LT1121IST-3.3#TRPBF_技术文档

LT1121/LT1121-3.3/LT1121-5

Micropower Low Dropout

Regulators with Shutdown

FEATURES

DESCRIPTION

The LT^®1121/LT1121-3.3/LT1121-5 are micropower low

dropout regulators with shutdown. These devices are ca-

pableofsupplying150mAofoutputcurrentwithadropout

voltage of 0.4V. Designed for use in battery-powered sys-

tems, thelowquiescentcurrent, 30µAoperatingand16µA

in shutdown, makes them an ideal choice. The quiescent

current is well-controlled; it does not rise in dropout as it

does with many other low dropout PNP regulators.

n

0.4V Dropout Voltage

n

150mA Output Current

n

30µA Quiescent Current

No Protection Diodes Needed

n

Adjustable Output from 3.75V to 30V

n

3.3V and 5V Fixed Output Voltages

n

Controlled Quiescent Current in Dropout

n

Shutdown

n

16µA Quiescent Current in Shutdown

OtherfeaturesoftheLT1121/LT1121-3.3/LT1121-5include

the ability to operate with very small output capacitors.

They are stable with only 0.33µF on the output while most

older devices require between 1µF and 100µF for stability.

Small ceramic capacitors can be used, enhancing manu-

facturability. Also the input may be connected to ground

or a reverse voltage without reverse current flow from

output to input. This makes the LT1121 series ideal for

backuppowersituationswheretheoutputisheldhighand

the input is at ground or reversed. Under these conditions

only 16µA will flow from the output pin to ground.

n

Stable with 0.33µF Output Capacitor

n

Reverse Battery Protection

ꢀ

n

No Reverse Current with Input Low

Thermal Limiting

Available in the 8-Lead SO, 8-Lead PDIP, 3-Lead

SOT-23 and 3-Lead TO-92 Packages

APPLICATIONS

n

Low Current Regulator

n

Regulator for Battery-Powered Systems

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

n

Post Regulator for Switching Supplies

TYPICAL APPLICATION

5V Battery-Powered Supply with Shutdown

Dropout Voltage

0.5

8

1

3.3V

OUT

IN

OUT

LT1121-3.3

150mA

0.4

0.3

0.2

0.1

0

+

1μF

5V

SOLID TANTALUM

5

SHDN

GND

3

V

(PIN 5) OUTPUT

SHDN

<0.25

>2.8

NC

OFF

ON

LT1121 • TA01

80

OUTPUT CURRENT (mA)

0

20 40 60

100 120 140 160

LT1121 • TA02

1121fg

1

LT1121/LT1121-3.3/LT1121-5

ABSOLUTE MAXIMUM RATINGS

(Note 1)

Input Voltage

Output Short-Circuit Duration ....................... Indefinite

Operating Junction Temperature Range (Note 3)

LT1121C-X............................................ 0°C to 125°C

LT1121I-X ........................................ –40°C to 125°C

Storage Temperature Range ..................– 65°C to 150°C

Lead Temperature (Soldering, 10 sec)...................300°C

LT1121 .............................................................. 30V

LT1121HV............................................... +36V, –30V

Output Pin Reverse Current ................................. 10mA

Adjust Pin Current ................................................ 10mA

Shutdown Pin Input Voltage (Note 2).......... 6.5V, – 0.6V

Shutdown Pin Input Current (Note 2) .................. 20mA

PIN CONFIGURATION

TOP VIEW

PIN 2 = NC FOR LT1121-3.3/LT1121-5

= ADJ FOR LT1121

PINS 6 AND 7 ARE FLOATING (NO

INTERNAL CONNECTION) ON THE

STANDARD S8 PACKAGE.

PINS 6 AND 7 CONNECTED TO GROUND

ON THE A VERSION OF THE LT1121 (S8 ONLY).

CONNECTING PINS 6 AND 7 TO THE

GROUND PLANE WILL REDUCE THERMAL

RESISTANCE. SEE THERMAL RESISTANCE

TABLES IN THE APPLICATIONS INFORMATION

SECTION.

*

FRONT VIEW

BOTTOM VIEW

OUT

NC/ADJ*

GND

1

2

3

4

IN

8

7

6

5

**

NC**

SHDN

3

2

1

OUTPUT

GND

IN

GND OUT

TAB IS

GND

NC

V

IN

N8 PACKAGE

8-LEAD PDIP

Z PACKAGE

3-LEAD PLASTIC TO-92

T = 150°C, θ = 150°C/W

JMAX

ST PACKAGE

3-LEAD PLASTIC SOT-223

S8 PACKAGE

8-LEAD PLASTIC SO

T

= 150°C, θ = 50°C/W

JMAX

JA

T

JMAX

T

JMAX

= 150°C, θ = 120°C/W (N8, S8)

JA

= 150°C, θ = 70°C/W (AS8)

