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BQ25792: BQ25792 TS pin and ExtFET for Cutoff Battery

Sathiyan Durai
Prodigy 50 points
Part Number: BQ25792
Other Parts Discussed in Thread: CSD17575Q3

Tool/software:

Hi,

1. I am using a separate temperature monitor for the battery inside the pack. In that case, what should I do with the TS pin?

2. If I am using a separate MOSFET to disconnect my battery via the MSP430 microcontroller when charging is complete or under no-charge conditions, do I still need the CSD17575Q3 (taken from development board)?
If not, what should I do with the SDRV, BAT_0/BAT_1, and BATP pins?"

Thanks

Sathiyan

  • 0
    TI__Guru**** 165786 points

    Hi Sathiyan,

    Regarding 1, to hardware disable TS function, place matching resistor from REGN to TS to GND (e.g. 2 10kohm resistors).  To software disable after POR, the EN_TS bit can be set to 1.

    Regarding 2, If charge is still enabled (CE pin and bit) when the MOFET disconnects the battery with only the min recommended capacitance at BAT pin, the charger's BAT and BATP pins hit battery OVP and turn off the converter for 30ms.  This results in SYS collapsing.  If your software/firmware can disable charge and then turn off the FET, no issue.  Of course, your software/firmware would have to monitor the battery voltage for discharge and then, first, turn on the MOSFET and then re-enable charge.  The charger's ADC can help with the monitoring.  Alternatively, you can add 200uF of capacitance on BAT to prevent the OVP event.

    If not used SDRV needs a 1000pF cap to ground.  BAT_0/BAT1 must be connected to the input side of your MOSFET.  If you want to implement ship mode using your MOSFET, BATP must be connected to the battery (output side of the MOSFET).  If not, BATP must be tied to BAT.  BATP cannot be left floating.

    Regards,

    Jeff