Datasheet

V
O
V
IN
V
CC
V
REF
-
+
R
2
R
1
V
+
V
REF
V
IN
V
O
-
+
V
-
LMV761, LMV762
www.ti.com SNOS998H –FEBRUARY 2002–REVISED MARCH 2013
APPLICATION INFORMATION
BASIC COMPARATOR
A basic comparator circuit is used to convert analog input signals to digital output signals. The comparator
compares an input voltage (V
IN
) at the non-inverting input to the reference voltage (V
REF
) at the inverting pin. If
V
IN
is less than V
REF
the output (V
O
) is low (V
OL
). However, if V
IN
is greater than V
REF
, the output voltage (V
O
) is
high (V
OH
).
Figure 24. Basic Comparator
HYSTERESIS
The basic comparator configuration may oscillate or produce a noisy output if the applied differential input is near
the comparator's input offset voltage. This tends to occur when the voltage on one input is equal or very close to
the other input voltage. Adding hysteresis can prevent this problem. Hysteresis creates two switching thresholds
(one for the rising input voltage and the other for the falling input voltage). Hysteresis is the voltage difference
between the two switching thresholds. When both inputs are nearly equal, hysteresis causes one input to
effectively move quickly past the other. Thus, moving the input out of the region in which oscillation may occur.
Hysteresis can easily be added to a comparator in a non-inverting configuration with two resistors and positive
feedback Figure 25. The output will switch from low to high when V
IN
rises up to V
IN1
, where V
IN1
is calculated by
V
IN1
= [V
REF
(R
1
+R
2
)] / R
2
(1)
The output will switch from high to low when V
IN
falls to V
IN2
, where V
IN2
is calculated by
V
IN2
= [V
REF
(R
1
+R
2
) – (V
CC
R
1
)] / R
2
(2)
The Hysteresis is the difference between V
IN1
and V
IN2
.
ΔV
IN
= V
IN1
- V
IN2
= [V
REF
(R
1
+R
2
) / R
2
] - [V
REF
(R
1
+R
2
)] - [(V
CC
R
1
) / R
2
] = V
CC
R
1
/ R
2
(3)
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