LTC1443/LTC1444/LTC1445
10
144345fe
applicaTions inForMaTion
Level Detector
The LTC1444 is ideal for use as a multisupply micropower
level detector as shown in Figure 5.
R1 and R2 form a voltage divider from V1 to the non-
inverting comparator A input. R6 and R7 are used to
divide down V2, while R8 is the output pull-up resistor
for the comparator outputs. R3 and R4 set the hysteresis
voltage and R5 and C1 bypass the reference output.
IN A
+
5
OUT B
OUT A
V
+
R3
15k, 1%
R5
430Ω
5%
R4
2.4M
1%
C1
1.0µF
IN A
–
HYST
REF
4
14
8
IN B
+
7
IN B
–
6
–
+
144345 F05
1/2LTC1444
3
9
2
1
R1
1.21M
1%
R2
3.40M
1%
V1
R7
1.21M
1%
R6
1.82M
1%
V2
R8
2M
1%
5V
–
+
V
–
1.2V
+
–
Figure 5. Glitch-Free Level Detector with Hysteresis
The following design procedure can be used to select the
component values:
1. Choose the V1 voltage trip level, in this example 4.65V.
2. Calculate the required resistive divider ratio.
Ratio = V
REF
/V
IN
Ratio = 1.221V/4.65V = 0.263
3. Choose the required hysteresis voltage band at the input,
V
HBIN
, in this example 60mV. Calculate the hysteresis
voltage band referred to the comparator input V
HB
.
V
HB
= (V
HBIN
)(Ratio)
V
HB
= (60mV)(0.263)
V
HB
= 15.78mV
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.
R1 = V
REF
/I
BIAS
= 1.221V/1µA ≈ 1.21M
R2 = R1
( )
V
IN
V
REF
+
V
HB
2
− 1
R2 = 1.21M
( )
4.65V
1.221V +
15mV
2
− 1
Using the same equations, R6 and R7 are 1.82M and
1.21M, respectively, to set the trip level at 3V for V2.
