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Original question:

TMUX1208: TMUX1208 recommended soldering profile

TMUX1208: propagation delay of TMUX1208

Ben Kuo
Expert 7520 points
Part Number: TMUX1208
Other Parts Discussed in Thread: TMUX1308

Dear team,

Could you share propagation delay of TMUX1208? (the time taken by the output of the device to rise or fall 50% after the input signal has risen or fallen past the 50% threshold)

Thanks.

Ben

  • 0
    TI__Mastermind 48307 points

    Hi Ben,

    We are on holiday today and will be returning 7/6/2021 - we will answer your inquiry within 24 - 48 hours.

    Best,

    Parker Dodson

  • 0
    TI__Mastermind 48307 points

    Hi Ben,

    We don't have a prop delay measurement for the TMUX1208.

    This is because the prop delay greatly relies on output loading conditions.

    You can approximate the prop delay by using passive stand-ins for the mux - which is essentially a low pass RC filter.

    Many loads can be approximated as a resistor and capacitor in parallel  to ground - if this is the case the following model can be used:

    If the circuit is set-up this way the prop-delay is ~1 RC time constant where R is equal to [(R_ON * RL) / (RL + R_ON)] and C is equal to [C_ON + CL] - this is based on the thevenin eq. circuit which allows us to convert this above circuit into an RC with the aforementioned values.   

    If the system does not match above than you can use our PSPICE/TINA Models for this part and connect them with the output loading conditions (Either other models or RLC equivalents).  Please see here for models:  TINA  PSPICE.

    If you have any other questions please let me know!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    TI__Expert 7520 points

    Hi Parker,

    Thanks for your comments.

    May I double confirm if this part is suitable for SPI interface(30MHz)?

    Regards,

    Ben

  • 0 in reply to Ben Kuo
    TI__Mastermind 48307 points

    Hi Ben,

    The TMUX1208 has a nominal bandwidth of 65MHz (-3dB frequency). This is measured using a 50 ohm + 5pF in parallel as a load. For transmitting data you want between 1.5 - 3 x the bandwidth with the closer to 3 times you get a less attenuated signal. This device is running at 2.167 times the clock frequency so it is possible to use this device in a 30MHz application, but output capacitance (due to traces or other devices on the line) needs to be minimized as the more capacitive the output of the mux is the lower the bandwidth it will become. 

    That being said - the TMUX1208 is pretty low frequency when it comes to our 8:1 multiplexers and we have other 8:1's better suited for digital SPI applications. The one part that comes to mind is the TMUX1308 which has a higher bandwidth (350MHz - 500MHz typical depending on VDD) and is good for passing digital signals. 

    While the TMUX1208 should be able to pass 30MHz SPI, its bandwidth is dependent on the system that the mux is placed in. Having less than 3x bandwidth will put more constraints on layout and other components. If the TMUX1208 proves difficult to implement I'd suggest looking into the TMUX1308 as well.

    If you have any other questions please let me know!

    Best,

    Parker Dodson