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BQ40Z80: FA Advice: Can't talk to gauge over I2C

Hale Konopka
Prodigy 70 points
Part Number: BQ40Z80
Other Parts Discussed in Thread: EV2400

Hello, 

We have a battery pack that came back from a customer which I am unable to read with the EV2400 + BQ studio. I have...

  1. Held PACK+ at 18V to wake up the gauge
  2. Measured 17V across the PBI cap (which is the same as the total cell stack voltage) indicating that the gauge is not in shutdown
  3. Scoped I2C and rise/fall times look fine. I increased pull-up strength without success and compared to a known good sample which looks the same.

This pack worked for a period of time but then stopped allowing charging when the gauge seems to have spontaneously failed and our microcontroller could no longer communicate with the gauge (also over the same I2C bus). Can someone please suggest some next steps? 

  • 0
    TI__Mastermind 28470 points

    Hi Hale,

    What is the voltage being seen at BAT at this time? How are the cells or power source being attached to the device?

    Hale Konopka said:
    This pack worked for a period of time but then stopped allowing charging when the gauge seems to have spontaneously failed

    Would you happen to have a log file of the data from the gauge when this occurred?

    Regards,

    Anthony Baldino

  • 0 in reply to Anthony
    Prodigy 70 points

    Hi Anthony, 

    The voltage seen at BAT is 16.53V (the same as top of cell stack). 

    The cells are hooked up to VC1-5 and I measure ~3.3V/cell. 

    Additionally I apply 18V to the PACK pin to wake the device out of shutdown (and measure 17V across PBI)

    I do not have any log file of the data from the gauge when this occurred.

  • 0 in reply to Hale Konopka
    TI__Mastermind 28470 points

    Hi Hale,

    Thank you for the details. It is difficult to directly find a root cause of the issue without a log file, however has a power on reset been attempted with this gauge? There could be a hardware protection triggering, where a power on reset should reset these protections as well.

    Regards,

    Anthony Baldino

  • 0 in reply to Anthony
    Prodigy 70 points

    Hi Anthony,

    I am not sure what kind of log file you are looking for, we do not log anything from the gauge and the gauge is in a bricked state which is what I am trying to root cause. How would you perform a power on reset if it I can't communicate with the gauge over I2C?

    When I connect the EV2400, I see the first I2C message where the box tries to communicate with my DUT, then the clock is held low for ~26ms, after which I see a second message. 

    Are you familiar with any failure modes like this where the gauge seems to power on fine but doesn't talk over I2C?

    Can you provide some guidance for additional places to measure for hardware faults or ways to reset the gauge? 

    Thanks

    Hale

  • 0 in reply to Hale Konopka
    TI__Mastermind 37761 points

    Hello,

    Today's a holiday and no one is in the office. We will get back to you tomorrow.

    Regards,

    Nick Richards

  • 0 in reply to Adrian
    TI__Mastermind 28470 points

    Hi Hale,

    A power on reset for the device can be achieved by removing all power from the IC by disconnecting it from the battery cell and reconnecting it. Please let me know if this is possible to do with the pack from the customer.

    Also, the functionality of the gauge can be observed from the TS1 pin of the gauge. If pulses of around 1s are being seen through a scope on TS1, then the device is in normal mode, and if pulses are around 4s then the device is in sleep mode. Please let me know what is being seen from this pin at this time.

    Regards,

    Anthony Baldino