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TCA9617B: Relying on output 5V tolerance to do translation "the wrong way around"

Part Number: TCA9617B
Other Parts Discussed in Thread: TCA9509,

I have design requirements where:

  • I2C need to be translated from 2.5V to 2.5V, 3.3V or 5V; reconfigurable through end user selected jumper.
  • The internal I2C device is fairly weak and it need to face a long multidrop bus, so a redriver is preferred over simple translator.
  • For compatibility reason any voltage pedestal if exist should not face outward. I can not guarantee that two "B" side won't meet, or if there are other weak driver connected to the bus.

The usual recommendation is TCA9509 but it does have the annoying Vcc_b > Vcc_a + 1 requirement.

Another possibility is a translator and then a redriver, but that add significant BOM and area cost.

I notice that most I2C redrivers are rated 5V tolerant. Can I, say, power a TCA9617B at 2.5V for both sides, face the A side outward, and put pulls up to 5V?

Are there any concern for long term usage that way? Are there any concern with signal integrity with that setup? Or maybe any other recommendation that fulfill the requirement?

 

Thank you,

  • Hi Ardian,

    I notice that most I2C redrivers are rated 5V tolerant. Can I, say, power a TCA9617B at 2.5V for both sides, face the A side outward, and put pulls up to 5V?

    Are there any concern for long term usage that way? Are there any concern with signal integrity with that setup? Or maybe any other recommendation that fulfill the requirement?

    So to clarify what you would like to do, VCCA = 2.5V, VCCB = 2.5V, add pull-up resistor to SDAA, SCLA, pulled up to 5V? 

    We do specify 5.5V tolerant I2C. This is also defined in VIH

    So at the conditions mentioned, the maximum VIH = 5.5V. Pulling up A-side to 5V while VCCA = 2.5V is a valid use case for the device. 

    Regards,

    Tyler