JA

ORDER INFORMATION

LEAD FREE FINISH

TAPE AND REEL

PART MARKING

LT1121CN8

LT1121CN8-3.3

LT1121CN8-5

LT1121IN8

LT1121IN8-3.3

LT1121IN8-5

1121

PACKAGE DESCRIPTION

8-Lead Plastic PDIP

8-Lead Plastic S0

TEMPERATURE RANGE

0°C to 125°C

LT1121CN8#PBF

LT1121CN8#TRPBF

LT1121CN8-3.3#TRPBF

LT1121CN8-5#TRPBF

LT1121IN8#TRPBF

LT1121CN8-3.3#PBF

LT1121CN8-5#PBF

LT1121IN8#PBF

0°C to 125°C

–40°C to 125°C

0°C to 125°C

LT1121IN8-3.3#PBF

LT1121IN8-5#PBF

LT1121CS8#PBF

LT1121IN8-3.3#TRPBF

LT1121IN8-5#TRPBF

LT1121CS8#TRPBF

LT1121CS8-3.3#TRPBF

LT1121CS8-5#TRPBF

LT1121HVCS8#TRPBF

LT1121IS8#TRPBF

LT1121CS8-3.3#PBF

LT1121CS8-5#PBF

LT1121HVCS8#PBF

LT1121IS8#PBF

11213

0°C to 125°C

11215

0°C to 125°C

1121HV

–40°C to 125°C

0°C to 125°C

1121I

LT1121IS8-3.3#PBF

LT1121IS8-5#PBF

LT1121HVIS8#PBF

LT1121ACS8#PBF

LT1121ACS8-3.3#PBF

LT1121ACS8-5#PBF

LT1121IS8-3.3#TRPBF

LT1121IS8-5#TRPBF

LT1121HVIS8#TRPBF

LT1121ACS8#TRPBF

121I3

121I5

121HVI

1121A

LT1121ACS8-3.3#TRPBF 1121A3

LT1121ACS8-5#TRPBF 1121A5

0°C to 125°C

1121fg

2

LT1121/LT1121-3.3/LT1121-5

ORDER INFORMATION

LEAD FREE FINISH

LT1121AHVCS8#PBF

LT1121AIS8#PBF

LT1121AIS8-3.3#PBF

LT1121AIS8-5#PBF

LT1121AHVIS8#PBF

LT1121CST-3.3#PBF

LT1121IST-3.3#PBF

LT1121CST-5#PBF

LT1121IST-5#PBF

LT1121CZ3-3#PBF

LT1121IZ3-3#PBF

LT1121CZ-5#PBF

LT1121IZ-5#PBF

TAPE AND REEL

PART MARKING

121AHV

PACKAGE DESCRIPTION

8-Lead Plastic S0

TEMPERATURE RANGE

0°C to 125°C

LT1121AHVCS8#TRPBF

LT1121AIS8#TRPBF

121AI

8-Lead Plastic S0

–40°C to 125°C

0°C to 125°C

LT1121AIS8-3.3#TRPBF 121AI3

8-Lead Plastic S0

LT1121AIS8-5#TRPBF

LT1121AHVIS8#TRPBF

LT1121CST-3.3#TRPBF

LT1121IST-3.3#TRPBF

LT1121CST-5#TRPBF

LT1121IST-5#TRPBF

LT1121CZ3-3#TRPBF

LT1121IZ3-3#TRPBF

LT1121CZ-5#TRPBF

LT1121IZ-5#TRPBF

121AI5

8-Lead Plastic S0

21AHVI

8-Lead Plastic S0

11213

3-Lead Plastic SOT-223

3-Lead Plastic TO-92

121I3

–40°C to 125°C

0°C to 125°C

11215

1121I5

–40°C to 125°C

0°C to 125°C

LT1121CZ3-3

LT1121IZ3-3

LT1121CZ-5

LT1121IZ-5

–40°C to 125°C

0°C to 125°C

–40°C to 125°C

Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.

Consult LTC Marketing for information on nonstandard lead based finish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/

ELECTRICAL CHARACTERISTICS ^Thel denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C.

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Regulated Output Voltage (Note 4)

LT1121-3.3

V

= 3.8V, I

= 1mA, T = 25ºC

3.25

3.2

3.3

3.35

3.4

V

IN

OUT

J

l

4.3V < V < 20V, 1mA < I

< 150mA

OUT

IN

LT1121-5

V

= 5.5V, I

= 1mA, T = 25ºC

4.925

4.85

5

5.075

5.15

V

IN

OUT

J

6V < V < 20V, 1mA < I

< 150mA

OUT

IN

LT1121 (Note 5)

V

= 4.3V, I

= 1mA, T = 25ºC

3.695

3.64

3.75

3.805

3.86

V

IN

OUT

J

4.8V < V < 20V, 1mA < I

< 150mA

OUT

IN

l

Line Regulation

Load Regulation

1.5

10

mV

LT1121-3.3

LT1121-5

ΔV = 4.8V TO 20V, I

IN

= 1mA

IN

OUT

ΔV = 5.5V TO 20V, I

LT1121 (Note 5) ΔV = 4.3V TO 20V, I

IN

–12

–20

–17

–28

–12

–18

–25

–40

–35

–50

–25

–40

mV

LT1121-3.3

ΔI

= 1mA to 150mA, T = 25ºC

LOAD

J

l

ΔI

= 1mA to 150mA

LT1121-5

= 1mA to 150mA, T = 25ºC

LOAD

J

ΔI

= 1mA to 150mA

LT1121 (Note 5) ΔI

ΔI

= 1mA to 150mA, T = 25ºC

J

= 1mA to 150mA

Dropout Voltage (Note 6)

I

= 1mA, T = 25ºC

0.13

0.16

0.25

V

LOAD

J

l

= 1mA

I

= 50mA, T = 25ºC

0.3

0.35

0.5

V

LOAD

J

= 50mA

I

= 100mA, T = 25ºC

0.37

0.42

0.45

0.6

V

LOAD

J

= 100mA

I

= 150mA, T = 25ºC

0.55

0.7

V

LOAD

J

= 150mA

1121fg

3

LT1121/LT1121-3.3/LT1121-5

ELECTRICAL CHARACTERISTICS ^Thel denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T_A= 25°C.

