1
LT1120A
■
20µA Supply Current
■
8-Lead SOIC
■
125mA Output Current
■
2.5V Reference
■
Reference Output Sources 4mA and Sinks 4mA
■
Open Collector
■
Comparator Sinks 10mA
■
Logic Shutdown
■
0.2V Dropout Voltage
■
Thermal Limiting
The LT1120A is a combination micropower positive regu-
lator and free collector comparator on a single monolithic
chip. With only 20µA supply current, the LT1120A can
supply over 125mA of output current. Input voltage range
is from 4.5V to 36V and dropout voltage is 0.6V at 125mA.
Dropout voltage decreases with lower load currents. Also
included on the chip is a class B output 2.5V reference that
can either source or sink current. This allows it to be used
as a supply splitter or auxiliary output. A shutdown pin
allows logic shutdown of the output.
The comparator can be used for system or battery moni-
toring. For example, the comparator can be used to warn
of low system voltage. Frequency compensation of the
comparator for amplifier applications can be obtained by
adding external output capacitance.
■
Battery Systems
■
Battery Backup System
■
Portable Terminals
■
Portable Instruments
■
Memory Keep Alive
Micropower Regulator with
Comparator and Shutdown
FEATURES
DESCRIPTION
U
APPLICATIONS
U
TYPICAL APPLICATION
U
Dropout Voltage and Supply Current5V Regulator
1120A TA01
V
IN
> 5.2V
I
Q
= 20µA
10µF
1M
SHUTDOWN
13
54
2
0.001µF
25µF
1M
5V
LT1120A
V
OUT
V
IN
GND FB
++
OUTPUT CURRENT (mA)
0.1
0.01
DROPOUT VOLTAGE (V)
1.00
1 1000
1120A TA02
10
0.10
100 0.1
SUPPLY CURRENT (mA)
10
1
2
LT1120A
8
7
6
54
3
2
1GND
FEEDBACK
SHUTDOWN
V
OUT
V
IN
REF
COMP OUT
–INPUT
TOP VIEW
N8 PACKAGE
8-LEAD PLASTIC DIP S8 PACKAGE
8-LEAD PLASTIC SOIC
1120A POI01
LT1120A
Input Voltage ........................................................... 36V
NPN Collector Voltage ............................................. 36V
Output Short-Circuit Duration.......................... Indefinite
Power Dissipation............................... Internally Limited
Operating Temperature Range
LT1120AC.............................................. 0°C to 100°C
Storage Temperature Range
LT1120AC.......................................... –65°C to 150°C
ABSOLUTE MAXIMUM RATINGS
W
WW
U
PACKAGE/ORDER INFORMATION
W
UU
ORDER PART
NUMBER
LT1120ACN8
LT1120ACS8
S8 PART
MARKING
1120A
Consult factory for Industrial and Military grade parts.
TJ = 25°C
ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Reference
Reference Voltage 4.5V ≤ V
IN
≤ 36V 2.46 2.50 2.54 V
Line Regulation 4.5V ≤ V
IN
≤ 36V 0.01 0.015 %/V
Load Regulation –2.0mA ≤ I
REF
≤ 2mA, V
IN
= 12V 0.3 0.6 %
Output Source Current V
IN
= 5V 2 4 mA
Output Sink Current V
IN
= 5V 2 4 mA
Temperature Stability 1%
Regulator
Supply Current V
IN
= 6V, I
OUT
≤ 100µA2025µA
V
IN
= 36V, I
OUT
≤ 100µA3040µA
V
IN
= 12V, I
OUT
= 125mA 11 20 mA
Output Current (V
IN
– V
OUT
) ≥ 1V, V
IN
≥ 6V 125 mA
Load Regulation (V
IN
– V
OUT
) ≥ 1V, V
IN
≥ 6V 0.2 0.5 %
Line Regulation 6V ≤ V
IN
≤ 36V 0.01 0.015 %/V
Dropout Voltage I
OUT
= 100µA 0.02 0.05 V
I
OUT
= 125mA 0.40 0.65 V
Feedback Sense Voltage V
IN
= 12V 2.44 2.5 2.56 V
Shutdown Pin Voltage Normal 0.4 V
V
OUT
≤ 0.5V Shutdown 2.2 1.4 V
Shutdown Pin Current V
IN
= 1.4V 10 µA
Feedback Bias Current 15 40 nA
Minimum Load Current V
IN
= 36V 1 5 µA
Short Circuit Current V
IN
= 36V 250 400 mA
Comparator
Offset Voltage V
IN
= 36V 3 7 mV
Bias Current V
IN
= 36V 15 40 nA
Gain ∆V
OUT
= 29V, R
L
= 20k 2000 10000 V/V
Power Supply Rejection 4.5V ≤ V
S
≤ 36V 80 96 dB
Output Sink Current V
IN
= 4.5V 10 18 mA
Saturation Voltage I
OUT
= 1mA 0.4 0.6 V
Input Voltage Range 0 V
IN
– 1 V
Response Time 5 µs
Leakage Current V
IN
= 36V, V(Pin 7) = 36V 2 µA
TJMAX = 110°C, θJA = 130°C/W (N)
TJMAX = 110°C, θJA = 190°C/W (S)
3
LT1120A
TEMPERATURE (°C)
–50
0
SHORT-CIRCUIT CURRENT (mA)
350
150
1120A G03
300
250
200
150
100
50
110
–10 30 70
REGULATOR OUTPUT CURRENT (mA)
0.1
0.01
SUPPLY CURRENT (mA)
0.1
100
1 1000
1120A G02
10
1
100
10
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the operating temperature range.
