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BQ24075: Charging Current not correct and PGOOD LED not working

Meris Veladzic
Prodigy 10 points
Part Number: BQ24075

Hello,

I have recently made a breakout board for the BQ24075RGTR chip.

To try it out, i connected all external components on a breadboard. 

VBUS is a DC Power Supply which also displays the output current.

When i connect the battery, CHG goes LOW so the LED turns on.

PGOOD doesn't light up.

The charge current is about 100mA but it drifts randomly but slowly (minutes) in the range from 100mA to 60mA.

The output voltage is 5.5V when VBUS is connected and 4.2V when disconnected.

Values from my measurements:

  • VBUS = 6V
  • VBAT = 5.5V (don't confuse it with the battery voltage, it is the output of the BQ24075 on the schematic)
  • Battery Voltage:
    • = 4.2V on the Pin
    • = 3.9V at the battery terminals
  • Current at ISET Resistor is precisely 1/400 of the charge current
  • V_CHG = 0V
  • V_PGOOD = around 3V (so High Impedance i think)
  • V_SYSOFF = 0V
  • 0
    TI__Mastermind 22760 points

    Hello, 

    Thank you for reaching out via E2E. The current is likely low because the BQ24075 device is measuring 4.2V at BAT pin. With BAT pin voltage at the Vbat(reg) threshold the device is in the CV taper phase of charge as shown in figure 9-8 on page 29 of the datasheet. I recommend you attempt to charge a further discharged battery to see if charge current will match expectation based on ISET pin setting.

    Meris Veladzic said:
    The output voltage is 5.5V when VBUS is connected and 4.2V when disconnected.

    This is expected. With input connected out pin voltage is regulated to 5.5V. Once input supply is disconnected out pin is regulated below the battery voltage. 

    Regarding the PGOOD signal please help to provide a waveform showing IN voltage and PGOOD voltage at the time when DC power supply is connected and battery is already connected to the charger. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 10 points

    Thanks for your response!

    Here are the waveforms when the battery is still connected:

    Green=VIN, Blue=PGOOD

    Green is VIN and Blue is PGOOD

    PGOOD is around 4V when VIN is unconnected but jumps to around 5.5V when it is connected (because of the pull up resistors).

    Datasheet says:

    VBAT + VIN(DT) < VIN < VOVP          ----->        Low

    This should technically be true because VBAT is 4.1V, VIN(DT) is typ. 80mV and VOVP is typ. 6.6V.

    4.1V + 0.08V < ~6V < 6.6V

    Garrett Kreger said:
    With BAT pin voltage at the Vbat(reg) threshold the device is in the CV taper phase of charge

    This would mean that Vbat should output the battery voltage and the current should decrease with time. With my observations, it stays relatively the same and goes sometimes up (shouldnt be the case when CV taper is active, right?)

  • 0 in reply to Meris Veladzic
    TI__Mastermind 22760 points

    Hi Meris, 

    Thank you for your response.

    You mention you are using a breadboard for external connections. Can you help to double check that the PGOOD LED has a solid connection to the pin? In general we have not had reports in the past on issues with PGOOD pin function and the fact you have charge current flowing to the battery and CHG goes LOW indicates you do have a valid input supply connected. 

    Meris Veladzic said:
    With my observations, it stays relatively the same and goes sometimes up (shouldnt be the case when CV taper is active, right?)

    What is the amount of time you observed the battery being charged in this state? I recommend first confirming you can observe the set fast charge current with a lower battery voltage. Once confirmed we can shift the conversation to checking if termination is functioning as expected. 

    Best Regards,

    Garrett