LT1121CZ-5#TRPBF_技术文档

LT1121/LT1121-3.3/LT1121-5

Micropower Low Dropout

Regulators with Shutdown

U

FEATURES

DESCRIPTIO

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

dropout regulators with shutdown. These devices are

capable of supplying 150mA of output current with a

dropout voltage of 0.4V. Designed for use in battery-

powered systems, the low quiescent current, 30μA oper-

ating and 16μA 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.

■

0.4V Dropout Voltage

■

150mA Output Current

■

30μA Quiescent Current

No Protection Diodes Needed

■

Adjustable Output from 3.75V to 30V

■

3.3V and 5V Fixed Output Voltages

■

Controlled Quiescent Current in Dropout

■

Shutdown

■

16μA Quiescent Current in Shutdown

■

Stable with 0.33μF Output Capacitor

Other features of the LT1121/LT1121-3.3/LT1121-5 in-

clude the ability to operate with very small output capaci-

tors. They are stable with only 0.33μF on the output while

most older devices require between 1μF and 100μF for

stability.Smallceramiccapacitorscanbeused,enhancing

manufacturability. 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 backup power situations where the output is held high

and the input is at ground or reversed. Under these

conditions only 16μA will flow from the output pin to

ground.

■

Reverse Battery Protection

■

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

U

APPLICATIO S

■

Low Current Regulator

■

Regulator for Battery-Powered Systems

■

Post Regulator for Switching Supplies

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

U

TYPICAL APPLICATIO

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

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LT1121/LT1121-3.3/LT1121-5

W W U W

ABSOLUTE AXI U RATI GS _{(Note 1)}

Input Voltage

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

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

W U

/O

PACKAGE RDER I FOR ATIO

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.

*

BOTTOM VIEW

FRONT 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

ST PACKAGE

3-LEAD PLASTIC SOT-223

S8 PACKAGE

8-LEAD PLASTIC SO

T

_JMAX= 150°C, θ_JA≈ 50°C/W

T_JMAX= 150°C, θ_JA≈ 150°C/W

T_JMAX= 150°C, θ_JA≈ 120°C/W (N8, S8)

T_JMAX= 150°C, θ_JA≈ 70°C/W (AS8)

S8 PART

MARKING

ORDER PART

NUMBER

ST PART

MARKING

ORDER PART

NUMBER

ORDER PART NUMBER

LT1121CN8

LT1121IS8-3.3

121I3

121I5

LT1121CST-3.3

LT1121IST-3.3

11213

121IS3

11215

1121I5

LT1121CZ-3.3

LT121IZ-3.3

LT1121CZ-5

LT1121IZ-5

LT1121CN8-3.3 LT1121IS8-5

LT1121CN8-5

LT1121IN8

LT1121IN8-3.3 LT1121ACS8-3.3

LT1121IN8-5

LT1121CS8

LT1121HVIS8

LT1121ACS8

121HVI LT1121CST-5

1121A

121A3

121A5

121AHV

LT1121IST-5

LT1121ACS8-5

LT1121AHVCS8

1121

LT1121CS8-3.3 LT1121AIS8

LT1121CS8-5 LT1121AIS8-3.3

LT1121HVCS8 LT1121AIS8-5

LT1121IS8 LT1121AHVIS8

11213 121AI

11215 121AI3

1121HV 121AI5

1121I

21AHVI

Order Options Tape and Reel: Add #TR

Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF

Lead Free Part Marking: http://www.linear.com/leadfree/

Consult LTC Marketing for parts specified with wider operating temperature ranges.

