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bq27621 hibernation

Johan Stenström
Intellectual 605 points
Other Parts Discussed in Thread: TM4C123GH6ZRB

Hi,

When I'm setting the hibernation flag of the bq27621 from the host MCU (TM4C123GH6ZRB), I can see that the flag is cleared within 1 second (at the same time the OCVCMDCOMP is cleared and later set). Is this expected behavior? Do the host system need to enter low power mode (hibernate) within less than one second after requesting battery gauge hibernation?

Best Regards,
Johan

  • 0
    Intellectual 605 points

    Still no success despite our efforts.

    Does the battery gauge need to be in any certain state when setting the hibernation flag (e.g. sleep or NOT sleep)? Can the battery gauge clear the hibernation flag by itself under any circumstances (apart from when waking up from hibernation)?

    Best Regards, 
    Johan 

  • 0 in reply to Johan Stenström
    TI__Expert 8230 points

    Hello Johan,

    Before going into hibernation, our gauges usually take an OCV measurement prior to entering the low power state. The CVCMDCOMP bit indicates that the OCV measurement is complete. 

    In order to enter Hibernate, the gauge must go through Normal>Sleep>Wait_Hibernate>Hibernate, it cannot skip a mode (e.g. the gauge cannot go from Normal to Hibernate directly, it must go through Sleep and Exit_Hibernate first). When you issue the SET_HIBERNATE command (0x0011), the gauge must be in Sleep mode.

    Is there any current flowing at the moment you are trying to enter Hibernate? Current can trigger the gauge to exit Hibernate mode by itself if the current is higher than HibernateCurrent.

    Also, any I2C communication directed to the gauge will wake it up. I2C communication can still happen between any other peripherals. If the gauge detects I2C communication but it's to addressed to it, it will exit Hibernate momentary and go back into Hibernate.

    Thank you.

  • 0 in reply to Fernando Lopez
    Intellectual 605 points

    Thank you for your attention Fernando!

    So, if I understand it correctly, the gauge must be in sleep mode and the EffectiveCurrent must be below HibernationCurrent at the time of issuing the SET_HIBERNATE command for the gauge to enter hibernation mode.

    In other words it is not possible to set the hibernation bit in advance and then wait for the host MCU to power down the system.

    Can you please confirm?

  • 0 in reply to Johan Stenström
    TI__Expert 8230 points
    Hello Johan,

    Yes. The gauge must be in Sleep mode first. After sending the 0x0011 command to Set Hibernate, the current must be below the EffectiveCurrent. If these conditions are met, the gauge will go into EXIT_HIBERNATE (it's a bit confusing, but this is the mode prior to HIBERNATE). The gauge will enter Hibernate, if the cell voltage is relaxed.