LT1121-3.3_技术文档

LT1121/LT1121-3.3/LT1121-5

Micropower Low Dropout

Regulators with Shutdown

U

DESCRIPTIO

EATURE

S

F

■

The LT1121/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 3.8V to 20V

3.3V and 5V Fixed Output Voltages

Controlled Quiescent Current in Dropout

Shutdown

16µA Quiescent Current in Shutdown

Stable with 0.33µF Output Capacitor

Reverse Battery Protection

No Reverse Current with Input Low

Thermal Limiting

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. Small ceramic capacitors can be used, enhanc-

ing 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.

O U

PPLICATI

S

A

■

Low Current Regulator

Regulator for Battery-Powered Systems

Post Regulator for Switching Supplies

U

O

TYPICAL APPLICATI

Dropout Voltage

5V Battery-Powered Supply with Shutdown

0.5

8

1

3.3V OUT

150mA

IN

OUT

LT1121-3.3

0.4

0.3

0.2

0.1

0

+

1µF

5V

SOLID TANTALUM

5

SHDN

GND

3

V

(PIN 5) OUTPUT

< 0.25

> 2.8

SHDN

OFF

ON

LT1121 • TA01

NC

ON

80

OUTPUT CURRENT (mA)

0

20 40 60

100 120 140 160

LT1121 • TA02

1

LT1121/LT1121-3.3/LT1121-5

W W W

U

ABSOLUTE AXI U RATI GS

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

Operating Junction Temperature Range (Note 2)

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

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

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

*For applications requiring input voltage ratings greater than 30V, contact the factory.

Input Voltage ...................................................... ±30V*

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

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

Shutdown Pin Input Voltage (Note 1) ........ 6.5V, – 0.6V

Shutdown Pin Input Current (Note 1) .................. 20mA

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

W

U

/O

PACKAGE RDER I FOR ATIO

TOP VIEW

FRONT VIEW

BOTTOM 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.

*

OUT

NC/ADJ*

GND

1

2

3

4

IN

8

7

6

5

3

2

1

3

2

1

OUTPUT

GND

**

NC**

SHDN

IN

GND OUT

TAB IS

GND

NC

V

IN

N8 PACKAGE

8-LEAD PLASTIC DIP

Z PACKAGE

3-LEAD PLASTIC TO-92

ST PACKAGE

3-LEAD PLASTIC SOT-223

S8 PACKAGE

8-LEAD PLASTIC SOIC

LT1121 • PO03

LT1121 • PO02

θ_JA≈ 120°C/W (N8, S8)

θ_JA≈ 70°C/W (AS8)

θ_JA≈ 150°C/W

θ

_JA≈ 50°C/W

ORDER PART

NUMBER

S8 PART

ORDER PART

NUMBER

ORDER PART NUMBER

LT1121IS8

MARKING

1121A

1121

LT1121CN8

LT1121CST-3.3

LT1121IST-3.3

LT1121CST-5

LT1121IST-5

LT1121CZ-3.3

LT1121IZ-3.3

LT1121CZ-5

LT1121IZ-5

LT1121IS8-3.3

LT1121IS8-5

LT1121ACS8

121A3

121A5

121AI

11213

11215

1121I

121I3

121I5

LT1121CN8-3.3

LT1121CN8-5

LT1121IN8

LT1121ACS8-3.3

LT1121ACS8-5

LT1121AIS8

LT1121AIS8-3.3

LT1121AIS8-5

121AI3

121AI5

LT1121IN8-3.3

LT1121IN8-5

LT1121CS8

LT1121CS8-3.3

LT1121CS8-5

Consult factory for Military grade parts.

