Datasheet
LTC15 4 0
8
1540fb
For more information www.linear.com/LTC1540
APPLICATIONS INFORMATION
TYPICAL APPLICATIONS
Hysteresis
Hysteresis can be added to the LTC1540 by connecting a
resistor (R1) between the REF and HYST pins and a second
resistor (R2) from HYST to V
–
(Figure 5).
The difference between the upper and lower threshold volt-
ages, or hysteresis voltage band (V
HB
), is equal to twice
the voltage difference between the REF and HYST pins.
When more hysteresis is added, the upper threshold in-
creases the same amount as the low threshold decreases.
The maximum voltage allowed between REF and HYST
pins is 50mV, producing a maximum hysteresis voltage
band of 100mV
. The hysteresis band may vary by up to
15%. 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 the value of
R1 (kΩ) is equal to the value of V
HB
(mV).
Figure 5. Programmable Hysteresis
Figure 6. Glitch-Free Level Detector with Hysteresis
Level Detector
The LTC1540 is ideal for use as a nanopower level detector
as shown in Figure 6. R1 and R2 form a voltage divider
from V
IN
to the noninverting comparator input. 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 V
IN
voltage trip level, in this example 4.65V.
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 hysteresis
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) = 15k, V
HB
(mV) = 15mV
5. Choose the values for R1 and R2 to set the trip point.
6
R2
HYST
V
–
REF
5
R1
1540 • F05
LTC1540
2
I
REF
R1 =
V
HB
(2)(I
REF
)
R2 =
I
REF
1.182V –
( )
V
HB
2
V
+
R5
430Ω
5%
R3
15k
1%
C1
1µF
OUT
V
–
2 1
7
5V
V
IN
8
GND
LTC1540
1540 F06
IN
+
IN
–
HYST
REF
3
4
5
6
–
+
R2
3.4M
1%
R1
1.18M
1%
R4
2.4M
1%
R1
=
R2 = R1
– 1
= = 1.18M
V
REF
I
BIAS
V
REF
+
V
IN
V
HB
2
1.182V
1µA
R2 = 1.18M
R2 = 3.40M
– 1
1.182V +
4.65V
15mV
2
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