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BQ24616: Both VIN and BAT appear to SYSTEM power sometimes.

Chase Jeong
Genius 4670 points
Part Number: BQ24616

Hello TI experts,

My customer tests BQ24616 in their own PCB, and they found one problem.

Here is some conditions of fault situation.

1. they attached battery to a charger first, and apply VIN (DC adapter, 12V)

2. and they could see VIN and BAT voltage on SYSTEM power repetitively.

3. they tested 100 pcs of charger and saw it 5. and it could be more because it appears ramdomly.

4. They can see it for all batteries (not particular battery), especially the battery with 98% or more capacity.

I attach a schematic and the waveform of each point. You can see it at point 1.

BQ24616_sch1.pptx

I think that V_OUT should be same with VIN when VIN is present. could you check why does it happen?

Please check this issue. Thanks.

Best regards,

Chase

  • 0
    TI__Mastermind 30025 points

    Hello Chase,

    Can you please plot the input voltage, PH voltage, output voltage, and charge current when this is happening? Also, correct me if I am wrong, but are you using a 12 V input to charge a 16.8 V battery? This will not work unfortunately as the input voltage needs to always be above the battery voltage as this is a buck converter.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Genius 4670 points

    Dear Michael,

    Thank you for your support.

    Actually my customer tested several days to measured the waveform you mentioned, but finally they could not reproduced the symptom. they keep trying now.

    and please check the additional questions of my customer below.

    1. when does BQ24616 control the signal of BATDRV(23P) and ACDRV(3P)?

    2. if the BQ24616 detects battery overvoltage, could it happen that SYS voltage changes into VIN and BAT repeatedly?

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Mastermind 30025 points

    Hi Chase,

    1. Please read Section 8.3.8 System Power Selector. In short if the device is in SLEEP mode the Battery is Connected to the System through the BATFET. If the device is not in SLEEP mode the Input is connected to the System through the input FETs.

    2. In the event that a battery overvoltage occurs the high side FET will remain off until the BAT voltage goes below 102% of the regulation voltage. However, if the device is not in SLEEP mode the body diode of the BATFET will block voltage from travelling from the System to the Battery. Also due to the nature of not being in SLEEP mode, the input is higher than the battery which means the System voltage will also be higher than the Battery. In conclusion this means no current will travel from the Battery to the System. If the device is in SLEEP mode, the BATFET will conduct and the input will be blocked.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Genius 4670 points

    Dear Mike,

    Thank you for your support.

    In this case, I think that BATFET and ACDFET are switching (enter sleep mode and wakeup and so on..), so this symptom happens.

    What are some situations in which sleep and wakeup can occur repeatedly?

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Mastermind 30025 points

    Hello Chase,

    If your input is constantly cycling from below the battery voltage to above the battery voltage you would go in and out of SLEEP. Can you capture of waveform of the input voltage, PH voltage, battery voltage, and charge current to check?

    Regards,

    Mike Emanuel 

  • 0 in reply to Michael Emanuel35
    Genius 4670 points

    Dear Michael,

    Thank you for your support. I requested waveforms what you mentioned to my customer.

    And here is another question;

    When VIN is 17.6V and BAT is 16.5V, SYS pin is connected to BAT(16.5V)

    Is it right operation? I think VIN is higher than BAT, so SYS should be connected to VIN.

    or is there any threshold that BAT is connected to SYS regardless VIN is higher than BAT?

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Mastermind 30025 points

    Hi Chase,

    Can you please capture the VCC, ACDRV, BATDRV, STAT1, STAT2, PG and ACN voltages with a multimeter when this is in a steady state (in order for me to answer your most recent question)? Looking forward to seeing your waveform.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Genius 4670 points

    Dear Michael,

    Thank you for your support. I requested those waveforms to my customer.

    is there any possibility that SYS is connected to BAT although BAT is lower than VIN?

    or is there any other threshold that SYS is connected to VIN?

    It would be very helpful if you check the conditions above. Thanks.

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Mastermind 30025 points

    Hi Chase,

    I await the customer waveforms.

    When the device has BAT lower than VCC the device is NOT in SLEEP mode and the BATFET is turned off. At the same time the input is connected directly to the SYS.

    When the device has BAT higher than VCC the device is in SLEEP mode and the BATFET is kept on. At the same time the input is disconnected from the SYS. There is no other condition. Please see Section 8.3.8 to learn more about the gate drive of BATDRV and ACDRV.

    Regards,

    Mike Emanuel