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Original question:

BQ76942: High-Side Driver for BQ76942

BQ76942: Internal structure questions

Emma Wang
Expert 5190 points
Part Number: BQ76942
Other Parts Discussed in Thread: BQ76952

Hi expert,

I have a customer is using BQ76942 and they have several questions.

1. Whether the pin is suspended or equal to Vbat when pchg / pdsg is off;

2.pull-up the RST_SHUT will exit the sleep mode. If it lasts for 1s, BQ76942 will enter the shutdown mode. What is the effective recognition time for exiting the sleep mode? How long of the high-level time will cause malfunction?

3. The recommended value of CP1 in the specification is 100nF ~ 2200nf. What may happen if I increase the capacitance to 4700uf?

BR

Emma

  • 0
    TI__Guru* 81034 points

    Hi Emma,

    For #1, the first answer in this E2E thread helps to explain the PCHG/PDSG a little more: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/933173/bq76952evm-bq76952-evm-showing-pchg-and-pdsg-showing-1-7v-difference-while-toggling

    2. I am not sure I understand your question. The RST_SHUT pin can be used to put the device into Shutdown mode. To exit Shutdown mode, the TS2 pin needs to see a falling edge or the LD pin needs to see a rising edge. The device cannot exit Shutdown mode using the TS2 pin.

    3. You can read more about the charge pump capacitor value in Section 4 of the Multiple FETs application report here: https://www.ti.com/lit/an/sluaa09a/sluaa09a.pdf You should not use a capacitor larger than 2.2 uF. If you use a larger value, the charge pump voltage will not reach its value before the FET turns on.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    TI__Expert 5190 points

    Matt,

    for the second questions.

    it is about exiting sleep mode method, it showed in TRM:

    "The BQ76952 device will exit SLEEP mode if a protection fault occurs, or current begins flowing, or a charger
    is attached, or the 0x009A SLEEP_DISABLE() subcommand is sent, or if the RST_SHUT pin is asserted for < 1 s."

    and this 

    "While the BQ76952 device is in NORMAL or SLEEP mode, the device can also be configured to
    enter SHUTDOWN mode if the internal temperature measurement exceeds     Power:Shutdown:Shutdown
    Temperature     for Power:Shutdown:Shutdown Temperature Delay seconds.
    When the SHUTDOWN mode sequence has been initiated by the     0x0010 SHUTDOWN() subcommand or the
    RST_SHUT pin driven high for 1 s,"

    it told us the 1s is the boundary of exiting sleep mode and entering shutdown mode.

    they just want to know min time of exiting sleep mode?

    BR

    Emma

  • 0 in reply to Emma Wang
    TI__Guru* 81034 points

    Hi Emma, 

    Waking from SLEEP mode is fast - the Wake Comparator is used to transition to Normal mode quickly if a current is detected above the Wake Comparator Current setting. The different speed options for this comparator are described in Table 7-2 of the TRM.

    Best regards,

    Matt