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BQ76952: minimum time requirement to maintain shutdown mode after power on

Emma Wang
Expert 5190 points
Part Number: BQ76952

Hi expert,

Everytime the machine power on, we will put BQ76952 into shutdown mode and then wake it up.

They found that the BQ76952 remains in shutdown mode for different times, which will affect the time from MCU ouput is high to DSG output is high, after waking up.

Their drive circuit is like this, due to special needs.

1st setting: BQ76952 in shutdown mode 19.6ms, the time from MCU ouput is high to DSG output is high: 1.79s, which seems too long.

CH1 – DDSG

CH2 – MCU, Gate drive signal

CH3- discharge MOS VGS

CH4- TS2 – TS2

second setting: BQ76952 in shutdown mode 530ms, the time from MCU output is high to DSG output is high: 48ms.

Need to confirm:

  1. Is there a minimum time requirement to maintain shutdown mode?
  2. Why is the delay time different?

Emma

  • 0
    TI__Mastermind 25980 points

    Hi Emma,

    It looks like TS2 is being held low normally and then pulled up for the wake signal. Is that correct?

    If it is, and the device tries to enter SHUTDOWN mode while the pin is held low, the device will instead be stuck in a soft-shutdown state until the pin is pulled high again (usually by the internal pullup). This FAQ discusses soft shutdown in more detail, but that could be why there is a long delay: the device is stuck in soft shutdown -> TS2 pulls high, allowing the device to enter SHUTDOWN mode -> falling edge on TS2, waking the device from SHUTDOWN mode.

    Regards,

    Max Verboncoeur