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BQ24770: Switching interruptions right after turning on

Alexander Sharapov
Prodigy 50 points
Part Number: BQ24770

Dear All,

We have found that BQ24770 has a strange switching behavior right after start up.
This issue can be reproduced on DevKit BQ24770EVM.

It looks like an interruption of switching at sound frequency. So it can be even heard as a sound produced by inductor.
In case of  the first rewriting a register 0x15 (Maximum Charge Voltage) even with default value 0x34C0 (13,504mV) makes  the controller to work continually without any interruptions.

This way, a connected via SMBus battery (fuel gauge controller) normally do this task after a short time when system is started.
But in case of absence of a battery (we are considering such scenario in our device as normal) it might be a problem.


Please advise.

The waveform before and after the inductor:

Thank you and best regards,

Alex

  • 0
    TI__Guru 56650 points

    bq24770 has auto wake-up function to wake up a deeply discharged battery. This function provides a small current when the battery terminal voltage is lower than the minimum system voltage setting.

    If there is no battery is connected to the battery terminal, the small auto wake-up current can push the output voltage high. And then, charger stops auto wake-up. After the voltage drops below the minimum system voltage setting, it will resume switching. That should be what you see on the output.

    Any charger voltage and current command makes charger stop auto  wake-up because the host controller knows the battery charge voltage and current info. bq24770 doesn't need auto wake-up the battery. That is why writting 13.5V to 0x15H, makes  the controller to work continually without any interruptions.

  • 0 in reply to Wang5577
    Prodigy 50 points
    Dear Wang5577,

    Thank you for your comments.

    I still have two questions:

    1. Is it normal to even hear a sound from the inductor?

    2. Since my FPGA+Processor system is using SYS Power from the bq24770 it experienced a voltage pulses during startup before a software can write to register. So, how I can to prevent such behavior at the startup?


    Thank you,
    Alex
  • 0 in reply to Alexander Sharapov
    TI__Guru 56650 points
    After verify this is auto wake-up issue:
    1. If the host disables the auto wake-up function from charge option register, they don't have this auto wake-up waveform and noise.
    2. bq24770 is a charger IC. Does the system have a battery? If there is a battery, we don't have this low frequency output ripple and audible noise.
    If you really don't need the auto wake-up function, please contact your local TI sales team to order bq24777A sample. bq24777A doesn't have the auto wake-up function.
  • 0 in reply to Wang5577
    Prodigy 50 points
    Thank you a lot again!

    1. As far I understand my host should be started up first. I have no chance to make a charger register state permanent. I mean there is no any config flash or eprom present in the charger design. Please correct me if I wrong.

    2. We have both scenarios in the device with and without a battery. I've started from there. Please try to disconnect a battery...

    So, if I understand you right, I have only chance to use bq24777A to exclude a ripple effect during starting up my system without a battery connected.
    Please confirm.


    Best regards,
    Alex
  • 0 in reply to Alexander Sharapov
    Prodigy 50 points
    Dear Wang5577,

    I've found that BQ24777A is out of stock in knowing for me suppliers.
    Is it something new or some special edition?
    What is the bet way to buy it in Europe?
    When we could expect this component for a mass run?


    Looking forward to hearing from you.


    Thank you,
    Alex
  • 0 in reply to Alexander Sharapov
    TI__Guru 56650 points
    bq24777A is a custom part with long lead time. Let us discuss it offline. Please send an request email to your local sales and copy me wang-li@ti.com