Datasheet

12
LTC1440/LTC1441/LTC1442
144012fd
APPLICATIONS INFORMATION
WUU
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2. Calculate the required resistive divider ratio.
Ratio = V
REF
/V
IN
Ratio = 1.182V/4.65V = 0.254
3. Choose the required hysteresis voltage band at the
input V
HBIN
, in this example 60mV. Calculate the hyster-
esis voltage band referred to the comparator input V
HB
.
V
HB
= (V
HBIN
)(Ratio)
V
HB
= (60mV)(0.254)
V
HB
= 15.24mV
4. Choose the values for R3 and R4 to set the hysteresis.
R4 = 2.4M
R3(kΩ) = V
HB
= 15k
5. Choose the values for R1 and R2 to set the trip point.
R
V
I
V
A
M
RR
V
V
V
REF
BIAS
IN
REF
HB
1
1 182
1
118
21
2
1
== =
=
+
−
⎡
⎣
⎢
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
⎥
.
.
µ
RM
V
V
mV
RM
2118
465
1 182
15
2
1
2340
=
+
−
⎡
⎣
⎢
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
⎥
=
.
.
.
.
Low Voltage Operation
It is important to note that the voltage references internal
to the LTC1440 and LTC1442 can exceed the common
mode range of the comparators at low supply voltages.
The input common mode range of the LTC1440/LTC1441/
LTC1442 comparators is guaranteed to extend up to (V
+
-
1.3V). Therefore, if one of the comparator inputs is at the
1.182V reference voltage, the minimum supply voltage is
2.5V for a valid output reading.
The guaranteed minimum operating voltage for the
LTC1440/LTC1441/LTC1442 is 2V (or ±1V). However,
both the reference and comparator(s) will function with a
supply voltage as low as 1.5V, but performance will
degrade as the voltage goes below 2V. The voltage refer-
ence temperature coefficient will degrade slightly, and the
comparators will have less output drive with an increase in
propagation delay. At the reduced supply voltages, the
input common mode range of the comparator(s) will still
typically extend from the negative supply to approximately
1.1V below the positive supply.