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BQ29700EVM-610: BQ29700DSER battery protect chip used with battery with isolation switch

Part Number: BQ29700EVM-610

Hi,

We are using a BQ29700DSER chip. It works very well with the charger. When the charger is disconnected, the battery powers the circuit. We added an isolation switch so the user can turn the power off. When the switch is turned back on, nothing works until GND (also called VSS) is shorted to the V- pin 6 on the battery protection chip.

In the real world, this is not feasible operation. Is there any way to get the battery to power up with shorting these two pins? Otherwise, is there a better place to put the isolation switch? Any help would be much appreciated. Thanks

  • Hello Fergus,

    The device when first connecting the battery would be in an "over-discharged" state. Which requires V- to be connected to Vss or to connect the charger between PACK+ and PACK-. 

    There is a CAUTION about this in Section 9.4.1 Normal Operation of the datasheet.

    The protector would have to always be connected to the battery. If you want to stop power-up of other systems, you may just want to place it after the R32, so BAT is always connected.

    Best Regards,

    Luis Hernandez Salomon

  • Great thanks. The BQ29700 uses 5.5uA so the 600mAhr 14500 (Lithium AA) battery will take 12.5 year to discharge.