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Original question:

BQ24074: Reverse current protection

BQ24074: Is reverse current flow from OUT to BAT possible?

Sven Grüner
Prodigy 50 points
Part Number: BQ24074

In my circuit it might be neccessary to cap some overvoltages. The battery would be a safe place for dumping a couple of milliamps (unless it is already fully charged, even a couple of hundred mA). Assuming I direct those currents towards the OUT pin, would the BQ2407x block them, or could they flow via BAT pin into the battery?

  • +1
    TI__Mastermind 23410 points

    Hi Sven,

    Yes, there is a reverse current flow that is possible from OUT to BAT. Unlike the OUT to IN path which prevents reverse current by having a set of back to back FETs, the OUT to BAT path is only faced with a single FET. In the case that there is a sufficiently greater voltage on the OUT pin than the BAT pin, the body diode on this FET would allow for current to get through. 

    I'll need to reserve some time in the lab to get a rough estimate to you and to check if my understanding is correct. What voltage are you expecting to see when you offload a couple of milliamps? Also, for my curiosity, what is the nature of your application and what is the source of the overvoltages if you're able to share?

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 50 points

    There is no specific scenario, just the "what if". The OUT powers an LDO which in turn is providing power to the great unknown that the user might connect to a terminal. To save the LDO, I added a reverse bypass diode (pity, that most LDOs still come without an integrated one). But that would be of little use, if the current can not go any further. I am not really trying to protect the circuit against all contingencies, but when a diode for 1 ct can improve the chances of survival against some threats, I take the bait.

    Knowing, that there is a body diode, which is allowed to come into effect, is good enough for me. Thank you, and please don't bother measuring specific values for my unspecific scenario.

  • 0 in reply to Sven Grüner
    TI__Mastermind 23410 points

    Understood!

    As this is not intended behavior, be aware that this may lead to behaviors not seen in the datasheet and is not an intended behavior we design around. Best of luck in your application! 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 50 points

    Sure, will do.

    Thank you very much Anthony!