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Configurable NDIR gas sensing and pH sensing AFEs

March 08, 2012 // Paul Buckley

Configurable NDIR gas sensing and pH sensing AFEs

Texas Instruments Incorporated has introduced two configurable analog front ends (AFE) that provide an easy-to-use, modular solution for bridging the gap between the microprocessor and sensor. Design engineers can reduce their development time by using a single AFE across multiple nondispersive infrared (NDIR) gas sensor and pH sensor platforms instead of designing several complex discrete solutions.

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The AFEs team with TIs WEBENCH Sensor AFE Designer software and bench-top development system. The tools allow engineers to select a sensor, design and configure the solution and download configuration data to the sensor AFE for immediate prototyping.

The highly-integrated LMP91050 NDIR gas sensing AFE supports multiple thermopile sensors for NDIR sensing, indoor CO2 monitoring, demand control ventilation, HVAC, alcohol breath analysis, greenhouse gas monitoring and Freon detection.

The LMP91050 NDIR Gas Sensing AFE integrates a programmable gain amplifier (PGA), dark phase offset cancellation circuitry, adjustable common-mode generator, and SPI interface to simplify system design. The device features low gain range and high gain range, allowing the use of thermopiles with different sensitivities.

The LMP91050 offers low gain drift of 100 ppm/degrees C (maximum), output offset drift of 1.2 mV/C, phase delay variation of 500 ns, low noise at 0.1 V rms (0.1 to 10 Hz), and operation between -40C to 105C provide optimized system performance. Integration shrinks package to 3 mm x 4.9 mm, enabling smaller end products.

The highly-integrated LMP91200 pH sensing AFE supports two electrode pH sensors used in analyzer platforms for emissions monitoring, steam and water quality monitoring, chemical/petrochemical plants, food processing and more.

The LMP91200 pH Sensing AFE integrates a PGA, ultra-low input-bias pH buffer, signal guarding, temperature and measurement calibration, and common-mode generation and diagnostics circuitry, allowing use of a single chip to interface to most of todays pH sensors.

The devices on-board sensor test ensures proper connection and functionality, and ultra-low bias current of 0.4 pA (maximum) boosts system reliability and accuracy while also protecting the pH electrodes during no supply situations.

Operation from 1.8 V to 5.5 V and -40C to 125C, with a guaranteed low pH buffer input bias current across the operating range, provides maximum flexibility. Integration shrinks package to 5 mm x 6.4 mm, enabling smaller end products.

TI offers the entire signal chain for sensing applications, enabling engineers to combine components from the following families: Sensor AFE, MSP430 ultra low power 16-bit microcontroller, and 4 to 20mA transmitters such as the DAC161P997 and XTR117.

Available in volume, the LMP91050 gas sensing AFE is offered in a 10-pin MSOP package, and the LMP91200 pH sensing AFE is supplied in a 16-pin TSSOP package.

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