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bq 78350 FETs state when sleep

Yoav Gross
Intellectual 365 points
Other Parts Discussed in Thread: BQ78350, BQ76930

Hello,

I am using bq78350  and bq76930 AFE,

I want the FETs to turn off power when My micro controller is going to sleep, and turn on when waking up.

I am using SMB command 0x2B HostFETControl() to turn FETs on/off, most of the times it is working....

I noticed that while charging (current is 3A-4A) if I set FETs off and go to sleep, the FETs are turned off then after a few milliseconds they turn back on....  

This happens only while charging, not while discharging or at rest.

Can anyone explain this? and suggest a fix?

  • 0
    Intellectual 365 points

    Hi Again, I want to give more details for scenario above:

    1, I am sending the 0x2B HostFETControl()  to turn both charge and discharge FETs on and off. The command is working under all conditions.

    2. The only exception is while under charge current - then right after the FETs are turned off - The discharge FET is suddenly turned on - the charge FET stays off - there is no charge current. 

    Can anyone help?

  • 0
    Mastermind 8415 points

    It's been a while since I looked at the documentation of the BQ78350, so I can't remember how the FETs on/off command works.
    But I would suggest to use the PRES pin to control the FETs. When no system is detected is detected both FETs will be off. It is an active low pin, so you should put a pull up to make sure that the BQ78350 doesn't detect a system, when there is none.
    If that still doesn't fix your problem, I would suggest looking at your battery and pack connections to make sure that you're not toggling the power to your BQ78350 and BA76930.