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SN74CBTLV3257: SPI MUX application

Stanley Wang
Prodigy 10 points
Part Number: SN74CBTLV3257
Other Parts Discussed in Thread: TMUX1574,

We are study 74CBTLV3257 in SPI MUX application.

At default setting in 74CBTLV3257, function chip will read its own SPI ROM.

If SPI ROM need to update, will use SPI control IC to update SPI ROM of each function chip .

And SPI control IC will make other 74CBTLV3257 be floating.

There are something need your help.

1.

If can use 74CBTLV3257 as SPI MUX, does 74CBTLV3257 have quantitative restrictions in SPI bus?

2.

If 74CBTLV3257 have quantitative restrictions in SPI bus, how many parts that can use in our design?

3.

Do you have formula to evaluate how many 74CBTLV3257 that can support in this application?

 

  • 0
    TI__Genius 10974 points

    Hi Stanley,

    The things you are going to need to look out for is the voltage of SPI signal you are going to be passing as well as the frequency you are going to be running for SPI. Do you have a schematic of what you are trying to accomplish? From what I understand, you have more than 2 devices you would like to communicate with, therefore needing more than 1 74CBTLV3257 device. By putting more 74CBTLV3257 devices on the SPI line, you will be increasing your capacitance, therefore reducing the maximum bandwidth you can run your application at.

    We do not have any formulas to evaluate this effect, but is more related to how low your bandwidth can go and still be acceptable for your application.

    Thanks!
    Bryan

  • 0
    TI__Intellectual 2694 points

    Hi Stanley,

    I would recommend the newer/better TMUX1574 as it is pin to pin to the SN74CBTLV3257 and has higher bandwidth, lower channel capacitance, wider supply and temperature range.

    Thank you,

    Regards,

    Sandesh