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BQ25619: BQ25619-register status

switch
Genius 3710 points
Part Number: BQ25619

Hi ti team,

The MCU cannot immediately read the register status of the BQ25619 when the USB is plugged in. What is the recommended delay in seconds to read the BQ25619 register status?

  • 0
    TI__Mastermind 21715 points

    Hi switch,

    What are you using as your pull-up source for the I2C lines? Depending on the set-up you may need a longer delay before accessing I2C.

    Regards,

    James

  • 0 in reply to James Steenbock
    Genius 3710 points

    Hi James,

    Currently, we set a 500ms delay to read. I would like to know how much the minimum time can be set?

  • 0 in reply to switch
    TI__Mastermind 21715 points

    Hi switch,

    I2C communication is possible as soon as VBUS rises above VBUS_UVLO or VBAT rises above VBAT_UVLO threshold (See below picture from datasheet):

    However, I2C communication can only function if you have the SDA and SCL lines pulled up above the minimum VIH threshold (1.3V). If you have the SDA and SCL lines above 1.3V when VBUS or VBAT crosses their UVLO threshold, I2C communication will be available.

    If SDA and SCL lines are held below VIH (1.3V) until a certain time, I suggest you wait until they are above VIH before sending I2C commands from the external host.

    In the below scope capture, I am using the BQ25619EVM. I do not have an external pull-up source for SDA and SCL lines. The pull-up source comes from VSYS through a jumper connection on the board. The I2C lines are pulled high ~300ms after VBUS rises above VBUS_UVLO. There is no minimum wait time specified in the datasheet as it depends on how you have the I2C lines set up. I2C communication is possible once VBUS or VBAT crosses the rising UVLO threshold.

    In the second scope capture below, I have the SDA and SCL lines pulled up to 2V before VBUS crosses VBUS_UVLO. Here, I can successfully send an I2C read command before REGN LDO is enabled since VBUS is above UVLO and the I2C lines are above VIH.

    Scope capture showing I2C lines going high ~300ms after VBUS_UVLO threshold is crossed

    Scope capture showing an I2C read starting successfully before REGN LDO is enabled (external  2V pull-up source on SDA and SCL)

    Regards,

    James