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TCAL9539: TCAL9539 I2C Timing Spec

Allan Fan
Expert 7500 points

Part Number: TCAL9539

Hi experts,

Customer used TCAL9539 and runs at standard mode. The question is their stop bit setup time now is 3.95us and have some difficulties to enlarge this timing at this moment. Is 3.95us acceptable for TCAL9539?

 

BR,

Allan 

  • 0
    TI__Guru 55898 points

    Hi Allan,

    The TCAL9539 is rated up to 1 MHz FM+ and is backwards compatible to 100kHz speeds. 0.26us is the minimum stop condition setup time for 1 MHz.

    3.95 us is okay.

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    TI__Expert 7500 points

    Hi Tyler,

    I’m confused because in DS we spec different timings for different speed modes.  In standard mode which customer used the minimum stop condition time is 4us.  If what you saying the 1Mhz spec is backwards compatible to 100Khz, and we can just refer to the spec of FM+, then what’s the reason we still spec for standard mode? 

    BR,

    Allan

  • 0 in reply to Allan Fan
    TI__Guru 55898 points

    Hi Allan,

    We list the 3 modes of I2C and their timing specs according to the I2C standard. 

    If you operate TCAL9539 at 100kHz, then it is recommended to operate according to the standard since those times are defined by the I2C spec. The TCAL9539 is rated for up to 1 MHz, so it can handle setup times that are much faster. If you place a TCAL9539 on an I2C bus at 100kHz with 3.95us setup time, I see no problem. IF you use an older IO expander that is rated strictly for 100kHz, then I would suggest that this is out of specification. Since TCAL9539 can operate in any of the three modes, the 0.05 us deficit is okay. 

    We show all three modes in the datasheet to show it is compliant to the 3 basic modes of I2C. 

    Regards,

    Tyler