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BQ25155: Reverse Protection on LDO and BAT Pin

SUMIT RANJAN
Expert 2005 points
Part Number: BQ25155

Hi Team,

1) Does BQ25155 have protection of wrong polarity connection on battery terminal? I can see there is Back to back diode MOSFET in functional block diagram at BAT Pin. So  i believe there wont be issue if someone has connected battery with wrong polarity.

2) Query on LDO side: LDO is getting operated by VINLS and it has default voltage of 1.8V. Will it  be any issue if someone applied some external voltage of near by 3.3V at LDO pin without connecting Input voltage at IN pin and Battery at BAT Pin? Actually, in my use case i am  going to operate with default voltage of 1.8V but i need to flash the MCU and at that time i need to operate at 3.3V.

As per block diagram again there is P-MOSFET, so i think there is internal protection.

Please confirm on my both above query.

  • 0
    TI__Mastermind 21590 points

    Hello,

    1) The back to back diode will present current leakage however, the battery pin could be damaged since the pin is rated for a minimum of -0.3V

    2) The maximum LDO voltage is 5.5V so this should be fine if there is no input voltage to the VINLS pin.

  • 0 in reply to Raheem
    Expert 2005 points

    Hi Raheem,

    Yes, you are right. I did not notice of -0.3V, My bad.

    But I  am wondering that Pin specs is less for reverse polarity and generally what is the use of Back to back MOSFET here then?

    Which leakage current prevention is required by using this back to back MOSFET? Just for more information, I want to understand little bit more here.

  • 0 in reply to SUMIT RANJAN
    TI__Mastermind 21590 points

    The back to back FETs are there to prevent leakage from the battery in cases where either PMID or IN are shorted to ground