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BQ76940: Current sense accuracy

Part Number: BQ76940

Hi there,

I am trying to determine the accuracy to expect on the current shunt.

I estimated it using the errors (offset) ect listed in the datasheet, and the % and PPM/C of the shunt, but am measuring slightly worse error in real life.

I have a suspicion the 100R series resistors on the shunt may be adding to the error?

Could you provide the sources of error for the current sense reading on this device?

Here is the schematic:

  • Hi Cameron,

    You can consider the specs included in the datasheet Electrical Characteristics section related to the coulomb counter, which includes gain error, gain drift, offset, and INL.  You might evaluate whether the error you are seeing is an offset or a gain error - does it remain constant as you vary the current across the entire range, or is mostly a gain error, so that the error is changing with the current used?  Note that the shunt and PCB will heat when a large current is applied, so you may see some heating effect due to that on the IC as well as the shunt resistor and the impedance of the PCB traces.  The 100-Ohm resistors should not be adding significant error, since there is only minimal current that flows through those (due to input resistance of the data converter while operating).