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SN74CBT3257: Is this device can used for 3.3V SPI signal

Andy_Lin
Intellectual 2230 points
Part Number: SN74CBT3257

Hi Team,

As subject , my customer is using this device as solution and ask if this device can used for 3.3V SPI signal ?

Andy

  • 0
    TI__Genius 9132 points

    Hi Andy,

    The SN74CBT3257 can be used for 3.3V SPI signal - however the SN74CBTXXXX family of switches are single N-channel FET switches.  This means it will not support voltages up to Vcc on the signal path.  As you can see below the transfer function of the input to the output is very linear until the input voltage reaches Vcc - ~1V.  At this point the FET is beginning to turn off and will clip voltages above Vcc - ~1V. 

    If you bias the switch Vcc = 5V you will be able to support 3.3 V signals without issue but 5V signals will be clipped to about 4V..

    In similar configuration,  the new TMUX1574. can support input signals that can range from 0V to VDD and supports SPI signals in addition to other features (1.8-V compatible control inputs, Fail-safe logic).

    Regrads

    Saminah

  • 0 in reply to Saminah C
    TI__Intellectual 2230 points

    Hi Saminah,

    nice to reach out again !

    follow up on your feedback , customer using 5V as VCC for SN74CBT3257  in their design , so I think it would work for 3.3V SPI signal.

    Andy 

  • 0 in reply to Andy_Lin
    TI__Genius 9132 points

    Hi Andy,

    yes, with 5V Vcc and 3.3V input SPI signal, the CB3T part will work fine.

    Thanks

    Saminah