Datasheet

9
LTC1443/LTC1444/LTC1445
144345fc
producing a maximum hysteresis voltage band of 100mV. If
hysteresis is not wanted, the HYST pin should be shorted to
REF. Acceptable values for I
REF
range from 0.1µA to 5µA. If
2.4M is chosen for R2, then R1(kΩ) = V
HB
(mV).
Level Detector
The LTC1444 is ideal for use as a multisupply micropower
level detector as shown in Figure 5.
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
RR
V
V
V
RM
V
V
mV
RM
IN
REF
HB
21
2
1
2121
465
1 221
15
2
1
2340
=
()
+
−
⎡
⎣
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
=
()
+
−
⎡
⎣
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
=
.
.
.
.
Using the same equations, R6 and R7 are 1.82M and 1.21M
respectfully to set the trip level at 3V for V2.
APPLICATIO S I FOR ATIO
WUUU
IN A
+
5
OUT B
OUT A
V
+
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
–
+
LTC1443/44/45 • 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
–
+
Figure 5. Glitch-Free Level Detector with Hysteresis
R1 and R2 form a voltage divider from V1 to the noninverting
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. The following design procedure
can be used to select the component values: