SN74HCS04: Hysteresis variation with temperature and supply voltage

Hi Colin,

Colin Hice said:

Is there any data available on how the hysteresis voltage changes with variation of supply voltage and temperature?

The differences in supply are listed in the datasheet for 2V, 4.5V, and 6V, so you can infer directly from the provided values how supply affects the thresholds.

Generally speaking, thresholds are not linearly related to temperature -- they depend on multiple variables. The input thresholds are not precise and can only be guaranteed within the min/max specs of the datasheet. If precision thresholds are required, I would recommend using a comparator instead.

For the hysteresis - ie the difference between the thresholds - generally speaking the value is lower at higher temperatures. Because of the nonlinearity of the thresholds, this may not hold across the entire temperature range - but all the data I have shows 125C as the worst and -55C as the best for hysteresis (I have data at -55C, -40C, 25C, 85C, and 125C). The thresholds, on the other hand, sometimes invert their relation with temperature.

Colin Hice said:

To add onto this, are these variations modeled in the SPICE model?

No, temperature is not modelled in the behavioral PSpice model. If it were, it would likely be misleading as I said above that there are multiple variables in the threshold value and if a customer expects it to be consistent across many products, they will find that it is not. Do not use a logic Schmitt-trigger device for precision thresholds.