ELECTRICAL CHARACTERISTICS

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Regulated Output Voltage

(Note 3)

LT1121-3.3

V

= 3.8V, I

= 1mA, T = 25°C

3.250

3.200

4.925

4.850

3.300

5.000

3.350

3.400

5.075

5.150

V

IN

OUT

J

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

V

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

< 150mA

●

IN

OUT

LT1121-5

= 5.5V, I

IN

= 1mA, T = 25°C

IN

OUT

J

< 150mA

OUT

LT1121 (Note 4)

V

= 4.3V, I

= 1mA, T = 25°C

3.695

3.640

3.750

1.5

3.805

3.860

10

V

mV

IN

OUT

J

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

∆V = 4.8V to 20V, I

∆V = 5.5V to 20V, I

∆V = 4.3V to 20V, I

IN

< 150mA

●

IN

OUT

Line Regulation

LT1121-3.3

LT1121-5

LT1121 (Note 4)

= 1mA

IN

OUT

IN

2

LT1121/LT1121-3.3/LT1121-5

ELECTRICAL CHARACTERISTICS

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Load Regulation

LT1121-3.3

∆I

= 1mA to 150mA, T = 25°C

= 1mA to 150mA

–12

–20

–17

–28

–12

–18

0.13

0.30

0.37

0.42

–20

–30

–45

–20

–30

0.16

0.25

0.35

0.50

0.45

0.60

0.55

0.70

50

120

500

2.5

mV

V

µA

LOAD

J

●

LT1121-5

= 1mA to 150mA, T = 25°C

LOAD

J

= 1mA to 150mA

LT1121 (Note 4)

= 1mA to 150mA, T = 25°C

LOAD

J

= 1mA to 150mA

Dropout Voltage

(Note 5)

I

= 1mA, T = 25°C

= 1mA

LOAD

J

I

= 50mA, T = 25°C

= 50mA

LOAD

J

LOAD

I

= 100mA, T = 25°C

= 100mA

LOAD

J

I

= 150mA, T = 25°C

= 150mA

LOAD

J

●

Ground Pin Current

(Note 6)

I

= 0mA

= 1mA

= 10mA

= 50mA

= 100mA

= 150mA

30

90

LOAD

350

1.5

4.0

7.0

150

1.2

0.75

6

15

58

µA

mA

nA

V

µA

dB

7.0

14.0

300

2.8

Adjust Pin Bias Current (Notes 4, 7)

Shutdown Threshold

T = 25°C

J

V

= Off to On

= On to Off

●

OUT

0.25

50

Shutdown Pin Current (Note 8)

Quiescent Current in Shutdown (Note 9)

Ripple Rejection

V

= 0V

●

10

22

SHDN

= 6V, V

= 0V

SHDN

IN

– V

= 1V (Avg), V

= 0.5V

,

OUT

RIPPLE

P-P

f

= 120Hz, I

= 0.1A

RIPPLE

LOAD

Current Limit

Input Reverse Leakage Current

Reverse Output Current (Note 10)

V

– V

= –20V, V

= 7V, T = 25°C

200

500

1.0

25

mA

µA

IN

OUT

J

= 0V

●

OUT

LT1121-3.3

LT1121-5

LT1121 (Note 4)

V

= 3.3V, V = 0V

16

OUT

IN

= 5V, V = 0V

IN

= 3.8V, V = 0V

IN

The

range.

Note 1: 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.

●

denotes specifications which apply over the operating temperature

Note 4: The LT1121 (adjustable version) is tested and specified with the

adjust pin connected to the output pin.

Note 5: 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 6: Ground pin current is tested with V = V

(nominal) and a

IN

OUT

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

Note 7: Adjust pin bias current flows into the adjust pin.

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

< 1mA, output voltage

J

OUT

Note 8: Shutdown pin current at V

= 0V flows out of the shutdown pin.

SHDN

may increase by 1%.

Note 9: Quiescent current in shutdown is equal to the sum total of the

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

Note 10: 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 3: 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.

