DIO20874B

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DIO20874B• Rev. 1.2

Application Information

Hysteresis

If the applied differential input voltage is near the offset voltage of the comparator, the basic comparator

configuration may oscillate or produce a noisy "chatter" output. This oscillation usually occurs when the input

signal is moving very slowly across the switching threshold of the comparator.

Adding hysteresis or positive feedback can prevent the problem.

The hysteresis transfer curve is shown in Figure 2. This curve is a function of three components: VTH, VOS, and

VHYST:

• VTH is the actual set voltage or threshold trip voltage.

• VOS is the internal offset voltage between VIN+ and VIN–. This voltage is added to VTH to form the actual trip

point at which the comparator must respond to change output states.

• VHYST is the hysteresis (or trip window) that is designed to reduce comparator sensitivity to noise.

Figure 2. Hysteresis transfer curve

Inverting comparator with hysteresis

The inverting comparator with hysteresis requires a three-resistor network that is referenced to the comparator

supply voltage (VCC), as shown in Figure 3.

Figure 3. Inverting configuration with hysteresis

Figure 4 is the equivalent resistor networks when the output is high and low. Note that RPU should be in series

with R3 when the output is high. RPU should be at least 10 times less than R3.