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BQ76952: OCD and SCD recovery query in the context of Electric Vehicles.

Ananya KC
Prodigy 60 points
Part Number: BQ76952

We are using BQ76952 chip in our BMS which will be used in EVs. I have a query regarding the recovery method for OCD1,2,3 and SCD.

OCD1, OCD2, OCD3, OCDL Recovery

The datasheet says that to recover from OCD1,2 or 3 a charge current greater than the recovery threshold must be provided for recovery time seconds. When an EV is operational it is not possible to give charging current. Then the only way to recover is to set OCD latch to a certain number and recover using subcommand 0x009B OCDL_RECOVER() sent by the host when the latch counter exceeds latch limit. Is this logic correct?

There is another option saying recovery from time.

" If recovery is preferred based only on time, then the recovery based on charging current can be used, with the current threshold set to a small discharge current."

I did not understand this completely.

SCD Recovery

For recovery from SCD a similar method should be used as recovery using charging current cannot be used in EVs. Again I did not understand this line:

" If recovery is preferred based only on time, then the recovery based on charging current can be used, with the current threshold set to a small discharge current."

In this case too the only way to recover from the fault is to set the SC latch to a number and when the latch counter exceeds the limit the host sends the 0x009C SCDL_RECOVER() subcommand. Is this logic correct?

Are there better ways to recover other than the two mentioned above.

Thank you.

  • +1
    TI__Mastermind 42060 points

    Hello Ananya,

    The Technical Reference Manual (TRM) goes into detail on the protection recovery mechanisms for these. I'd suggest to read it for more detail.

    "If recovery is preferred based only on time, then the recovery based on charging current can be used, with the current threshold set to a small discharge current."
    Typically to recover from OCD1/2/3, you would require a charging current for the required Protections:Recovery:Time. However, if you'd like time-based recovery, you can actually set the recovery threshold to be a small discharging current (instead of the typical charging current). This would allow recovery solely based on time.

    The alternative as you said, is to use OCD latch (OCDL), with a Protections:OCDL:Latch Limit of 1. Then you can recover based on commands.

    Both would be valid.

    For SCD Recover, this is actually recovered based on time only. So no charging current is required. This is explained in Section 5.2.6 Short Circuit in Discharge Protection of the TRM.

    Alternatively, you can also use SCD latch (SCDL) and recover with a command.

    Best Regards,

    Luis Hernandez Salomon