5

LMV331TP / LMV393TP

General Purpose, 1.8V, RRI, Open-Drain Output Comparators

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REV1.4

Chip

1 kΩ

1 kΩ

Core

+In

-In

Figure 2. Equivalent Input Structure

Internal Hysteresis

Most high-speed comparators oscillate in the linear region because of noise or undesired parasitic feedback. This

tends to occur when the voltage on one input is at or equal to the voltage on the other input. To counter the

parasitic effects and noise, the LMV331-393 implement internal hysteresis.

The hysteresis in a comparator creates two trip points: one for the rising input voltage and one for the falling input

voltage. The difference between the trip points is the hysteresis. When the comparator’s input voltages are equal,

the hysteresis effectively causes one comparator input voltage to move quickly past the other, thus taking the

input out of the region where oscillation occurs. Figure 3. illustrates the case where IN- is fixed and IN+ is varied.

If the inputs were reversed, the figure would look the same, except the output would be inverted.

0

Hysteresis

Band

Time

Non-Inverting Comparator Output

2

0

Inverting Comparator Output

Hysteresis

Band

Time

2

Figure 3. Comparator’s hysteresis and offset

External Hysteresis

Greater flexibility in selecting hysteresis is achieved by using external resistors. Hysteresis reduces output

chattering when one input is slowly moving past the other. It also helps in systems where it is best not to cycle

between high and low states too frequently (e.g., air conditioner thermostatic control). Output chatter also

increases the dynamic supply current.

Non-Inverting Comparator with Hysteresis

A non-inverting comparator with hysteresis requires a two-resistor network, as shown in Figure 4 and a voltage

Figure 4. Non-Inverting Configuration with Hysteresis