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LT1121/LT1121-3.3/LT1121-5

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the 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 = 25°C

3.250

3.200

3.300

3.350

3.400

V

IN

OUT

J

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

< 150mA

●

IN

OUT

LT1121-5

V

= 5.5V, I

IN

= 1mA, T = 25°C

4.925

4.850

5.000

5.075

5.150

V

IN

OUT

J

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

< 150mA

OUT

LT1121 (Note 5)

V

= 4.3V, I

= 1mA, T = 25°C

3.695

3.640

3.750

3.805

3.860

V

IN

OUT

J

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

< 150mA

●

IN

OUT

Line Regulation

Load Regulation

LT1121-3.3

LT1121-5

ΔV = 4.8V to 20V, I

= 1mA

1.5

10

mV

IN

OUT

ΔV = 5.5V to 20V, I

IN

LT1121 (Note 5)

LT1121-3.3

ΔV = 4.3V to 20V, I

IN

ΔI

= 1mA to 150mA, T = 25°C

= 1mA to 150mA

–12

–20

–25

–40

mV

LOAD

J

●

LT1121-5

ΔI

= 1mA to 150mA, T = 25°C

= 1mA to 150mA

–17

–28

–35

–50

mV

LOAD

J

LT1121 (Note 5)

ΔI

= 1mA to 150mA, T = 25°C

= 1mA to 150mA

–12

–18

–25

–40

mV

LOAD

J

Dropout Voltage

(Note 6)

I

= 1mA, T = 25°C

0.13

0.30

0.37

0.42

0.16

0.25

V

LOAD

J

= 1mA

I

= 50mA, T = 25°C

0.35

0.50

V

LOAD

J

= 50mA

I

= 100mA, T = 25°C

= 100mA

0.45

0.60

V

LOAD

J

I

= 150mA, T = 25°C

= 150mA

0.55

0.70

V

LOAD

J

●

Ground Pin Current

(Note 7)

I

= 0mA

30

90

50

120

500

2.5

μA

LOAD

= 1mA

= 10mA

= 50mA

= 100mA

= 150mA

350

1.5

4.0

7.0

150

μA

mA

nA

7.0

14.0

300

2.8

Adjust Pin Bias Current (Notes 5, 8)

Shutdown Threshold

T = 25°C

J

V

= Off to On

= On to Off

●

1.2

0.75

V

OUT

0.25

50

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

,

OUT

RIPPLE

P-P

f

= 120Hz, I

= 0.1A

RIPPLE

LOAD

Current Limit

V

– V

= 7V, T = 25°C

200

500

1.0

mA

IN

OUT

J

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

= 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 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

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LT1121/LT1121-3.3/LT1121-5

ELECTRICAL CHARACTERISTICS

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.

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

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

voltage will be equal to: (V – V

).

IN

DROPOUT

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

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

(nominal) and a

OUT

IN

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

< 1mA, output voltage

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.

J

OUT

may increase by 1%.

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.

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

Note 9: Shutdown pin current at V

= 0V flows out of the shutdown pin.

SHDN

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

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

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

adjust pin connected to the output pin.

U W

TYPICAL PERFOR A CE CHARACTERISTICS

Quiescent Current

Guaranteed Dropout Voltage

Dropout Voltage

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

50

40

30

20

10

0

V

= 6V

=

IN

LOAD

R

∞

I

= 150mA

LOAD

T

J

≤ 125°C

V

SHDN

= OPEN

I

= 100mA

LLOAD

T

J

≤ 25°C

I

= 50mA

LOAD

V

= 0V

SHDN

I

= 1mA

LOAD

= TEST POINTS

0

40 60 80 100 120 140 160

OUTPUT CURRENT (mA)

–50

0

25

50

75 100 125

–50

–25

0

25

50

75 100 125

20

–25

TEMPERATURE (°C)

1121 G27

1121 G14

1121 G11

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

LOAD

T

R

V

= 25°C

J

R

J

R

J

=

∞

=

∞

=

∞

LOAD

= V

OUT

ADJ

V

= OPEN

V

= OPEN

SHDN

V

= OPEN

SHDN

V

= 0V

7

V

= 0V

8

V

= 0V

7

SHDN

6

SHDN

7

SHDN

6

0

1

2

3

4

5

8

9

10

0

1

2

3

4

5

6

9

10

0

1

2

3

4

5

8

9

10

INPUT VOLTAGE (V)

1121 G04

1121 G02

1121 G03

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LT1121/LT1121-3.3/LT1121-5

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TYPICAL PERFOR A CE CHARACTERISTICS

