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BQ25896 VSYS regulation

Adrian Rothenbuhler53
Prodigy 160 points
Other Parts Discussed in Thread: BQ25896

Based on the datasheet it sounds like the BQ25896 regulates VSYS to always be above 3.5V. The datasheet does not always explicitly state that the V_SYS_MIN =3.5 only applies for when external power is present, so I am a bit confused as to what is really the case, but based on my testing and what I found on this forum, V_SYS_MIN = 3.5 only applies when external power is present. Otherwise it will follow the battery voltage.

If this is truly the case, is there another battery charger that has a switching regulator built in that will keep V_SYS above 3.5V (or similar) even when run only off the battery?

My current design uses a TPS6300x buck/boost converter to generate a stable 3.3V at all times, but I'd like to consolidate to a simpler architecture with only a single IC.

Any suggestions are welcome.

  • 0
    TI__Guru*** 148825 points
    All of our power path switchers, including bq25896, regulate SYS to a minimum voltage of V_SYS_MIN, typically 3.5V even with no or discharged battery. When the battery exceeds this voltage, SYS will always be slightly higher than the battery voltage when it exceeds V_MIN_SYS.
  • 0 in reply to Jeff F
    Prodigy 160 points
    Jeff,
    Thanks for the reply. My concern is with the battery ONLY case (i.e. no external power/USB input present), not running it without a battery. Based on what I'm seeing with the BQ25896EVM, VSYS drops below 3.5V when running off the battery. Again, this is with no USB or external power plugged in; battery only.

    My question only pertains to the "battery only" or "running off the battery" case. For example, if the battery is at 3.1V and continues to drop, I want V_SYS to stay at 3.5V. However, without external power, V_SYS is simply connected to V_BAT through the BATFET, so V_SYS drops with V_BAT.
    Or is this assumption incorrect???
  • 0 in reply to Adrian Rothenbuhler53
    TI__Guru*** 148825 points
    With no input source, there is no buck converter running. BAT is tied to SYS through a switch.