drift and low noise. With advanced curvature compensation, this bandgap reference achieves 1.5ppm/°C drift with predictable temperature behavior, and an initial voltage accuracy of 0.1%. It also offers 0.5ppm_P-P noise and very low temperature cycling hysteresis.

The LT6657 is a low dropout reference that can be powered from as little as 50mV above the output voltage, up to 40V. The buffered output supports ±10mA of output drive with low output impedance and precise load regulation. The high sink current capability allows operation as a negative voltage reference with the same precision as a positive reference. This part is safe under reverse battery conditions, and includes current protection when the output is short-circuited and thermal shutdown for overload conditions. A shutdown is included to allow power reduction while enabling a quick turn-on.

The LT6657 is fully specified over the temperature range of –40°C to 125°C. It is available in the 8-lead MSOP package.

Applications

• High Temperature Industrial
• High Resolution Data Acquisition Systems
• Instrumentation and Process Control
• Automotive Control and Monitoring
• Medical Equipment
• Shunt and Negative Voltage References

The LT6658 is a family of precision dual output references combining the performance of a precision voltage reference and a linear regulator that we call the Refulator^™. Both outputs are ideal for driving the reference inputs of high resolution ADCs and DACs, even with heavy loading, while simultaneously powering microcontrollers and other circuitry. Both outputs have the same precision specifications and track each other over temperature and load. Each output can be configured with external resistors to give an output voltage up to 6V.

Using Kelvin connections, the LT6658 typically has 0.1ppm/mA load regulation with up to 150mA load current. A noise reduction pin is available to band-limit and lower the total integrated noise.

Separate supply pins are provided for each output, providing an option to reduce power consumption and isolate the buffer amplifiers. The outputs have excellent supply rejection and are stable with 1µF to 50µF capacitors.

The LT6658 is available in a 16-lead MSOP and DFN with an exposed pad for thermal management. Short circuit and thermal protection help to prevent thermal overstress.

APPLICATIONS

• Microcontroller or FPGA with ADC/DAC Applications
• Data Acquisition Systems
• Automotive Control and Monitoring
• Precision Low Noise Regulators
• Instrumentation and Process Control

The AD7175-2 is a low noise, fast settling, multiplexed, 2-/4- channel (fully/pseudo differential) Σ-Δ analog-to-digital converter (ADC) for low bandwidth inputs. It has a maximum channel scan rate of 50 kSPS (20 µs) for fully settled data. The output data rates range from 5 SPS to 250 kSPS.

The AD7175-2 integrates key analog and digital signal conditioning blocks to allow users to configure an individual setup for each analog input channel in use. Each feature can be user selected on a per channel basis. Integrated true rail-to-rail buffers on the analog inputs and external reference inputs provide easy to drive high impedance inputs. The precision 2.5 V low drift (2 ppm/°C) band gap internal reference (with output reference buffer) adds embedded functionality to reduce external component count.

The digital filter allows simultaneous 50 Hz/60 Hz rejection at 27.27 SPS output data rate. The user can switch between different filter options according to the demands of each channel in the application. The ADC automatically switches through each selected channel. Further digital processing functions include offset and gain calibration registers, configurable on a per channel basis.

The device operates with a 5 V AVDD1, or ±2.5 V AVDD1/AVSS, and 2 V to 5 V AVDD2 and IOVDD supplies. The specified operating temperature range is −40°C to +105°C. The AD7175-2 is in a 24-lead TSSOP package.

Applications

• Process control: PLC/DCS modules
• Temperature and pressure measurement
• Medical and scientific multichannel instrumentation
• Chromatography

The AD7177-2 is a 32-bit low noise, fast settling, multiplexed, 2-/4-channel (fully/pseudo differential) Σ-Δ analog-to-digital converter (ADC) for low bandwidth inputs. It has a maximum channel scan rate of 10 kSPS (100 µs) for fully settled data. The output data rates range from 5 SPS to 10 kSPS.

The AD7177-2 integrates key analog and digital signal conditioning blocks to allow users to configure an individual setup for each analog input channel in use. Each feature can be user selected on a per channel basis. Integrated true rail-to-rail buffers on the analog inputs and external reference inputs provide easy to drive high impedance inputs. The precision 2.5 V low drift (2 ppm/°C) band gap internal reference (with output reference buffer) adds embedded functionality to reduce external component count.

The digital filter allows simultaneous 50 Hz and 60 Hz rejection at a 27.27 SPS output data rate. The user can switch between different filter options according to the demands of each channel in the application. The ADC automatically switches through each selected channel. Further digital processing functions include offset and gain calibration registers, configurable on a per channel basis.

The device operates with a 5 V AVDD1 supply, or with ±2.5 V AVDD1/AVSS, and 2 V to 5 V AVDD2 and IOVDD supplies. The specified operating temperature range is −40°C to +105°C. The AD7177-2 is available in a 24-lead TSSOP package.

Applications

• Process control: PLC/DCS modules
• Temperature and pressure measurement
• Medical and scientific multichannel instrumentation
• Chromatography

The ADuCM360 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 ADuCM360 is designed for direct interfacing to external precision sensors in both wired and battery-powered applications. The ADuCM361 contains all the features of the ADuCM360 except that only one 24-bit Σ-Δ ADC (ADC1) is available.

The ADuCM360/ADuCM361 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 (SPI, UART, and I2C). Also integrated on chip are 128 kB of nonvolatile Flash/EE memory and 8 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.

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 ref-erence, but they can be configured to accept one or two external reference sources in ratiometric measurement configurations. 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 ADuCM360/ADuCM361 integrate a range of on-chip peripherals, which can be configured under microcontroller software control as required in the application. The peripherals include UART, 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 ADuCM360/ADuCM361 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 ADuCM360/ADuCM361 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 device. This mode allows the part to operate with ultralow power and still respond to asynchronous external or periodic events.

APPLICATIONS

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