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

l

Ground Pin Current (Note 7)

I

= 0mA

30

90

350

1.5

4

50

120

500

2.5

7

µA

LOAD

= 1mA

= 10mA

= 50mA

= 100mA

= 150mA

µA

mA

7

14

Adjust Pin Bias Current (Notes 5, 8)

Shutdown Threshold

T = 25ºC

150

300

2.8

nA

J

l

V

OUT

V

OUT

= Off to On

= On to Off

1.2

0.75

V

0.25

50

l

Shutdown Pin Current (Note 9)

Quiescent Current in Shutdown (Note 10)

Ripple Rejection

V

= 0V

6

10

22

µA

dB

SHDN

= 6V, V

= 0V

SHDN

16

58

IN

– V

= 1V (Avg), V

= 0.5V , f

= 120Hz,

IN

OUT

RIPPLE

P-P RIPPLE

I

= 0.1A

LOAD

Current Limit

V

– V

= 7V, T = 25ºC

200

500

1

mA

IN

OUT

J

l

Input Reverse Leakage Current

Reverse Output Current (Note 11)

= –20V, V

= 0V

OUT

LT1121-3.3

LT1121-5

LT1121 (Note 5)

V

= 3.3V, V = 0V

16

25

µA

OUT

IN

= 5V, V = 0V

IN

V

= 3.8V, V = 0V

IN

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 5: The LT1121 (adjustable version) is tested and specified with the

adjust pin connected to the output pin.

Note 6: Dropout voltage is the minimum input/output voltage required to

maintain regulation at the specified output current. In dropout the output

Note 2: The shutdown pin input voltage rating is required for a low

impedance source. Internal protection devices connected to the shutdown

pin will turn on and clamp the pin to approximately 7V or –0.6V. This

range allows the use of 5V logic devices to drive the pin directly. For high

impedance sources or logic running on supply voltages greater than 5.5V,

the maximum current driven into the shutdown pin must be limited to less

than 20mA.

voltage will be equal to: (V – V

Note 7: Ground pin current is tested with V = V

current source load. This means that the device is tested while operating in

its dropout region. This is the worst case ground pin current. The ground

pin current will decrease slightly at higher input voltages.

Note 8: Adjust pin bias current flows into the adjust pin.

Note 9: Shutdown pin current at V

Note 10: Quiescent current in shutdown is equal to the sum total of the

shutdown pin current (6µA) and the ground pin current (9µA).

).

IN

DROPOUT

(nominal) and a

IN

OUT

= 0V flows out of the shutdown pin.

SHDN

Note 3: For junction temperatures greater than 110°C, a minimum load

of 1mA is recommended. For T > 110°C and I

< 1mA, output voltage

J

OUT

may increase by 1%.

Note 11: Reverse output current is tested with the input pin grounded and

the output pin forced to the rated output voltage. This current flows into

the output pin and out of the ground pin.

Note 4: Operating conditions are limited by maximum junction

temperature. The regulated output voltage specification will not apply

for all possible combinations of input voltage and output current. When

operating at maximum input voltage, the output current range must be

limited. When operating at maximum output current the input voltage

range must be limited.

1121fg

4

LT1121/LT1121-3.3/LT1121-5

TYPICAL PERFORMANCE CHARACTERISTICS

Guaranteed Dropout Voltage

Dropout Voltage

Quiescent Current

50

40

30

20

10

0

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

V

= 6V

LOAD

IN

R

= ∞

I

= 150mA

LOAD

T ≤ 125°C

J

V

= OPEN

SHDN

I

= 100mA

LOAD

T ≤ 25°C

J

I

= 50mA

LOAD

V

= 0V

SHDN

I

= 1mA

LOAD

= TEST POINTS

–50

0

25

50

75 100 125

–25

0

40 60 80 100 120 140 160

OUTPUT CURRENT (mA)

–50

0

25

50

75 100 125

20

–25

TEMPERATURE (°C)

1121 G03

1121 G01

1121 G02

LT1121-3.3

Quiescent Current

LT1121-5

Quiescent Current

LT1121

Quiescent Current

120

100

80

60

40

20

0

120

100

80

60

40

20

0

120

100

80

60

40

20

0

T = 25°C

LOAD

T = 25°C

J

R

J

R

= ∞

R

= ∞

LOAD

OUT

V

= V

ADJ

V

= OPEN

V

= OPEN

SHDN

V

= OPEN

SHDN

V

= 0V

7

V

= 0V

7

V

= 0V

8

SHDN

0

1

2

3

4

5

6

8

9

10

0

1

2

3

4

5

6

8

9

10

0

1

2

3

4

5

6

7

9

10

INPUT VOLTAGE (V)

1121 G06

1121 G04

1121 G05

LT1121-3.3

Output Voltage

LT1121-5

Output Voltage

LT1121

Adjust Pin Voltage

3.83

3.81

3.79

3.77

3.75

3.73

3.71

3.69

3.67

3.38

3.36

3.34

3.32

3.30

3.28

3.26

3.24

3.22

5.08

5.06

5.04

5.02

5.00

4.98

4.96

4.94

4.92

I

= 1mA

I

= 1mA

OUT

I

= 1mA

OUT

0

25

TEMPERATURE (°C)

50

75 100 125

–50

0

25

50

75 100 125

–50

0

25

50

75 100 125

–50

–25

TEMPERATURE (°C)

