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BQ24195: VSYS / PMID Operation

Matthew Force104227
Prodigy 130 points
Part Number: BQ24195

I have a fundamental question about operation that I was not able to glean from the datasheet.  I want to understand the relationship to VSYS and PMID for the 4 following cases:

1) If powered from 5V on VBUS and VBAT = 3.8V: PMID = 5V (follows VBUS) and VSYS = ~3.8V (follows battery)

2) If powered from 5V on VBUS and VBAT = 3.0V: PMID = 5V (follows VBUS) and VSYS = ~3.5V (boost to Vsys_min)

3) If VBUS is not present and VBAT = 3.8V: PMID = 5.1V (boost) and VSYS = ~3.8V (follows battery)

4) If VBUS is not present and VBAT = 3.0V: PMID = 5.1V (boost) and VSYS = ??? (does it follow the battery or maintain the 3.5V Vsys_min)

If case 4), can the device boost both PMID and VSYS from a battery below Vsys_min?

  • 0
    TI__Mastermind 46591 points

    Hi,

    1) Yes if VBAT > the minimum system voltage setting.

    2) VSYS should be the minimum system voltage setting +150mV.

    3) Yes.

    4) VSYS still follows VBAT. In boost mode, VBAT (VSYS as well) is the input and PMID is the output.

    VBAT needs to be above BATLOWV threshold (VBATLOWV set by REG04[1]) in order to support boost mode.

    If only battery is present and the voltage is above depletion threshold (VBAT_DEPL), the BATFET turns on and connects battery to system, then VSYS follows VBAT.

    It is highly recommended to get familiar with the BQ24195 charger operation by evaluating the BQ24195 EVM before working on your own design.

    Thanks,

    Ning.