+

CE

WE

RE

Potentiostat (Bias Loop)

+

Transimpedance Amplifier (I to V conversion)

CO Sensor

U1

U2

R2

10

NŸ

C1

0.1µF

2.5V

Riso

49.9 k

C2

1µF

R1

10 k

15

LPV801, LPV802

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SNOSCZ3 – AUGUST 2016

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Copyright © 2016, Texas Instruments Incorporated

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LPV80x is a ultra-low power operational amplifier that provides 8 kHz bandwidth with only 320nA typical

quiescent current, and near precision drift specifications at a low cost. These rail-to-rail input and output

amplifiers are specifically designed for battery-powered applications. The input common-mode voltage range

extends to the negative supply rail and the output swings to within millivolts of the rails, maintaining a wide

dynamic range.

8.2 Typical Application: Three Terminal CO Gas Sensor Amplifier

Figure 44. Three Terminal Gas Sensor Amplifer Schematic

8.2.1 Design Requirements

Figure 44 shows a simple micropower potentiostat circuit for use with three terminal unbiased CO sensors,

though it is applicable to many other type three terminal gas sensors or electrochemical cells.

The basic sensor has three electrodes; The Sense or Working Electrode (“WE”), Counter Electrode (“CE”) and

Reference Electrode (“RE”). A current flows between the CE and WE proportional to the detected concentration.

The RE monitors the potential of the internal reference point. For an unbiased sensor, the WE and RE electrodes

must be maintained at the same potential by adjusting the bias on CE. Through the Potentiostat circuit formed by

R1 is to maintain stability due to the large capacitence of the sensor. C1 and R2 form the Potentiostat integrator

and set the feedback time constant.

U2 forms a transimpedance amplifer ("TIA") to convert the resulting sensor current into a proportional voltage.

(2)

output filter and ADC reservoir capacitor to drive the ADC.