LT1121-3.3

LT1121-5

LT1121

Adjust Pin Voltage

3.83

Output Voltage

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

3.81

3.79

3.77

3.75

3.73

3.71

3.69

3.67

–50

0

25

50

75 100 125

–25

–50

0

25

50

75 100 125

–50

0

25

50

75 100 125

–25

TEMPERATURE (°C)

1121 G24

1121 G22

1121 G23

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

OUT

T

= 25°C

T

= 25°C

J

R

I

= 150Ω

LOAD

V

= V

ADJ

= 25mA*

R

= 200Ω

LOAD

R

I

= 130Ω

LOAD

I

= 25mA*

R

I

= 500Ω

= 10mA*

R

= 330Ω

= 10mA*

LOAD

R

= 380Ω

= 10mA*

LOAD

I

LOAD

I

*FOR V

= 3.75V

*FOR V

= 3.3V

*FOR V

= 5V

R

OUT

= 5k

= 1mA*

R

I

= 3.8k

LOAD

R

= 3.3k

= 1mA*

LOAD

I

= 1mA*

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 G06

1121 G08

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

OUT

J

V

= V

ADJ

R

I

= 22Ω

LOAD

R

= 33Ω

LOAD

R

= 25Ω

= 150mA*

LOAD

I

= 150mA*

I

= 150mA*

R

= 33Ω

LOAD

R

= 50Ω

= 100mA*

LOAD

I

= 100mA*

R

= 38Ω

= 100mA*

LOAD

I

R

I

= 100Ω

= 50mA*

R

= 66Ω

= 50mA*

LOAD

R

I

= 75Ω

LOAD

= 50mA*

LOAD

I

LOAD

*FOR V

= 3.3V

6

*FOR V

= 5V

7

*FOR V

OUT

= 3.75V

OUT

5

OUT

6

0

2

4

8

10

0

2

4

8

10

1

3

7

9

1

3

5

9

0

2

6

8

9

10

4

1

3

5

7

INPUT VOLTAGE (V)

1121 G09

1121 G05

1121 G07

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LT1121/LT1121-3.3/LT1121-5

U W

TYPICAL PERFOR A CE CHARACTERISTICS

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

I

= 150mA

LOAD

10 IN DROPOUT

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

TEMPERATURE (°C)

50

75 100 125

–50 –25

0

25

50

75 100 125

20

–25

TEMPERATURE (°C)

1121 G29

1121 G16

1121 G17

LT1121

Adjust Pin Bias Current

Shutdown Pin Current

Shutdown Pin Input Current

400

350

300

250

200

150

100

50

10

9

8

7

6

5

4

3

2

1

0

25

20

V

SHDN

= 0V

15

10

5

0

–50

0

25

50

75 100 125

–50

0

25

50

75 100 125

–25

0

1

2

3

4

5

6

7

8

9

TEMPERATURE (°C)

SHUTDOWN PIN VOLTAGE (V)

1121 G25

1121 G15

1121 G28

Reverse Output Current

Current Limit

30

25

20

15

10

5

400

350

300

250

200

150

100

50

400

350

300

250

200

150

100

50

V

= 0V

V

= 7V

V

= 0V

OUT

IN

OUT

IN

= 5V (LT1121-5)

= 3.3V (LT1121-3.3)

= 3.8V (LT1121)

= 0V

OUT

0

–50

0

25

50

75 100 125

0

2

3

4

5

6

7

–50

0

25

50

75

125

–25

1

–25

100

TEMPERATURE (°C)

INPUT VOLTAGE (V)

TEMPERATURE (°C)

1121 G13

1121 G20

1121 G19

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LT1121/LT1121-3.3/LT1121-5

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TYPICAL PERFOR A CE CHARACTERISTICS

Reverse Output Current

Ripple Rejection

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

90

80

70

60

50

40

30

20

10

0

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

–50

0

25

50

75 100 125

0

2

4

6

8

10

–25

1

3

5

7

9

FREQUENCY (Hz)

TEMPERATURE (°C)

