LT1761ES5-1.2#TRM_技术文档

LT1761 Series

100mA, Low Noise,

LDO Micropower

Regulators in SOT-23

U

FEATURES

DESCRIPTIO

The LT^®1761 series are micropower, low noise, low

dropout regulators. With an external 0.01μF bypass

capacitor, output noise drops to 20μV_RMSover a 10Hz to

100kHz bandwidth. Designed for use in battery-powered

systems, the low 20μA quiescent current makes them an

ideal choice. In shutdown, quiescent current drops to less

than 0.1μA. The devices are capable of operating over an

input voltage from 1.8V to 20V, and can supply 100mA of

output current with a dropout voltage of 300mV. Quies-

cent current is well controlled, not rising in dropout as it

does with many other regulators.

■

Low Noise: 20μV_RMS(10Hz to 100kHz)

■

Low Quiescent Current: 20μA

■

Wide Input Voltage Range: 1.8V to 20V

Output Current: 100mA

■

Very Low Shutdown Current: < 0.1μA

■

Low Dropout Voltage: 300mV at 100mA

Fixed Output Voltages: 1.2V, 1.5V, 1.8V, 2V, 2.5V,

2.8V, 3V, 3.3V, 5V

■

Adjustable Output from 1.22V to 20V

Stable with 1μF Output Capacitor

Stable with Aluminum, Tantalum or

Ceramic Capacitors

The LT1761 regulators are stable with output capacitors

as low as 1μF. Small ceramic capacitors can be used

without the series resistance required by other regulators.

■

Reverse Battery Protected

No Reverse Current

No Protection Diodes Needed

Overcurrent and Overtemperature Protected

^{Available in Tiny}U^{5-Lead SOT-23 Package}

Internal protection circuitry includes reverse battery pro-

tection, current limiting, thermal limiting and reverse

current protection. The device is available in fixed output

voltages of 1.2V, 1.5V, 1.8V, 2V, 2.5V, 2.8V, 3V, 3.3V and

5V, and as an adjustable device with a 1.22V reference

voltage. The LT1761 regulators are available in the 5-lead

SOT-23 package.

APPLICATIO S

■

Cellular Phones

Pagers

Battery-Powered Systems

Frequency Synthesizers

■

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

All other trademarks are the property of their respective owners.

■

Wireless Modems

U

TYPICAL APPLICATIO

10Hz to 100kHz Output Noise

5V Low Noise Regulator

5V AT100mA

20μV NOISE

10μF

IN

OUT

BYP

V

RMS

IN

+

5.4V TO

20V

1μF

0.01μF

V

LT1761-5

OUT

20μV

RMS

100μV/DIV

SHDN

GND

1761 TA01

1761 G48

1761sfc

1

LT1761 Series

ABSOLUTE AXI U RATI GS

W W U W

(Note 1)

IN Pin Voltage........................................................ 20V

OUT Pin Voltage .................................................... 20V

Input to Output Differential Voltage ....................... 20V

ADJ Pin Voltage ...................................................... 7V

BYP Pin Voltage.................................................... 0.6V

SHDN Pin Voltage................................................. 20V

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

Operating Junction Temperature Range

E Grade (Note 2)............................... –40°C to 125°C

MP Grade (Note 2) ........................... –55°C to 125°C

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

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

U W

U

PACKAGE/ORDER I FOR ATIO

TOP VIEW

IN 1

GND 2

BYP 3

5 OUT

4 ADJ

IN 1

GND 2

5 OUT

4 ADJ

IN 1

GND 2

5 OUT

4 BYP

SHDN 3

S5 PACKAGE

5-LEAD PLASTIC SOT-23

S5 PACKAGE

5-LEAD PLASTIC SOT-23

S5 PACKAGE

5-LEAD PLASTIC SOT-23

T_JMAX= 150°C, θ_JA= 250°C/ W

SEE THE APPLICATIONS INFORMATION SECTION.

S5 PART

MARKING

ORDER PART

NUMBER

ORDER PART

NUMBER

S5 PART

MARKING

S5 PART

MARKING

ORDER PART

NUMBER

LTGC

LTGH

LT1761ES5-1.2

LT1761ES5-1.5

LT1761ES5-1.8

LT1761MPS5-1.8

LT1761ES5-2

LTCDS

LTMT

LTJM

LTDCH

LTJE

LT1761ES5-BYP

LT1761ES5-SD

LT1761ES5-2.5

LT1761ES5-2.8

LT1761ES5-3

LT1761ES5-3.3

LT1761ES5-5

LTGD

LTLB

LTGE

LTGF

LTGG

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.

1761sfc

2

LT1761 Series

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are T_A= 25°C. (Note 2)

PARAMETER

CONDITIONS

= 100mA

MIN

TYP

MAX

UNITS

Minimum Input Voltage (Notes 3, 11)

I

●

1.8

2.3

V

LOAD

Regulated Output Voltage

(Note 4)

LT1761-1.2

LT1761-1.5

LT1761-1.8

LT1761-2

V

= 2V, I

= 1mA

1.185

1.170

1.150

1.2

1.215

1.230

1.240

V

IN

LOAD

2.3V < V < 20V, 1mA < I

< 50mA

●

IN

LOAD

2.3V < V < 20V, 1mA < I

< 100mA

V

= 2V, I

= 1mA

1.478

1.457

1.436

1.5

1.522

1.538

1.555

V

IN

LOAD

2.5V < V < 20V, 1mA < I

< 50mA

●

IN

LOAD

2.5V < V < 20V, 1mA < I

V

= 2.3V, I

= 1mA

LOAD

1.775

1.750

1.725

1.8

1.825

1.845

1.860

V

IN

2.8V < V < 20V, 1mA < I

< 50mA

< 100mA

●

IN

LOAD

2.8V < V < 20V, 1mA < I

V

= 2.5V, I

IN

= 1mA

LOAD

1.970

1.945

1.920

2

2.030

2.045

2.060

V

IN

3V < V < 20V, 1mA < I

< 50mA

< 100mA

●

LOAD

3V < V < 20V, 1mA < I

LT1761-2.5

LT1761-2.8

V

= 3V, I

= 1mA

2.465

2.435

2.415

2.5

2.535

2.565

2.575

V

IN

LOAD

3.5V < V < 20V, 1mA < I

< 50mA

●

IN

LOAD

3.5V < V < 20V, 1mA < I

< 100mA

V

= 3.3V, I

= 1mA

LOAD

2.762

2.732

2.706

2.8

2.838

2.868

2.884

V

IN

3.8V < V < 20V, 1mA < I

< 50mA

< 100mA

●

IN

LOAD

IN

LT1761-3

V

= 3.5V, I

IN

= 1mA

LOAD

2.960

2.930

2.900

3

3.040

3.070

3.090

V

IN

4V < V < 20V, 1mA < I

< 50mA

< 100mA

●

LOAD

4V < V < 20V, 1mA < I

LT1761-3.3

V

= 3.8V, I

= 1mA

LOAD

3.250

3.230

3.190

3.3

3.350

3.370

3.400

V

IN

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

< 50mA

< 100mA

●

IN

LOAD

IN

LT1761-5

LT1761

V

= 5.5V, I

IN

= 1mA

LOAD

4.935

4.900

4.850

5

5.065

5.100

5.120

V

IN

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

< 50mA

< 100mA

●

LOAD

IN

ADJ Pin Voltage

(Note 3, 4)

