Linear Technology LT1120A Datasheet

FEATURES

■

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

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APPLICATIONS

■

Battery Systems

■

Battery Backup System

■

Portable Terminals

■

Portable Instruments

■

Memory Keep Alive

LT1120A

Micropower Regulator with

Comparator and Shutdown

U

DESCRIPTION

The LT1120A is a combination micropower positive regu­lator 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 moni­toring. 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.

TYPICAL APPLICATION

VIN > 5.2V

= 20µA

I

Q

10µF

54

V

IN

++

SHUTDOWN

LT1120A

V

OUT

2

FB

GND

13

U

0.001µF

1M

1M

5V

25µF

1120A TA01

Dropout Voltage and Supply Current5V Regulator

1.00

0.10

DROPOUT VOLTAGE (V)

0.01
0.1

1 1000
OUTPUT CURRENT (mA)

10

SUPPLY CURRENT (mA)

1

10

100

0.1

1120A TA02

1

LT1120A

WW

W

ABSOLUTE MAXIMUM RATINGS

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

ELECTRICAL CHARACTERISTICS

PARAMETER CONDITIONS MIN TYP MAX UNITS
Reference

Reference Voltage 4.5V ≤ VIN ≤ 36V 2.46 2.50 2.54 V
Line Regulation 4.5V ≤ VIN ≤ 36V 0.01 0.015 %/V
Load Regulation –2.0mA ≤ I
Output Source Current VIN = 5V 2 4 mA
Output Sink Current VIN = 5V 2 4 mA
Temperature Stability 1%

Regulator

Supply Current VIN = 6V, I

V

IN

V

IN

Output Current (VIN – V
Load Regulation (VIN – V
Line Regulation 6V ≤ VIN ≤ 36V 0.01 0.015 %/V
Dropout Voltage I

Feedback Sense Voltage VIN = 12V 2.44 2.5 2.56 V
Shutdown Pin Voltage Normal 0.4 V

Shutdown Pin Current VIN = 1.4V 10 µA
Feedback Bias Current 15 40 nA
Minimum Load Current VIN = 36V 1 5 µA
Short Circuit Current VIN = 36V 250 400 mA

Comparator

Offset Voltage VIN = 36V 3 7 mV
Bias Current VIN = 36V 15 40 nA
Gain ∆V
Power Supply Rejection 4.5V ≤ VS ≤ 36V 80 96 dB
Output Sink Current VIN = 4.5V 10 18 mA
Saturation Voltage I
Input Voltage Range 0 VIN – 1 V
Response Time 5 µs
Leakage Current VIN = 36V, V(Pin 7) = 36V 2 µA

I

V

OUT
OUT

OUT

OUT

REF

OUT

= 36V, I

OUT

= 12V, I

OUT

) ≥ 1V, VIN ≥ 6V 125 mA

OUT

) ≥ 1V, VIN ≥ 6V 0.2 0.5 %

OUT

= 100µA 0.02 0.05 V
= 125mA 0.40 0.65 V

≤ 0.5V Shutdown 2.2 1.4 V

= 29V, RL = 20k 2000 10000 V/V

OUT

= 1mA 0.4 0.6 V

U

U

W

U

PACKAGE/ORDER INFORMATION

ORDER PART

TOP VIEW

1GND

FEEDBACK

SHUTDOWN

8-LEAD PLASTIC DIP

Consult factory for Industrial and Military grade parts.

2
3

V

OUT

N8 PACKAGE

T

= 110°C, θJA = 130°C/ W (N)

JMAX

= 110°C, θJA = 190°C/ W (S)

T

JMAX

LT1120A

8-LEAD PLASTIC SOIC

–INPUT

8
7

COMP OUT

6

REF

54

V

IN

S8 PACKAGE

1120A POI01

TJ = 25°C

≤ 2mA, VIN = 12V 0.3 0.6 %

≤ 100µA2025µA

≤ 100µA3040µA
= 125mA 11 20 mA

NUMBER

LT1120ACN8
LT1120ACS8

S8 PART

MARKING

1120A

2

LT1120A

TEMPERATURE (°C)

–50

0

SHORT-CIRCUIT CURRENT (mA)

350

150

1120A G03

300

250

200

150

100

50

110

–10

30 70

ELECTRICAL CHARACTERISTICS

PARAMETER CONDITIONS MIN TYP MAX UNITS
Reference

Reference Voltage 4.5V ≤ VIN ≤ 36V ● 2.40 2.50 2.55 V
Line Regulation 4.5V ≤ VIN ≤ 36V ● 0.01 0.02 %/V
Load Regulation –2.0mA ≤ I
Output Source Current VIN = 5V ● 2mA
Output Sink Current VIN = 5V ● 2mA

