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OPA4374: OPA4374 test accuracy deviation

Part Number: OPA4374

Dear TI:

     My client used OPA4374 to test the current load of product, they found there are a few pieces test result is deviation, and they replace a new OPA4374 on the board, the test result will right.

     The right load value is 5A, and the deviation value is 3.5A or 7A, the schematic as below, please help to check if the design has some problem, or it is a IC quality problem?

  • The test deviation device put in a new board, the test still wrong, so the failure is follow with the device.
  • Hi Eric,

    what is the supply voltage of OPAmp?

    Take care, the output of OPAmp cannot fully go down to the negative rail.

    Kai
  • Hi Eric,

    Is this an issue of offset voltage? The OPA4374 has an offset voltage maximum of 5mV at 25C. Looking at your circuit, 5A through 3 parallel 5mOhm resistors (1.67mOhm Req) will produce an input voltage of just 8.35mV. This is very close to the allowed offset for the device which means you have the potential for high error.

    For example, if the offset voltage is 5mV, you'll get an output voltage due to offset of 100mV. For a 5A input current, you have an output of 167mV. Therefore, the total output voltage is 267mV which means you have 38% error!

    Each device has a different offset voltage, some worse than others so changing the device can change the result. You can choose a lower offset voltage device so that your error is lower or you can change your circuit so that you have a bigger voltage drop across Rsense. Also, do you do any calibration on your systems? Performing calibration can greatly help.

    -Paul