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MUX36S16: Output On-Capacitance Simulation Does Not Match Datasheet

Brenton Yiu
Prodigy 80 points
Part Number: MUX36S16
Other Parts Discussed in Thread: TINA-TI

I am trying to simulate the on-capacitance for the MUX36S16 and the simulation does not seem to match the datasheet.

My TINA-TI design is set up with:
VDD = 30V
VSS = 0V
Input: Voltage source on S1 with 100k series resistor
Output: D

AC Analysis Settings:
Start: 100
Stop: 1G
Points: 100
Sweep Type: Logarithmic

The on capacitance is calculated by finding the -3dB point of the transfer characteristic and then plugging in the series resistance and -3dB frequency to this equation: 

C(on) = 1 / (2 * pi * R * f_3dB)

When using VDD=15 and VSS=-15, I get values that correspond to the datasheet. When using VDD=30 and VSS=0, I get 70pF for the on-capacitance but the datasheet specifies around 25pF

I used a similar process to the one described in this TI blog post to simulate the on-capacitance:
https://e2e.ti.com/blogs_/b/analogwire/posts/spice-it-up-extracting-the-input-capacitance-of-an-op-amp-part-3

sbomaa5.tsc 

  • 0
    TI__Mastermind 31203 points

    Hey Brenton, 

    Was there a reason you wanted to back calculate it the capacitance? The method you're using isn't entirely accurate. It's not a simple first order RC filter. You have capacitance on the both sides of the RON

    We have a video that goes over bandwidth here. There's an equation provided as well but the equation admittedly makes some assumptions so is more of an approximation than an exact formula. 

    That being said, I would expect the +/-15 case to be very closer to the 30V case. In the model, I would honestly expect them to be the exact same. Let me look into it and see if anything was changed or how they're going about modeling this. TINA is a little older syntax that I don't use, as TI has shifted to PSPICE for TI, but I'll see what I can get out of it

    Thanks,
    Rami