Datasheet

V
A2
=
V
CC
(R
2
||R
3
)
R
1
+ (R
2
||R
3
)
V
A1
=
V
CC
R
2
(R
1
||R
3
) + R
2
LMV7271
www.ti.com SNOSA56H –FEBRUARY 2003–REVISED FEBRUARY 2013
HYSTERESIS
It is a standard procedure to use hysteresis (positive feedback) around a comparator, to prevent oscillation, and
to avoid excessive noise on the output because the comparator is a good amplifier of its own noise.
Inverting Comparator with Hysteresis
The inverting comparator with hysteresis requires a three resistor network that is referenced to the supply voltage
V
CC
of the comparator (Figure 29). When V
IN
at the inverting input is less than V
A
, the voltage at the non-
inverting node of the comparator (V
IN
< V
A
), the output voltage is high (for simplicity assume V
O
switches as high
as V
CC
). The three network resistors can be represented as R
1
||R
3
in series with R
2
. The lower input trip voltage
V
A1
is defined as
(1)
When V
IN
is greater than V
A
(V
IN
> V
A
), the output voltage is low and very close to ground. In this case the three
network resistors can be presented as R
2
//R
3
in series with R
1
. The upper trip voltage V
A2
is defined as
(2)
The total hysteresis provided by the network is defined as
ΔV
A
= V
A1
- V
A2
(3)
A good typical value of ΔV
A
would be in the range of 5 to 50mV. This is easily obtained by choosing R
3
as 1000
to 100 times (R
1
||R
2
) for 5V operation, or as 300 to 30 times (R
1
||R
2
) for 1.8V operation.
Copyright © 2003–2013, Texas Instruments Incorporated Submit Documentation Feedback 13
Product Folder Links: LMV7271