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BQ25703A: bq25703_

Belhaj ltaief Samir
Intellectual 380 points
Part Number: BQ25703A 
can we power the system and the battery with different voltage?
how?
  • 0
    TI__Expert 5330 points

    Hello Belhaj,

    You can power the system at a higher voltage than the battery is being charged with, but the system voltage is never below the battery voltage.

    Having a higher system voltage than battery charge voltage will happen automatically if the MinSystemVoltage register is set to a value higher than the battery voltage.  Note that in this condition, the BATFET will be driven in LDO mode (in order to generate the appropriate lower voltage for charging the battery), which will be less efficient charging than when MinSystemVoltage is below the battery voltage and the BATET is fully enabled and the battery is being charged directly from the output of the switching regulator.

    Regards,

    Steve 

  • 0 in reply to Steve Preissig
    Intellectual 380 points
    hello Steve;
    I chose the system voltage is 5V and the battery 4.8V (peak 5.68V).
    if the battery is fully charged the battery voltage will be 5.68V?
    What happens?

    Cordially;
  • 0 in reply to Belhaj ltaief Samir
    TI__Expert 5330 points
    Hello Belhaj,

    In this case, VSYS will be regulated to BATTERY + 160 mV if not charging and BATTERY + (R_DSON * I_CHRG) if charging.

    So when you are fully charged, you should see about 6V on SYS if the adapter is attached and then it will drop down to BATT - R_DSON*I_SYS if adapter is removed.

    Note that the backgate diode of the BATFET will conduct if VSYS is less than VBATT + V_F (forward voltage of backgate diode), so this is the main reason why sys has to be held above battery voltage since we want adapter to power the system and not the battery when adapter is attached.

    Regards,
    Steve