SN74AC00-Q1: high level input voltage inconsistency

luan nguyen

Part Number: SN74AC00-Q1
Other Parts Discussed in Thread: SN74AC00

Tool/software:

I noticed that the threshold for high input voltage of the NAND gate SN74AC00 is inconsistent with the SPICE model parameter. The datasheet said the VIH minimum is 1.85 but the provided SPICE model considers 2.5-3V as the threshold. I'm using 5V for VCC. Is changing the threshold as simple as changing 2.5 to 1.85V

8 months ago

0 Albert Xu1 8 months ago

TI__Mastermind 43995 points

Hi Luan,

Yes that is how you can change it.

I can check to see how these models were made. I'm not entirely sure why it is these numbers.

0 luan nguyen 8 months ago in reply to Albert Xu1

Prodigy 10 points

can you check why it's those numbers? Thank you

+1 Albert Xu1 8 months ago in reply to luan nguyen

TI__Mastermind 43995 points

Hi Luan,

When our models are made, they were made using a script to simulate "ideal" devices.

As you can see the threshold voltages are 1/2 Vcc. From the datasheet, it lists the "worst case" values for the thresholds. Ideally, thresholds are always 1/2Vcc.

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SN74AC00-Q1: high level input voltage inconsistency