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BQ25756: 14S charger :: REGN at 0V, STAT1 and STAT2 low/active

Will Brown
Intellectual 451 points
Part Number: BQ25756

I am bringing up a BQ25756RRVR battery charger in 14S configuration for the first time, and am stumped.  It is unhappy, in that REGN is 0V, and both STAT1 and STAT2 are asserted.  Initially I had pin 32 floating, but found the schematic checklist which said to short to pin 33, so I did that, with no change in operation.  Node voltages are annotated in red.  PG and FBG are both acting like it is happy with the power input.  We are not using I2C at this time, those lines just sit at +3.3V.  The battery is nearly full, but low enough I think a charge cycle should be starting.  I guess I'm missing some aspect of care-and-feeding of the BQ25756 but I can't seem to figure it out. Thanks in advance for reading this and any tips or pointers.

Thanks

Will

acwcb.pdf

  • 0
    Intellectual 451 points

    I guess what I could use TIs help with specifically, is to fill in the blanks on what is included in the "etc" portion of possible charging faults.  From the datasheet, Table 8-6, STAT1 and STAT2 both being ON is described as "Charging fault detected (TS out of range, safety timer fault, etc.) "

  • 0 in reply to Will Brown
    TI__Expert 3070 points

    Hi Will,

    Thank you for your question. I suggest that you disconnect REGN and DRV_SUP using JP12 and try to see if the circuit and IC work with an external drive voltage. That will really help in narrowing down the scope of the problem. Please let me know your results so that I can further analyze the issue.

  • 0 in reply to Utsav Gupta
    Intellectual 451 points

    Hi Utsav,

    Thanks for the reply. I brought up a second board, which acts more reasonable with respect to REGN operating when it's supposed to.


    The first board must have been an infant mortality of some sort. I wonder if it is the VAC pins 32 and 33 not being connected together on the first board during initial bring-up that damaged it. So my question now is, can you explain the purpose and correct connection of Pin 32, VAC (OUT).

    * The datasheet sort of mentions that pin 32 is a VAC "output" and doesn't say what to do with it.
    * The schematic checklist says pins 32 and 33 must always be shorted together.
    * The EVM connects pins 32 and 32 through R101 (zero ohms).

    Is is possible the IC was damaged because it had VAC applied with pin 32 floating? How are pins 32 and 33 connected inside the IC, and what is the purpose of pin 32?


    Thanks

    Will

  • 0 in reply to Will Brown
    TI__Expert 3070 points

    Hi Will,

    It is definitely possible that the IC was damaged because Pin 32 and 33 were not shorted together and rather pin 32 was left floating. Pin 33 is the main VAC pin and the ACUV and ACOV calculation must be done using that pin. The input bias to power the IC is also through pin 33. When Reverse Mode is enabled, pin 32 is regulated to VAC_REV.

  • 0 in reply to Utsav Gupta
    Intellectual 451 points

    So I had pin 33 connected to VAC... Pin 32 was floating.  I never use reverse mode.  But you are saying that floating pin 32 in charge-only mode will cause damage, correct?

  • +1 in reply to Will Brown
    TI__Expert 3070 points

    Yes that is possible. They must be shorted.

  • 0 in reply to Will Brown
    TI__Expert 3070 points

    You"re welcome