Configurable AFE for (NDIR) Sensing Applications

The LMP91051 is a dual channel programmable integrated Sensor Analog Front End (AFE) optimized for thermopile sensors, as typically used in NDIR applications. It provides a complete signal path solution between a sensor and microcontroller that generates an output voltage proportional to the thermopile voltage. The LMP91051’s programmability enables it to support multiple thermopile sensors with a single design as opposed to the multiple discrete solutions.

The LMP91051 features a programmable gain amplifier (PGA), “dark phase” offset cancellation, and an adjustable common mode generator (1.15V or 2.59V) which increases output dynamic range. The PGA offers a low gain range of 167V/V to 1335V/V plus a high gain range of 1002V/V to 7986V/V which enables the user to utilize thermopiles with different sensitivities. The PGA is highlighted by low gain drift (20 ppm/°C), output offset drift (230 mV/°C at G = 1002 V/V), phase delay drift (300 ns) and noise specifications (0.1 µVRMS 0.1 to 10Hz) . The offset cancellation circuitry compensates for the “dark signal” by adding an equal and opposite offset to the input of the second stage, thus removing the original offset from the output signal. This offset cancellation circuitry allows optimized usage of the ADC full scale and relaxes ADC resolution requirements.

The LMP91051 allows extra signal filtering (high pass, low pass or band pass) through dedicated pins A0 and A1, in order to remove out of band noise. The user can program through the on board SPI interface. Available in a small form factor 14 pin TSSOP package, the LMP91051 operates from –40 to +105°C.