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Original question:

Prevent/detect wrong polarity of charger on BMS

BQ76952: Different reverse charge protections in BMS reference design

Carlos Sanza
Prodigy 20 points
Part Number: BQ76952
Other Parts Discussed in Thread: TIDA-010208

In TIDA-010208 reference design, I see there are 2 different circuits that protect from reverse charger connection in PACK terminals:

- D47 flyback diode

- Q29 reverse charge circuit as described in  https://www.ti.com/lit/an/sluaa09a/sluaa09a.pdf

But if I am not wrong, if D47 diode is present, a reverse charge voltage in PACK would be limited to -Vd, preventing Q29 circuit to perform its function. 

If both solutions are not compatible, which one, by your experience, has more advantages?

Thank you

  • +1
    TI__Expert 4085 points

    Dear Carlos,

    Both solutions are compatible. D47 will turn on to redirect current faster than Q29 can. This will protect device early on with a reverse charger attachment. However, there is a high chance that the amount of current the diode would have to handle with the reverse protection will be enough to destroy the component if the charger is running long enough. However the diode should provide enough time for the FETs to be set properly to disable current flow.

    If you are set on only using one, I would go with the FET based solution, not the diode. While the diode is cheaper, the FET will be more robust in the long run.

    Best,

    Asher Nederveld