Note 1: For T
A
≤ –40°C output sink current drops to 2.5mA.
Regulator Load Regulation Supply Current Regulator Short-Circuit Current
TYPICAL PERFORMANCE CHARACTERISTICS
UW
OUTPUT CURRENT (mA)
0.1
–0.3
OUTPUT VOLTAGE CHANGE (%)
0.3
10 1000
1120A G01
100
1
0.2
0.1
0
–0.1
–0.2
T
J
= –55°C
T
J
= 25°C
T
J
= 125°C
PRE-LOAD = 100 µA
PARAMETER CONDITIONS MIN TYP MAX UNITS
Reference
Reference Voltage 4.5V ≤ V
IN
≤ 36V ●2.40 2.50 2.55 V
Line Regulation 4.5V ≤ V
IN
≤ 36V ●0.01 0.02 %/V
Load Regulation –2.0mA ≤ I
REF
≤ 2mA, V
IN
= 12V ●0.4 0.8 %
Output Source Current V
IN
= 5V ●2mA
Output Sink Current V
IN
= 5V ●2mA
Regulator
Supply Current V
IN
= 6V, I
OUT
≤ 100µA●30 40 µA
V
IN
= 36V, I
OUT
≤ 100µA●40 50 µA
V
IN
= 12V, I
OUT
= 125mA ●11 20 mA
Output Current (V
IN
– V
OUT
) ≥ 1V, V
IN
≥ 6V ●125 mA
Load Regulation (V
IN
– V
OUT
) ≥ 1V, V
IN
≥ 6V ●1%
Line Regulation 6V ≤ V
IN
≤ 36V ●0.02 %/V
Dropout Voltage I
OUT
= 100µA●0.06 V
I
OUT
= 125mA ●0.85 V
Feedback Sense Voltage V
IN
= 12V ●2.38 2.5 2.57 V
Feedback Bias Current ●50 nA
Minimum Load Current V
IN
= 36V ●50 µA
Short Circuit Current V
IN
= 36V ●240 400 mA
Comparator
Offset Voltage V
IN
= 36V ●10 mV
Bias Current V
IN
= 36V ●15 60 nA
Gain ∆V
OUT
= 29V, R
L
= 20k ●1000 V/V
Output Sink Current (Note 1) V
IN
= 4.5V ●510 mA
Leakage Current V
IN
= 36V, V(Pin 7) = 36V ●8µA
4
LT1120A
REGULATOR OUTPUT CURRENT (mA)
0.1
0
FEEDBACK PIN CURRENT (nA)
40
1 1000
1120A G10
10
20
100
35
30
25
15
10
5
T
J
= –55°C
T
J
= 25°C
T
J
= 125°C
REGULATOR OUTPUT CURRENT (mA)
0.1
0.01
REGULATOR INPUT-OUTPUT DIFFERENTIAL (V)
1
1 1000
1120A G04
10
0.1
100
∆V
OUT
= 100mV
Regulator Minimum Load Current Regulator Ripple Rejection
Supply Current at Dropout Reference Regulation
TYPICAL PERFORMANCE CHARACTERISTICS
UW
TEMPERATURE (°C)
70
1
MINIMUM LOAD CURRENT (µA)
100
80 150
1120A G05
110
10
13090 100 120 140
RIPPLE FREQUENCY (Hz)
10
30
RIPPLE REJECTION (dB)
70
1k 100k
1120A G06
10k
100
65
60
55
50
45
40
35
I
OUT
= 100mA
I
OUT
= 10mA
V
IN
= 10VDC,
1Vp-p
V
OUT
= 5V
C
OUT
= 10µF
I
OUT
= 1mA
REGULATOR INPUT-OUTPUT DIFFERENTIAL (V)
0
0.01
SUPPLY CURRENT (mA)
0.1
10
0.2 0.6
1120A G08
0.3
1
0.1 0.5
I
OUT
= 100mA
I
OUT
= 10mA
I
OUT
= 1mA
0.4
REFERENCE OUTPUT CURRENT (mA)
–1.5
–4
REFERENCE VOLTAGE CHANGE (mV)
4
0 1.5
1120A G09
0.5
–1.0
3
2
1
0
–1
–2
–3
–0.5 1.0
Dropout Voltage
Supply Current
REGULATOR INPUT-OUTPUT DIFFERENTIAL (V)
1
0.01
SUPPLY CURRENT (mA)
0.1
10
10 25
1120A G07
15
1
5 20
I
OUT
= 100mA
I
OUT
= 10mA
V
OUT
= 5V
I
OUT
= 1mA
Feedback Pin Current Regulator Thermal Regulation Turn-On Characteristic
TIME (ms)
0
OUTPUT CURRENT (mA)
0.1
180
1120A G11
80
0
–0.1
50
0 20 40 60 100 120 140 160
OUTPUT VOLTAGE CHANGE (%)
V
IN
= 15V
V
OUT
= 5V
INPUT VOLTAGE (V)
0
5.5
1120A G12
0
OUTPUT VOLTAGE (V)
5.0
4.5
4.0
3.5
3.0
2.5
2.0
12345678
V
OUT
= 5V
NO LOAD
R
L
= 500Ω
R
L
= 50Ω
5
LT1120A
BLOCK DIAGRAM
W
Pin 1 (Ground).
Pin 2 (Feedback): This is the feedback point of the
