OPA396 datasheet(17/30 Pages) TI

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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, as well as validating and testing their design

implementation to confirm system functionality.

8.1 Application Information

The OPA396 is a unity-gain stable, precision operational amplifier free from unexpected output and phase

reversal. The OPA396 is optimized for full rail-to-rail input, allowing for low-voltage, single-supply operation or

split-supply use. These miniature, high-precision, low-noise amplifiers offer high-impedance inputs that have a

common-mode range 100 mV beyond the supplies and can tolerate the full supply voltage across the input. The

OPA396 precision amplifier is designed for sensor amplification, low-power analog signal chain applications in

low or high gains, as well as a low-power discrete MOSFET or bipolar driver.

8.2 Typical Applications

8.2.1 Three-Terminal CO Gas Sensor

Figure 8-1 shows a simple micropower potentiostat circuit for use with three-terminal unbiased CO sensors.

This same design is applicable to many other type of 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 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 must be

maintained at the same potential by adjusting the bias on CE. Through the potentiostat circuit formed by U1, the

servo feedback action maintains the RE pin at a potential set by VREF. R1 maintains stability as a result of the

large capacitance of the sensor. C1 and R2 form the potentiostat integrator and set the feedback time constant.

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

The transimpedance gain, and resulting sensitivity, is set by RF according to Equation 1:

VTIA = (–I * RF) + VREF

(1)

RLoad is a load resistor with a value that is normally specified by the sensor manufacturer (typically, 10 Ω). The

potential at WE is set by the applied VREF.

REF

OPA396

OUT

LOAD

Figure 8-1. Three-Terminal CO Gas Sensor

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OPA396

SBOSA65 – JULY 2021

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