1121 G09

1121 G07

1121 G08

1121fg

5

LT1121/LT1121-3.3/LT1121-5

TYPICAL PERFORMANCE CHARACTERISTICS

LT1121-3.3

Ground Pin Current

LT1121-5

Ground Pin Current

LT1121

Ground Pin Current

800

700

600

500

400

300

200

100

0

800

700

600

500

400

300

200

100

0

800

700

600

500

400

300

200

100

0

T = 25°C

J

V

J

R

I

= 150Ω

LOAD

= V

OUT

ADJ

= 25mA*

R

= 200Ω

LOAD

R

I

= 130Ω

LOAD

I

= 25mA*

R

I

= 500Ω

= 10mA*

R

= 330Ω

= 10mA*

LOAD

R

= 380Ω

= 10mA*

LOAD

I

*FOR V

= 3.75V

*FOR V

= 3.3V

*FOR V

= 5V

R

OUT

R

I

= 3.8k

LOAD

= 1mA*

= 5k

= 1mA*

R

= 3.3k

= 1mA*

LOAD

I

LOAD

0

1

2

3

4

5

6

7

8

9

10

0

1

2

3

4

5

6

7

8

9

10

0

1

2

3

4

5

6

7

8

9

10

INPUT VOLTAGE (V)

1121 G10

1121 G12

1121 G11

LT1121-3.3

Ground Pin Current

LT1121-5

Ground Pin Current

LT1121

Ground Pin Current

10

9

8

7

6

5

4

3

2

1

0

10

9

8

7

6

5

4

3

2

1

0

10

9

8

7

6

5

4

3

2

1

0

T = 25°C

J

V

= V

OUT

ADJ

R

I

= 22Ω

LOAD

R

= 33Ω

LOAD

R

= 25Ω

= 150mA*

LOAD

I

= 150mA*

I

= 150mA*

R

I

= 33Ω

LOAD

R

= 50Ω

= 100mA*

LOAD

= 100mA*

R

= 38Ω

= 100mA*

LOAD

I

LOAD

R

I

= 66Ω

= 50mA*

R

= 100Ω

LOAD

R

I

= 75Ω

LOAD

= 50mA*

LOAD

I

= 50mA*

LOAD

*FOR V

= 3.3V

*FOR V

= 5V

*FOR V

= 3.75V

OUT

0

2

4

6

8

10

1

3

5

7

9

0

2

6

8

10

4

1

3

5

7

9

2

6

0

4

8

10

1

3

5

7

9

INPUT VOLTAGE (V)

1121 G13

1121 G14

1121 G15

Shutdown Pin Threshold

(On-to-Off)

Shutdown Pin Threshold

(Off-to-On)

Ground Pin Current

14

12

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

V

= 3.3V (LT1121-3.3)

= 5V (LT1121-5)

= 3.75V (LT1121)

I

= 1mA

IN

LOAD

DEVICE IS OPERATING

10 IN DROPOUT

I

= 150mA

LOAD

T

= 125°C

J

8

6

4

2

0

I

= 1mA

LOAD

T

= 25°C

J

T

= –55°C

J

0

40 60 80 100 120 140 160

OUTPUT CURRENT (mA)

–50

0

25

50

75 100 125

20

–25

–50

0

25

50

75 100 125

–25

TEMPERATURE (°C)

1121 G16

1121 G18

1121 G17

1121fg

6

LT1121/LT1121-3.3/LT1121-5

TYPICAL PERFORMANCE CHARACTERISTICS

LT1121

Adjust Pin Bias Current

Shutdown Pin Current

Shutdown Pin Input Current

10

9

8

7

6

5

4

3

2

1

0

400

350

300

250

200

150

100

50

25

20

V

= 0V

SHDN

15

10

5

0

–50

0

25

50

75 100 125

1

2

3

5

7

8

9

–50

0

25

50

75 100 125

–25

0

4

6

–25

TEMPERATURE (°C)

SHUTDOWN PIN VOLTAGE (V)

1121 G19

1121 G21

1121 G20

Reverse Output Current

Current Limit

400

350

300

250

200

150

100

50

400

350

300

250

200

150

100

50

30

25

20

15

10

5

V

= 0V

V

= 7V

V

= 0V

OUT

IN

OUT

IN

= 0V

= 5V (LT1121-5)

= 3.3V (LT1121-3.3)

= 3.8V (LT1121)

OUT

0

2

3

4

5

6

7

–50

0

25

50

75 100 125

1

–25

–50

0

25

50

75 100 125

–25

INPUT VOLTAGE (V)

TEMPERATURE (°C)

1121 G23

1121 G24

1121 G22

Reverse Output Current

Ripple Rejection

100

90

80

70

60

50

40

30

20

10

0

64

62

60

58

56

54

52

50

100

90

80

70

60

50

40

30

20

10

0

I

= 100mA

T = 25°C

V

IN

= V

OUT

(NOMINAL) + 1V

OUT

IN

J

IN

V

= 6V + 50mV

RIPPLE

V

= 0V

RMS

+ 0.5V RIPPLE AT f = 120Hz

P-P

= 100mA

CURRENT FLOWS

INTO OUTPUT PIN

I

OUT

C

= 47μF

OUT

SOLID TANTALUM

LT1121

= V

(V

)

ADJ

OUT

LT1121-3.3

C

= 1μF

OUT

SOLID TANTALUM

LT1121-5

10

100

1k

10k

100k

1M

0

2

4

6

8

10

1

3

5

7

9

–50

0

25

50

75

125

–25

100

FREQUENCY (Hz)

TEMPERATURE (°C)

OUTPUT VOLTAGE (V)

1121 G27

1121 G25

1121 G26

1121fg

7

LT1121/LT1121-3.3/LT1121-5

TYPICAL PERFORMANCE CHARACTERISTICS

LT1121-5

Load Regulation

Load Transient Response

0

–5

V

C

= 6V

ΔI

LOAD

= 1mA TO 150mA

V

C

= 6V

IN

0.2

0.1

= 0.1μF

= 1μF

0.2

0.1

= 0.1μF

= 3.3μF

OUT

LT1121*

LT1121-3.3

–10

–15

–20

–25

–30

–35

–40

0

–0.1

–0.2

–0.1

–0.2

150

100

50

LT1121-5

150

100

* ADJ PIN TIED TO

OUTPUT PIN

0.1

0.3 0.4 0.5 0.6 0.7

TIME (ms)

0.9

0.8

1.0

0

0.2

0.4 0.5

0.7

0.9

0.8

1.0

50

75 100 125

0

0.1 0.3

0.2

0.6

–50

0

25

–25

TEMPERATURE (°C)

TIME (ms)

1121 G29

1121 G30

1121 G28

PIN FUNCTIONS

Input Pin: Power is supplied to the device through the

input pin. The input pin should be bypassed to ground if

the device is more than six inches away from the main

input filter capacitor. In general the output impedance of

a battery rises with frequency so it is usually adviseable to

include a bypass capacitor in battery-powered circuits. A

bypass capacitor in the range of 0.1µF to 1µF is sufficient.

