LTC1445 Linear Technology, LTC1445 Datasheet - Page 9

• Manufacturer Part Number: LTC1445
• Description: Ultralow Power Quad Comparators with Reference
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
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 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:
1. Choose the V1 voltage trip level, in this example 4.65V.
2. Calculate the required resistive divider ratio.
3. Choose the required hysteresis voltage band at the input,
V
voltage band referred to the comparator input V
HBIN
Ratio = V
Ratio = 1.221V/4.65V = 0.263
V
V
V
, in this example 60mV. Calculate the hysteresis
HB
HB
HB
= (V
= (60mV)(0.263)
= 15.78mV
HBIN
REF
U
/V
)(Ratio)
IN
U
V2
R6
1.82M
1%
R7
1.21M
1%
W
Figure 5. Glitch-Free Level Detector with Hysteresis
V1
R2
3.40M
1%
R1
1.21M
1%
15k, 1%
R4
2.4M
1%
U
R3
HB
.
R5
430
5%
C1
1.0 F
14
6
4
8
7
5
IN B
IN B
IN A
IN A
HYST
REF
+
–
+
–
4. Choose the values for R3 and R4 to set the hysteresis.
5. Choose the values for R1 and R2 to set the trip point.
Using the same equations, R6 and R7 are 1.82M and 1.21M
respectfully to set the trip level at 3V for V2.
+
–
+
–
5V
V
+
3
9
1/2LTC1444
LTC1443/44/45 • F05
V
–
R4 = 2.4M
R3(k ) = V
R1 = V
R
R
R
LTC1443/LTC1444/LTC1445
2
2
2 3 40
OUT B
OUT A
1 21
REF
R
.
.
1
1
2
/I
M
BIAS
M
HB
V
REF
= 15k
R8
2M
1%
1 221
= 1.221V/1 A 1.21M
V
.
IN
V
HB
2
4 65
V
.
V
15
1
mV
2
1
9