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BQ24725A Circuit Failures

nathan meyer
Prodigy 150 points
Other Parts Discussed in Thread: BQ24725A, BQ3060

Hello, I have a battery charger that we are producing and i am seeing higher than expected failure rates of the charging circuit.  The circuit is powered by a 15V SMPS, uses at BQ24725A with a PIC18F25K22 micro to talk to a 12.6V Li-ion battery that uses a BQ3060 GG chip.  In production we do a quick functional test of the circuit board and we are finding 5+% failure rate.  The failure is that the circuit will not charge.  From my testing, it appears that the PIC18F25K22 is correctly requesting charger voltage and current from the BQ24725A, but the chip is not able to provide charge current.  I have been reviewing boards and it appears that i have potentially two failures 1.  The BQ24725A chip itself or 2. Q2 transistor (as listed in the EVM for this chip).  My circuit for the charge is almost identical to the EVM schematic and i use the same transistor for Q1 and Q2 as the EVM.  I am concerned that there is some input transient voltage spike that is damaging either Q2 or the BQ24725A.  I have a TVS on the input and the RC filter as well.  Originally the TVS was a 36V clamping part, but i have changed this to a 18V clamping part and still seeing similar failures.  (Q2 is a 30V Vds part). Does anyone have suggestions on how i can track down what is causing these failures?

Thanks Nathan

  • 0
    TI__Mastermind 19430 points

    Can you please capture ACOK, ACDRV, and DCIN? 

  • 0 in reply to Jing Zou
    Prodigy 150 points
    Here is what i see from one of the "failed" boards: (battery voltage 10.5V)
    ACOK- 0V
    ACDRV- 0V
    VCC- 15V
    REGN-0V
    LODRV- 0V, no pulsing
    HIDRV- 10.5V
    There is communication between my PIC and the chip.
  • 0 in reply to nathan meyer
    Prodigy 150 points
    Disregard that information. I found on that board the assembler had mis-populated a few resistors that was pulling the ACDET low. I will find some boards with the U1 or Q1 (I had listed Q2 in my email above, but i meant Q1) issue that i am seeing.
  • 0 in reply to nathan meyer
    TI__Mastermind 19430 points

    Can you please provide the scope capture along with your schematic?

    It is more helpful to see the scope capture instead of DC measurements. 

    Inductance of the wire/cable can introduce voltage spike at hot plug in. Those voltage spike cannot be capture by dc measurements.

    I suggest take scope capture both on a "good" board and "failed" board.

  • 0 in reply to Jing Zou
    Prodigy 150 points
    Values from a different board: same 10.5V battery, SMBus communication is being broadcast by pic to BQ24725A
    ACOK- 3.28V (too high?)
    ACDRV- 21.2V
    Vcc- 15V
    Iout- 0V
    REGN- 5.8V
    LODRV- 0V
    HIDRV - 10.5V
  • 0 in reply to nathan meyer
    TI__Mastermind 19430 points

    Please see my response in my last post. We need to see scope plots not just dc measurements.

    Also please reference to the datasheet section 8.4.5. Please make sure all these conditions listed are verified on your board.

  • 0 in reply to Jing Zou
    Intellectual 370 points

    Hi,

    I have issues in seeing the battery voltage getting reflected at the VBAT when register are set accordingly.

    1.   * Battery voltage (VBAT)   = 8.5V

    •   * Input current (IIN) and voltage (VBUS) - 2A &12V
    •   * System voltage (VSYS) and current (ISYS) = 10v & 0.5A
    •   * Charge current (ICHG)                  =   1Amp
    •   * Registers setup

    via battery system is working, while  connecting the AC adaptor - not seeing the set charge voltage - (8V) but instead see around 1.2V all the time with the battery removed.

    other info

    BATDRV -  will be 13.3V - while working on battery 7.5V

    BATDRV -  will be 7.5V - while working on AC adaptor

    REGN    - 5.99V

    ACOK    -  3.3V

    ACDET -  2.82V

    ILIM   -  2.79V

    IOUT -  0.02V

    do let know if some thing is missed

  • 0 in reply to jvps
    TI__Mastermind 19430 points

    When adapter is plugged in, ACDET rise within the valid range. ACOK will be pulled high by external pull up resistor. BATFET will be turned off and ACFET and RBFET will be turned on to power the system from adapter. Therefore, you do not see the charge voltage set in the register.

    You will need to enable charge by setting a current int he charge current register to turn on the BATFET.

  • 0 in reply to Jing Zou
    Intellectual 370 points

    Hi Jing Zou,

    thanks for your time.

    I could get the charge voltage appearing at the BAT terminal.

    while charging is happening if the AC adaptor is removed and connected back will the charging will resume  or  do we need to reinitialize the register settings dynamically every time ACOK fails and returns.

    regards,

    Jvps

  • 0 in reply to jvps
    Intellectual 370 points
    typoerr

    Question:
    while charging is happening, if the AC adaptor is removed and connected back, will the charging resume on its own or do we need to reinitialize the register settings dynamically every time ACOK fails and returns.

    regards,
    jvps
  • 0 in reply to jvps
    TI__Mastermind 19430 points

    You will need to re-enable charge when power cycle the input source.

    We strongly recommend ordering an EVM for evaluation.