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BQ21040: BQ21040 charge current drop

Star Xu
Genius 9645 points
Part Number: BQ21040

Hi

For the abnormal charging current describe as below:

1. VBUS = 5V, VBAT = 3.13V, charging current 615mA, the charging current in the constant current stage has not reached the design value 800mA.

2. VBUS = 5V, VBAT = 4V, the charging current starts to decrease, and the constant voltage stage is not entered at this time.

3. VBUS = 5.3V, VBAT = 4V, the charging current is restored to 800mA, what is the requirement for VBUS input voltage to maintain the maximum current charging?
The voltage and current test data are as follows:

VBUS(v)

VBAT(v)

Ibat(mA)-D2002在位

Ibat(mA)-去掉D2002

5

3.13

615

537

5

3.23

671

565

5

3.33

735

600

5

3.43

808

639

5

3.54

808

685

5

3.65

808

741

5

3.74

790

803

5

3.83

732

808

5

3.96

674

807

5

4.03

600

782

5

4.16

539

723

5

4.2

471

434
The Schematic as below:
Thanks
Star
  • 0
    TI__Mastermind 19195 points

    Hi Star,

    At low VBAT, the voltage drop within charger is highest, so charging may not be reaching 800mA due to hitting thermal regulation. At higher VBAT, it could be limitation of the VIN to VBAT drop which could be causing drop in current. The charger needs enough headroom for best performance as the battery voltage goes high. Typical dropout voltage for charger is 325mV at 500mA charging. Dropout at 800mA will need to be even higher than this.

    What is BQ21040 VIN pin voltage during these tests? I suspect it is lower than 5V as there are diodes in input path. 

    Best,

  • 0 in reply to Nick Brylski
    TI__Mastermind 19195 points

    Hi there,

    I haven’t heard back from you, I’m assuming you were able to resolve your issue. If not, just post a reply below or create a new thread if the thread has locked due to time-out.

    Regards,