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BQ25306: STAT pin is strange when battery pack is not attached

Chase Jeong
Genius 5000 points
Part Number: BQ25306

Hello TI team,

My customer is testing their own PCB with BQ25306.

I think the charging function works well so far, but the STAT pin is little strange.

when the battery pack is not attached in the system, STAT pin is not just low or high, it makes a pulse about 19.8Hz. the screen shot is as below;

and here is the STAT pin status when the battery pack is attached;

as you see, STAT pin is constantly low, so we can control LED for the user.

but the status without battery pack, the STAT pin is not the constant, so we cannot control LED as we want.

could you check what is wrong?

if you need more information especially the schematic, please let me know your personal email address. Thanks.

Best regards,

Chase

  • 0
    TI__Mastermind 24075 points

    Hi Chase,

      This is expected behavior. The capacitor on BAT is small (10uF or 20uF) so when no battery is attached, the output cap is being charged and discharged. The STAT will flash according to termination and recharge deglitch timer.

  • 0 in reply to Kedar Manishankar
    Genius 5000 points

    Hi Kedar,

    Thank you for your reply.

    I understand that this is expected behaviour, Now we should control the status LED. now it blinks about 19.8Hz as i said. it looks strange to end customers.

    is there any way not to blink the LED when no charging situation? how about removing output capacitor?

    or if you know other ways to control LED with no charging situation, please let me know. Thanks.

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Mastermind 24075 points

    Hi Chase,

       If you were to disable the charger using the /EN pin, this would disable REGN which is the pulllup for STAT pin. When REGN is disabled, you will not see the STAT LED lit up. When battery is detected, you can enable the charger, so REGN will be enabled and STAT indication will operate like normal.

    You cannot remove the output capacitor as this is needed for the feedback loop stability during normal charge operation.

  • 0 in reply to Kedar Manishankar
    Expert 1125 points

    hi

    STAT LED is controlled by controlling the EN as you said. but it need to configure additional circuit.

    I provided the CC25306EVM to my customer and did the same test.

    The same symptons were also found in CC25306EVM.

    When Vbus is 5V and JP5 connected, STAT LED is not blinking.

    but when Vbus is 8.6V or higherJP5 connected, STAT LED is blinking.

    This doesn't seem to be the 10uF charge/discharge operation you mentioned.

    Please kindly explain.

    thanks.

  • 0 in reply to robin Moon
    TI__Mastermind 24075 points

    Hi Robin,

        This is  buck charger so input voltage has to be higher than output voltage. JP5 is the 2S setting that corresponds to 8.4V. You can't use a lower input voltage to boost up to output. In your5V case you are in a fault condition called SLEEP mode. In SLEEP mode REGN is disabled so you don't observe any LED light up on STAT

  • 0 in reply to Kedar Manishankar
    Expert 1125 points

    Hi

    Sorry. I have mistook it.

    when Vbus is 8.6 or higher,  and no battery, explain how to disable LED Blinking except for EN Control.

    thanks.

  • 0 in reply to robin Moon
    TI__Mastermind 24075 points

    Hi Robin,

       Disabling the charger through EN is the main way to disable STAT pin indication when battery is absent. You can try adding a pulldown resistor on the output as this will pull the output voltage down. The downside is that STAT would be lit the whole time, and this could be interpreted as charge in progress even though the battery is absent. Along with this you would have higher battery leakage current when only battery is present in the system.