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SN74CBTLV3257: Whether the device SN74CBTLV3257 can support 25Mhz SPI signal

Part Number: SN74CBTLV3257

Hi team,

My customer wants to use the device for 25Mhz SPI signal. Not sure whether the device can support such data rate. The datasheet only list tests with 200Mhz. Thanks.

  • There is no lower limit on the frequency. 25 MHz will work.

  • Hi  Frank,

    Clemens is correct, this part will work fine.

    The general rule of thumb I use is the multiplexer bandwidth needs to be >= than 2 to 3 times the datarate to support accurate data transmission.  

    Best,


    Parker Dodson

  • HI team,

    Thanks. Whether the tdelay has connection with the data frequency? Thanks.

  • The conditions in footnote (1) are probably not the same in your real circuit.

  • Hi Frank,

    The timing parameters will have some effect on maximum data rate. The propagation delay will limit the maximum throughput of the device, but for analog Multiplexers this is very small and will not have a large affect on system performance at a clock speed of 25MHz. Essentially can be thought of as a delay, every bit or signal will take a maximum of 250ps at a Vcc of 3.3V +/- 0.3V(- See Footnote 1 below). For a digital application as long as the propagation delay isn't longer than the time it takes for a new bit to show up at the input of the switch it won't limit datarate. As Clemens mentioned here is footnote 1:

    (1) The propagation delay is the calculated RC time constant of the typical on-state resistance of the switch and the specified load capacitance, when driven by an ideal voltage source (zero output impedance).

    This means that the propagation delay is calculated from a more ideal scenario - the propagation delay may be larger depending on the system setup - however the switch itself will not add much to the delay, and with the current application you are describing you shouldn't run into any issues.

    Best,

    Parker Dodson