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BQ25756: ADC error - VBAT

Michal Bialas
Prodigy 10 points
Part Number: BQ25756

Tool/software:

Hello,

We are working on a project in the company that uses the BQ25756 as a charger for a supercapacitor pack. The schematic was copied from the BQ25756EVM. The system works fine but we have a problem with the readings of the pack voltage. The value between the ADC reading is about 250mV lower than the actual value. This voltage difference seems to be more or less constant over the entire output voltage range of the charger. The problem occurs on all PCBs manufactured for us. Readings from other ADC channels are much more accurate.

1) Is there any way to fix this (apart from writing a software calibration)?

2) I was unable to find this information in the datasheet. From which pin does the integrated circuit take the voltage for measurement?

Best Regards,
Michał

  • 0
    TI__Mastermind 31085 points

    Hello Michal,

    Thanks for working on this.

    Michal Bialas said:
    1) Is there any way to fix this (apart from writing a software calibration)?

    The ADC is intended as a general indicator. I don't recommend using the ADC for precise measurements. I recommend using a battery gauge or battery monitor for more accurate measurements. This FAQ has more information.

    Michal Bialas said:
    2) I was unable to find this information in the datasheet. From which pin does the integrated circuit take the voltage for measurement?

    The circuit measures VBAT from the SRN pin.

    Let me know if you have any other questions about this.

    Best Regards,
    Ethan Galloway