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FST3253 Switch clarification

Discussion in 'Sensors and Actuators' started by camerart, Feb 8, 2020.

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  1. camerart


    Aug 18, 2010
    I'm using a FST3253 Switch for switching 3x different RX DATA signals, into a RX PIC.

    I would like some clarification please.

    If OE1 and OE2 is connected to GND, is it ok to switch using only S0 and S1?

    All of the PCB, DATA and PICs are 3.3V, the FST3253 requires 5V. Is it ok to use this 5V switch to switch 3.3V?
    Thanks, Camerart.
    Last edited: Feb 8, 2020
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Of course it is.
    OE1 and OE2 are Output Enable signals to activate the respectibe outputs 1A and 2A. These signals have nothing to do with the switch selection. The switches are controlled by S0 and S1 solely.
    Difficult to answer definitely. The switch is designed and specified for 5 VB operation. The logic inputs require a minimum Vih of 2 V or more. The logic diagram suggests that the selector is made from pass transistors. If that is truly the case, operating it with 5 V power and 3.3 V logic signals should be possible.

    However, these switches are bi-directional, a feature you don't need here as the data direction is clearly defined. You could use a 74HC151 multiplexer instead (for example, there are also other multiplexer chips). This chip can operate from 3.3 V so there is full compatibility with your logic levels.
  3. camerart


    Aug 18, 2010
    Hi H,
    It looks then that they will most likely be ok. As I have them, I'll give them a try first.
    Cheers, C.
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