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BQ24780S: backup power configuration

Part Number: BQ24780S

Hi team,

My customer wants to build a backup power module with the following configuration, the BATFET is disconnected from the input sense resistor.

Can you comment on whether this idea is feasible? Thanks!

Best regards,

Sam Ting

  • Hi Sam,


    This configuration is not recommended.


    The BQ24780S is a hybrid boost charger. In a typical application scenario, the adapter can power SYS directly while simultaneously charging the battery. If the system load draws more power than the adapter can provide, then the BQ24780S can enter hybrid power boost mode. The battery voltage is boosted up through the converter, and the battery discharges to help the adapter power the heavy system load.


    However, if the path from Rac to SYS is cut, as you showed in your diagram, then the adapter cannot power the system load. Hybrid power boost mode is not available either. This is not an intended use case for the BQ24780S, and I don't see the benefit of cutting this path compared to the typical application diagram.


    Best regards,