Datasheet

V
IN
+
-
+V
CC
R
1
1M:
V
OUT
+
-
C
1
10PF
-V
CC
V
IN
+
-
+V
CC
R
2
1 M:
C1
10 PF
V
OUT
-
+
LMV7291
SNOSA86E –FEBRUARY 2004–REVISED MARCH 2013 www.ti.com
5. When the signal source is applied through a resistive network to one input of the comparator, it is usually
advantageous to connect the other input with a resistor with the same value, for both DC and AC
consideration. Input traces should be laid out symmetrically if possible.
6. All pins of any unused comparators should be tied to the negative supply.
Typical Applications
POSITIVE PEAK DETECTOR
A positive peak detect circuit is basically a comparator operated in a unity gain follower configuration, with a
capacitor as a load to maintain the highest voltage. A diode is added at the output to prevent the capacitor from
discharging through the output, and a 1MΩ resistor added in parallel to the capacitor to provide a high
impedance discharge path. When the input V
IN
increases, the inverting input of the comparator follows it, thus
charging the capacitor. When it decreases, the cap discharges through the 1MΩ resistor. The decay time can be
modified by changing the resistor. The output should be accessed through a follower circuit to prevent loading.
Figure 29. Positive Peak Detector
NEGATIVE PEAK DETECTOR
For the negative detector, the output transistor of the comparator acts as a low impedance current sink. Since
there is no pull-up resistor, the only discharge path will be the 1MΩ resistor and any load impedance used.
Decay time is changed by varying the 1MΩ resistor.
Figure 30. Negative Peak Detector
SQUARE WAVE GENERATOR
A typical application for a comparator is as a square wave oscillator. The circuit below generates a square wave
whose period is set by the RC time constant of the capacitor C
1
and resistor R
4
. The maximum frequency is
limited by the large signal propagation delay of the comparator, and by the capacitive loading at the output,
which limits the output slew rate.
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