LMC7215, LMC7225

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SNOS882E – SEPTEMBER 1999 – REVISED MARCH 2013

APPLICATION INFORMATION

RESPONSE TIME

Depending upon the amount of overdrive, the delay will typically be between 10

μs to 200 μs. The curve showing

delay vs. overdrive in the " Typical Characteristics" section shows the delay time when the input is preset with

100 mV across the inputs and then is driven the other way by 1 mV to 500 mV.

The transition from high to low or low to high is fast. Typically 1

μs rise and 400 ns fall.

With a small signal input, the comparators will provide a square wave output from sine wave inputs at

frequencies as high as 25 kHz. Figure 13 shows a worst case example where a ±5 mV sine wave is applied to

the input. Note that the output is delayed by almost 180°.

Figure 13.

NOISE

Most comparators have rather low gain. This allows the output to spend time between high and low when the

input signal changes slowly. The result is the output may oscillate between high and low when the differential

input is near zero.

The exceptionally high gain of these comparators, 10,000 V/mV, eliminates this problem. Less then 1

μV of

change on the input will drive the output from one rail to the other rail.

If the input signal is noisy, the output cannot ignore the noise unless some hysteresis is provided by positive

feedback.

Figure 14.

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