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Simulation SN74LVC2G132

Other Parts Discussed in Thread: SN74LVC2G132

I tried to use PSpice for TI to simulate the power ONOFF logic with SN74LVC2G132. Schematic and simulation output are below.

Why the voltage at U2 input A can only reach to 0.5V? I checked the PSpice model of the SN74LVC2G132, 

.PARAM RA = 220000000,

then the voltage should reach up to 3.2V.

What is the problem? Thanks.

  • Hello,

    Can you share your project files so I can test on my system? I couldn't duplicate the issue using the model that I have -- you may be using an older version of the software. Mine is:

  • Thanks for reply. I have loaded the model to the official PSpice 17.4, and got the same result. Attached is the project files. Thanks.

  • My apologies, I should have realized earlier that your 5000k resistor was not 5kΩ but 5MΩ -- the units and value together threw me off. I would recommend against using such a large resistor value with a device that can have input leakage on the order of 1uA. At max leakage, the 5Mohm resistor would drop all of your voltage.

    The model includes input leakage current in the form of the resistance value you previously identified (RA = 220MΩ), which is inaccurate. This value _should_ be 5.5MΩ. The input leakage can be as much as 1uA for this device:

    There's also an internal pull-down resistor, intended only to prevent a floating node, of value 1MΩ (RDA1 NA1 GND 1e6), that is causing additional leakage. I'll make a note that we need to fix this in the next version of the model by increasing it to 1E9.

    To fix the model, replace RA = 220000000 with RA = 5.5E6, and RDA1 NA1 GND 1e6 with RDA1 NA1 GND 1e9

    For your application, I would recommend to reduce the resistor to 500kΩ or less (and if you want the same time constant, increase C1 to 10uF).

  • Understood, thanks.