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LPV801, LPV802

SNOSCZ3 – AUGUST 2016

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Typical Application: Three Terminal CO Gas Sensor Amplifier (continued)

8.2.2 Detailed Design Procedure

For this example, we will be using a CO sensor with a sensitivity of 69nA/ppm. The supply votlage and maximum

ADC input voltage is 2.5V, and the maximum concentration is 300ppm.

resolution, as well as allowance for "footroom" for the minimum swing on the CE terminal, since the CE terminal

generally goes negative in relation to the RE potential as the concentration (sensor current) increases. Bench

measuements found the difference between CE and RE to be 180mV at 300ppm for this particular sensor.

To allow for negative CE swing "footroom" and voltage drop across the 10k resistor, 300mV was chosen for

where

•

•

(3)

Next we calculate the maximum sensor current at highest expected concentration:

where

•

•

•

ppmMAX is the maximum required ppm reading

(4)

Now find the available output swing range above the reference voltage available for the measurement:

where

•

•

(5)

current:

(6)