ST  (Schmitt Trigger)

ST Schmitt trigger calculator gives you the resistor values to turn a analog comparitor into a Schmitt trigger. The resistor values calculated can be any of the standard resistor values, you select which standard in the popup menu on the right. The comparitor should be a push-pull output type, there are many good choices from several manufactures. Examples include:

Analog Devices: ADCMP371.

National Semiconductor: LMC7215 or LMV7271.

Texas Instruments: TLV3501, TLV3502, TLV3702, TLV3492, or TLC3702.

If you must use a open collector/drain output device, then your pull up resistor on the output must be much smaller than R1.

Be careful with your resistor selection, if your resistor values are too high, your comparitors input bias current can cause threshold errors, especially at higher temperatures.

You can select either inverting, non-inverting, or non-inverting with resistor divider Schmitt triggers from the popup at the top.

Each version has its advantages and disadvantages.

The Non-Inverting version’s input current changes when the output state changes, but if you are flexable with your Vref value, you may be able to use a part like the Analog Devices ADCMP356 with a build in reference.

The Inverting versions offers a high input impedance

ST allows equation entry for all four input and output threshold voltages and the R2 edit fields. So if you know you need 0.65 volts of noise immunity, and your rising threshold has to be 2.461 volts, you simply enter  2.461-0.65  for your falling input. You don’t have to use a calculator to use this calculator. Your output voltage levels will typically be the voltage supply rails of the comparator chip used.

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