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BQ24735: BQ24735 Charger IC Start-Up Condition

user6505074
Prodigy 40 points
Part Number: BQ24735
Hi,
Initially, a quantity of ~ 10 (quantities) PCB assemblies were built and the majority are working well. However, we have noticed that at least 2 of the boards exhibit a condition whereby the charger IC (BQ24735) initially starts up but then cuts off the ACFET and/or(?) RBFET. We see this start-up condition repeat ..... whereby the circuit powers up and then cuts off.
We use a 24V PSU. ACDET = 2.8V.
There are no shorts on the board, as when a battery pack is plugged in, the 3.3V, 5V and 12V rails are all good and current is normal etc.
Any ideas in terms of a debug strategy?
Thanks
  • 0
    TI__Genius 11850 points

    Hi,

    Can you please describe the test conditions in more detail? In addition to your 24V PSU at the input, do you also have a battery and a system load connected at the output? Also, when you say the ACFET/RBFET are cut off after the BQ24735 initially starts up, do you mean that ACDRV is pulled low soon after the converter starts switching?

    It would be helpful to see a waveform so that I can better understand the behavior. Some helpful traces to capture would be ACDET, ACDRV, ACOK, and PHASE. This would be a good starting point to determine which direction to go for further debugging. I’m also curious whether all 10 boards will exhibit the same behavior given the same test conditions, or whether this only occurs on 2 of the 10 boards.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Prodigy 40 points

    Hi Angelo,

    With no battery in circuit, the system initially powered up (from a 24V supply) and then cuts off.

    By cutting off, I mean ACDRV is pulled low (after briefly going high initially). ACDET ~ 2.8V.

    I do not see the converter beginning to switch at all. No pulse on LODRV pin at all.

    With a battery plugged in, the system powers up (on battery power), however ACDRV is pulled low (after briefly going high initially). ACDET ~ 2.8V.

    I can share the schematic privately is you can provide an email address?

  • 0 in reply to user6505074
    Prodigy 40 points

    Hi,

    Just checking whether you have had any thoughts on this?

  • 0 in reply to user6505074
    TI__Genius 11850 points

    Hi,

    Thanks for the clarification. According to your description, regardless of whether or not the battery is connected, ACDRV briefly goes high and then goes low to turn off the ACFET/RBFET.

    How long does ACDRV stay high before going low? It would be helpful to see a waveform since the timing may provide clues about the cause.

    The conditions that must be true for ACDRV to be high are shown below. Please verify that these conditions have all been met, and please capture waveforms showing ACDET, ACDRV, ACOK, VCC, and SRN as ACDRV goes low and turns off the ACFET/RBFET.

    Best regards,

    Angelo