V

= 2V, I

= 1mA

1.205

1.190

1.170

1.220

1.235

1.250

1.260

V

IN

LOAD

2.3V < V < 20V, 1mA < I

< 50mA

< 100mA

●

IN

LOAD

IN

Line Regulation

LT1761-1.2

LT1761-1.5

LT1761-1.8

LT1761-2

LT1761-2.5

LT1761-2.8

LT1761-3

LT1761-3.3

LT1761-5

LT1761 (Note 3) ΔV = 2V to 20V, I

ΔV = 2V to 20V, I

= 1mA

●

1

10

mV

IN

LOAD

ΔV = 2V to 20V, I

IN

LOAD

ΔV = 2.3V to 20V, I

= 1mA

IN

LOAD

ΔV = 2.5V to 20V, I

= 1mA

IN

LOAD

ΔV = 3V to 20V, I

IN

= 1mA

IN

LOAD

ΔV = 3.3V to 20V, I

= 1mA

LOAD

ΔV = 3.5V to 20V, I

IN

ΔV = 3.8V to 20V, I

IN

ΔV = 5.5V to 20V, I

IN

= 1mA

IN

LOAD

1761sfc

3

LT1761 Series

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are T_A= 25°C. (Note 2)

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Load Regulation

LT1761-1.2

V

= 2.3V, ΔI

= 1mA to 50mA

= 1mA to 100mA

1

6

mV

IN

LOAD

●

12

50

1

LT1761-1.5

LT1761-1.8

LT1761-2

V

= 2.5V, ΔI

= 1mA to 50mA

10

14

20

35

30

55

mV

IN

LOAD

●

V

= 2.8V, ΔI

= 1mA to 50mA

= 1mA to 100mA

10

15

20

35

30

60

mV

IN

LOAD

●

V

= 3V, ΔI

= 1mA to 50mA

= 1mA to 100mA

10

15

20

35

65

mV

IN

LOAD

= 3V, ΔI

●

LOAD

LT1761-2.5

LT1761-2.8

LT1761-3

V

= 3.5V, ΔI

= 1mA to 50mA

10

20

35

40

80

mV

IN

LOAD

= 1mA to 50mA

= 1mA to 100mA

●

LOAD

V

= 3.8V, ΔI

= 1mA to 50mA

= 1mA to 100mA

10

20

38

40

86

mV

IN

LOAD

●

V

= 4V, ΔI

= 1mA to 50mA

= 1mA to 100mA

10

20

40

90

mV

IN

LOAD

= 4V, ΔI

●

LOAD

LT1761-3.3

LT1761-5

V

= 4.3V, ΔI

= 1mA to 50mA

= 1mA to 100mA

10

20

40

mV

IN

LOAD

●

100

V

= 6V, ΔI

= 1mA to 50mA

= 1mA to 100mA

15

25

30

60

65

mV

IN

LOAD

= 6V, ΔI

●

LOAD

150

LT1761 (Note 3) V = 2.3V, ΔI

= 1mA to 50mA

1

6

mV

IN

LOAD

V

= 2.3V, ΔI

= 1mA to 50mA

= 1mA to 100mA

●

12

50

IN

LOAD

Dropout Voltage

I

= 1mA

0.10

0.17

0.24

0.30

0.15

0.19

V

LOAD

V

= V

●

IN

OUT(NOMINAL)

(Notes 5, 6, 11)

I

= 10mA

0.22

0.29

V

LOAD

I

= 50mA

0.28

0.38

V

LOAD

I

= 100mA

0.35

0.45

V

LOAD

1761sfc

4

LT1761 Series

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are T_A= 25°C. (Note 2)

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

GND Pin Current

I

= 0mA

= 1mA

= 10mA

= 50mA

= 100mA

●

20

55

230

1

45

100

400

2

μA

LOAD

V

= V

IN

OUT(NOMINAL)

(Notes 5, 7)

μA

mA

2.2

4

Output Voltage Noise

ADJ Pin Bias Current

Shutdown Threshold

C

= 10μF, C

= 0.01μF, I

= 100mA, BW = 10Hz to 100kHz

20

30

μV

OUT

BYP

LOAD

RMS

(Notes 3, 8)

100

2

nA

V

= Off to On

= On to Off

●

0.8

0.65

V

OUT

0.25

SHDN Pin Current

(Note 9)

V

= 0V

= 20V

●

0

1

0.5

3

μA

SHDN

Quiescent Current in Shutdown

Ripple Rejection (Note 3)

V

= 6V, V

= 0V

SHDN

0.01

65

0.1

μA

IN

– V

= 1.5V (Avg), V

= 0.5V , f

P-P RIPPLE

= 120Hz,

= –5%

55

dB

IN

OUT

RIPPLE

I

= 50mA

LOAD

Current Limit

V

= 7V, V

= 0V

200

mA

IN

OUT

OUT(NOMINAL)

= V

+ 1V or 2.3V (Note 12), ΔV

●

110

OUT

Input Reverse Leakage Current

V

= –20V, V

= 0V

OUT

1

mA

IN

Reverse Output Current

(Note 10)

LT1761-1.2

LT1761-1.5

LT1761-1.8

LT1761-2

LT1761-2.5

LT1761-2.8

LT1761-3

LT1761-3.3

LT1761-5

LT1761 (Note 3) V

V

= 1.2V, V < 1.2V

10

5

20

10

μA

OUT

IN

V

= 1.5V, V < 1.5V

IN

= 1.8V, V < 1.8V

IN

= 2V, V < 2V

IN

= 2.5V, V < 2.5V

IN

= 2.8V, V < 2.8V

IN

= 3V, V < 3V

IN

= 3.3V, V < 3.3V

IN

= 5V, V < 5V

IN

= 1.22V, V < 1.22V

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 6: Dropout voltage is the minimum input to output voltage differential

needed to maintain regulation at a specified output current. In dropout, the

output voltage will be equal to: V – V

.