The LT1121 is designed to withstand reverse voltages on

the input pin with respect to both ground and the output

pin. In the case of a reversed input, which can happen if

a battery is plugged in backwards, the LT1121 will act as

if there is a diode in series with its input. There will be

no reverse current flow into the LT1121 and no reverse

voltage will appear at the load. The device will protect both

itself and the load.

off. This pin is active low. The device will be shut down if

the shutdown pin is pulled low. The shutdown pin current

with the pin pulled to ground will be 6µA. The shutdown

pin is internally clamped to 7V and –0.6V (one V ). This

BE

allowstheshutdownpintobedrivendirectlyby5Vlogicor

by open collector logic with a pull-up resistor. The pull-up

resistor is only required to supply the leakage current of

the open collector gate, normally several microamperes.

Pull-up current must be limited to a maximum of 20mA.

A curve of shutdown pin input current as a function of

voltageappearsintheTypicalPerformanceCharacteristics.

If the shutdown pin is not used it can be left open circuit.

The device will be active, output on, if the shutdown pin

is not connected.

Adjust Pin: For the adjustable LT1121, the adjust pin

Output Pin: The output pin supplies power to the load. An

output capacitor is required to prevent oscillations. See

the Applications Information section for recommended

value of output capacitance and information on reverse

output characteristics.

is the input to the error amplifier. This pin is internally

clamped to 6V and –0.6V (one V ). It has a bias current

BE

of 150nA which flows into the pin. See Bias Current curve

in the Typical Performance Characteristics. The adjust

pin reference voltage is 3.75V referenced to ground. The

output voltage range that can be produced by this device

is 3.75V to 30V.

Shutdown Pin: This pin is used to put the device into

shutdown. In shutdown the output of the device is turned

1121fg

8

LT1121/LT1121-3.3/LT1121-5

APPLICATIONS INFORMATION

The LT1121 is a micropower low dropout regulator with

shutdown, capable of supplying up to 150mA of output

current at a dropout voltage of 0.4V. The device operates

with very low quiescent current (30µA). In shutdown the

quiescent current drops to only 16µA. In addition to the

low quiescent current the LT1121 incorporates several

protection features which make it ideal for use in battery-

powered systems. The device is protected against both

reverse input voltages and reverse output voltages. In

battery backup applications where the output can be held

up by a backup battery when the input is pulled to ground,

the LT1121 acts like it has a diode in series with its output

and prevents reverse current flow.

approximately 15ppm/°C. The adjust pin bias current has

anegativetemperaturecoefficient. Theseeffectsaresmall

and will tend to cancel each other.

The adjustable device is specified with the adjust pin tied

to the output pin. This sets the output voltage to 3.75V.

Specifications for output voltage greater than 3.75V will

be proportional to the ratio of the desired output voltage

to3.75V(V /3.75V).Forexample:loadregulationforan

OUT

output current change of 1mA to 150mA is –12mV typical

at V

= 3.75V. At V

= 12V, load regulation would be:

OUT

12V

3.75V

⎛

⎝

⎞

⎠

• –12mV = –38mV

( ) (

)

⎜

⎟

Adjustable Operation

Thermal Considerations

TheadjustableversionoftheLT1121hasanoutputvoltage

range of 3.75V to 30V. The output voltage is set by the

ratio of two external resistors as shown in Figure 1. The

device servos the output voltage to maintain the voltage

at the adjust pin at 3.75V. The current in R1 is then equal

to 3.75V/R1. The current in R2 is equal to the sum of the

current in R1 and the adjust pin bias current. The adjust

pin bias current, 150nA at 25°C, flows through R2 into the

adjust pin. The output voltage can be calculated according

to the formula in Figure 1. The value of R1 should be less

than 400k to minimize errors in the output voltage caused

by the adjust pin bias current. Note that in shutdown the

output is turned off and the divider current will be zero.

Curves of Adjust Pin Voltage vs Temperature and Adjust

Pin Bias Current vs Temperature appear in the Typical

Performance Characteristics. The reference voltage at the

adjust pin has a slight positive temperature coefficient of

Power handling capability will be limited by maximum

rated junction temperature (125°C). Power dissipated by

the device will be made up of two components:

1. Output current multiplied by the input/output voltage

differential: I

• (V – V ), and

OUT

IN OUT

2. Ground pin current multiplied by the input voltage:

• V .

I

GND

IN

The ground pin current can be found by examining the

Ground Pin Current curves in the Typical Performance

Characteristics. Power dissipation will be equal to the

sum of the two components listed above.

TheLT1121seriesregulatorshaveinternalthermallimiting

designedtoprotectthedeviceduringoverloadconditions.

Forcontinuousnormalloadconditionsthemaximumjunc-

tion temperature rating of 125°C must not be exceeded.

It is important to give careful consideration to all sources

of thermal resistance from junction to ambient. Additional

heat sources mounted nearby must also be considered.

