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BQ27750: FET OFF time and Delay time

Yusuke Mukuno
Expert 7395 points

Part Number: BQ27750

Hi

My customer has an issue with BQ27750.

They are using the push button switch for startup and shutdown control as below,

 (Switch control)

  Push switch > System startup

  Push switch under a few sec (that is monitored by MCU) > Send shutdown command from MCU 

(Issue)

Customer try to push the switch for startup Immediately after shutdown. (If they wait long time after shutdown, it is no problem.)

System is powered up between pushed switch, however, the system goes down when the switch is released.

(Questions)

1. Can they set 0 sec for both FET OFF time and Delay time?

  Datasheet description: Delay time must set longer than FET OFF time.

2. Does the device need some interval time from shutdown?

    Also, do you have any idea for the reason of this issue?

Thanks

Muk

  • 0
    TI__Guru* 76230 points

    Hi Yusuke,

    I am not sure i fully comprehend the issue.

    1. However, yes you can set both times to 0. It just means that as the system turns off the gauge will also shutdown immediately as well. Typically, you will want your system to turn off first before the gauge turns off. But I am not aware of any potential harzard doing that.

    2. There is time for latency for the gauge to process the shutdown command and then go into shutdown

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    TI__Expert 7395 points

    Hi Onyx-san,

    Thank you for your answer!

    Regarding #1, Thank you for your answer.

    Regarding #2,

    >There is time for latency for the gauge to process the shutdown command and then go into shutdown

    >> Does it mean that there is a delay time even if it is set to 0s?
    >> Also they would like to know if an interval is required from shutdown to startup.(Not the interval until shutdown)

    Muk

  • 0 in reply to Yusuke Mukuno
    TI__Guru* 76230 points

    Hi Muk,

    it is firmware controlled, so there must be some latency. Even if it is hardware controlled, there will still be some latency.

    For shutdown to start up, the gauge looks at the rising edge of the charger signal on the packp. However, upon wakeup the gauge has to take initial measurements and perform SOC calculations before it can be used. That process takes about 2s.

    thanks

    Onyx