Regulator

Supply Current VIN = 6V, I

= 36V, I

V

IN

VIN = 12V, I
Output Current (VIN – V
Load Regulation (VIN – V
Line Regulation 6V ≤ VIN ≤ 36V ● 0.02 %/V
Dropout Voltage I

= 100µA ● 0.06 V

OUT

I

= 125mA ● 0.85 V

OUT

Feedback Sense Voltage VIN = 12V ● 2.38 2.5 2.57 V
Feedback Bias Current ● 50 nA
Minimum Load Current VIN = 36V ● 50 µA
Short Circuit Current VIN = 36V ● 240 400 mA

Comparator

Offset Voltage VIN = 36V ● 10 mV
Bias Current VIN = 36V ● 15 60 nA
Gain ∆V

OUT

Output Sink Current (Note 1) VIN = 4.5V ● 510 mA
Leakage Current VIN = 36V, V(Pin 7) = 36V ● 8 µA

The ● denotes specifications which apply over the operating temperature range.
Note 1: For TA ≤ –40°C output sink current drops to 2.5mA.

≤ 2mA, VIN = 12V ● 0.4 0.8 %

REF

≤ 100µA ● 30 40 µA

OUT

≤ 100µA ● 40 50 µA

OUT

= 125mA ● 11 20 mA

OUT

) ≥ 1V, VIN ≥ 6V ● 125 mA

OUT

) ≥ 1V, VIN ≥ 6V ● 1%

OUT

= 29V, RL = 20k ● 1000 V/V

TYPICAL PERFORMANCE CHARACTERISTICS

Regulator Load Regulation Supply Current

0.3

PRE-LOAD = 100 µA

0.2

0.1

0

–0.1

OUTPUT VOLTAGE CHANGE (%)

–0.2

–0.3

0.1

TJ = –55°C

TJ = 25°C

TJ = 125°C

1
OUTPUT CURRENT (mA)

10 1000

100

W

1120A G01

U

SUPPLY CURRENT (mA)

0.01

100

10

1

0.1

0.1

1 1000

REGULATOR OUTPUT CURRENT (mA)

Regulator Short-Circuit Current

10

100

1120A G02

3

LT1120A

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

VIN = 10VDC,
1Vp-p
V

OUT

= 5V

C

OUT

= 10µF

I

OUT

= 1mA

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

RL = 500Ω

RL = 50Ω

W

U

TYPICAL PERFORMANCE CHARACTERISTICS

Dropout Voltage

1

∆V

= 100mV

OUT

0.1

REGULATOR INPUT-OUTPUT DIFFERENTIAL (V)

0.01
0.1

1 1000

REGULATOR OUTPUT CURRENT (mA)

10

100

Supply Current

10

I

= 100mA

OUT

1

I

0.1

SUPPLY CURRENT (mA)

0.01

= 10mA

OUT

I

= 1mA

OUT

5

1

REGULATOR INPUT-OUTPUT DIFFERENTIAL (V)

10 25

V

OUT

15

20

1120A G04

= 5V

1120A G07

Regulator Minimum Load Current

100

10

MINIMUM LOAD CURRENT (µA)

1

70

80 150

110

TEMPERATURE (°C)

Supply Current at Dropout

10

I

= 100mA

OUT

1

I

0.1

SUPPLY CURRENT (mA)

I

= 1mA

OUT

0.01

0.1

0

REGULATOR INPUT-OUTPUT DIFFERENTIAL (V)

= 10mA

OUT

0.2 0.6

0.3

0.4

13090 100 120 140

0.5

1120A G05

1120A G08

Regulator Ripple Rejection

Reference Regulation

4

3

2

1

0

–1

–2

REFERENCE VOLTAGE CHANGE (mV)

–3

–4

–1.0

–1.5

–0.5 1.0

REFERENCE OUTPUT CURRENT (mA)

0 1.5

0.5

1120A G09

Feedback Pin Current Regulator Thermal Regulation

40

35

30

25

20

15

10

FEEDBACK PIN CURRENT (nA)

5

0

0.1

4

TJ = –55°C

TJ = 25°C

TJ = 125°C

REGULATOR OUTPUT CURRENT (mA)

10

1 1000

100

1120A G10

0.1
VIN = 15V

= 5V

V

OUT



0



–0.1

OUTPUT VOLTAGE CHANGE (%)

50

0

0 20 40 60 100 120 140 160

OUTPUT CURRENT (mA)

80

TIME (ms)

Turn-On Characteristic

180

1120A G11

PIN FUNCTIONS

LT1120A

UUU

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 VIN or ground without
damaging device.

