7
LTC1841/LTC1842/LTC1843
APPLICATIONS INFORMATION
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The LTC1841/LTC1842/LTC1843 are dual micropower
comparators with a built-in 1.182V reference (LTC1842/
LTC1843). Features include programmable hysteresis,
wide supply voltage range (2V to 11V) and the ability for
the reference to drive up to a 0.01µF capacitor without
oscillation. The comparators’ open-drain outputs can typi-
cally sink greater than 20mA and the supply current
glitches that normally occur when switching logic states
have been eliminated.
Power Supplies
The comparators operate from a single 2V to 11V (2.5V to
11V for LTC1842/LTC1843) or dual ±1V to ±5.5V supply
(±1.25V to ±5.5V for LTC1842/LTC1843). If the reference
output is required to source more than 1mA or the supply
source impedance is high, V
+
should be bypassed with a
0.1µF capacitor.
Comparator Inputs
The comparators’ input can swing from the negative
supply V
–
to within 1.3V (max) of the positive supply V
+
.
The input can be forced 300mV below V
–
or above V
+
without damage and the typical input leakage current is
only ±10pA.
Comparator Outputs
Each comparator output is an open-drain pull-down to V
–
typically capable of sinking greater than 20mA. The low
output leakage current while in three-state mode allows a
high value pull-up resistor to be used. The open-drain
outputs can be wire OR-ed or used in level shifting
applications.
Voltage Reference
The internal bandgap reference has an output voltage of
1.182V referenced to V
–
. The reference accuracy is 1.5%
from –40°C to 85°C. It can typically source greater than
1mA and sink up to 10µA with a 5V supply. The reference
can drive a bypass capacitor of up to 0.01µF without
oscillation. By inserting a series resistor, capacitance
values up to 100µF can be used (Figure 1).
Figure 1. Damping the Reference Output
Figure 3 shows the bypassed reference output with a
square wave applied to the V
+
pin. Resistors R2 and R3 set
a 10mV hysteresis voltage band while R1 damps the
reference response. Note that the comparator output
doesn’t trip.
CAPACITOR VALUE (µF)
0.001
0.1
RESISTOR VALUE (kΩ)
10
0.01 0.1 101
1841/43 F02
1
100
Figure 2. Damping Resistance vs Bypass Capacitor Value
LTC1843
V
–
REF
R1
C1
REFERENCE
OUTPUT
1841/43 F01
Figure 2 shows the resistor value required for different
capacitor values to achieve critical damping. Bypassing
the reference can help prevent false tripping of the com-
parators by preventing glitches on V
+
or reference load
transients from disturbing the reference output voltage.
