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HPA 495 (Advanced BQMTester)

Other Parts Discussed in Thread: BQ40Z50-R1

I have just finished making a jig with an HPA495. I have it all wired up and it mostly works, however the current calibration isn't very accurate. When I turn off the current, my fuel gauge thinks there is a current of about 30mA flowing when the current source is off.

I attached my PCB to a battery and calibrated by pulling 2A  from the battery - this was all OK. When the load was stopped, the current was 0.

I then put the board back on the HPA, applied only a voltage and the BQ40z50-R1 told me there was -32mA flowing. I'm measuring about 0.05mV across the sense resistors which I assume is the problem but I cannot find where this is coming from.

The FET is off. The resistor values all appear OK. B- vs Cell1- is 0. I have a large wire on B- for the current and a thin wire for the voltage - both joined at the same point on the board. 

Any ideas? Do I need a new HPA? The circuit all appears to be OK - is there a device in particular that I need to check?