IN

DROPOUT

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

or V = 2.3V

IN

OUT(NOMINAL)

Note 2: The LT1761 regulators are tested and specified under pulse load

conditions such that T ≈ T . The LT1761E is 100% production tested at

(whichever is greater) and a current source load. This means the device is

tested while operating in its dropout region or at the minimum input

voltage specification. This is the worst-case GND pin current. The GND pin

current will decrease slightly at higher input voltages.

J

A

T = 25°C. Performance at –40°C and 125°C is assured by design,

A

characterization and correlation with statistical process controls. The

LT1761MP is 100% tested and guaranteed over the –55°C to 125°C

temperature range.

Note 3: The LT1761 (adjustable versions) are tested and specified for

these conditions with the ADJ pin connected to the OUT 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.

Note 8: ADJ pin bias current flows into the ADJ pin.

Note 9: SHDN pin current flows into the SHDN pin.

Note 10: Reverse output current is tested with the IN pin grounded and the

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

pin and out the GND pin.

Note 11: For the LT1761, LT1761-1.2, LT1761-1.5, LT1761-1.8 and

LT1761-2 dropout voltage will be limited by the minimum input voltage

specification under some output voltage/load conditions. See the curve of

Minimum Input Voltage in the Typical Performance Characteristics.

Note 12: To satisfy requirements for minimum input voltage, current limit

Note 5: To satisfy requirements for minimum input voltage, the LT1761

(adjustable version) is tested and specified for these conditions with an

external resistor divider (two 250k resistors) for an output voltage of

2.44V. The external resistor divider will add a 5μA DC load on the output.

is tested at V = V

+ 1V or V = 2.3V, whichever is greater.

IN

OUT(NOMINAL)

IN

1761sfc

5

LT1761 Series

TYPICAL PERFOR A CE CHARACTERISTICS

U W

Typical Dropout Voltage

Dropout Voltage

Guaranteed Dropout Voltage

500

450

400

350

300

250

200

150

100

50

500

450

400

350

300

250

200

150

100

50

500

450

400

350

300

250

200

150

100

50

= TEST POINTS

T ≤ 125°C

J

T

= 125°C

J

I

= 100mA

L

T ≤ 25°C

J

I

= 50mA

= 10mA

L

T

= 25°C

J

I

L

I

= 1mA

L

0

–50

0

25

50

75 100 125

–25

40

50 60 70 80 90 100

0

10 20 30

50 60 70 80 90 100

0

10 20 30

TEMPERATURE (°C)

OUTPUT CURRENT (mA)

1761 G01.1

1761 G00

1761 G01

LT1761-1.2

Output Voltage

LT1761-1.5

Output Voltage

Quiescent Current

1.528

1.521

1.514

1.507

1.500

1.493

1.486

1.479

1.472

40

35

30

25

20

15

10

5

1.220

1.215

1.210

1.205

1.200

1.195

1.190

1.185

1.180

I

= 1mA

V

= 6V

L

IN

L

I = 1mA

L

R

= ∞ (250k FOR LT1761-BYP, -SD)

I

L

= 0 (5μA FOR LT1761-BYP, -SD)

V

SHDN

= V

IN

V

= 0V

50

SHDN

0

–50

–25

0

25

50

75

125

–25

0

25

75

125

–25

0

25

50

75

125

–50

100

–50

100

TEMPERATURE (°C)

1761 G51

1761 G03

1761 G05

LT1761-2.5

Output Voltage

LT1761-1.8

Output Voltage

LT1761-2

Output Voltage

1.84

1.83

1.82

1.81

1.80

1.79

1.78

1.77

1.76

2.54

2.53

2.52

2.51

2.50

2.49

2.48

2.47

2.46

2.04

2.03

2.02

2.01

2.00

1.99

1.98

1.97

1.96

I

= 1mA

I = 1mA

L

I

= 1mA

L

–25

0

25

50

75

125

–25

0

25

50

75

125

–50

100

–25

0

25

50

75

125

–50

100

–50

100

TEMPERATURE (°C)

1761 G06

1761 G08

1761 G07

1761sfc

6

LT1761 Series

U W

TYPICAL PERFOR A CE CHARACTERISTICS

LT1761-2.8

Output Voltage

LT1761-3

Output Voltage

LT1761-3.3

Output Voltage

2.84

2.83

2.82

2.81

2.80

2.79

2.78

2.77

2.76

3.360

3.345

3.330

3.315

3.300

3.285

3.270

3.255

3.240

3.060

3.045

3.030

3.015

3.000

2.985

2.970

2.955

2.940

I

= 1mA

I = 1mA

L

I

= 1mA

L

–25

0

25

50

75

125

–25

0

25

50

75

125

–50

100

–50

100

–25

0

25

50

75

125

–50

100

TEMPERATURE (°C)

1761 G52

1761 G11

1761 G09

LT1761-5

Output Voltage

LT1761-BYP, LT1761-SD

ADJ Pin Voltage

LT1761-1.2

Quiescent Current

5.08

5.06

5.04

5.02

5.00

4.98

4.96

4.94

4.92

1.240

1.235

1.230

1.225

1.220

1.215

1.210

1.205

1.200

250

225

200

175

150

125

100

75

I

= 1mA

L

I = 1mA

L

T

= 25°C

= ∞

J

L

R

50

V

= V

IN

SHDN

25

= 0V

8

SHDN

0

–25

0

25

50

75

125

–50

100

–25

0

25

50

75

125

–50

100

0

1

2

3

4

5

6

7

9

10

TEMPERATURE (°C)

INPUT VOLTAGE (V)

1761 G12

1761 G10

1761 G10b

LT1761-1.5

Quiescent Current

LT1761-1.8

Quiescent Current

LT1761-2

Quiescent Current

200

175

150

125

100

75

200

175

150

125

100

75

200

175

150

125

100

75

T

= 25°C

= ∞

T

= 25°C

= ∞

T

= 25°C

R = ∞

L

J

L

J

L

J

R

50

V

= V

IN

V

= V

V

= V

IN

SHDN

IN

SHDN

25

= 0V

8

= 0V

8

= 0V

8

SHDN

0

1

2

3

4

5

6

7

9

10

0

1

2

3

4

5

6

7

9

10

0

1

2

3

4

5

6

7

9

10

INPUT VOLTAGE (V)

