6
LT1120
1120fd
GND (Pin 1): Ground.
FB (Pin 2): Feedback. This is the feedback point of the
regulator. When operating, it is nominally at 2.5V. Opti-
mum source resistance is 200k to 500k. The feedback pin
should not be driven below ground or more positive than
5V.
SHDN (Pin 3): Shutdown. A logic 1 shuts off the main
regulator. Caution: noise or leakage into the shutdown pin
can affect output voltage.
V
OUT
(Pin 4): Regulator Output. Main output, requires a
10μF output capacitor. Can be shorted to V
IN
or ground
without damaging the device.
PI FU CTIO S
UUU
V
IN
(Pin 5): Input Supply. Bypass with a 10μF capacitor.
Must always be more positive than ground.
REF (Pin 6): Reference. 2.5V can source or sink current.
May be shorted to ground or up to 5V. Voltages in excess
of 5V can damage the device.
COMPOUT (Pin 7): Comparator Output. Open Collector
NPN Output. May be connected to any voltage from
ground to 36V more positive than ground (operates above
V
IN
). Short-circuit protected.
– INPUT (Pin 8): Comparator Input. Inverting comparator
input.
BLOCK DIAGRA
W
50k
1120 BD
–
+
REF
2.5V
4
6
V
OUT
COMPOUT
60k
5V
IN
2FB
3 SHDN
GND
REF
8
–INPUT
–
+
1
7
APPLICATIO S I FOR ATIO
WUU
U
The LT1120 is especially suited for micropower system
applications. For example, the comparator section of the
LT1120 may be used as a battery checker to provide an
indication of low battery. Another type of system applica-
tion for the LT1120 would be to generate the equivalent of
split supplies off of a single power input. The regulator
section provides regulated output voltage and the refer-
ence, which can both source and sink current, is then an
artificial system ground providing a split supply for the
system.
For many applications the comparator can be frequency
compensated to operate as an amplifier. Compensation
values for various gains are given in the data sheet. The
comparator gain is purposely low to make it easier to
frequency compensate as an amplifier. The NPN output is
capable of sinking 10mA and can drive loads connected to
voltages in excess of the positive power supply. This is
useful for driving switches or linear regulators off of a
higher input voltage.
