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BQ27Z746: bq27z746 I2C rise/fall time spec. definition.

justin hsieh
Prodigy 40 points
Part Number: BQ27Z746

Tool/software:

Dear Team,

We observed that the I2C rise/fall time specification of the BQ27Z746 is defined from 10% to 90% of Vcc.

I2C rise/fall time spec. @400KHz

However, in general, the rise/fall time on the SoC side is defined with respect to VIL-VIH levels.

It seems challenging to meet the rise/fall time specification of the BQ27Z746. Would it be acceptable to measure the rise/fall time with respect to VIL-VIH levels for specification compliance?

Please advise

Justin.

  • 0
    TI__Mastermind 24931 points

    Hello Justin, 

    I believe that both specs must be met, 10% to 90% in a maximum of 300 ns, 90% to 10% in a maximum of 300 ns, and the bus voltage levels must meet the specifications in the datasheet. 

    Regards, 

    Robert. 

  • 0 in reply to Jonny
    Prodigy 40 points

    Hi Robert,

    If the rise/fall time specifications were based on VIL/VIH for the specification, it would easily meet the requirements. For the BQ27Z746, where VIL is 0.54V and VIH is 1.26V, it means the specification ranges from 16% to 38%.

    This range is much more relaxed than the specification on the SoC side, which is defined as 30% to 70% (0.99V to 2.31V).

    However, if the specification were to use 10% to 90%, the range would be 0.33V to 2.97V, making it much more challenging to meet the requirements.

    Currently, our project can not meet the requirement if the rise/fall spec. was 10% to 90% of VCC.

    That's why we want to know if we can use the VIL/VIH values for the specification for the I2C rise/fall time test.

    Thanks,

    Justin.

  • 0 in reply to justin hsieh
    TI__Mastermind 37761 points

    Hello,

    Today is a national holiday. We will get back to you later this week.

    Regards,

    BMS Apps Team

  • 0 in reply to Adrian
    TI__Mastermind 24931 points

    Hello Justin, 

    It is my understanding that you should be able to use the VIH and VIL for the I2C rise and fall time test. You can always test this out using an EVM or your custom PCB. 

    Regards, 

    Robert.