1761 G53

1761 G18

1761 G19

1761sfc

7

LT1761 Series

TYPICAL PERFOR A CE CHARACTERISTICS

U W

LT1761-2.5

Quiescent Current

LT1761-2.8

Quiescent Current

LT1761-3

Quiescent Current

200

175

150

125

100

75

200

175

150

125

100

75

200

175

150

125

100

75

T

= 25°C

= ∞

T

= 25°C

R = ∞

L

T

= 25°C

= ∞

J

L

J

L

R

50

V

= V

IN

V

= V

IN

V

= V

IN

SHDN

25

V

= 0V

8

V

= 0V

8

V

= 0V

8

SHDN

0

1

2

3

4

5

6

7

9

10

0

1

2

3

4

5

6

7

9

10

0

1

2

3

4

5

6

7

9

10

INPUT VOLTAGE (V)

1761 G13

1761 G54

1761 G14

LT1761-3.3

Quiescent Current

LT1761-5

Quiescent Current

LT1761-BYP, LT1761-SD

Quiescent Current

200

175

150

125

100

75

200

175

150

125

100

75

30

25

20

15

10

5

T = 25°C

T

= 25°C

= ∞

T

= 25°C

R = ∞

L

J

R

J

L

J

= 250k

R

L

I

= 5μA

V

= V

IN

SHDN

50

V

= V

V

= V

IN

SHDN

IN

SHDN

25

V

= 0V

8

V

= 0V

8

SHDN

0

2

4

6

8

10 12 14 16 18 20

0

1

2

3

4

5

6

7

9

10

0

1

2

3

4

5

6

7

9

10

INPUT VOLTAGE (V)

1761 G17

1761 G16

1761 G15

LT1761-1.8

GND Pin Current

LT1761-1.2

GND Pin Current

LT1761-1.5

GND Pin Current

2.50

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0

2.50

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0

2.50

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0

T = 25°C

J

T

= 25°C

J

*FOR V

= 1.2V

*FOR V

= 1.8V

*FOR V

= 1.5V

OUT

R

L

= 12Ω

R

L

= 18Ω

L

R

L

= 15Ω

L

I

= 100mA*

I

= 100mA*

I

= 100mA*

R

L

= 24Ω

L

R = 36Ω

L

R

L

= 30Ω

L

I

= 50mA*

I

= 50mA*

L

I

= 50mA*

R

L

= 1.2k

L

R

L

= 1.8k

R

I

= 1.5k

L

R

L

= 120Ω

R

L

= 180Ω

L

R

L

= 150Ω

L

I

= 1mA*

I

= 1mA*

I

= 10mA*

I

= 10mA*

I

= 10mA*

4

0

1

2

3

5

6

7

8

9

10

0

1

2

3

5

6

7

8

9

10

4

0

1

2

3

5

6

7

8

9

10

INPUT VOLTAGE (V)

1761 G17b

1761 G02

1761 G55

1761sfc

8

LT1761 Series

U W

TYPICAL PERFOR A CE CHARACTERISTICS

LT1761-2

GND Pin Current

LT1761-2.5

GND Pin Current

LT1761-2.8

GND Pin Current

2.50

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0

2.50

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0

2.50

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0

T = 25°C

T

= 25°C

T = 25°C

J

*FOR V

= 2.5V

*FOR V

= 2.8V

*FOR V

= 2V

OUT

R

L

= 25Ω

L

R

L

= 28Ω

L

I

= 100mA

I

= 100mA

R

L

= 20Ω

L

I

= 100mA*

R

L

= 50Ω

R

L

= 56Ω

L

R

L

= 40Ω

L

I

= 50mA*

I

= 50mA*

I

= 50mA*

R

L

= 2.5k

R

L

= 2k

R = 2.8k

L

I = 1mA*

L

R

L

= 250Ω

R

L

= 200Ω

R

= 280Ω

L

I

= 1mA*

I

= 1mA*

I

= 10mA*

I

= 10mA*

I

= 10mA*

L

4

0

1

2

3

5

6

7

8

9

10

4

0

1

2

3

5

6

7

8

9

10

0

1

2

3

5

6

7

8

9

10

INPUT VOLTAGE (V)

1761 G20

1761 G04

1761 G56

LT1761-3

GND Pin Current

LT1761-3.3

GND Pin Current

LT1761-5

GND Pin Current

2.50

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0

2.50

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0

2.50

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0

T = 25°C

J

T = 25°C

J

*FOR V

OUT

= 3V

*FOR V

= 3.3V

OUT

*FOR V = 5V

OUT

R

L

= 50Ω

L

I

= 100mA

R

L

= 30Ω

L

R

L

= 33Ω

L

I

= 100mA*

I

= 100mA*

R

L

= 100Ω

L

R

L

= 66Ω

L

R

L

= 60Ω

I

= 50mA*

L

I

= 50mA*

I

= 50mA*

R

L

= 5k

= 1mA*

L

R

L

= 3k

= 1mA*

R = 3.3k

L

R

= 500Ω

= 10mA*

R

L

= 300Ω

R

L

= 330Ω

L

I

= 1mA*

L

I

L

I

= 10mA*

I

= 10mA*

4

5

4

0

1

2

3

5

6

7

8

9

10

0

1

2

3

6

7

8

9

10

0

1

2

3

6

7

8

9

10

5

INPUT VOLTAGE (V)

1761 G21

1761 G22

1761 G23

SHDN Pin Threshold

(On-to-Off)

LT1761-BYP, LT1761-SD

GND Pin Current

GND Pin Current vs I_LOAD

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

2.50

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0

2.50

2.25

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0

I

= 1mA

L

V

= V

+ 1V

OUT(NOMINAL)

T = 25°C

IN

J

*FOR V

= 1.22V

OUT

R

L

= 12.2Ω

L

I

= 100mA*

R

L

= 24.4Ω

L

I

= 50mA*

R

L

= 1.22k

L

R

L

= 122Ω

L

I

= 1mA*

I

= 10mA*

40

50 60 70 80 90 100

0

10 20 30

4

–50

0

25

50

75

125

0

1

2

3

5

6

7

8

9

10

–25

100

TEMPERATURE (°C)

OUTPUT CURRENT (mA)

INPUT VOLTAGE (V)

1761 G25

1761 G24

1761 G26

1761sfc

9

LT1761 Series

U W

TYPICAL PERFOR A CE CHARACTERISTICS

SHDN Pin Threshold

(Off-to-On)

