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BQ21080: Questions of BQ21080

Jimmy Lai
Expert 6845 points
Part Number: BQ21080

Dear Team,

Could you help to review the schematic as below?

Many Thanks,

Jimmy

  • 0
    TI__Genius 17615 points

    Hi Jimmy,

    The BAT pin appears to be missing a 1 uF capacitor close to the IC as well as a 10 uF capacitor close to the SYS pin.

    Additionally I'm trying to understand the interaction between USB5V and the VBAT-VBATT FET. It looks like VBATT will only be connected to VBAT when VIN voltage is present or when the on switch is connected. Is this a power saving method to manually disconnect the battery from the system?

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    TI__Expert 6845 points

    Hi Ospina,

    Customer just want to know how to input the register to make sure Vbat at 4.2V to charge the battery.

     

    Please support and reply. Thanks.

  • 0 in reply to Jimmy Lai
    TI__Genius 17615 points

    Hi,

    To set VBAT regulation voltage to 4.2V, the customer will have to write VBAT_CTRL (Register 0x03) to 0x46. This is the default value of the register so the customer should not need any I2C transaction to see the behavior. It should charge to 4.2V by default.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    TI__Expert 6845 points

    Hi Juan,

    We appreciated your great support.

    I try to remove the Q1, Q2 and let battery connected to charger and test the BQ21080 at no I2C and register setting.

    I didn’t measure 4.2V on BAT,

    Battery looks like charging but very slowly (3.79V to 3.81V for 1HR)

    is this normal?

    I would like to ask about the application of BQ21080 in the circuit.
    When there is no I2C communication and Register is defaulted
    Will the BAT pin have a 4.2V output?

    Attached is our current circuit
    Because the preliminary measurement is under the condition that there is no I2C communication and Register is defaulted
    The BAT pin only has the voltage of the battery itself, It's 4V.

    Many Thanks,

    Jimmy

  • 0 in reply to Jimmy Lai
    TI__Genius 17615 points

    Hi Jimmy,

    Jimmy Lai said:
    Attached is our current circuit

    I think you may be missing an attachment.

    Jimmy Lai said:

    Battery looks like charging but very slowly (3.79V to 3.81V for 1HR)

    is this normal?

    This depends on the battery size, do you know how many mAh the battery is? The default charge current for the charger is 10 mA so for a big battery it may take a long time to charge. This setting can be changed only through I2C communication.

    Jimmy Lai said:
    When there is no I2C communication and Register is defaulted
    Will the BAT pin have a 4.2V output?

    Yes, the default register value for VBATREG is 4.2V so by default the charger should attempt to charge to 4.2V

    Jimmy Lai said:
    Because the preliminary measurement is under the condition that there is no I2C communication and Register is defaulted
    The BAT pin only has the voltage of the battery itself, It's 4V.

    BAT pin will always be the voltage of the battery. As the battery gets charged it should rise to the regulation voltage (4.2V) minus a very small offset due to termination and any resistance voltage losses between the BAT pin and the Battery.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    TI__Expert 6845 points

    Hi Juan,

    Adding SYS is difficult due to PCB space
    We are still trying to add SYS capacitor.
    Just confirm, will it be affected if the SYS capacitor is not added? Thanks a lot.

    Many Thanks,

    Jimmy

  • 0 in reply to Jimmy Lai
    TI__Genius 17615 points

    Hi Jimmy

    Without the SYS capacitor the device may have some stability difficulties. Although it may still charge the device hasn't been characterized without this capacitor so we can't guarantee the device behavior.

    Jimmy Lai said:

    Battery looks like charging but very slowly (3.79V to 3.81V for 1HR)

    is this normal?

    Was the customer able to resolve this issue? I don't believe this would be caused by the missing SYS capacitor.

    Best Regards,

    Juan Ospina