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PCA9546A: Clarification on MUX

Jexy Liew
Prodigy 410 points
Part Number: PCA9546A

Tool/software:

Experts,

Customer would like some clarification regarding the PCA9546 mux switches.  Have couple of questions:

  1. Once the channel is selected, the pass FET is acting as a short between the input and selected output channels, right?
  2. Not clear on the datasheet which side is the source and which is the drain.  Does the pass FET actually turns off when the input signal is high (3.3V) and VDD is 3.3V.  What is the gate voltage?
  3. I see the Cio (off) for SCL/SDA vs the channels.  But if the switch is on, what is the Cio for the total path?

Looking forward to your help,

Jexy Liew

  • 0
    Guru 287860 points

    1. Yes. But note that there is only an N-channel MOSFET, not a full transmission gate, so only low voltage are passed through. (For high voltages, the switch is off, and the output voltage is determined only by the pull-up resistor. This allows level shifting.)

    2. The MOSFET is perfectly symmetric, with the body connected to ground. Either side can be seen as source or drain.

    3. This is not specified. It's probably somewhat larger than the sum of the Cio(off) values.