SHDN Pin Input Current

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

V

= 20V

SHDN

I

= 100mA

L

I

= 1mA

L

–50

0

25

50

75 100 125

–50

–25

0

25

50

75 100 125

–25

4

0

1

2

3

5

6

7

8

9

10

TEMPERATURE (°C)

SHDN PIN VOLTAGE (V)

1761 G27

1761 G29

1761 G28

Current Limit

ADJ Pin Bias Current

100

90

80

70

60

50

40

30

20

10

0

350

300

250

200

150

100

50

350

300

250

200

150

100

50

V

T

= 0V

V

= 7V

OUT

J

IN

= 25°C

= 0V

0

–50

0

25

50

75 100 125

0

1

2

3

4

5

6

7

–50

–25

0

25

50

75 100 125

–25

TEMPERATURE (°C)

INPUT VOLTAGE (V)

TEMPERATURE (°C)

1761 G30

1761 G31

1761 G32

Reverse Output Current

Input Ripple Rejection

80

70

60

50

40

30

20

10

0

25.0

22.5

100

V

= 0V

T = 25°C

IN

CURRENT FLOWS

INTO OUTPUT PIN

LT1761-BYP

LT1761-SD

IN

I

= 100mA

J

L

V

= 1.22V (LT1761-BYP, -SD)

= 1.2V (LT1761-1.2)

= 1.5V (LT1761-1.5)

= 1.8V (LT1761-1.8)

= 2V (LT1761-2)

OUT

90 V = 0V

= V

+

IN

OUT(NOMINAL)

LT1761-BYP

LT1761-5

1V + 50mV

C

RIPPLE

RMS

V

80

70

60

50

40

30

20

10

0

20.0 OUT

= 0

V

OUT

V

OUT

V

OUT

V

OUT

V

OUT

V

OUT

V

OUT

BYP

LT1761-1.2

V

= V

OUT

ADJ

17.5

15.0

12.5

10.0

7.5

(LT1761-BYP,-SD)

= 2.5V (LT1761-2.5)

= 2.8V (LT1761-2.8)

= 3V (LT1761-3)

LT1761-1.5

LT1761-1.8

LT1761-2

C

= 10μF

OUT

= 3.3V (LT1761-3.3)

= 5V (LT1761-5)

LT1761-2.5

LT1761-2.8

LT1761-3

LT1761-BYP,-SD

5.0

C

OUT

= 1μF

LT1761-1.2,-1.5,-1.8,-2,

-2.5,-2.8,-3,-3.3,-5

LT1761-3.3

2.5

LT1761-5

0

–50

10

100

1k

10k

100k

1M

4

0

1

2

3

5

6

7

8

9

10

0

25

50

75 100 125

–25

FREQUENCY (Hz)

TEMPERATURE (°C)

OUTPUT VOLTAGE (V)

1761 G35

1761 G33

1761 G34

1761sfc

10

LT1761 Series

U W

TYPICAL PERFOR A CE CHARACTERISTICS

LT1761-5

Input Ripple Rejection

LT1761-BYP, LT1761-SD

Minimum Input Voltage

Input Ripple Rejection

80

70

60

50

40

30

20

10

0

2.5

2.0

1.5

1.0

0.5

0

80

70

60

50

40

30

20

10

0

C

= 0.01μF

BYP

C

= 1000pF

BYP

I

= 100mA

L

I

= 50mA

L

C

BYP

= 100pF

V

= V

+

I

= 100mA

= V

IN

OUT (NOMINAL)

P-P

L

IN

1V + 0.5V RIPPLE

V

+

OUT(NOMINAL)

AT f = 120Hz

1V + 50mV

RIPPLE

RMS

I

= 50mA

C

= 10μF

L

OUT

10

100

1k

10k

100k

1M

–25

0

25

50

75

125

–50

0

25

50

75

125

–50

100

–25

FREQUENCY (Hz)

TEMPERATURE (°C)

1761 G36

1761 G37

1761 G38

Load Regulation

ΔI_L= 1mA to 50mA

Load Regulation

ΔI_L= 1mA to 100mA

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

LT1761-BYP, -SD, -1.2

LT1761-1.5

LT1761-BYP, -SD, -1.2

LT1761-1.5

LT1761-1.8

LT1761-2

–5

–10

–15

–20

–25

–30

–35

–40

LT1761-1.8

LT1761-2

LT1761-2.5

LT1761-2.8

LT1761-3

LT1761-2.5

LT1761-2.8

LT1761-3

LT1761-3.3

LT1761-5

–25

0

25

50

75

125

–25

0

25

50

75

125

–50

100

–50

100

TEMPERATURE (°C)

1761 G39

1761 G40

RMS Output Noise vs

Bypass Capacitor

Output Noise Spectral Density

140

120

100

80

10

C

L

= 10μF

OUT

LT1761-5

LT1761-3.3

LT1761-3

LT1761-2.8

LT1761-2.5

I

= 100mA

LT1761-3.3

f = 10Hz TO 100kHz

LT1761-2.8,-3

LT1761-2.5

LT1761-5

C

= 1000pF

BYP

1

0.1

C

= 100pF

BYP

LT1761-BYP,

-SD, 1.2

60

LT1761-BYP

LT1761-1.5

0.1

LT1761-1.8

LT1761-2

C

BYP

= 0.01μF

40

LT1761-1.8, -2

100

C

L

= 10μF

= 0

= 100mA

OUT

BYP

20

C

L

= 10μF

LT1761-1.5

OUT

LT1761-BYP, -1.2

I = 100mA

I

0

0.01

10

1k

10k

10

100

1k

FREQUENCY (Hz)

10k

100k

10

100

1k

FREQUENCY (Hz)

10k

100k

C

(pF)

BYP

1761 G43

1761 G41

1761 G42

1761sfc

11

LT1761 Series

U W

TYPICAL PERFOR A CE CHARACTERISTICS

LT1761-5

10Hz to 100kHz Output Noise

C_BYP= 100pF

LT1761-5

10Hz to 100kHz Output Noise

C_BYP= 0

RMS Output Noise vs

Load Current (10Hz to 11kHz)

160

140

120

100

80

C

= 10μF

OUT

C

= 0

BYP

C

= 0.01μF

BYP

LT1761-5

V_OUT

100μV/DIV

V_OUT

100μV/DIV

LT1761-BYP

LT1761-5

60

40

1ms/DIV

C_OUT= 10μF

I_L= 100mA

1ms/DIV

20

C

_OUT= 10μF

LT1761-BYP

10 100

1761 G46

I_L= 100mA

1761 G45

0

0.01

0.1

1

LOAD CURRENT (mA)