regulator. When operating, it is nominally at 2.5V.
Optimum source resistance is 200k to 500k. The feedback
pin should not be driven below ground or more positive
than 5V.
Pin 3 (Shutdown): A logic 1 shuts off main regulator.
Caution: noise or leakage into the shutdown pin can affect
output voltage.
Pin 4 (Regulator Output): Main output, requires 10µF
output capacitor. Can be shorted to V
IN
or ground without
damaging device.
PIN FUNCTIONS
UUU
Pin 5 (Input Supply): Bypass with 10µF cap. Must always
be more positive than ground.
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.
Pin 7 (Comparator Output): May be connected to any
voltage from ground to 36V more positive than ground
(operates above V
IN
). Short circuit protected.
Pin 8 (Comparator Input): Inverting comparator input.
–
+
100k
5
7
6
REFERENCE
8
–INPUT
120k
V
IN
COMPARATOR
OUT
4V
OUT
2 FEEDBACK
3 SHUTDOWN
1 GROUND
REF
2.5V
1120A BD01
The LT1120A is especially suited for micropower system
applications. For example, the comparator section of the
LT1120A may be used as a battery checker to provide an
indication of low battery. Another type of system applica-
tion for the LT1120A would be to generate the equivalent
of split supplies off of a single power input. The regulator
section provides regulated output voltage and the
reference, which can both source and sink current is then
an artificial system ground providing a split supply for
the system.
APPLICATIONS INFORMATION
WUU U
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.
6
LT1120A
APPLICATIONS INFORMATION
WUU U
Reference
Internal to the LT1120A is a 2.5V trimmed class B output
reference. The reference was designed to be able to source
or sink current so it could be used in supply splitting
applications as well as a general purpose reference for
external circuitry. The design of the reference allows it to
source and sink typically 4mA. The available source and
sink current decreases as temperature increases. It is
sometimes desirable to decrease the AC output imped-
ance by placing an output capacitor on Pin 6. The reference
in the LT1120A becomes unstable with large capacitive
loads placed directly on it. When using an output capaci-
tor, about 20Ω should be used to isolate the capacitor
from the reference pin. This 20Ω resistor can be placed
directly in series with the capacitor or alternatively the
reference line can have 20Ω placed in series with it and
then a capacitor to ground. This is shown in Figure 1. Other
than placing large capacitive loads on the reference, no
other precautions are necessary and the reference is
stable with nominal stray capacitances.
1120A AI01
20Ω
6
10µF
OUTPUT
REF
+
20Ω
6
10µF
REF
+
OUTPUTOR
Figure 1. Bypassing Reference
Overload Protection
The main regulator in the LT1120A is current limited at
approximately 250mA. The current limit is stable with both
input voltage and temperature.
