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BQ25890: How to understand the VSYS vs VBAT curve?

Zhu Allen
Prodigy 30 points
Part Number: BQ25890

Hi TI Expert,

The figure 10 descrie the VSYS vs VABT curve, why does VSYS start to drop when VBAT is 3.5V and charge is disabled? 

Why doesn't VSYS drop when VBAT is 3.5V and charge is enabled? 

Thanks and Best Regards!

Allen

  • 0
    TI__Guru 57701 points

    Allen,

    Referring to 9.3.5.1 Narrow VDC Architecture on the d/s, before VBAT reaches VSYSMIN, BATFET is working in LDO mode, after VBAT reaches VSYSMIN, VBAT will fully turn on. So there is a transition. The BATFET transition between LDO mode and fully on mode is the characteristics of the built-in BATFET.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 30 points

    Hi Ning,

    That makes sense for the red line if charge is enabled, however, the red line is the curve when charge is disabled, I think the BATFET will never turn on if charge is disabled. Is it possible that the red curve should be noted with SYS(Charge Enabled) rather than SYS(Charge Disabled)?

    Thanks and Best Regards!

    Allen

  • +1 in reply to Zhu Allen
    TI__Guru 57701 points

    Allen,

    It looks like the legends for SYS(Charge Enabled) and SYS(Charge Disabled) are reversed.

    Thanks,

    Ning.