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BQ21040: Charging Termination Problem

Part Number: BQ21040

Hi.

Please help me about below issue.

Please refer schematic.

(Condition)

Vin : 5V_IN

R1 :  1K (540mA Charging Current)

TS :  10K to VSS, NTC is not using.

CHG :  10K Pull up and connected to MCU

VBAT :  Main battery voltage or Charger Output(VOUT) voltage. VBAT is also using as 5V boost converter(FP6715)'s input source.

Boost Converter (5V_OUT) : 5V_OUT is using as charging source of another small battery device.

Case1)

1. When Boost converter is disabled (Only main battery charging)

2. Main battery charging and termination operation is good.

Case2)

1. When Boost converter is enabled and charging another small battery device.

2. Main battery charging is OK.

3. Another small battery device is full charged and main battery charging current is under 20mA(Full Charged). Total VOUT current is under 30mA.

4. As I know termination current is 54mA, 10% of fast charging current. But CHG state is still LOW. Charging Termination is not occurred.

-. Vin = 5V

-. Vout = 4.18V

-. TP1 current is under 30mA

-. TP2 current is under 20mA

-. TP3 current is under 10mA

5. At this situation, when boost converter is disable, CHG is changed to 3V High.

6. And then if boost converter is enable, CHG is still 3V High.

7. When 5V_IN is removed and inserted, Termination is not working again.

Obviously, VOUT current (TP1) is below 30mA, which is less than the termination current of 54mA.

Why termination is not working?

Please let me know how can I fix this.

Thank you.

  • Please check upper question.
  • Hello
    I think the problem could be caused by the bq21040 Termination Deglitch time (29ms) combined with the Boost converter load.
    If the boost converter is generating a pulse load that is above the termination current during a 29ms time the bq21040 will not terminate.
    Could you check the boost converter input current with a scope?
  • Hello. Bill.

    Thank you for reply.

    I re-checked this issue.
    In the above case2, the charge termination operation is performed.
    However, it operates when the termination current is under 15mA (BAT Charging Current 3~4mA + System Current 10~11mA)

    When DCDC(Boost Converter) is disabled, Termanation Current is about 50mA, It is normal.
    But When DCDC(Boost Converter) is enabled, Termanation Current is about 15mA.

    Why are this symptom occurring?
    How can I modify it to normal operation?

    Please help me.

    Thanks.
  • It is common for a converters to have  light output load mode that is a short operating burst to charge output and then sleep until voltage decreases.  This could be what is happening with boost convert U5.  If during this light load condition the converter pulsing on / off it could be preventing the battery charger from reaching termination current due to the deglitch circuit.

    Have you measured the boost convert input circuit during lite load?

  • I will check the boost converter input current during light load.

    And OK, I understand your opinion.

    If so, How can I modify this? I need to use boost converter.