Like most other IC regulators, a minimum load is required
on the output of the LT1120A to maintain regulation. For
most standard regulators this is normally specified at
5mA. Of course, for a micropower regulator this would be
a tremendously large current. The output current must be
large enough to absorb all the leakage current of the pass
transistor at the maximum operating temperature. It also
affects the transient response; low output currents have
long recovery times from load transients. At high operat-
ing temperatures the minimum load current increases and
having too low of a load current may cause the output to
go unregulated. Devices are tested for minimum load
current at high temperature. The output voltage setting
resistors to the feedback terminal can usually be used to
provide the minimum load current.
Frequency Compensation
The LT1120A is frequency compensated by a dominant
pole on the output. An output capacitor of 10µF is usually
large enough to provide good stability. Increasing the
output capacitor above 10µF further improves stability.
In order to ensure stability, a feedback capacitor is needed
between the output pin and the feedback pin. This is
because stray capacitance can form another pole with the
large value of feedback resistors used with the LT1120A.
Also, a feedback capacitor minimizes noise pickup and
improves ripple rejection.
With the large dynamic operating range of the output
current, 10000:1, frequency response changes widely.
Low AC impedance capacitors are needed to insure
stability. While solid tantalum are best, aluminum
electrolytics can be used but larger capacitor values may
be needed.
7
LT1120A
TYPICAL APPLICATIONS
U
1120A TA04
–
+
C1
R1
AT AV = 100,
SLEW RATE = +0.05V/µs
–6V/µs
1M
C2
R2
IN
6
VREF
7
50µA
AV
–1
–10
–100
R1
33Ω
100Ω
10k
C1
0.1µF
0.047µF
0.002µF
C2
0.001µF
–
–
R2
1M
100k
10k
Compensating the Comparator as an Op Amp
Regulator with Output Voltage Monitor
1120A TA03
+
–
LOGIC 500k
5V
LOGIC OUTPUT
7
REF
6
LT1120A
5
V
IN
OUTPUT
1
GND
FEEDBACK
4
8
2
0.001µF98k
2k
100k
10µF
OUTPUT
5V
LOGIC OUTPUT GOES LOW WHEN
V
OUT
DROPS BY 100mV
+
Current Limited 1 Amp Regulator
LT1120A
1
GND
1M
100k
220µF
†
+
0.22µF
V
OUT
270Ω
2.2k
5
V
IN
4
2
FB
0.5Ω*V
IN
V
OUT
5V AT 1A
*SETS CURRENT
LIMIT BUT INCREASES
DROPOUT VOLTAGE
BY 0.5V.
MUST HAVE LOW
ESR. SEVERAL 100µF
CAPACITORS CAN BE
PARALLELED.
†
1120A TA06
MJE2955 2N3906*
Battery Backup Regulator
1120A TA05
V
OUT
FB
4
V
OUT
5V
20.001µF1M
50k
1M
10µF
LT1120A
1
GND
5V
IN
BATTERY
INPUT V
IN
FB
LT1120A
1
GND
V
OUT
5MAIN
POWER
INPUT
+
4
2
V
IN
V
OUT
INTERNAL PARASITIC
DIODES OF LT1120A
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
8
LT1120A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900
●
FAX
: (408) 434-0507
●
TELEX
: 499-3977
LT/GP 0494 10K • PRINTED IN USA
LINEAR TECHN OLOGY CORPORATION 1994
Dimension in inches (millimeters) unless otherwise noted.
PACKAGE DESCRIPTION
U
N8 Package
8-Lead Plastic DIP
S8 Package
8-Lead Plastic SOIC (Narrow)
1234
0.150 – 0.157
(3.810 – 3.988)
8765
0.189 – 0.197
(4.801 – 5.004)
0.228 – 0.244
(5.791 – 6.197)
0.010 – 0.020
(0.254 – 0.508)
0.016 – 0.050
0.406 – 1.270
× 45°
0°– 8° TYP
0.008 – 0.010
(0.203 – 0.254)
SO8 0392
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
N8 0392
0.045 ± 0.015
(1.143 ± 0.381)
0.100 ± 0.010
(2.540 ± 0.254)
0.065
(1.651)
TYP
0.045 – 0.065
(1.143 – 1.651)
0.130 ± 0.005
(3.302 ± 0.127)
0.020
(0.508)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
0.125
(3.175)
MIN
12 34
8765
0.250 ± 0.010
(6.350 ± 0.254)
0.400
(10.160)
MAX
0.009 – 0.015
(0.229 – 0.381)
0.300 – 0.320
(7.620 – 8.128)
0.325 +0.025
–0.015
+0.635
–0.381
8.255
()