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Original question:

BQ2057W: Unexpected battery float voltage in BQ2057WSN charging Circuit and battery not charging

BQ2057W: Charginf state is continuosly ON & IC is not cutting off the charging cycle.

Yash Deshmukh
Prodigy 10 points
Part Number: BQ2057W

Hi,

We have designed a charging module using BQ2057WSN IC to charge a 8.4V, 2400mAH 2S 18650 Li-ion battery. My supply power is 9V 5W SMPS. I have set my charging current  to mA. The battery is charging continuosly and does not cutoff charging even if the pack voltage has reahed 8.4V. But in some of the I found that the IC is showing both the staus indicators of full charged and also in charging at the same time. I have measured the input power supply voltage and found it as 9V which is fine. Then I have measure the battery float voltage accross Pin No. 2 & Ground it is 9.35V. I have found that in some of the circuits it is different. So, what could be possible reasons of getting such unexpected state where it is continuosly charging baterry beyond 8.4V. Is there any flaws in my design or the IC is faulty ( But remember IC is not showing any short circuit).

I also found that out of these circuits,idealy 50% of circuits are facing this issue.

I am attaching my schematic and some images related to the circuit. R1 or R8 is 0.47ohm 

  • 0
    TI__Guru* 75806 points

    Hello

    The unit should set charge complete when voltage reaches 8.4V and charge current has dropped to 10%.  

    Couple of things to check:

    1.) Is input current decreasing to the 10% point.

    2.) Do you have additional loads connected to the battery during charging? This would prevent current decreasing to required level.

    3.) Double check the input voltage, 9V it is very close to 8.4V and you have two diode drops along with loss in resistor.  Possibly test with higher input voltage.

    4.) Many batteries have a protection circuit that will prevent charge voltage from increasing above 8.4V and will disconnect battery from terminal.  May want to check if 9.35V may be an open circuit voltage.