1761 G44

LT1761-5

10Hz to 100kHz Output Noise

C_BYP= 1000pF

C_BYP= 0.01μF

V_OUT

100μV/DIV

V_OUT

100μV/DIV

1ms/DIV

C_OUT= 10μF

I_L= 100mA

C_OUT= 10μF

I_L= 100mA

1761 G47

1761 G48

LT1761-5 Transient Response

C_BYP= 0

LT1761-5 Transient Response

C_BYP= 0.01μF

V

C

= 6V

IN

V

C

= 6V

IN

0.04

0.02

0

0.2

0.1

= 10μF

OUT

= 10μF

OUT

0

–0.02

–0.04

–0.1

–0.2

100

50

0

100

50

0

80

0

20 40 60

100 120 140 160 180 200

800

TIME (μs)

0

400

1200

1600

2000

TIME (μs)

1761 G50

1761 G49

1761sfc

12

LT1761 Series

U

PI FU CTIO S

IN (Pin 1): Input. Power is supplied to the device through

the IN pin. A bypass capacitor is required on this pin 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 advisable to include a

bypass capacitor in battery-powered circuits. A bypass

capacitor in the range of 1μF to 10μF is sufficient. The

LT1761 regulators are designed to withstand reverse

voltages on the IN pin with respect to ground and the OUT

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

battery is plugged in backwards, the device will act as if

there is a diode in series with its input. There will be no

reverse current flow into the regulator and no reverse

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

itself and the load.

function if the SHDN pin is not connected. For the

LT1761-BYP, the SHDN pin is internally connected to V_IN.

BYP (Pins 3/4, Fixed/-BYP Devices): Bypass. The BYP

pin is used to bypass the reference of the LT1761 regula-

tors to achieve low noise performance from the regulator.

The BYP pin is clamped internally to 0.6V (one V_BE) from

ground. A small capacitor from the output to this pin will

bypass the reference to lower the output voltage noise. A

maximumvalueof0.01μFcanbeusedforreducingoutput

voltage noise to a typical 20μV_RMSover a 10Hz to 100kHz

bandwidth. If not used, this pin must be left unconnected.

ADJ (Pin 4, Adjustable Devices Only): Adjust Pin. For the

adjustable LT1761, this is the input to the error amplifier.

This pin is internally clamped to 7V. It has a bias current

of30nAwhichflowsintothepin(seecurveofADJPinBias

Current vs Temperature in the Typical Performance Char-

acteristicssection).TheADJpinvoltageis1.22Vreferenced

to ground and the output voltage range is 1.22V to 20V.

GND (Pin 2): Ground.

SHDN (Pin 3, Fixed/-SD Devices): Shutdown. The SHDN

pin is used to put the LT1761 regulators into a low power

shutdown state. The output will be off when the SHDN pin

is pulled low. The SHDN pin can be driven either by 5V

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

pull-up resistor is required to supply the pull-up current of

the open-collector gate, normally several microamperes,

and the SHDN pin current, typically 1μA. If unused, the

SHDN pin must be connected to V_IN. The device will not

OUT (Pin 5): Output. The output supplies power to the

load. A minimum output capacitor of 1μF is required to

prevent oscillations. Larger output capacitors will be

required for applications with large transient loads to limit

peak voltage transients. See the Applications Information

section for more information on output capacitance and

reverse output characteristics.

1761sfc

13

LT1761 Series

W U U

U

APPLICATIO S I FOR ATIO

TheLT1761seriesare100mAlowdropoutregulatorswith

micropowerquiescentcurrentandshutdown.Thedevices

are capable of supplying 100mA at a dropout voltage of

300mV. Output voltage noise can be lowered to 20μV_RMS

over a 10Hz to 100kHz bandwidth with the addition of a

0.01μFreferencebypasscapacitor. Additionally, therefer-

ence bypass capacitor will improve transient response of

the regulator, lowering the settling time for transient load

conditions. The low operating quiescent current (20μA)

drops to less than 1μA in shutdown. In addition to the low

quiescentcurrent, theLT1761regulatorsincorporatesev-

eral protection features which make them ideal for use in

battery-powered systems. The devices are protected

against both reverse input 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 LT1761-X acts like it has a diode in series with its

output and prevents reverse current flow. Additionally, in

dual supply applications where the regulator load is

returned to a negative supply, the output can be pulled

below ground by as much as 20V and still allow the device

to start and operate.

pinbiascurrent.Notethatinshutdowntheoutputisturned

off and the divider current will be zero. Curves of ADJ

Pin Voltage vs Temperature and ADJ Pin Bias Current

vs Temperature appear in the Typical Performance

Characteristics.

The adjustable device is tested and specified with the ADJ

pin tied to the OUT pin for an output voltage of 1.22V.

Specifications for output voltages greater than 1.22V will

be proportional to the ratio of the desired output voltage to

1.22V: V_OUT/1.22V. For example, load regulation for an

output current change of 1mA to 100mA is –1mV typical

at V_OUT= 1.22V. At V_OUT= 12V, load regulation is:

(12V/1.22V)(–1mV) = –9.8mV

Bypass Capacitance and Low Noise Performance

The LT1761 regulators may be used with the addition of a

bypass capacitor from V_OUTto the BYP pin to lower output

voltage noise. A good quality low leakage capacitor is rec-

ommended. This capacitor will bypass the reference of the

regulator, providing a low frequency noise pole. The noise

pole provided by this bypass capacitor will lower the out-

put voltage noise to as low as 20μV_RMSwith the addition

ofa0.01μFbypasscapacitor.Usingabypasscapacitorhas

theaddedbenefitofimprovingtransientresponse.Withno

bypass capacitor and a 10μF output capacitor, a 10mA to

100mA load step will settle to within 1% of its final value

in less than 100μs. With the addition of a 0.01μF bypass

capacitor, the output will stay within 1% for a 10mA to

100mA load step (see LT1761-5 Transient Response in

Typical Performance Characteristics section). However,

regulator start-up time is inversely proportional to the size

of the bypass capacitor, slowing to 15ms with a 0.01μF

bypass capacitor and 10μF output capacitor.

