LMC7215_15 Datasheet, PDF (7/19 Pages) Texas Instruments – Micro-Power, Rail-to-Rail CMOS Comparators with Push-Pull/Open-Drain Outputs

LMC7215, LMC7225
www.ti.com
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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