V

IN

OUT

ADJ

OUT

LT1121

R2

R1

Heat sinking, for surface mount devices, is accomplished

by using the heat spreading capabilities of the PC board

and its copper traces. Copper board stiffeners and plated

through holes can also be used to spread the heat gener-

ated by power devices. Tables 1 through 5 list thermal

resistances for each package. Measured values of thermal

resistance for several different board sizes and copper

areas are listed for each package. All measurements were

taken in still air, on 3/32" FR-4 board with 1oz copper. All

1121fg

+

SHDN

GND

1121 • F01

R2

V

I

= 3.75V 1 +

+ I

(

• R2

ADJ

)

OUT

ADJ

(

)

R1

= 3.75V

= 150nA AT 25°C

ADJ

OUTPUT RANGE = 3.75V TO 30V

Figure 1. Adjustable Operation

9

LT1121/LT1121-3.3/LT1121-5

APPLICATIONS INFORMATION

NC leads were connected to the ground plane.

Table 5. TO-92 Package THERMAL RESISTANCE

Package alone

220ºC/W

175ºC/W

Package soldered into PC board with plated through

holes only

Table 1. N8 Package*

COPPER AREA

Package soldered into PC board with 1/4 sq. inch of

copper trace per lead

145ºC/W

160ºC/W

THERMAL RESISTANCE

TOPSIDE

BACKSIDE BOARD AREA JUNCTION TO AMBIENT

Package soldered into PC board with plated through

holes in board, no extra copper trace, and a clip-on type

heat sink: Thermalloy type 2224B

2500 sq mm 2500 sq mm 2500 sq mm

1000 sq mm 2500 sq mm 2500 sq mm

225 sq mm 2500 sq mm 2500 sq mm

1000 sq mm 1000 sq mm 1000 sq mm

80ºC/W

85ºC/W

91ºC/W

Aavid type 5754

135ºC/W

* Device is mounted on topside. Leads are through hole and are

soldered to both sides of board.

Calculating Junction Temperature

Example: given an output voltage of 3.3V, an input voltage

range of 4.5V to 7V, an output current range of 0mA to

100mA, and a maximum ambient temperature of 50°C,

what will the maximum junction temperature be?

Table 2. S8 Package

COPPER AREA

THERMAL RESISTANCE

JUNCTION TO AMBIENT

TOPSIDE*

BACKSIDE BOARD AREA

2500 sq mm 2500 sq mm 2500 sq mm

1000 sq mm 2500 sq mm 2500 sq mm

225 sq mm 2500 sq mm 2500 sq mm

100 sq mm 1000 sq mm 1000 sq mm

* Device is mounted on topside.

120ºC/W

125ºC/W

131ºC/W

Power dissipated by the device will be equal to:

I

• (V

– V ) + (I

• V )

GND IN

OUT MAX

IN MAX

OUT

where, I

= 100mA

= 7V

OUT IN

OUT MAX

V

IN MAX

I

at (I

= 100mA, V = 7V) = 5mA

GND

Table 3. AS8 Package*

so,

P =100mA • (7V – 3.3V) + (5mA • 7V)

COPPER AREA

= 0.405W

THERMAL RESISTANCE

JUNCTION TO AMBIENT

TOPSIDE** BACKSIDE BOARD AREA

2500 sq mm 2500 sq mm 2500 sq mm

1000 sq mm 2500 sq mm 2500 sq mm

225 sq mm 2500 sq mm 2500 sq mm

100 sq mm 2500 sq mm 2500 sq mm

IfweuseanSOT-223package,thenthethermalresistance

will be in the range of 50°C/W to 65°C/W depending on

copperarea. So the junction temperature rise above ambi-

ent will be less than or equal to:

60ºC/W

68ºC/W

74ºC/W

0.405W • 60°C/W = 24°C

* Pins 3, 6 and 7 are ground.

** Device is mounted on topside.

The maximum junction temperature will then be equal to

the maximum junction temperature rise above ambient

plus the maximum ambient temperature or:

Table 4. SOT-223 Package

(Thermal Resistance Junction-to-Tab 20ºC/W)

COPPER AREA

T

= 50°C + 24°C = 74°C

JMAX

THERMAL RESISTANCE

JUNCTION TO AMBIENT

TOPSIDE*

BACKSIDE BOARD AREA

Output Capacitance and Transient Performance

2500 sq mm 2500 sq mm 2500 sq mm

1000 sq mm 2500 sq mm 2500 sq mm

225 sq mm 2500 sq mm 2500 sq mm

100 sq mm 2500 sq mm 2500 sq mm

1000 sq mm 2500 sq mm 1000 sq mm

50ºC/W

58ºC/W

64ºC/W

57ºC/W

60ºC/W

The LT1121 is designed to be stable with a wide range of

outputcapacitors.Theminimumrecommendedvalueis1µF

with an ESR of 3Ω or less. For applications where space

is very limited, capacitors as low as 0.33µF can be used if

combined with a small series resistor. Assuming that the

ESR of the capacitor is low (ceramic) the suggested series

1000 sq mm

0

1000 sq mm

* Tab of device attached to topside copper.

1121fg

10

LT1121/LT1121-3.3/LT1121-5

APPLICATIONS INFORMATION

resistor is shown in Table 6. The LT1121 is a micropower

device and output transient response will be a function of

output capacitance. See the Transient Response curves

in the Typical Performance Characteristics. Larger values

of output capacitance will decrease the peak deviations

and provide improved output transient response. Bypass

capacitors, used to decouple individual components

powered by the LT1121, will increase the effective value

of the output capacitor.

short-circuit current of the device and will protect itself by

thermal limiting. For the adjustable version of the device,

the output pin is internally clamped at one diode drop

below ground. Reverse current for the adjustable device

must be limited to 5mA.

