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BQ76940: IN Ship mode, REG PIN existence 1.5V

WU YISYUAN
Expert 2165 points
Part Number: BQ76940

Hi,

     I used BQ76940 on 15 series batteries application.

    But now we find in ship mode PIN8 REGOUT have exist 1.5V.

    I try to discharge C34 with tweezers, and 1.5V still exists after releasing
   

  CON4 connect NTC between PIN1 to PIN2, PIN3 & PIN4 No connect.

What is the cause of this phenomenon?


   In theory, ship mode regout should be pulled down.
 
 

The schematic diagram is as follows:

   

thanks.

  • 0
    TI__Guru 54715 points

    Hi Wu,

    The leakage out of REGOUT is not normal.  SCL and SDA will not pull up REGOUT, but pull-up resistors for SCL and SDA may if there is voltage on the lines.  ALERT may be able to feed through to REGOUT.  In the schematic it seems the BQ76940 REGOUT is powering the MCU.  Check for the highest voltage on the MCU and of the ALERT, SDA, and SCL signals. Look for voltages between GND-A and GND-M, it seems they should be the same.

    If you have multiple boards, check to see if others perform similarly.  One different board could have a damaged device or assembly issue, although all may be processed in the same way.  Check for voltages across the various pull up resistors to see if there is an unexpected source.  If needed lift or cut the REGOUT pin to see if the voltage comes from the IC or from the net.  If you have to replace the IC, check for the voltage with the IC removed.

    I think one of these suggestions should allow you to find the issue, please let us know what you find.