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Original question:

BQ25792: Charger + BMS board review

BQ25792: Does the BQ25792 support powering SYS from battery?

Norbert Bonnici
Prodigy 20 points
Part Number: BQ25792
Other Parts Discussed in Thread: BQ25798

BQ25798 shows that it supports backup mode, where it powers the system via PMID instead of SYS when VBUS is not present. Is this required if all I need is to charge the LiPo and when use the battrey voltage via sys when the charger is not connected?

  • +1
    TI__Guru**** 169466 points

    Hi Norbert,

    Backup mode assumes that the system is connected to PMID all the time.  When there is power at VBUS, the FET between VBUS and PMID is fully on.  VBUS current flows through to PMID.  When VBUS power is removed, the charger quickly starts working in reverse and maintains a voltage at PMID.  The SYS pin is always connected to the battery through the internal BATFET.  So any load at SYS pin gets battery power and, when there is power at VBUS, gets whatever power remains after PMID gets is fill.

    Regards,

    Jeff