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BQ25792: Operation of Narrow VDC Architecture

Kiran Kerai
Intellectual 380 points
Part Number: BQ25792

With reference to section 8.3.8.1 of the datasheet:

Figure 8-6 shows VBAT (in green) and VSYS (in purple). VSYS appears to be below VBAT in the charge enabled phase. Please explain how this is possible, whilst the battery is being charged I would expect VSYS to be higher by RDS(ON) x charging current.

Also confirm that when the charge is disabled, VSYS is regulated 200mV or 600mV above battery voltage. It appears that both VBAT and VSYS are 200mV above VSYS_MIN.

  • 0
    TI__Guru**** 167196 points

    HI Kiran,

    Both curves are VSYS. Green is charge disabled and purple is charge enabled.  Battery voltage is along the x-axis.  When charge is disabled, VSYS regulates to VSYSMIN when battery is less than VSYSMIN and then regulates to ~ 150mV above V(BAT) when battery is above SYSMIN.  When charge is enabled battery is above VSYSMIN, V(SYS)=ICHG*RDSon+VBAT.  The datasheet curve is oversimplified and needs to be shifted up.

    Regards,

    Jeff