Adjustable Operation

The adjustable version of the LT1761 has an output

voltage range of 1.22V to 20V. The output voltage is set by

theratiooftwoexternalresistorsasshowninFigure1.The

device servos the output to maintain the ADJ pin voltage

at 1.22V referenced to ground. The current in R1 is then

equalto1.22V/R1andthecurrentinR2isthecurrentinR1

plus the ADJ pin bias current. The ADJ pin bias current,

30nA at 25°C, flows through R2 into the ADJ pin. The

output voltage can be calculated using the formula in

Figure 1. The value of R1 should be no greater than 250k

to minimize errors in the output voltage caused by the ADJ

IN

OUT

ADJ

V

OUT

⎛

⎞

⎟

R2

R1

V

= 1.22V 1+

+ I

(

R2

+

)(

)

OUT

ADJ

⎜

V

IN

⎝

⎠

R2

R1

LT1761

GND

V

= 1.22V

ADJ

I

= 30nA AT 25°C

ADJ

OUTPUT RANGE = 1.22V TO 20V

1761 F01

Figure 1. Adjustable Operation

1761sfc

14

LT1761 Series

W U U

APPLICATIO S I FOR ATIO

U

bypass capacitor or larger, a 3.3μF output capacitor is

recommended. The shaded region of Figure 2 defines the

region over which the LT1761 regulators are stable. The

minimumESRneededisdefinedbytheamountofbypass

capacitance used, while the maximum ESR is 3Ω.

Output Capacitance and Transient Response

The LT1761 regulators are designed to be stable with a

wide range of output capacitors. The ESR of the output

capacitor affects stability, most notably with small

capacitors. A minimum output capacitor of 1μF with an

ESR of 3Ω or less is recommended to prevent oscilla-

tions. The LT1761-X is a micropower device and output

transient response will be a function of output capaci-

tance. Larger values of output capacitance decrease the

peakdeviationsandprovideimprovedtransientresponse

for larger load current changes. Bypass capacitors, used

to decouple individual components powered by the

LT1761-X, will increase the effective output capacitor

value. With larger capacitors used to bypass the refer-

ence (for low noise operation), larger values of output

capacitors are needed. For 100pF of bypass capacitance,

2.2μF of output capacitor is recommended. With a 330pF

Extra consideration must be given to the use of ceramic

capacitors. Ceramic capacitors are manufactured with a

variety of dielectrics, each with different behavior across

temperature and applied voltage. The most common

dielectricsusedarespecifiedwithEIAtemperaturecharac-

teristiccodesofZ5U, Y5V, X5RandX7R. TheZ5UandY5V

dielectrics are good for providing high capacitances in a

small package, but they tend to have strong voltage and

temperature coefficients as shown in Figures 3 and 4.

When used with a 5V regulator, a 16V 10μF Y5V capacitor

can exhibit an effective value as low as 1μF to 2μF for the

DC bias voltage applied and over the operating tempera-

ture range. The X5R and X7R dielectrics result in more

stable characteristics and are more suitable for use as the

output capacitor. The X7R type has better stability across

temperature, while the X5R is less expensive and is avail-

able in higher values. Care still must be exercised when

using X5R and X7R capacitors; the X5R and X7R codes

only specify operating temperature range and maximum

capacitancechangeovertemperature.Capacitancechange

due to DC bias with X5R and X7R capacitors is better than

Y5VandZ5Ucapacitors,butcanstillbesignificantenough

to drop capacitor values below appropriate levels. Capaci-

tor DC bias characteristics tend to improve as component

case size increases, but expected capacitance at operating

voltage should be verified.

4.0

3.5

3.0

STABLE REGION

2.5

2.0

C

= 0

1.5

1.0

0.5

0

BYP

C

= 100pF

BYP

C

= 330pF

BYP

C

> 3300pF

BYP

1

3

6 9 10

7 8

2

4

5

OUTPUT CAPACITANCE (μF)

1761 F02

Figure 2. Stability

40

20

0

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

X5R

0

–20

–40

–60

–80

–100

–40

Y5V

–60

Y5V

–80

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10μF

–100

50

TEMPERATURE (°C)

100 125

–50 –25

0

25

75

0

8

12 14

2

4

6

10

16

DC BIAS VOLTAGE (V)

1761 F04

1761 F03

Figure 3. Ceramic Capacitor DC Bias Characteristics

Figure 4. Ceramic Capacitor Temperature Characteristics

1761sfc

15

LT1761 Series

U

W U U

APPLICATIONS INFORMATION

Voltage and temperature coefficients are not the only

sources of problems. Some ceramic capacitors have a

piezoelectric response. A piezoelectric device generates

voltage across its terminals due to mechanical stress,

similar to the way a piezoelectric accelerometer or

microphone works. For a ceramic capacitor the stress

can be induced by vibrations in the system or thermal

transients. The resulting voltages produced can cause

appreciable amounts of noise, especially when a ceramic

capacitor is used for noise bypassing. A ceramic capaci-

tor produced Figure 5’s trace in response to light tapping

from a pencil. Similar vibration induced behavior can

masquerade as increased output voltage noise.

The LT1761 series regulators have internal thermal limit-

ing designed to protect the device during overload condi-

tions. For continuous normal conditions, the maximum

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.

For surface mount devices, heat sinking 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.

Thermal Considerations

The following table lists thermal resistance for several

different board sizes and copper areas. All measurements

were taken in still air on 3/32" FR-4 board with one ounce

copper.

The power handling capability of the device will be limited

by the maximum rated junction temperature (125°C). The

power dissipated by the device will be made up of two

components:

Table 1. Measured Thermal Resistance

COPPER AREA

THERMAL RESISTANCE

1. Output current multiplied by the input/output voltage

differential: (I_OUT)(V_IN– V_OUT), and

TOPSIDE*

2500mm²

1000mm²

225mm²

100mm²

50mm²

BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)

2500mm²

125°C/W

130°C/W

135°C/W

150°C/W

2. GND pin current multiplied by the input voltage:

(I_GND)(V_IN).

The ground pin current can be found by examining the

GND Pin Current curves in the Typical Performance Char-

acteristics section. Power dissipation will be equal to the

sum of the two components listed above.

*Device is mounted on topside.

LT1761-5

C

_OUT= 10μF

C_BYP= 0.01μF

I_LOAD= 100mA

V_OUT

500μV/DIV

100ms/DIV

1761 F05

Figure 5. Noise Resulting from Tapping on a Ceramic Capacitor

1761sfc

16

LT1761 Series

W U U

U

APPLICATIO S I FOR ATIO

Calculating Junction Temperature

Protection Features

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

rangeof4Vto6V, anoutputcurrentrangeof0mAto50mA

and a maximum ambient temperature of 50°C, what will

the maximum junction temperature be?

