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BQ76PL455A-Q1: Incorrect ADC output

Harsh Gugale
Prodigy 240 points
Part Number: BQ76PL455A-Q1
Other Parts Discussed in Thread: INA250

Hello,

I am using bq76pl455aq1 for EV application and right now trying to make a prototype BMS for 1/2 KWhr 48V system(52 Li - ion Al chem cells).I connected the IC according to the specifications in the datasheet with some modification.I have not designed any LPF between cell terminal and VSENSE since the drop in the resistor posed a problem in calibration.The IC communicates fine but when I execute command to procure ADC data the values are all messed up as shown below: (they should each be 3.76V)

I checked the pin voltages individually and they are fine.Also, it generates false Overvoltage and Undervoltage faults for different cells in both ADC and CMP comparison even though the thresholds are the same.The same circuit was working fine until the time I had not connected a current sensor INA250 to measure 3A of current.I don't know how but my MCU and BMS IC stopped responding so I had to change both the MCU and the BMS IC.After I replaced both I am facing this problem with the new ones.

All potentials of the analog die clamp to their respective voltages.

My project is stalled in between and any help would be highly appreciated.

Thanks so much

Harsh

  • 0
    TI__Intellectual 2795 points
    Hi Harsh,

    Please follow our recommended external circuit guidelines. The external VSENSE circuit has been carefully designed to provide necessary filtering for best accuracy and reliable performance, while also providing protection for in-rush current during hot-plug (series R provides current limit). Please provide your schematic for us to review, but I can already say if the there is no low-pass filter, there is a good chance you have damaged the internal ESD diodes during the hot-plug event.

    I can't really comment on the INA250 current sense circuit issues you mention. You may need to have an isolator between the INA250 and the MCU. Someone that knows the INA250 better should comment...

    Regards,
    Stephen
  • 0 in reply to Stephen Holland
    Prodigy 240 points
    Thank you, Stephen, for your quick response.

    Yes ,I recognize it was incorrect to omit the LPF. I thought since the input resistance is so high it wouldn't pose any problem.I'll try with the resistors now.Thanks again.

    Harsh