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Unable to calibrate BQ78PL116 on one board

Maxime Champagne
Intellectual 480 points
Other Parts Discussed in Thread: BQ76PL102, BQ78PL116

Hi,

I have a procedure to calibrate the current on my boards.  It's a board using a BQ78PL116 and a BQ76PL102 to manage 5 cells.  It's been working very well for 3 prototypes but there is something wrong when I try to calibrate the 4th prototype.

I'm charging the battery pack at 3 amps, I enter the value 3000mA and I push calibrate.  With the problematic board - it senses 6380mA with a gain of 2.000 - I expect the gain to change to realize it's 3amps instead of 6.3 but the gain is stock to 2.000.  I attach an image

Any idea why the gain is stock?

Anybody had this king of problem before ?

Regards, Max

  • 0
    Guru 22270 points

    Hello Max,

    If Prototype 4 is a different design from the others and not just the 4th board, then one possible thing to check would be the sense resistor value and that the settings are the same as in the previous designs.

    Thanks,

  • 0 in reply to Greenja
    Intellectual 480 points

    Hi Greenja,

    The prototype 4 is the same design - it should be the exact same thing.  Of more, I made the test and the voltage is 15mV across the sense resistor for each prototype including the 4th prototype - no hardware problem detected.

    Looking at the image - I think it should be calibrate by modifying the gain to 0.94 but BQ Wizard doesn't want to change the gain...  I'm wondering why?

    Thx

  • 0 in reply to Maxime Champagne
    Guru 22270 points

    Hello Max,

    From my limited experience with these things, I would have to say that there is a hardware problem on the 4th board.  The software is doesn't know what board you have connected, it only bases its calculations on the values it reads from the chip.  If the other 3 boards work correctly and there is an error on the 4th, it does seem to point to hardware.  Check your grounding, filter caps and inputs again.  Perhaps put a scope on the inputs to see what is going on.

    Thanks,