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BQ25628: System Voltage Crashing

Amin Rahmati
Prodigy 80 points
Part Number: BQ25628

Tool/software:

I am using BQ25628 to charge a battery and also provide power to the rest of the system. sometimes the system voltage (SYS) drops to ~2.8V and it causes the LDO after this to go down. the battery voltage is stable at all times. the ILIM resistor is set to provide ~560mA while the system does not take this much current, and the battery output current is less than this. the BQ25628 log is attached. before system voltage go down, I see watchdog is getting enabled while we keep it disable all the time. as I know, watchdog does not cause the system voltage to go down and just brings the settings back to POR moment. QON pin is not connected to anything, and it should be high with an internal 250K pullup which I confirmed this pin is high during voltage drop.

the I2C BUS is shared between this chip and a fuel gauge. does any sort of communication to the fuel gauge or anything on this BUS can cause this problem? 

BQ25628.xlsx

Please advise.

Thank you.

  • 0
    TI__Mastermind 27710 points

    Hi Amin, 

    Thank you for reaching out via E2E. 

    The BQ25628 has a known behavior where too fast of I2C communication may result in BATFET turning off for roughly 120msec when in battery only operation, which appears to match the VSYS off time in your provided waveform. 

    The recommended workaround is to reduce I2C clock frequency or add a required time delay between communications. This is described in datasheet section 8.5.1. 

    What I2C clock frequency does your system currently use? Additionally can you help to provide a photo of the top markings on the BQ25628 chip which shows the behavior? 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 80 points

    Hi Garrett,

    Thank you for the information.

    We are using 80kHz for the I2C clock. also please see the attached picture that shows the part marking.

    Based on your information, we plan to reduce clock frequency to 40Khz and increase delay between packet communication to 1msec. Let us know if you have any recommendations.

    Also, would you please let me know if there is any other marking available that solves this issue? or do you recommend any drag and drop option to replace this part with?

    Thank you,

    Amin.

  • +1 in reply to Amin Rahmati
    TI__Mastermind 27710 points

    Hi Amin, 

    Thank you for your response. Can you help to provide your email and I will reach out offline regarding best options moving forward? I have also sent you a friend request on E2E in case you prefer to share your email address via private channel rather than in this thread.

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    TI__Mastermind 27710 points

    Hi Amin, 

    Please consider this thread closed as we have shifted communication over to email. 

    Best Regards,

    Garrett