In circuits where a backup battery is required, several

different input/output conditions can occur. The output

voltage may be held up while the input is either pulled

to ground, pulled to some intermediate voltage, or is left

open circuit. Current flow back into the output will vary

depending on the conditions. Many battery-powered cir-

cuits incorporate some form of power management. The

following information will help optimize battery life. Table

7 summarizes the following information.

Table 6. Suggested Series Resistor Values

OUTPUT CAPACITANCE

SUGGESTED SERIES RESISTOR

0.33µF

0.47µF

0.68µF

>1µF

2Ω

1Ω

The reverse output current will follow the curve in Figure

2 when the input pin is pulled to ground. This current

flows through the output pin to ground. The state of the

shutdown pin will have no effect on output current when

the input pin is pulled to ground.

None Needed

Protection Features

The LT1121 incorporates several protection features

which make it ideal for use in battery-powered circuits.

In addition to the normal protection features associated

with monolithic regulators, such as current limiting and

thermal limiting, the device is protected against reverse

input voltages, reverse output voltages, and reverse volt-

ages from output to input.

In some applications it may be necessary to leave the

input to the LT1121 unconnected when the output is held

high. This can happen when the LT1121 is powered from

a rectified AC source. If the AC source is removed, then

the input of the LT1121 is effectively left floating. The

reverse output current also follows the curve in Figure 2

if the input pin is left open. The state of the shutdown pin

will have no effect on the reverse output current when the

input pin is floating.

Current limit protection and thermal overload protection

areintendedtoprotectthedeviceagainstcurrentoverload

conditions at the output of the device. For normal opera-

tion, the junction temperature should not exceed 125°C.

100

The input of the device will withstand reverse voltages of

30V. Current flow into the device will be limited to less

than 1mA (typically less than 100µA) and no negative

voltage will appear at the output. The device will protect

both itself and the load. This provides protection against

batteries that can be plugged in backwards.

T = 25°C

J

V

90

80

70

60

50

40

30

20

10

0

< V

IN

OUT

CURRENT FLOWS

INTO OUTPUT PIN

TO GROUND

LT1121

= V

(V

)

ADJ

OUT

LT1121-3.3

For fixed voltage versions of the device, the output can

be pulled below ground without damaging the device. If

the input is open circuit or grounded the output can be

pulled below ground by 20V. The output will act like an

open circuit, no current will flow out of the pin. If the input

is powered by a voltage source, the output will source the

LT1121-5

0

2

4

6

8

10

1

3

5

7

9

OUTPUT VOLTAGE (V)

1121• F02

Figure 2. Reverse Output Current

1121fg

11

LT1121/LT1121-3.3/LT1121-5

APPLICATIONS INFORMATION

5

4

3

2

1

0

When the input of the LT1121 is forced to a voltage below

its nominal output voltage and its output is held high, the

reverse output current will still follow the curve in Figure

2. This condition can occur if the input of the LT1121 is

connected to a discharged (low voltage) battery and the

output is held up by either a backup battery or by a second

regulator circuit. When the input pin is forced below the

output pin or the output pin is pulled above the input pin,

the input current will typically drop to less than 2µA (see

Figure 3). The state of the shutdown pin will have no effect

on the reverse output current when the output is pulled

above the input.

V

= 3.3V (LT1121-3.3)

= 5V (LT1121-5)

OUT

0

1

2

3

4

5

INPUT VOLTAGE (V)

1121 F03

Figure 3. Input Current

Table 7. Fault Conditions

INPUT PIN

SHDN PIN

OUTPUT PIN

<V

(Nominal)

Open (Hi)

Forced to V

(Nominal)

Reverse Output Current ≈ 15µA (See Figure 2)

Input Current ≈ 1µA (See Figure 3)

OUT

<V

(Nominal)

Grounded

Forced to V

Reverse Output Current ≈ 15µA (See Figure 2)

Input Current ≈ 1µA (See Figure 3)

OUT

Open

≤0.8V

>1.5V

Open (Hi)

Grounded

Open (Hi)

Grounded

Open (Hi)

Grounded

Forced to V

≤0V

(Nominal)

Reverse Output Current ≈ 15µA (See Figure 2)

Output Current = 0

OUT

≤0V

Output Current = 0

≤0V

Output Current = Short-Circuit Current

Output Current = 0

–30V < V < 30V

≤0V

IN

1121fg

12

LT1121/LT1121-3.3/LT1121-5

PACKAGE DESCRIPTION

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

N Package

8-Lead PDIP (Narrow .300 Inch)

(Reference LTC DWG # 05-08-1510 Rev I)

.400*

(10.160)

MAX

.130 ±.005

.300 – .325

.045 – .065

(3.302 ±0.127)

(1.143 – 1.651)

(7.620 – 8.255)

8

1

7

6

5

4

.065

(1.651)

TYP

.255 ±.015*

(6.477 ±0.381)

.008 – .015

(0.203 – 0.381)

.120

.020

(0.508)

MIN

(3.048)

MIN

+.035

–.015

2

3

.325

.018 ±.003

(0.457 ±0.076)

.100

(2.54)

BSC

+0.889

8.255

N8 REV I 0711

(

)

–0.381

NOTE:

INCHES

1. DIMENSIONS ARE

MILLIMETERS

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)

S8 Package

8-Lead Plastic Small Outline (Narrow .150 Inch)

(Reference LTC DWG # 05-08-1610 Rev G)

.189 – .197

(4.801 – 5.004)

.045 ±.005

NOTE 3

.050 BSC

7

5

8

6

.245

MIN

.160 ±.005

.150 – .157

(3.810 – 3.988)