3

LT1121/LT1121-3.3/LT1121-5

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

10

40

30

20

10

0

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

V

= 6V

IN

R

= ∞

LOAD

I

= 150mA

LOAD

T ≤ 125°C

J

V

SHDN

=

OPEN

0V

I

= 100mA

LLOAD

T ≤ 25°C

J

I

= 50mA

LOAD

V

SHDN

=

I

= 1mA

LOAD

= TEST POINTS

50

75 100 125

0

40 60 80 100 120 140 160

OUTPUT CURRENT (mA)

–50

0

25

50

75

125

–50

–25

0

25

20

–25

100

TEMPERATURE (°C)

1121 G11

1121 G27

1121 G14

LT1121-3.3

Quiescent Current

LT1121

Quiescent Current

LT1121-5

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

T = 25°C

J

R

J

=

∞

R

=

∞

R

= ∞

LOAD

OUT

V

= V

ADJ

V

= OPEN

V

= OPEN

SHDN

V

= OPEN

SHDN

V

= 0V

V

= 0V

7

V

= 0V

7

SHDN

6

SHDN

0

1

2

3

4

5

6

7

8

9

10

0

1

2

3

4

5

8

9

10

0

1

2

3

4

5

6

8

9

10

INPUT VOLTAGE (V)

1121 G02

1121 G03

1121 G04

LT1121

Adjust Pin Voltage

LT1121-5

Output Voltage

LT1121-3.3

Output 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

I

= 1mA

OUT

–50

0

25

50

75 100 125

–25

–50

0

25

50

75 100 125

50

TEMPERATURE (°C)

125

–25

–50

0

25

75 100

–25

TEMPERATURE (°C)

1121 G24

1121 G22

1121 G23

4

LT1121/LT1121-3.3/LT1121-5

U W

TYPICAL PERFOR A CE CHARACTERISTICS

LT1121-3.3

Ground Pin Current

LT1121

Ground Pin Current

LT1121-5

Ground Pin Current

800

700

600

500

400

300

200

100

0

800

700

600

500

400

300

200

100

0

800

T = 25°C

J

T = 25°C

J

T = 25°C

R

I

= 150Ω

J

V

LOAD

700

600

500

400

300

200

100

0

= V

= 25mA*

R

= 200Ω

OUT

ADJ

LOAD

R

I

= 130Ω

LOAD

I

= 25mA*

R

I

= 500Ω

= 10mA*

R

= 330Ω

= 10mA*

LOAD

R

= 380Ω

= 10mA*

LOAD

I

*FOR V

= 3.3V

*FOR V

= 5V

R

*FOR V

= 3.75V

OUT

= 5k

= 1mA*

R

= 3.3k

= 1mA*

R

I

= 3.8k

LOAD

I

= 1mA*

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

T = 25°C

J

OUT

T = 25°C

J

V

= V

ADJ

R

= 22Ω

LOAD

R

= 33Ω

LOAD

R

= 25Ω

I

= 150mA*

LOAD

I

= 150mA*

I

= 150mA*

R

I

= 33Ω

LOAD

R

= 50Ω

= 100mA*

LOAD

R

= 38Ω

= 100mA*

LOAD

I

LOAD

R

I

= 100Ω

= 50mA*

R

LOAD

= 66Ω

= 50mA*

LOAD

R

I

= 75Ω

LOAD

= 50mA*

LOAD

I

LOAD

*FOR V

= 3.3V

*FOR V

= 5V

7

*FOR V

= 3.75V

OUT

5

OUT

6

0

2

4

6

8

10

0

2

4

8

10

0

2

4

6

8

10

1

3

7

9

1

3

5

9

1

3

5

7

9

INPUT VOLTAGE (V)

1121 G09

1121 G05

1121 G07

Shutdown Pin Threshold

(On-to-Off)

Shutdown Pin Threshold

(Off-to-On)

Ground Pin Current

14

12

10

8

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

I

= 1mA

V

= 3.3V (LT1121-3.3)

= 5V (LT1121-5)

= 3.75V (LT1121)

LOAD

IN

I

= 150mA

DEVICE IS OPERATING

IN DROPOUT

LOAD

T = 125°C

J

I

= 1mA

LOAD

T = 25°C

J

6

T = –55°C

J

4

2

0

40 60 80 100 120 140 160

OUTPUT CURRENT (mA)