W

BLOCK DIAGRAM

REFERENCE

6

5

V

OUT

IN

7

+

COMPARATOR

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 VIN). Short circuit protected.

Pin 8 (Comparator Input): Inverting comparator input.

100k

–

REF

2.5V

8

–INPUT

U

WUU

APPLICATIONS INFORMATION

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 applica­tion 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.

4V

OUT

2 FEEDBACK

120k

3 SHUTDOWN

1 GROUND

1120A BD01

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.

5

LT1120A

U

WUU

APPLICATIONS INFORMATION

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 imped­ance 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 capaci­tor, 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.

REF

6

OUTPUT

20Ω

+

10µF

REF

6

20Ω

+

OUTPUTOR

10µF

1120A AI01

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 operat­ing 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.

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

6

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.

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TYPICAL APPLICATIONS

5V

LOGIC 500k

LOGIC OUTPUT

LOGIC OUTPUT GOES LOW WHEN
V

DROPS BY 100mV

OUT

7

Regulator with Output Voltage Monitor

5

V

IN

–

LT1120A

+

FEEDBACK

REF
6

OUTPUT

GND
1

4

0.001µF

8

2

98k

2k

100k

+

10µF

LT1120A

OUTPUT
5V

1120A TA03

Compensating the Comparator as an Op Amp

6

V

REF

+

–

R2

IN

A

V

–1

–10

–100

R1

33Ω

100Ω

10k

1M

C2

C1

0.1µF

0.047µF

0.002µF

BATTERY

INPUT

50µA

7

0.001µF

5

= 100,

AT A

V

SLEW RATE = +0.05V/µs
–6V/µs

R1

C1

C2

R2

1M

–

100k

–

10k

V

IN

LT1120A

GND

1

V

OUT

FB

1120A TA04

Battery Backup Regulator

4

0.001µF

2

1M

50k

V

OUT

5V

LT1120A

GND

+

10µF

Current Limited 1 Amp Regulator

2.2k

5
V

IN

V

OUT

4

2

FB

V

FB

270Ω

OUT

LT1120A

GND

1

1

4

2

MJE2955 2N3906*

0.22µF

1M

100k

MAIN

5

V

POWER

IN

INPUT

0.5Ω*

+

220µF

*

SETS CURRENT
LIMIT BUT INCREASES
DROPOUT VOLTAGE
BY 0.5V.


†

MUST HAVE LOW
ESR. SEVERAL 100µF
CAPACITORS CAN BE
PARALLELED.

V

IN

V

OUT

5V AT 1A

†

1120A TA06

INTERNAL PARASITIC

DIODES OF LT1120A

V

IN

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 represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

V

OUT

1M

1120A TA05

7

LT1120A

PACKAGE DESCRIPTION

U

Dimension in inches (millimeters) unless otherwise noted.

N8 Package

8-Lead Plastic DIP

0.400

(10.160)

MAX

876

5

12

0.300 – 0.320

(7.620 – 8.128)

0.065

(1.651)

0.009 – 0.015

(0.229 – 0.381)

+0.025

0.325

–0.015

+0.635

8.255

()

–0.381

TYP

0.045 ± 0.015

(1.143 ± 0.381)

0.100 ± 0.010

(2.540 ± 0.254)

0.045 – 0.065

(1.143 – 1.651)

3

S8 Package

8-Lead Plastic SOIC (Narrow)

0.189 – 0.197

(4.801 – 5.004)

7

8

0.250 ± 0.010

(6.350 ± 0.254)

4

0.130 ± 0.005

(3.302 ± 0.127)

0.125

(3.175)

MIN



0.018 ± 0.003

(0.457 ± 0.076)

5

6



0.020

(0.508)



MIN

N8 0392

8

0°– 8° TYP

0.010 – 0.020

(0.254 – 0.508)

0.016 – 0.050

0.406 – 1.270

× 45°

0.008 – 0.010

(0.203 – 0.254)

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7487

[phone]

●

FAX

: [phone]

●

TELEX

: 499-3977

0.228 – 0.244

(5.791 – 6.197)

0.053 – 0.069

(1.346 – 1.752)

0.014 – 0.019

(0.355 – 0.483)

0.150 – 0.157

(3.810 – 3.988)

1

3

2

4

0.004 – 0.010

(0.101 – 0.254)

0.050

(1.270)

BSC

SO8 0392

LT/GP 0494 10K • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1994