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Original question:

BQ25798: which supply is main supply for system load? pmid or sys (battery application)

BQ25798: When is the PMID supply used?

Yash Dave
Prodigy 70 points
Part Number: BQ25798

Tool/software:

So when is the PMID supply used, and as per the datasheet, it is used for backup mode. If we take the output from the SYS pin, there won’t be any issue, right? and 

When I remove the main USB 5V supply from the PD controller, the battery charger IC will provide 5V through the battery? (our battery voltage is 3.7V(3.7V)). In that case, our output will come from the SYS pin, right?

  • +1
    TI__Mastermind 32286 points

    Hello Yash,

    If you have any more queston related to PMID or SYS pin, Please respond to this thread, to help future customer with similar questions.

    Yash Dave said:
    When I remove the main USB 5V supply from the PD controller, the battery charger IC will provide 5V through the battery? (our battery voltage is 3.7V(3.7V)). In that case, our output will come from the SYS pin, right?

    I'm sorry for the confusion, I thought you were using this device at a higher power.

    If you are using an Input voltage of 5V and a battery voltage of 3.7V, I would recommend using PMID as the system load. PMID will equal VBUS when in forward mode(5V). In reverse mode it will equal to the OTG voltage, This can be set to 5V in REG0x0B  

    In your case the reason why I would not recommend the SYS pin, is that VSYS_MIN should not be set greater than the max battery voltage.  

    Best Regards,

    Christian.