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ADS131A02: High side nA current measurement

Ibrahim Kamal
Intellectual 460 points
Part Number: ADS131A02
Other Parts Discussed in Thread: ADS131A04

Hello,

I want to measure a high dynamic current (500nA to 60mA) using a shunt high side configuration with the ADS131A02. The common mode voltage will be between 1.8V and 3.6V. In the application, we need only a few tens of samples per second. DC accuracy is a must.

For this purpose, I will have 2 ranges, with 2 different shunts : 30 ohms and 3 kohms. The burden voltage of the shunt will be compensated thanks to an LDO. It means the ADC will be used in a pseudo-differential configuration where the AIN negative input will be held at a relatively constant voltage.

I know the ADC input differential impedance will change the gain of the whole chain, but I can calibrate it. 

However I wonder what is the common mode leakage current of the inputs, and if it can be compensated by doing an offset calibration? Or do I need to put high impedance buffers between the inputs and the ADC?

Many thanks,

Victor

  • 0
    TI__Guru* 97775 points

    Victor,


    There's not a lot of characterization data on the common-mode impedance of the ADS131A04, but it depends on whether or not the negative charge pump is in operation.

    I did a quick check with the EVM to look at the input currents. With the negative charge pump off, the common-mode input impedance looks like its about 2MΩ with  an offset of about 200nA of input current. With the negative charge pump on, the common-mode input is also about 2MΩ with an input offset of about 1.5uA.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Intellectual 460 points

    Hi Joseph,

    Ok thanks for the measurement. I guess I'll use high impedance buffers.

    Victor