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BQ25798: Efficiency Estimate with SYS and charging

Michael Balourdas
Expert 5525 points
Part Number: BQ25798


Hello,

I have a question about calculating efficiency of BQ25798. Let's say the battery is charging at 1A, and I also am supplying a load on SYS with 1A, would I just go to the 2A point on the Figure 7-1 efficiency curve? Or is it more complicated?

Thanks,

Michael

  • 0
    TI__Guru**** 169236 points

    Hi Michael,

    If the battery voltage is above the MINSYS voltage and your battery voltage is close to the same battery voltage per the efficiency curves, yes.  Your measured efficiency will be slightly better than the datasheet efficiency since only 1A of the 2A is going through the fully turned on BATFET (i.e. the ICHG^2*RDSonBFET losses will not be seen for 1A of the 2A total load).  If your battery voltage is below the MINSYS voltage, there are additional losses across the BATFET of (VMINSYS-VBAT)*ICHG that are not included in the efficiency curves.

    Regards,

    Jeff