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SN74CBTLV3257: SN74CBTLV3257 Ron value

Lauren Mayfield
Expert 7875 points
Part Number: SN74CBTLV3257
Other Parts Discussed in Thread: TMUX1574

Hi,

Do we have data that shows how Ron changes if at all over temperature? My customer wants to use this in an application that sits in very high temperatures (within the -40 to 125 C range) and wants to understand (1) how the Ron values change over temperature, and (2) if the impedance matching changes over temperature.

Thanks,
Lauren

  • 0
    TI__Genius 10552 points

    Hi Lauren,

    Unfortunately, this device is really old so we don't have any of that data on record. The Ron will likely increase about 20-50% across temperature range. As this is a relatively low Ron device, you can expect much less drift than a higher Ron device.

    Would I be correct in assuming that you have a pretty high source impedance and/or a high load impedance in this application? If so, this will lead to very little attenuation across the mux. Most likely this small deviation is not going to cause any discrepancies in the measurement.

    Thanks!

    Alex

  • 0 in reply to Alex Vish
    TI__Expert 7875 points

    Hi Alex,

    Their source impedance is 330 ohms in the worst case application. Since the mux has 5 ohms typical Ron, if the channel mismatch was 3 ohms then a 1% error to their ADC reading would occur. 

    Do we have any similar data for newer muxes? And when you say 20%-50% across the temperature range, can you elaborate on this? Do you mean from room temperature to the max operating temperature range it could be increased by 20%-50%? Is that concluded by informal testing done in the lab?

    Sorry for all the detailed questions, this is pretty important to my customer so just want to make sure we have our bases covered.

    Thanks,

    Lauren

  • 0 in reply to Lauren Mayfield
    TI__Genius 10552 points

    Hi Lauren,

    So for the % increase, this is relative to the max spec in the datasheet. Since the spec is for up to 85C, then we could say there's up to a 50% possible increase in resistance for each of these scenarios, depending on the loading conditions the customer is using. This percentage is concluded from historical fluctuations in Ron for other devices.

    Is there a reason the customer is going with the SN74CBTLV3257 over something like the TMUX1574? The TMUX1574 is a drop-in replacement with upgraded functionality and a much lower Ron spec. The datasheet for this device also has a visualization of how Ron changes over temp on page 9.

    Thanks!

    Alex

  • 0 in reply to Alex Vish
    TI__Expert 7875 points

    Thanks Alex!

    Ok so the customer and I had a misunderstanding. They don't actually want the data over temperature, they're looking for an electrical distribution plot of Ron values at room temperature. Do we have this for this device?

  • +1 in reply to Lauren Mayfield
    TI__Genius 10552 points

    Hi Lauren,

    Unfortunately, the same problem exists here where there is no historical data for this device due to its age. I can tell you that Ron will remain fairly flat until Vs/Vd approaches Vdd, at which point Ron approaches its max spec. I would say utilize the TMUX1574 datasheet as a good reference to see how Ron changes over voltage range at room temp. 

    Thanks!

    Alex