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Original question:

BQ76930: Questions: single part to support 4-6 cells and active balance question

BQ76920: Getting OV Fault and don't know why

Erik Anderson41
Intellectual 915 points
Part Number: BQ76920

Hi, 

This is a 4S design that was reviewed on here previously.  Everything is working fine except I get a continuous OV fault that cannot be cleared.  I've tried to set the OV threshold to 0xFF to no avail.  Any ideas what may be going on here?  Currently each cell is around 4.1V, so full pack voltage is ~16.4V.

Schematics attached.

Thanks,schematics.zip

Erik

  • 0
    Intellectual 915 points

    UPDATE:  Looks like I wasn't clearing the fault properly in my code.  Once I write a '1' to the OV bit in the status register for a few times it seems to clear OK.  But this fault occurs each time the BQ76920 is powered up (a new pack is built and the ship button is pressed).  Any idea why this fault happens?  We power the board one cell at a time, starting at the lowest cell and moving up to the highest cell.  When all cells are connected, we push the ship button.

  • 0 in reply to Erik Anderson41
    TI__Guru 54715 points

    Hi Erik,

    I don't see a reason for an OV at wake up and don't recall having experienced it, particularly with more than 1 unit.  Figure 12 is a simplified schematic, but you seem to have the essentials.  It is more common to filter REGSRC from battery transients, but the part should work fine as connected, at 14.4V you have good margin to abs max. 

    One thought is to be sure the GND is global in the design since it is not specifically wired on the TopLevel sheet.

    Another thought is to check the REGOUT voltage and the input voltages (VCn) during cell connection.  The only wakeup would seem to be from the switch so it should not be waking up with partial connection.  Similarly the input filter caps are small, so even with a transient on the input and if the part was awake during connnection the filters should settle too quickly to cause an OV. 

    Let us know what you find.