50

TEMPERATURE (°C)

125

20

50

TEMPERATURE (°C)

125

–50

0

25

75 100

–50

0

25

75 100

–25

1121 G29

1121 G17

1121 G16

5

LT1121/LT1121-3.3/LT1121-5

U W

TYPICAL PERFOR A CE CHARACTERISTICS

LT1121

Adjust Pin Bias Current

Shutdown Pin Input Current

Shutdown Pin 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

50

–25

–50

0

25

75 100 125

–25

0

1

2

3

4

5

6

7

8

9

TEMPERATURE (°C)

SHUTDOWN PIN VOLTAGE (V)

1121 G15

1121 G25

1121 G28

Current Limit

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

OUT

IN

OUT

V

= 0V

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 G20

1121 G19

1121 G13

Reverse Output Current

Ripple Rejection

64

62

60

58

56

54

52

50

100

90

80

70

60

50

40

30

20

10

0

100

90

80

70

60

50

40

30

20

10

0

T = 25°C

J

IN

V

IN

= V (NOMINAL) + 1V

OUT

I

= 100mA

OUT

IN

V

= 0V

V

= 6V + 50mV

RIPPLE

+ 0.5V RIPPLE AT f = 120Hz

RMS

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

–50

0

25

50

75 100 125

–25

10

100

1k

10k

100k

1M

0

2

4

6

8

10

1

3

5

7

9

TEMPERATURE (°C)

FREQUENCY (Hz)

OUTPUT VOLTAGE (V)

1121 G26

1121 G18

1121 G01

6

LT1121/LT1121-3.3/LT1121-5

U W

TYPICAL PERFOR A CE CHARACTERISTICS

LT1121-5

Load Transient Response

LT1121-5

Load Transient Response

Load Regulation

0

–5

∆I

= 1mA TO 150mA

LOAD

V

C

= 6V

V

C

= 6V

IN

0.2

0.1

0.2

0.1

= 0.1µF

= 3.3µF

= 0.1µF

= 1µF

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

0.4 0.5

0.7

0.9

0.8

1.0

0.2

0

0.1

0.3

0.6

0.2

TEMPERATURE (°C)

TIME (ms)

1121 G21

1121 G30

1121 G31

U

PI FU CTIO S

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.

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 6 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.

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

7

LT1121/LT1121-3.3/LT1121-5

O U

W

U

PPLICATI

S I FOR ATIO

A

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 20V. 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

areas are listed for each package. All measurements were

GND

1121 • F01

R2

V

= 3.75V 1 +

+ I

(

• R2

ADJ

)

OUT

(

)

R1

= 3.75V

ADJ

I

= 150nA AT 25°C

ADJ

OUTPUT RANGE = 3.75V TO 30V

Figure 1. Adjustable Operation

8

LT1121/LT1121-3.3/LT1121-5

O U

W

U

PPLICATI

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

NC leads were connected to the ground plane.

S I FOR ATIO

A

Table 5. TO-92 Package

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:

25°C/W

131°C/W

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

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)

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

= 0.405W

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 LTC1121 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

9

LT1121/LT1121-3.3/LT1121-5

O U

W

U

PPLICATI

S I FOR ATIO

A

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

gested series resistor is shown in Table 5. 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

6 summarizes the following information.

Table 5.

SUGGESTED SERIES

OUTPUT CAPACITANCE

RESISTOR

0.33µF

2Ω

0.47µF

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.

0.68µF

>1µF

1Ω

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

J

V

90

80

70

60

50

40

30

20

10

0

< V

IN

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.

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

10

LT1121/LT1121-3.3/LT1121-5

O U

W

U

PPLICATI

A

S I FOR ATIO

5

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

4

3

2

1

0

1

2

3

4

5

INPUT VOLTAGE (V)

1121 F03

Figure 3. Input Current

Table 6. 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

Open

≤ 0.8V

> 1.5V

OUT

≤ 0V

Output Current = 0

Output Current = Short-Circuit Current

Output Current = 0

–30V < V < 30V

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 represen-

tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.