OUTPUT VOLTAGE (V)

1121 G26

1121 G18

1121 G01

LT1121-5

Load Transient Response

LT1121-5

Load Transient Response

Load Regulation

0

–5

ΔI

= 1mA TO 150mA

V

C

= 6V

V

C

= 6V

LOAD

IN

0.2

0.1

0.2

0.1

= 0.1μF

= 1μF

= 3.3μF

OUT

LT1121*

LT1121-3.3

–10

–15

–20

–25

–30

–35

–40

0

–0.1

–0.2

–0.1

–0.2

LT1121-5

150

100

50

150

100

* ADJ PIN TIED TO

OUTPUT PIN

–50

0

25

50

75 100 125

–25

0

0.1

0.3 0.4 0.5 0.6 0.7

TIME (ms)

0.8

0.9

1.0

0

0.1

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.2

TEMPERATURE (°C)

TIME (ms)

1121 G21

1121 G30

1121 G31

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LT1121/LT1121-3.3/LT1121-5

U

PI FU CTIO S

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_BE). This

allows the shutdown pin to be driven directly by 5V logic

or 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 microam-

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

20mA. A curve of shutdown pin input current as a function

of voltage appears in the Typical Performance Character-

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

circuit.Thedevicewillbeactive,outputon,iftheshutdown

pin is not connected.

AdjustPin:FortheadjustableLT1121, theadjustpinisthe

input to the error amplifier. This pin is internally clamped

to 6V and –0.6V (one V_BE). It has a bias current of 150nA

which flows into the pin. See Bias Current curve in the

Typical Performance Characteristics. The adjust pin refer-

ence voltage is 3.75V referenced to ground. The output

voltage range that can be produced by this device is 3.75V

to 30V.

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.

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

shutdown. In shutdown the output of the device is turned

1121fe

8

LT1121/LT1121-3.3/LT1121-5

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APPLICATIO S I FOR ATIO

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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.

Specificationsforoutputvoltagegreaterthan3.75Vwillbe

proportional to the ratio of the desired output voltage to

3.75V (V_OUT/3.75V). For example: load regulation for an

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

at V_OUT= 3.75V. At V_OUT= 12V, load regulation would be:

⎛

⎞

12V

3.75V

• –12mV = –38mV

(

) (

)

⎜

⎟

⎝

⎠

Adjustable Operation

Thermal Considerations

The adjustable version of the LT1121 has an output

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

theratiooftwoexternalresistorsasshowninFigure1.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

currentinR1andtheadjustpinbiascurrent.Theadjustpin

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_OUT• (V_IN– V_OUT), and

2. Ground pin current multiplied by the input voltage:

I_GND• V_IN.

The ground pin current can be found by examining the

Ground Pin Current curves in the Typical Performance

Characteristics. Powerdissipationwillbeequaltothesum

of the two components listed above.

The LT1121 series regulators have internal thermal limit-

ing designed to protect the device during overload condi-

tions. For continuous normal load conditions the maxi-

mum junction temperature rating of 125°C must not be

exceeded. It is important to give careful consideration to

allsourcesofthermalresistancefromjunctiontoambient.

Additional heat sources mounted nearby must also be

considered.

V

IN

OUT

ADJ

OUT

LT1121

R2

R1

+

SHDN

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

GND

1121 • F01

R2

V

= 3.75V 1 +

+ I

(

• R2

)

OUT

ADJ

(

)

R1

= 3.75V

ADJ

I

= 150nA AT 25°C

ADJ

OUTPUT RANGE = 3.75V TO 30V

Figure 1. Adjustable Operation

areas are listed for each package. All measurements were

1121fe

9

LT1121/LT1121-3.3/LT1121-5

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APPLICATIO S I FOR ATIO

Table 5. TO-92 Package

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

NC leads were connected to the ground plane.

