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I'd like to model an output pin of a microcontroller (MSP430F5xxx) in SPICE. The datasheet contains this:

enter image description here

This is the I-V graph for a pin which is configured as output and set to logic low. There is an equivalent graph for a pin set to logic high, which is almost exactly the same shape but reversed (negative large current at V=0, zero current at V=3).

Is there a good way to reproduce this in SPICE?

Bonus question: How can this be made to produce either the logic low or logic high I-V based on an input voltage corresponding to the logic level?

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2 Answers 2

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You can model it with two customized (complementary) MOSFET models connected as a typical CMOS push-pull output.

Here is a link to a video How to model a MOSFET using a Datasheet showing how to model a MOSFET from a datasheet. If you google you can probably find other similar tutorials on creating models.

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The push-pull output of a CMOS device is a MOSFET P-N half-bridge. Simply choose or model MOSFETs that meet the characteristics described in the datasheet.

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  • \$\begingroup\$ I thought about that, but that would only have the linear part of the I-V curve. I'm not sure what the flat part (constant I) comes from. \$\endgroup\$
    – Alex I
    Sep 7, 2015 at 1:19
  • \$\begingroup\$ @AlexI It comes from the MOSFET characteristics in the saturation region. \$\endgroup\$ Sep 7, 2015 at 1:47
  • \$\begingroup\$ @SpehroPefhany: Thank you! I see where this curve comes from now. I still can't figure out how to model the right MOSFETs though. The Spice models have a ton of parameters and it is not clear how to pick them. Any tips for a simplified model with a certain Rds(on) and saturation region? \$\endgroup\$
    – Alex I
    Sep 7, 2015 at 7:06
  • \$\begingroup\$ P.S. There don't seem to be many existing discrete devices like this (and none with spice models). For one thing, Rds(on) ~50ohm... \$\endgroup\$
    – Alex I
    Sep 7, 2015 at 7:07

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