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BQ24040: BQ24040 CHG Issue

Rachel Zhou
Prodigy 70 points
Part Number: BQ24040

Dear Engineers，

1. BQ24040 is used in headset. When charging the battery, the CHG pin level will be abnormal, but the charging current is normal.When the battery voltage (voltage 2)reaches about 3.6~3.7v, CHG will be pulled high, and the Vout(voltage 1) is close to 4.2v. The circuit diagram is shown in figure 1:


                                               figure 1 

 

2、Charge and discharge the battery.Simulate the customer’s prototype, TS pin floating, discharge the battery voltage to about 3.0v, and then charge the battery. Switch the DC Power with the electronic load during the charging process, open 50S and close 5S, and monitor the relevant pin voltage and charging current curve during the charging process. The test figure is shown in figure 2:

 

I have checked the description of CHG in datasheet, but there is no explanation for this abnormal phenomenon.

Questions:    what causes this abnormal phenomenon?

                     Has this happened before?

                     Is there any solution?

 

  • 0
    TI__Guru* 76046 points

    Hello

    With the additional resistance in output lead this could cause the CHG pin to indicate a charge complete early.  The output voltage will be measured at the OUT pin with respect to IC gnd.  Resistance in the lead will increase voltage above the battery voltage during charging.  Also check if the ground or return lead has a similar voltage drop.

    For additional info on the charge pin see FAQ listed below:

    https://e2e.ti.com/support/power-management/f/196/t/753020

    The CHG pin will only be low for the first charge cycle and will go high at end of this cycle.  When the charge is restarted, voltage drops it will trigger a recharge but CHG is high.

    If the device detects that a new battery has been installed or power cycled the CHG could go low.