5
LTC1540
sn1540 1540fas
PIN FUNCTIONS
UUU
V
+
(Pin 7): Positive Supply operating voltage is from 2V
to 11V.
OUT (Pin 8): Comparator CMOS Output. Swings from
GND to V
+
. Output can source up to 40mA and sink 5mA.
GND (Pin 1): Ground. Connect to V
–
for single supply
operation.
V
–
(Pin 2): Negative Supply. Potential should be more
negative than GND. Connect to ground for single supply
operation.
IN
+
(Pin 3): Noninverting Comparator Input. Input com-
mon mode range from V
–
to V
+
– 1.3V. Input current
typically 10pA at 25°C.
IN
–
(Pin 4): Inverting Comparator Input. Input common
mode range from V
–
to V
+
– 1.3V. Input current typically
10pA at 25°C.
HYST (Pin 5): Hysteresis Input. Connect to REF if not
used. Input voltage range is from V
REF
to V
REF
– 50mV.
REF (Pin 6): Reference Output. 1.182V with respect
to V
–
. Can source up to 1mA and sink 10µA at 25°C. Drive
0.01µF bypass capacitor without oscillation.
1540 • PD
1
2
3
4
8
7
6
5
IN
+
IN
–
HYST
REF
V
+
OUT
–
+
V
–
GND
LTC1540
The LTC1540 is a nanopower comparator with a built-in
1.182V reference. Features include programmable hyster-
esis, wide supply voltage range (2V to 11V) and the ability
of the reference to drive up to a 0.01µF capacitor without
oscillation. The comparator’s CMOS outputs can source
up to 40mA while supply current glitches that normally
occur when switching logic states, have been eliminated.
Power Supplies
The comparator operates from a single 2V to 11V supply.
The LTC1540 includes a separate ground for the compara-
tor output stage, allowing a split supply ranging from ±1V
to ±5.5V. Connecting V
–
to GND will allow single supply
operation. If the comparator 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 comparator inputs can swing from the negative supply,
V
–
, to within 1.3V (max) of the positive supply V
+
. The
inputs can be forced 300mV below V
–
or above V
+
without
damage and the typical input leakage current is only ±10pA.
APPLICATIONS INFORMATION
WUU
U
Comparator Output
The comparator output swings between GND and V
+
to
assure TTL compatibility with a split supply. The output is
capable of sourcing up to 40mA and sinking up to 5mA
while still maintaining nanoampere quiescent currents.
The output stage does not generate crowbar switching
currents during transitions which helps minimize parasitic
feedback through the supply pins.
Voltage Reference
The internal bandgap reference has a voltage of 1.182V
referenced to V
–
. The reference accuracy is ±2.0% from
0°C to 70°C. It can source up to 1mA and sink up to 10µA
with a 5V supply. The reference can drive a bypass
capacitor of up to 0.01µF without oscillation and by
inserting a series resistor, capacitance values up to 10µF
can be used (Figure 1).
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.
