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Original question:

TCA9509: Vol when Vcca=Vccb=3.3V

TCA9509: works in VCCA=VCCB=3.3V

Jerry Chen
Expert 5110 points
Part Number: TCA9509

Hi team,

I see VCCA ≤ (VCCB – 1 V) should be true in datasheet, but I found in a customer project, the I2C communication works fine with VCCA=VCCB=3.3V. Could you pls explain the requirement of VCCA ≤ (VCCB – 1 V) from internal circuit point of view? I would like to find the reason that if this part can support VCCA=VCCB in some situations.

Their schematics is like below, but slave voltage level is 3.3V. (change 1.65V to 3.3V)

Thanks.

  • 0
    TI__Mastermind 49660 points

    Hi Jerry,

    The device was designed and electrical characterized to operate when VccB larger than VccA by atleast 1V however it is possible to use the device at the same voltage. This would technically be out of the electrical spec that the device was designed and characterized for so when you do this you can expect the electrical parameters to shift. One in particular which would be a concern is ViLc on A side of the device. If the I2C controller/device cannot drive below this voltage, then you may not be able to send a low from A side to B side during a contention case (like an data line hand off during ACKs). The VILc during this case would shift lower meaning the driver for the I2C controller/device would need to be stronger in order to meet the shifted value. This is not something we have characterized so the min value for this would be unknown to us.

    -Bobby