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BQ25882: PFM mode.

Kengo.Y
Guru 11165 points
Part Number: BQ25882

Hi team.

I'd like to know about PFM mode on Bq25882.

My customer said there is a squeal in the inductor when light road.

The waveform is follow(Charge current is 20mA).

Green:SW

Yellow:BAT voltage

Red:charge current

Is this a PFM mode?

If it is PFM mode, they sets OOA(out of audio) is Enable(default).

Why is SW frequency 3.5kHz?

Sincerely.

Kengo.

  • 0
    TI__Mastermind 40305 points

    Dear Kengo,

    Can you please provide more details about your waveform, such as what the offsets for each channel are and where they are referenced to on the left axis? I am having trouble understanding what voltage and current levels you are working with.

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • 0 in reply to Michael Emanuel35
    Guru 11165 points

    Hi Mike.

    Thank you for your reply.

    Sorry for being difficult to see.

    Could you check follow waveform?

    Green : SW

    Yellow : BAT voltage

    Purple : unknown

    Red : charge current

    I have some question about this waveform.

    1. Is PFM mode enabled even during charging?

    　Does intermittent operation work even in PWM mode?

    2. When it is operating intermittently, the charging current becomes unstable(0mA~100mA).

        How does the current determine that charging is complete?

    　We want to know how to determine the termination current.

    3. How can we avoid entering light load mode while charging?

    4. Is it charging during the Top-OFF time?

    Sincerely.
    Kengo.

  • 0 in reply to Kengo.Y
    TI__Mastermind 40305 points

    Dear Kengo,

    Is the offset for the switch node 0 V? What is the range of the switch node signal? Most importantly, are the dotted lines the level markers or are the solid lines?

    Can you please explain more about your setup? Do you have a battery attached? Is there a system load?

    1. PFM is enabled upon default for light load operation.

    2. Once the BAT pin reaches regulation voltage, the charger transitions from Constant Current mode to Constant Voltage mode. In Constant Voltage mode, the current is slowly tapered down. When the current reached the termination setting, the current drops to zero and the charger reports the charging has terminated.

    3. If you wish to prevent the charger from entering PFM, it can be disabled.

    4. The top-off timer is disabled on default. However, if enabled, it will continue to charge past termination based upon the selected register setting. See Section 8.3.7.3

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • 0 in reply to Michael Emanuel35
    Guru 11165 points

    Hi Mike.

    Thank you for your reply.

    I'll check to my customer about your comment.

    Could you tell me more detail on your answer?

    2.Will the charge turn off when the current drops below the termination current?

       Is the termination current confirmed as a peak or an average value?

      I'd like to know when the charging is completed when the charging current is changing.

    3. Is it correct to not enter PFM mode by disabling this register?

        

    Sincerely.

    Kengo.

  • 0 in reply to Kengo.Y
    TI__Mastermind 40305 points

    Dear Kengo,

    The termination is explained in Section 8.3.7.3 as well. When the battery voltage is above the recharge threshold and the battery current is below termination current, termination will happen and the BATFET turns off. Termination current accuracy is specified in the Electrical Characteristics and ranges from +/-40% to +/-20% depending on the termination setting.

    Setting PFM_DIS to 1 will disable PFM operation.

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.