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BQ25703A: Questions for VSYS

Tom Huang1
Prodigy 120 points
Part Number: BQ25703A
Other Parts Discussed in Thread: TPS65987D

We plan to use bq25703A for charging 6-cell (3S2P) 18650 Li-battery. Combine with TPS65987D to support USB PD charging.

What's the VSYS voltage for below cases?

(1) Battery is present but no input source

(2) Input source is present

      Battery is missing

(3) Both input source and Battery are present

      Input voltage < Battery voltage

      Charging is enabled

(4) Both input source and Battery are present

      Input voltage < Battery voltage

      Charging is disabled

(5) Both input source and Battery are present

      Input voltage > Battery voltage

      Charging is enabled

(6) Both input source and Battery are present

      Input voltage > Battery voltage

      Charging is disabled

 

  • 0
    TI__Mastermind 25800 points

    Hey Tom,

    For (1) VSYS = VSRP - ISYS x RDSon,BATFET. If you select the BATFETOFF_HIZ bit in the ChargeOption3() register, then VSYS = VSRp - Vf,body,BATFET. 

    For (2) VSYS = VSYSMIN setting. If charge is enabled, then VSYS = VBATREG setting.

    For (3) VSYS = higher of (VSYSMIN setting OR VSRN + ICHG x RDSon,BATFET). 

    For (4) If VSRN > VSYSMIN setting and charge is disabled, VSYS = VSRN + 160mV. If VSRN < VSYSMIN setting, then VSYS = VSYSMIN setting. 

    For (5) Same as (3). Because it is a buck boost charger, the input vs. battery voltage has no impact. 

    For (6) Same as (4). Because it is a buck boost charger, the input vs. battery voltage has no impact.

    Regards,

    Joel H