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BQ2057C: Why STAT pin is low level when reinsert battery to charger

Walsh
Intellectual 950 points
Part Number: BQ2057C

Hi,

I have designed a chager using BQ2057C. The battery and charger is separate. When i need recharge the battery, i found the LED is off but there is charge current.

Reappear process:

1. Charge the battery to full and the LED turn off(charge current drop to 0)

2. Discharge the battery until the voltage drop to 4V and there is no battery connenct to the charger.

3. Reinsert battery to charger. There is charge current but the LED is off. Why?

PS:

1. If I doesn't turn off the Vin, when plug and unplug the battery, the LED is off.

2. If I turn off the Vin, reinsert battery to charger. The LED is on.

Could you help to explain the phenomenon and advise how to accomplish LED is on when plug and unplug the battery under Vin.

Thanks

Walsh

  • 0 in reply to Walsh
    Intellectual 950 points
    Update:

    We find that when the battery is below 4.05V, the charger is OK and LED is on.
    When the battery between 4.05V and 4.1V, the charger is abnormal which have charge current(864mA) but LED is off.

    PS: The Vin power is always on line
  • 0 in reply to Walsh
    TI__Guru* 75656 points
    Hi Walsh
    I have checked the LED behavior in the lab (EVM) and do not see problems with it follows the flowchart, figure 2 in datasheet.
    The LED will be on during charging, current to battery. Off when charge is complete. Tested several scenarios of reducing battery voltage, disconnection and reinserting battery also cycling power supply.
    I could not duplicate the problem described above.

    Some differences between the EVM and above circuit:
    1.) Reverse protection diode D1 (EVM) missing.
    2.) Pass transistor Q1 (EVM) drive circuit
  • 0 in reply to Bill Johns
    Intellectual 950 points
    Hi Bill:

    Thanks. May i ask that is the Vin always on when you test the EVM?

    The issue is happened only when the supply voltage(Vin) is always on.

    We will do the test according to your advise.

    Walsh
  • 0 in reply to Walsh
    TI__Guru* 75656 points
    Hi Walsh
    Yes--tested with Vin aways on.
    Ran several conditions trying to duplicate this. Power supply on and off while battery was plugged in, battery fully charged and battery at about 4V.