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BQ27220: I2C tr spec check

Will Wang47
Expert 7670 points
Part Number: BQ27220

Hi team,

Customer get one question about the BQ27220 100kHz I2C rise time spec. Based on the I2C bus spec, the rise time under 100kHz should be 1000ns, 400kHz is 300ns; however in BQ27220 I2C spec, both 100kHz and 400kHz are 300ns, customer is wander if 100kHz should be 1000ns rise time. Could you help check this?

Thanks and Best regards,

Will

  • 0
    TI__Guru 57697 points

    Hello Will,

    The I2C spec specifies the maximum value. bq27220 has values lower than the allowed maximum.

    This means that it is not only compliant to the spec but exceeding the recommendation in the spec.

  • 0 in reply to Shirish
    TI__Expert 7670 points

    Hi Shirish,

    For the BQ27220 the tr time at 100kHz, it shows 300ns. I think this is the requirement of the tr time is 300ns. While the I2C spec requirement is 1000ns. That's to say BQ27220 get higher requirement of the tr time, for 300ns means the pull up resistor range is narrower than 1000ns. 

    Actually, customer would like to increase the pull up resistor to limit the current draw by the I2C signal, while they find it's easy to cause the tr(300ns) time violation. 

    So, could you help check if BQ27220 could support 1000ns tr time at 100kHz communication frequency?

  • 0 in reply to Will Wang47
    TI__Guru 57697 points

    Hello Will,

    There is no time violation. Max value per I2C spec is 1000ns. bq27220 value is 300ns. 300ns is less than 1000ns, therefore it is compliant to the spec. Customer can use higher value of pullup to increase the rise time if operating only at 100KHz.

    It looks like are requesting the Min value to be 1000ns. Is that right?

  • 0 in reply to Shirish
    TI__Expert 7670 points

    Hi Shirish,

    They are request the Max tr value to be 1000ns, aligned with I2C max timing spec. 

  • 0 in reply to Will Wang47
    TI__Guru 57697 points

    Hello Will,

    The max value is already compliant to I2C specification and it cannot be changed.

    You can try external methods like increasing capacitance on the wire but we cannot recommend that as it may result in unforeseen side effects.