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TCA9509: Level thresholds and noise immunity?

Larry Rachman
Prodigy 70 points

Part Number: TCA9509
Other Parts Discussed in Thread: TCA9517,

Is the input voltage 1/0 threshold of this device fixed at a voltage, or at a percentage of the VccA/VccB? Our application uses relatively long I2C signal lines that may pick up some noise, and if the threshold is Vcc-based, I will use a full 5 volts on the far side to get the maximum noise immunity. If it is a fixed threshold, I'll probably use something like the TCA9517 instead, with 3.3V on both sides.

  • 0
    TI__Guru* 79221 points
    Hey Larry,

    "Is the input voltage 1/0 threshold of this device fixed at a voltage, or at a percentage of the VccA/VccB?"
    The input voltage threshold is based off of I2C in which ViLA is around 0.3% of VccA and ViLB is around 0.3% of VccB.

    Both devices do have a static ViLc threshold (usually around 0.4V). For TCA9517, it is on B side, for TCA9509 it is on A side.

    Thanks,
    -Bobby
  • 0 in reply to BOBBY
    Prodigy 70 points
    Did you mean 0.3*Vcc, or 0.3% of Vcc, which would be 0.003*Vcc. The latter seems unreasonably low.

    Thx, -lr
  • 0 in reply to Larry Rachman
    TI__Guru* 79221 points
    Hey Larry,

    I meant 30% or 0.3*Vcc. (we actually typically set our threshold internally to something like 35% or 40% to leave room for margin to insure we meet datasheet specs)

    Sorry for the confusion.
    -Bobby