NOTE 3

.228 – .244

(5.791 – 6.197)

.030 ±.005

TYP

1

3

4

2

RECOMMENDED SOLDER PAD LAYOUT

.010 – .020

(0.254 – 0.508)

× 45°

.053 – .069

(1.346 – 1.752)

.004 – .010

(0.101 – 0.254)

.008 – .010

(0.203 – 0.254)

0°– 8° TYP

.016 – .050

(0.406 – 1.270)

.050

(1.270)

BSC

.014 – .019

(0.355 – 0.483)

TYP

NOTE:

INCHES

1. DIMENSIONS IN

(MILLIMETERS)

2. DRAWING NOT TO SCALE

3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)

4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE

SO8 REV G 0212

1121fg

13

LT1121/LT1121-3.3/LT1121-5

PACKAGE DESCRIPTION

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

ST Package

3-Lead Plastic SOT-223

(Reference LTC DWG # 05-08-1630)

.248 – .264

(6.30 – 6.71)

.129 MAX

.114 – .124

(2.90 – 3.15)

.059 MAX

.264 – .287

(6.70 – 7.30)

.248 BSC

.130 – .146

(3.30 – 3.71)

.039 MAX

.059 MAX

.090

BSC

.181 MAX

RECOMMENDED SOLDER PAD LAYOUT

.033 – .041

(0.84 – 1.04)

.0905

(2.30)

BSC

10° – 16°

.010 – .014

10°

MAX

.071

(1.80)

MAX

(0.25 – 0.36)

10° – 16°

.0008 – .0040

(0.0203 – 0.1016)

.024 – .033

(0.60 – 0.84)

.012

(0.31)

MIN

.181

(4.60)

BSC

ST3 (SOT-233) 0502

Z Package

3-Lead Plastic TO-92 (Similar to TO-226)

(Reference LTC DWG # 05-08-1410 Rev C)

.180 ± .005

(4.572 ± 0.127)

.060 ± .005

(1.524± 0.127)

.060 ± .010

DIA

(1.524 ± 0.254)

.90

(2.286)

NOM

.140 ± .010

(3.556 ± 0.127)

.180 ± .005

(4.572 ± 0.127)

3

2

1

10° NOM

5°

NOM

.500

(12.70)

MIN

.050

(1.270)

MAX

UNCONTROLLED

LEAD DIMENSION

.016 ± .003

(0.406 ± 0.076)

.015 ± .002

(0.381 ± 0.051)

Z3 (TO-92) 1008 REV C

.050

.098 +.016/–.04

(2.5 +0.4/–0.1)

2 PLCS

(1.27)

BSC

BULK PACK

TO-92 TAPE AND REEL

REFER TO TAPE AND REEL SECTION OF

LTC DATA BOOK FOR ADDITIONAL INFORMATION

1121fg

14

LT1121/LT1121-3.3/LT1121-5

REVISION HISTORY ^{(Revision history begins at Rev G)}

REV

DATE

DESCRIPTION

PAGE NUMBER

G

05/12 Changed Order Information top marking for 8-lead SO 3.3V and 5V options, C-grade

2

1121fg

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 representa-

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

15

LT1121/LT1121-3.3/LT1121-5

RELATED PARTS

PART NUMBER

DESCRIPTION

COMMENTS

LT1120

125mA Low Dropout Regulator with 20µA I

Includes 2.5V Reference and Comparator

50µA Quiescent Current

Q

LT1129

700mA Micropower Low Dropout Regulator

LT1175

500mA Negative Low Dropout Micropower Regulator

300mA Low Dropout Micropower Regulator with Shutdown

45µA I , 0.26V Dropout Voltage, SOT-223 Package

Q

LT1521

15µA, I , Reverse Battery Protection

Q

LT1529

3A Low Dropout Regulator with 50µA I

Inverting 1.4MHz Switching Regulator

500mV Dropout Voltage

Q

LT1611

5V to –5V at 150mA, Low Output Noise, SOT-23 Package

SOT-23 Package, Internally Compensated

Burst Mode™ Operation, Monolithic, 100% Duty Cycle

LT1613

1.4MHz Single-Cell Micropower DC/DC Converter

High Efficiency Synchronous Step-Down Switching Regulator

Doubler Charge Pump with Low Noise Linear Regulator

150mA, Low Noise, LDO Micropower Regulator

500mA, Low Noise, LDO Micropower Regulator

3A Fast Transient Response LDO

LT1627

LT1682

Low Output Noise: 60µV

(100kHz BW)

RMS

LT1762 Series

LT1763 Series

LT1764 Series

LT1962 Series

LT1963 Series

25µA Quiescent Current, 20µV

Noise

RMS

30µA Quiescent Current, 20µV

300mV Dropout, 40µV

Noise

RMS

300mA, Low Noise, LDO Micropower Regulator

1.5A Fast Transient Response LDO

30µA Quiescent Current, 20µV

Noise

RMS

300mV Dropout, 40µV

Noise

RMS

Burst Mode is a trademark of Linear Technology Corporation.

1121fg

LT 0512 REV G • PRINTED IN USA

16 ^{LinearTechnology Corporation}

1630 McCarthy Blvd., Milpitas, CA 95035-7417

●

 LINEAR TECHNOLOGY CORPORATION 1994

(408) 432-1900 FAX: (408) 434-0507 www.linear.com


型号：	LT1121IST-3.3#TRPBF
厂家：	Linear
描述：	LT1121 - Micropower Low Dropout Regulators with Shutdown; Package: SOT; Pins: 3; Temperature Range: -40°C to 85°C 光电二极管输出元件调节器
文件：	总16页 (文件大小：273K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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