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BQ76952: OCC Protection in charging and regeneration

Garrett Albers
Prodigy 20 points
Part Number: BQ76952
Other Parts Discussed in Thread: TIDA-010208

Hello,

I have a question regarding the behavior of the OCC protection setting from section 13.6.4.1 of the BQ769x2 datasheet.

For our use case we have two distinct modes in which we expect positive current flow from our design:

  • Regular constant charging provided external charger 
  • Large spikes of positive current during regenerative braking

For our design we want to limit constant charging current to 10A as provided by an external charger, but during regenerative braking events we want to allow as much as 25A of positive current for short durations of time.

My question boils down to:  Is the OCC protection able to recognize the difference between regeneration where the charge and discharge FET's both open, versus constant charging where only the charge FET closed and the discharge FET is open? 

Thanks!

  • 0
    TI__Genius 11315 points

    Hey Garrett,

    OCC protection is independent of FET state.

    In your last sentence, did you mean to say where the charge and discharge FETs are both "closed"? Open would indicate no connection between pack+ and bat+. 

    Another thing, what is the expected voltage during those large charging spikes? Our device may not be able to handle those voltages and will need further protection on the PACK and LD pin as seen and implemented in TIDA-010208 sheet 6. 

    Thanks,
    Caleb

  • 0 in reply to Caleb Perez
    Prodigy 20 points

    Woops, you are correct. In REGEN both Charge and Discharge FET's will be CLOSED allowing current to flow into the battery cells.
    During a REGEN event the max expected voltage is 55v. I believe the rated max for the LD and Pack pin is somewhere around 85v.

    Just to explicitly confirm you are saying that while both DCHG and CHG FET's are closed during a large regeneration event at 25A the OCC protection would see the 10A threshold get exceeded and would step in opening the charge FET?

  • +1 in reply to Garrett Albers
    TI__Genius 11315 points

    Yes, if the OCC is set at 10A and there are 25A measured across the sense resistor during charging the charge FET will open, regardless of the DCHG and CHG FET state.