THERMAL

RESISTANCE

Package alone

220°C/W

175°C/W

Table 1. N8 Package*

Package soldered into PC board with plated

through holes only

COPPER AREA

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

TOPSIDE

BACKSIDE

BOARD AREA

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

copper trace per lead

145°C/W

2500 sq mm 2500 sq. mm 2500 sq. mm

1000 sq mm 2500 sq. mm 2500 sq. mm

80°C/W

Package soldered into PC board with plated through holes

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

225 sq mm

2500 sq. mm 2500 sq. mm

85°C/W

heat sink:

Thermalloy type 2224B

Aavid type 5754

160°C/W

135°C/W

1000 sq mm 1000 sq. mm 1000 sq. mm

91°C/W

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

to both sides of board.

Calculating Junction Temperature

Table 2. S8 Package

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?

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.

120°C/W

Power dissipated by the device will be equal to:

I_{OUT MAX}• (V_{IN MAX}– V_OUT) + (I_GND• V_IN)

125°C/W

131°C/W

where, I_{OUT MAX}= 100mA

V_{IN MAX}= 7V

Table 3. AS8 Package*

COPPER AREA

I_GNDat (I_OUT= 100mA, V_IN= 7V) = 5mA

TOPSIDE**

BACKSIDE

BOARD AREA

so,

P =100mA • (7V – 3.3V) + (5mA • 7V)

= 0.405W

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

60°C/W

68°C/W

74°C/W

IfweuseanSOT-223package,thenthethermalresistance

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

copper area. So the junction temperature rise above

ambient will be less than or equal to:

*

Pins 3, 6, and 7 are ground.

** Device is mounted on topside.

0.405W • 60°C/W = 24°C

Table 4. SOT-223 Package

(Thermal Resistance Junction-to-Tab 20°C/W)

The maximum junction temperature will then be equal to

the maximum junction temperature rise above ambient

plus the maximum ambient temperature or:

COPPER AREA

THERMAL RESISTANCE

BOARD AREA

(JUNCTION-TO-AMBIENT)

TOPSIDE*

BACKSIDE

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 1000 sq. mm 1000 sq. mm

50°C/W

58°C/W

64°C/W

57°C/W

60°C/W

T_JMAX= 50°C + 24°C = 74°C

Output Capacitance and Transient Performance

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

output capacitors. The minimum recommended value is

1μF 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

1000 sq. mm

0

1000 sq. mm

* Tab of device attached to topside copper

1121fe

10

LT1121/LT1121-3.3/LT1121-5

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APPLICATIO S I FOR ATIO

U

that the ESR of the capacitor is low (ceramic) the sug-

gested series resistor is shown in Table 6. The LT1121 is

amicropowerdeviceandoutputtransientresponsewillbe

a function of output capacitance. See the Transient Re-

sponsecurvesintheTypicalPerformanceCharacteristics.

Larger values of output capacitance will decrease the peak

deviations and provide improved output transient re-

sponse. 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

SUGGESTED SERIES

OUTPUT CAPACITANCE

RESISTOR

0.33μF

0.47μF

0.68μF

>1μF

2Ω

1Ω

The reverse output current will follow the curve in Figure

2whentheinputpinispulledtoground. Thiscurrentflows

through the output pin to ground. The state of the shut-

down pin will have no effect on output current when the

input pin is pulled to ground.

None Needed

Protection Features

TheLT1121incorporatesseveralprotectionfeatureswhich

make it ideal for use in battery-powered circuits. In addi-

tion to the normal protection features associated with

monolithic regulators, such as current limiting and ther-

mal limiting, the device is protected against reverse input

voltages, reverse output voltages, and reverse voltages

from output to input.

Insomeapplicationsitmaybenecessarytoleavetheinput

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

outputcurrentalsofollowsthecurveinFigure2iftheinput

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

T = 25°C

IN

CURRENT FLOWS

INTO OUTPUT PIN

TO GROUND

J

V

90

80

70

60

50

40

30

20

10

0

< V

OUT

The input of the device will withstand reverse voltages of

30V.Currentflowintothedevicewillbelimitedtolessthan

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.

