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bq27421-G1 - Hardware Configuration Question (BIN)

Phillip Karls
Prodigy 250 points
Other Parts Discussed in Thread: BQ27421-G1

Hi all,

I'm trying to figure out the best way to configure the bq27421-G1 for the lowest power option.

In my design the supply voltage (Battery) is always connected. The device is in one of two two modes:

1. On - all system power rails enables and device operating as expected. In this mode the bq27421-G1 is fully used.

or

2. Off - all system power rails disabled. The device effectively off but there are low power parts (<50uA total) "sniffing" for an external enable. The external enable is magnetic. In this mode the bq27421-G1 is not used at all.

I can't seem to figure out how to configure the bq27421-G1 for the Off mode to ensure its current draw is minimal. The solution has to be a hardware configuration because there's never a guarantee that the host will be present to force the bq27421-G1 into shutdown.

Can anyone guide me on this or point me to a spot in the documentation that discusses this?

Thanks,

Phillip

  • 0
    TI__Expert 4115 points

    Hello Phillip,


    In order to get the '421 into SHUTDOWN mode (i.e. lowest current draw, < 1uA) the host has to send the SHUTDOWN_ENABLE (0x001B) Control() SubCommand and then the SHUTDOWN (0x001C) Control() SubCommand to put the device into SHUTDOWN mode.  Then, the only way to get the gauge out of SHUTDOWN mode is to toggle the GPOUT pin.

    Another mode, called HIBERNATE, exists with the '421 and will be ~10 uA of current draw.  The gauge will automatically enter HIBERNATE mode if the host has previously sent the SET_HIBERNATE Control() SubCommand, the AverageCurrent() is < DM.Hibernate Current (default 3 mA) and the battery is well relaxed (determined by the gauge).

    The power modes are outlined on p. 9 of the TRM (http://www.ti.com/lit/pdf/sluuac5)

    I hope this helps.

  • 0 in reply to Jared Casey
    Prodigy 250 points

    Hi Jared,

    Thank you for getting back to me.

    So it looks like its not possible for the device to enter shutdown mode or hibernate mode on power up.

    Do you know what the device is doing after it has initialized but its still waiting for the BAT_DET Flag?

    Thanks,

    Phillip