at page 42 of 5438 datasheet, listed schmitt-trigger input threshold when Vcc at 1.8V and 3.0V. if I have a design use 2.0V Vcc. how to calculate the threshold. should I use 1.8V number or 3.0V. is there an equation to estimate the threshold.
Schmitt-Triggers do not have 'the threshold'. They have two, one for going form low to high, and a lower one for going from high to low. That's why they are schmitt triggers.The minimum an dmaximum distance between the two is in the datasheet (hysteresis).
MSP is CMOS technology. So besides an offset, voltages scale more or less linearly with VCC. In some datasheets,the values are already given as factors relative to VCC. You can approximate the min/max values pretty good by a linear interpolation between 1.8V and 3V VCC table entries.
Note that the minimum high-going threshold entry is below the maximum low-going threshold. So given teh minimum hysteresis, the one cannot be at minimum when the other is at amximum. Buit on different MSPs, one or the other may be true. So to calculate the worst-case safe area, you'll have to play with the values and eliminate all voltages that are in an either/or region and ensure that your external signals are outside.I think TI has decided to not put a four-dimensional diagram into the datasheet for obvious reasons :)
david sun77114is there an equation to estimate the threshold
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got it, thanks
I have one more simple question for 3V environment, to make MSP5438 work safely, Schmitt-Trigger input should be over 2.1V for positive going and lower than 0.75V for negative going. right?
david sun77114 Schmitt-Trigger input should be over 2.1V for positive going and lower than 0.75V for negative going. right?
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