11

LT1121/LT1121-3.3/LT1121-5

U

Dimensions in inches (millimeters) unless otherwise noted.

PACKAGE DESCRIPTIO

N8 Package, 8-Lead Plastic DIP

0.400

(10.160)

MAX

0.130 ± 0.005

0.045 – 0.065

0.300 – 0.320

(7.620 – 8.128)

(3.302 ± 0.127)

(1.143 – 1.651)

8

1

7

6

5

4

0.065

(1.651)

TYP

0.009 – 0.015

(0.229 – 0.381)

0.250 ± 0.010

(6.350 ± 0.254)

0.125

(3.175)

MIN

0.020

(0.508)

MIN

+0.025

–0.015

0.045 ± 0.015

(1.143 ± 0.381)

0.325

2

3

+0.635

8.255

(

)

–0.381

0.100 ± 0.010

(2.540 ± 0.254)

0.018 ± 0.003

(0.457 ± 0.076)

0.189 – 0.197

(4.801 – 5.004)

S8 Package, 8-Lead Plastic SOIC

0.010 – 0.020

(0.254 – 0.508)

7

5

8

6

× 45°

0.053 – 0.069

(1.346 – 1.752)

0.004 – 0.010

(0.101 – 0.254)

0.008 – 0.010

(0.203 – 0.254)

0.228 – 0.244

0.150 – 0.157

(5.791 – 6.197)

(3.810 – 3.988)

0.016 – 0.050

0.406 – 1.270

0.050

(1.270)

BSC

0.014 – 0.019

(0.355 – 0.483)

0°– 8° TYP

1

2

3

4

0.248 – 0.264

(6.30 – 6.71)

ST Package, 3-Lead Plastic SOT-223

0.116 – 0.124

(2.95 – 3.15)

10° – 16°

0.264 – 0.287

(6.71 – 7.29)

0.010 – 0.014

(0.25 – 0.36)

10°

MAX

0.071

(1.80)

MAX

0.130 – 0.146

(3.30 – 3.71)

10° – 16°

0.025 – 0.033

(0.64 – 0.84)

0.0008 – 0.0040

(0.0203 – 0.1016)

0.012

(0.31)

MIN

0.181

(4.60)

NOM

0.033 – 0.041

(0.84 – 1.04)

0.090

(2.29)

NOM

Z Package, 3-Lead Plastic TO-92

0.060 ± 0.005

0.180 ± 0.005

(4.572 ± 0.127)

(1.524± 0.127)

DIA

0.060 ± 0.010

(1.524 ± 0.254)

0.180 ± 0.005

(4.572 ± 0.127)

0.140 ± 0.010

(3.556 ± 0.127)

0.90

(2.286)

NOM

5°

NOM

0.050

(1.270)

MAX

0.500

(12.79)

MIN

10° NOM

UNCONTROLLED

LEAD DIA

0.020 ± 0.003

(0.508 ± 0.076)

0.015 ± 0.02

(0.381 ± 0.051)

0.016 ± 0.03

(0.406 ± 0.076)

0.050 ± 0.005

(1.270 ± 0.127)

LT/GP 0594 5K REV A • PRINTED IN USA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7487

12

●

LINEAR TECHNOLOGY CORPORATION 1994

(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977


型号：	LT1121-3.3
厂家：	Linear
描述：	Micropower Low Dropout Regulators with Shutdown 微功率低压差稳压器，带有关断稳压器
文件：	总12页 (文件大小：271K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LT1121-3.3 [Linear]

相关型号：

LT1121-3.3_15

LT1121-5

LT1121-5_15

LT1121ACS8

LT1121ACS8#PBF

LT1121ACS8#TR

LT1121ACS8#TRPBF

LT1121ACS8-3.3

LT1121ACS8-3.3#PBF

LT1121ACS8-3.3#TR

LT1121ACS8-3.3#TRPBF

LT1121ACS8-5