LT1121

= V

(V

OUT

)

ADJ

LT1121-3.3

LT1121-5

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

0

2

4

6

8

10

1

3

5

7

9

OUTPUT VOLTAGE (V)

1121• F02

Figure 2. Reverse Output Current

1121fe

11

LT1121/LT1121-3.3/LT1121-5

W U U

U

APPLICATIO S I FOR ATIO

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

(Nominal)

Grounded

Forced to V

(Nominal)

Reverse Output Current ≈ 15μA (See Figure 2)

Input Current ≈ 1μA (See Figure 3)

OUT

Open

Open (Hi)

Grounded

Open (Hi)

Grounded

Open (Hi)

Grounded

Forced to V

(Nominal)

Reverse Output Current ≈ 15μA (See Figure 2)

Output Current = 0

OUT

≤0.8V

>1.5V

≤0V

Output Current = 0

Output Current = Short-Circuit Current

Output Current = 0

–30V < V < 30V

IN

1121fe

12

LT1121/LT1121-3.3/LT1121-5

U

PACKAGE DESCRIPTIO

N8 Package

8-Lead PDIP (Narrow 0.300)

(LTC DWG # 05-08-1510)

.400*

(10.160)

MAX

8

7

6

5

4

.255 ± .015*

(6.477 ± 0.381)

1

2

3

.130 ± .005

.300 – .325

.045 – .065

(3.302 ± 0.127)

(1.143 – 1.651)

(7.620 – 8.255)

.065

(1.651)

TYP

.008 – .015

(0.203 – 0.381)

.120

.020

(0.508)

MIN

(3.048)

MIN

+.035

.325

–.015

.018 ± .003

(0.457 ± 0.076)

.100

(2.54)

BSC

+0.889

8.255

(

)

N8 1002

–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 0.150)

(LTC DWG # 05-08-1610)

.189 – .197

(4.801 – 5.004)

.045 ±.005

.160 ±.005

NOTE 3

.050 BSC

7

5

8

6

.245

MIN

.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)

SO8 0303

1121fe

13

LT1121/LT1121-3.3/LT1121-5

U

PACKAGE DESCRIPTIO

ST Package

3-Lead Plastic SOT-223

(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

1121fe

14

LT1121/LT1121-3.3/LT1121-5

U

PACKAGE DESCRIPTIO

Z Package

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

(LTC DWG # 05-08-1410)

.180 ± .005

(4.572 ± 0.127)

.060 ± .005

(1.524± 0.127)

DIA

.90

(2.286)

NOM

.180 ± .005

(4.572 ± 0.127)

5°

NOM

.500

(12.70)

MIN

.050

(1.270)

MAX

UNCONTROLLED

LEAD DIMENSION

.016 ± .003

.015 ± .002

(0.406 ± 0.076)

(0.381 ± 0.051)

.050

(1.27)

BSC

.098 +.016/–.04

(2.5 +0.4/–0.1)

2 PLCS

Z3 (TO-92) 0801

.060 ± .010

TO-92 TAPE AND REEL

(1.524 ± 0.254)

REFER TO TAPE AND REEL SECTION OF

LTC DATA BOOK FOR ADDITIONAL INFORMATION

.140 ± .010

(3.556 ± 0.127)

3

2

1

10° NOM

1121fe

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-

tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.

15

LT1121/LT1121-3.3/LT1121-5

RELATED PARTS

PART NUMBER

DESCRIPTION

COMMENTS

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125mA Low Dropout Regulator with 20μA I

Includes 2.5V Reference and Comparator

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SOT-23 Package, Internally Compensated

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Low Output Noise: 60μV

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RMS

LT1762 Series

LT1763 Series

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30μA Quiescent Current, 20μV

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300mA, Low Noise, LDO Micropower Regulator

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Burst Mode is a trademark of Linear Technology Corporation.

1121fe

LT 0407 REV E • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

16

●

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


型号：	LT1121CZ-5#TRPBF
厂家：	Linear
描述：	LT1121 - Micropower Low Dropout Regulators with Shutdown; Package: TO-92; Pins: 3; Temperature Range: 0°C to 70°C 线性稳压器IC 调节器电源电路输出元件
文件：	总16页 (文件大小：173K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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