The LT1761 regulators incorporate several protection

featureswhichmakethemidealforuseinbattery-powered

circuits. In addition to the normal protection features

associated with monolithic regulators, such as current

limiting and thermal limiting, the devices are protected

against reverse input voltages, reverse output voltages

and reverse voltages from output to input.

The power dissipated by the device will be equal to:

I_OUT(MAX)(V_IN(MAX)– V_OUT) + I_GND(V_IN(MAX)

)

where,

Current limit protection and thermal overload protection

are intended to protect the device against current overload

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

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

I_OUT(MAX)= 50mA

V_IN(MAX)= 6V

I_GNDat (I_OUT= 50mA, V_IN= 6V) = 1mA

So,

The input of the device will withstand reverse voltages of

20V. 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

which can be plugged in backward.

P = 50mA(6V – 3.3V) + 1mA(6V) = 0.14W

The thermal resistance will be in the range of 125°C/W to

150°C/W depending on the copper area. So the junction

temperature rise above ambient will be approximately

equal to:

The output of the LT1761-X can be pulled below ground

without damaging the device. If the input is left open

circuitorgrounded,theoutputcanbepulledbelowground

by 20V. For fixed voltage versions, the output will act

like a large resistor, typically 500kΩ or higher, limiting

current flow to typically less than 100μA. For adjustable

versions, 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 short-circuit

current of the device and will protect itself by thermal

limiting. In this case, grounding the SHDN pin will turn

off the device and stop the output from sourcing the

short-circuit current.

0.14W(150°C/W) = 21.2°C

The maximum junction temperature will then be equal to

the maximum junction temperature rise above ambient

plus the maximum ambient temperature or:

T_JMAX= 50°C + 21.2°C = 71.2°C

The ADJ pin of the adjustable device can be pulled above

or below ground by as much as 7V without damaging the

device. If the input is left open circuit or grounded, the ADJ

pin will act like an open circuit when pulled below ground

and like a large resistor (typically 100k) in series with a

diode when pulled above ground.

In situations where the ADJ pin is connected to a resistor

divider that would pull the ADJ pin above its 7V clamp

voltage if the output is pulled high, the ADJ pin input

current must be limited to less than 5mA. For example, a

resistor divider is used to provide a regulated 1.5V output

1761sfc

17

LT1761 Series

W U U

U

APPLICATIO S I FOR ATIO

fromthe1.22Vreferencewhentheoutputisforcedto20V. circuit. Current flow back into the output will follow the

The top resistor of the resistor divider must be chosen to curve shown in Figure 6.

limitthecurrentintotheADJpintolessthan5mAwhenthe

When the IN pin of the LT1761-X is forced below the OUT

ADJ pin is at 7V. The 13V difference between output and

pin or the OUT pin is pulled above the IN pin, input current

ADJpindividedbythe5mAmaximumcurrentintotheADJ

will typically drop to less than 2μA. This can happen if the

input of the device is connected to a discharged (low

pin yields a minimum top resistor value of 2.6k.

In circuits where a backup battery is required, several voltage) battery and the output is held up by either a

different input/output conditions can occur. The output backup battery or a second regulator circuit. The state of

voltage may be held up while the input is either pulled to the SHDN pin will have no effect on the reverse output

ground, pulledtosomeintermediatevoltageorisleftopen current when the output is pulled above the input.

100

T = 25°C

IN

CURRENT FLOWS

INTO OUTPUT PIN

LT1761-BYP

LT1761-SD

J

90 V = 0V

80

70

60

50

40

30

20

10

0

LT1761-1.2

V

= V

OUT

ADJ

(LT1761-BYP,-SD)

LT1761-1.5

LT1761-1.8

LT1761-2

LT1761-2.5

LT1761-2.8

LT1761-3

LT1761-3.3

LT1761-5

4

0

1

2

3

5

6

7

8

9

10

OUTPUT VOLTAGE (V)

1761 F06

Figure 6. Reverse Output Current

1761sfc

18

LT1761 Series

U

PACKAGE DESCRIPTIO

S5 Package

5-Lead Plastic TSOT-23

(LTC DWG # 05-08-1635)

0.62

MAX

0.95

REF

2.90 BSC

(NOTE 4)

1.22 REF

1.50 – 1.75

(NOTE 4)

2.80 BSC

1.4 MIN

3.85 MAX 2.62 REF

PIN ONE

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

0.30 – 0.45 TYP

5 PLCS (NOTE 3)

0.95 BSC

0.80 – 0.90

0.20 BSC

DATUM ‘A’

0.01 – 0.10

1.00 MAX

0.30 – 0.50 REF

1.90 BSC

0.09 – 0.20

(NOTE 3)

NOTE:

S5 TSOT-23 0302 REV B

1. DIMENSIONS ARE IN MILLIMETERS

2. DRAWING NOT TO SCALE

3. DIMENSIONS ARE INCLUSIVE OF PLATING

4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR

5. MOLD FLASH SHALL NOT EXCEED 0.254mm

6. JEDEC PACKAGE REFERENCE IS MO-193

1761sfc

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

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

19

LT1761 Series

RELATED PARTS

PART NUMBER

LT1120

DESCRIPTION

COMMENTS

125mA Low Dropout Regulator with 20μA I

Includes 2.5V Reference and Comparator

Q

LT1121

150mA Micropower Low Dropout Regulator

30μA I , SOT-223 Package

Q

LT1129

700mA Micropower Low Dropout Regulator

50μA Quiescent Current

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

500mV Dropout Voltage

Q

LT1762 Series

LT1763 Series

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LT1963

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Doubler Charge Pump with Low Noise Linear Regulator

300mA, Low Noise, LDO Micropower Regulator

1.5A, Low Noise, Fast Transient Response LDO

3A, Low Noise, Fast Transient Response LDO

25μA Quiescent Current, 20μV

30μA Quiescent Current, 20μV

Noise

RMS

Low Output Noise: 60μV

(100kHz BW)

RMS

30μA Quiescent Current, 20μV

Noise

RMS

40μV

, SOT-223 Package

RMS

LT1764

, 340mV Dropout Voltage

RMS

LTC3404

High Efficiency Synchronous Step-Down Switching Regulator

Burst Mode^TMOperation, Monolithic, 100% Duty Cycle

Burst Mode is a trademark of Linear Technology Corporation.

1761sfc

LT 0507 REV C • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

20

●

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


型号：	LT1761ES5-1.2#TRM
厂家：	Linear
描述：	暂无描述线性稳压器IC 调节器电源电路光电二极管输出元件
文件：	总20页 (文件大小：257K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LT1761ES5-1.2#TRM [Linear]

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