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BQ76930: BQ76930: Randomly CAP2 Pin showing 7V instead of 3.3V and Chip fault appearing.

PUSHPENDER
Prodigy 60 points
Part Number: BQ76930

Application: BQ76930 working in 6S configuration.

Problam 1:

  1. Chip fault occurs after 4-10 seconds boot time.
  2. CAP2 shows 7V
  3. Cap from VC5X to VC5B shows 400mV and CAP from VC6 to VC20X shows 2.9V ( total  cell voltage is 3300mV)
  4. Behaviour is random. Communication to IC is smooth as Regout is proper 3V.

When Chip fault is not there, CAP2 shows 3.3V properly.

Impedance of CAP2 w.r.t VC5X is 300K which is normal.

Any clue why this is happening.

  • 0
    TI__Guru 54715 points

    Hi Pushpender,

    Three possibilities come to mind:

    1. Something comes loose on the board causing odd voltage measurements. Check all solder joints and related components for damage, however your check of VC5x in (3) seems to indicate the VC5X is not far from normal.
    2. The IC is damaged in some manner which shows as this inability to regulate CAP2 voltage.
    3. There is some short on the board which pulls up CAP2 intermittently.  Check for contamination around the pin and capacitor and in the board. 

    Abs max for CAP2 is 3.6V with respect to VC5X.  A high voltage on the pin from whatever cause will likely cause extra curernt out of VC5X to the cell, so the VC5X voltage will rise, which may be what you measure in (3).  With the abs max violation if a fault is found on the board the IC should still be replaced as the part could have been damaged by the high voltage.  If the part is damaged it would need to be replaced. 

    Item (3) mentions VC20X, if it is a stacked design check that the part is not being overstressed during cell connection.