Thermistor

This circuit shows how the ADuC7122 precision analog microcontroller can be used in an accurate thermistor temperature monitoring application. The ADuC7122 integrates a multichannel 12-bit SAR ADC, twelve 12-bit DACs, a 1.2 V internal reference, as well as an ARM7 core, 126 kB flash, 8 kB SRAM, and various digital peripherals, such as UART, timers, SPI, and two I²C interfaces. The ADuC7122 is connected to a 4.7 kΩ thermistor.

Due to the small form factor of the ADuC7122 (7 mm × 7 mm, 108-ball BGA package) the entire circuit will fit on an extremely small PCB, thus further reducing cost.

Similar in function to an RTD, thermistors are low cost temperature sensitive resistors and are constructed of solid semiconductor materials, which exhibit a positive or negative temperature coefficient. Thermistors are inexpensive and have high sensitivity. They detect small variations in temperature, which could not be observed with an RTD or a thermocouple. However, thermistors are highly nonlinear; thus, they are limited to applications with very narrow temperature ranges if linearization techniques are not applied. Circuit linearization techniques can be accomplished in software; however, that will not be discussed here.

Despite the powerful ARM7 core and high speed SAR ADCs, the ADuC7122 still provides a low power solution. With the ARM7 core running at 326.4 kHz and the primary ADC active and measuring the external temperature sensor, the entire circuit typically consumes 7 mA. Between temperature measurements, the ADC and/or the microcontroller can be switched off to further save on power consumption.

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 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 ADG1208 and ADG1209 are monolithic, iCMOS^® analog multiplexers comprising eight single channels and four differential channels, respectively. The ADG1208 switches one of eight inputs to a common output as determined by the 3-bit binary address lines A0, A1, and A2. The ADG1209 switches one of four differential inputs to a common differential output as determined by the 2-bit binary address lines A0 and A1. An EN input on both devices enable or disable the device. When disabled, all channels are switched off. When on, each channel conducts equally well in both directions and has an input signal range that extends to the supplies.

The iCMOS (industrial CMOS) modular manufacturing process combines high voltage CMOS (complementary metal-oxide semiconductor) and bipolar technologies. It enables the development of a wide range of high performance analog ICs capable of 33 V operation in a footprint that no other generation of high voltage devices has been able to achieve. Unlike analog ICs using conventional CMOS processes, iCMOS components can tolerate high supply voltages while providing increased performance, dramatically lower power consumption, and reduced package size.

The ultralow capacitance and exceptionally low charge injection of these multiplexers make them ideal solutions for data acquisition and sample-and-hold applications, where low glitch and fast settling are required. There is minimum charge injection over the entire signal range of the device. iCMOS construction also ensures ultralow power dissipation, making the ds ideally suited for portable and battery-powered instruments.

Applications

• Audio and video routing
• Automatic test equipment
• Data-acquisition systems
• Battery-powered systems
• Sample-and-hold systems
• Communication systems

The ADG1208 and ADG1209 are monolithic, iCMOS^® analog multiplexers comprising eight single channels and four differential channels, respectively. The ADG1208 switches one of eight inputs to a common output as determined by the 3-bit binary address lines A0, A1, and A2. The ADG1209 switches one of four differential inputs to a common differential output as determined by the 2-bit binary address lines A0 and A1. An EN input on both devices enable or disable the device. When disabled, all channels are switched off. When on, each channel conducts equally well in both directions and has an input signal range that extends to the supplies.

The iCMOS (industrial CMOS) modular manufacturing process combines high voltage CMOS (complementary metal-oxide semiconductor) and bipolar technologies. It enables the development of a wide range of high performance analog ICs capable of 33 V operation in a footprint that no other generation of high voltage devices has been able to achieve. Unlike analog ICs using conventional CMOS processes, iCMOS components can tolerate high supply voltages while providing increased performance, dramatically lower power consumption, and reduced package size.

The ultralow capacitance and exceptionally low charge injection of these multiplexers make them ideal solutions for data acquisition and sample-and-hold applications, where low glitch and fast settling are required. There is minimum charge injection over the entire signal range of the device. iCMOS construction also ensures ultralow power dissipation, making the ds ideally suited for portable and battery-powered instruments.

Applications

• Audio and video routing
• Automatic test equipment
• Data-acquisition systems
• Battery-powered systems
• Sample-and-hold systems
• Communication systems

The ADA4096-2 dual and ADA4096-4 quad operational amplifiers feature micropower operation and rail-to-rail input and output ranges. The extremely low power requirements and guaranteed operation from 3 V to 30 V make these amplifiers perfectly suited to monitor battery usage and to control battery charging. Their dynamic performance, including 27 nV/√Hz voltage noise density, recommends them for battery-powered audio applications. Capacitive loads to 200 pF are handled without oscillation.

The ADA4096-2 and ADA4096-4 have overvoltage protection inputs and diodes that allow the voltage input to extend 32 V above and below the supply rails, making this device ideal for robust industrial applications. The ADA4096-2 and ADA4096-4 feature a unique input stage that allows the input voltage to exceed either supply safely without any phase reversal or latch-up; this is called overvoltage protection, or OVP.

The dual ADA4096-2 is available in 8-lead LFCSP (2 mm × 2 mm) and 8-lead MSOP packages. The ADA4096-2 is available in 16-lead LFCSP (3 mm × 3 mm) and 14-lead TSSOP packages. The ADA4096-2W is qualified for automotive applications and is available in an 8-lead MSOP package.

The ADA4096-2 family is specified over the extended industrial temperature range of (−40°C to +125°C) and is part of the growing selection of 30 V, low power op amps from Analog Devices, Inc.

Applications

• Battery monitoring
• Sensor conditioners
• Portable power supply controls
• Portable instrumentation

The ADA4096-2 dual and ADA4096-4 quad operational amplifiers feature micropower operation and rail-to-rail input and output ranges. The extremely low power requirements and guaranteed operation from 3 V to 30 V make these amplifiers perfectly suited to monitor battery usage and to control battery charging. Their dynamic performance, including 27 nV/√Hz voltage noise density, recommends them for battery-powered audio applications. Capacitive loads to 200 pF are handled without oscillation.

The ADA4096-2 and ADA4096-4 have overvoltage protection inputs and diodes that allow the voltage input to extend 32 V above and below the supply rails, making this device ideal for robust industrial applications. The ADA4096-2 and ADA4096-4 feature a unique input stage that allows the input voltage to exceed either supply safely without any phase reversal or latch-up; this is called overvoltage protection, or OVP.

The dual ADA4096-2 is available in 8-lead LFCSP (2 mm × 2 mm) and 8-lead MSOP packages. The ADA4096-2 is available in 16-lead LFCSP (3 mm × 3 mm) and 14-lead TSSOP packages. The ADA4096-2W is qualified for automotive applications and is available in an 8-lead MSOP package.

The ADA4096-2 family is specified over the extended industrial temperature range of (−40°C to +125°C) and is part of the growing selection of 30 V, low power op amps from Analog Devices, Inc.

Applications

• Battery monitoring
• Sensor conditioners
• Portable power supply controls
• Portable instrumentation

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 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 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 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 AD7175-8 is a low noise, fast settling, multiplexed, 8-/16- 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 ìs) for fully settled data. The output data rates range from 5 SPS to 250 kSPS.

The AD7175-8 integrates key analog and digital signal condition-ing 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 . AVSS supply, or with ±2.5 V AVDD1/AVSS, and 2.5 V to 5 V AVDD2 and IOVDD supplies. The specified operating temperature range is .40°C to +105°C. The AD7175-8 is available in a 40-lead LFCSP package.

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