LT3081EFE#PBF - LINEAR TECHNOLOGY

LT3081

3081fc

For more information www.linear.com/LT3081

Typical applicaTion

FeaTures DescripTion

1.5A Single Resistor

Rugged Linear Regulator

with Monitors

The LT

3081 is a 1.5A low dropout linear regulator de-

signed for rugged industrial applications. Key features of

the IC are the extended safe operating area (SOA), output

current monitor, temperature monitor and programmable

current limit. The LT3081 can be paralleled for higher

output current or heat spreading. The device withstands

reverse input and reverse output-to-input voltages without

reverse current flow.

The LT3081’s precision 50µA reference current source

allows a single resistor to program output voltage to

any level between zero and 34.5V. The current reference

architecture makes load regulation independent of output

voltage. The LT3081 is stable with or without input and

output capacitors.

The output current monitor (IOUT/5000) and die junction

temperature output (1µA/°C) provide system monitoring

and debug capability. In addition, a single resistor pro-

grams current limit.

Internal protection circuitry includes reverse-battery and

reverse-current protection, current limiting and thermal

limiting. The LT3081 is offered in the 16-lead TSSOP (with

exposed pad for improved thermal performance), 7-lead

TO-220, 7-lead DD-Pak, and an 12-lead 4mm × 4mm DFN.

Wide Safe Operating Area Supply

applicaTions

n Extended Safe Operating Area

n Maximum Output Current: 1.5A

n Stable with or without Input/Output Capacitors

n Wide Input Voltage Range: 1.2V to 36V

n Single Resistor Sets Output Voltage

n Output Current Monitor: IMON = IOUT/5000

n Junction Temperature Monitor: 1µA/°C

n Output Adjustable to 0V

n 50µA SET Pin Current: 1% Initial Accuracy

n Output Voltage Noise: 27µVRMS

n Parallel Multiple Devices for Higher Current or

Heat Spreading

n Programmable Current Limit

n Reverse-Battery and Reverse-Current Protection

n <1mV Load Regulation Typical Independent of VOUT

n <0.001%/V Line Regulation Typical

n Available in Thermally-Enhanced 12-Lead 4mm × 4mm

DFN and 16-Lead TSSOP, 7-Lead DD-Pak and 7-Lead

TO-220

n All Surface Mount Power Supply

n Rugged Industrial Power Supply

n Post Regulator for Switching Supplies

n Low Output Voltage Supply

n Intrinsic Safety Applications

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

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

TEMPERATURE (°C)

–50

49.5

SET PIN CURRENT (µA)

49.6

49.8

49.9

50.0

50.5

50.2

050 75

3081 TA01b

49.7

50.3

50.4

50.1

–25 25 100 125 150

IL = 5mA

SET Pin Current

3081 TA01a

1k 4.53k

10µF*

*OPTIONAL

IMON ILIM

OUT

–

LT3081

ILOAD/5000

IOUT

1.5V

VIN

300Ω*

1µA/°C

SET

30.1k

TEMP

50µA

LT3081

3081fc

For more information www.linear.com/LT3081

absoluTe MaxiMuM raTings

IN Pin to OUT Pin Differential Voltage .....................±40V

SET Pin Current (Note 6) .....................................±25mA

SET Pin Voltage (Relative to OUT, Note 6) .............. ±10V

TEMP Pin Voltage (Relative to OUT) .................1V, –40V

ILIM Pin Voltage (Relative to OUT) .........................±0.2V

IMON Pin Voltage (Relative to OUT) ...................1V, –40V

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

(Note 1) All Voltages Relative to VOUT.

TOP VIEW

OUT

DF PACKAGE

12-LEAD (4mm × 4mm) PLASTIC DFN

1IN

TEMP

IMON

OUT

ILIM

SET 67

TJMAX = 125°C, θJA = 32°C/W, θJC = 4°C/W

EXPOSED PAD (PIN 13) IS OUT, MUST BE SOLDERED TO PCB

FE PACKAGE

16-LEAD PLASTIC TSSOP

TOP VIEW

OUT

LIM

SET

OUT

TEMP

IMON

OUT

TJMAX = 150°C, θJA = 29°C/W, θJC = 8°C/W

EXPOSED PAD (PIN 17) IS OUT, MUST BE SOLDERED TO PCB

R PACKAGE

7-LEAD PLASTIC DD

FRONT VIEW

TAB IS

OUT

TEMP

OUT

IMON

SET

ILIM

TJMAX = 125°C, θJA = 15°C/W, θJC = 3°C/W

T7 PACKAGE

7-LEAD PLASTIC TO-220

TAB IS

OUT

TEMP

OUT

IMON

SET

ILIM

FRONT VIEW

TJMAX = 150°C, θJA = 40°C/W, θJC = 3°C/W

pin conFiguraTion

Operating Junction Temperature Range (Note 2)

E-, I-Grades ....................................... –40°C to 125°C

H-Grade ............................................. –40°C to 150°C

MP-Grade .......................................... –55°C to 150°C

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

Lead Temperature (Soldering, 10 sec)

FE, R, T7 Packages Only ...................................300°C

LT3081

3081fc

For more information www.linear.com/LT3081

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TJ = 25°C. (Note 2)

elecTrical characTerisTics

orDer inForMaTion

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LT3081EDF#PBF LT3081EDF#TRPBF 3081 12-Lead (4mm × 4mm) Plastic DFN –40°C to 125°C

LT3081IDF#PBF LT3081IDF#TRPBF 3081 12-Lead (4mm × 4mm) Plastic DFN –40°C to 125°C

LT3081EFE#PBF LT3081EFE#TRPBF 3081FE 16-Lead Plastic TSSOP –40°C to 125°C

LT3081IFE#PBF LT3081IFE#TRPBF 3081FE 16-Lead Plastic TSSOP –40°C to 125°C

LT3081HFE#PBF LT3081HFE#TRPBF 3081FE 16-Lead Plastic TSSOP –40°C to 150°C

LT3081MPFE#PBF LT3081MPFE#TRPBF 3081FE 16-Lead Plastic TSSOP –55°C to 150°C

LT3081ER#PBF LT3081ER#TRPBF LT3081R 7-Lead Plastic DD-Pak –40°C to 125°C

LT3081IR#PBF LT3081IR#TRPBF LT3081R 7-Lead Plastic DD-Pak –40°C to 125°C

LT3081ET7#PBF NA LT3081T7 7-Lead Plastic TO-220 –40°C to 125°C

LT3081IT7#PBF NA LT3081T7 7-Lead Plastic TO-220 –40°C to 125°C

LT3081HT7#PBF NA LT3081T7 7-Lead Plastic TO-220 –40°C to 150°C

LT3081MPT7#PBF NA LT3081T7 7-Lead Plastic TO-220 –55°C to 150°C

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

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

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

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

PARAMETER CONDITIONS MIN TYP MAX UNITS

SET Pin Current ISET VIN = 2V, ILOAD = 5mA

2V ≤ VIN ≤ 36V, 5mA ≤ ILOAD ≤ 1.5A

49.5

48.75

50.5

51.25

µA

Offset Voltage VOS

(VOUT – VSET)

VIN = 2V, ILOAD = 5mA

–1.5

–3.5

1.5

3.5

ISET Load Regulation ∆ILOAD = 5mA to 1.5A –0.1 nA

VOS Load Regulation ∆ILOAD = 5mA to 1.5A

(Note 7)

DF, FE Packages l–0.5 –3 mV

R, T7 Packages l–1.5 –4 mV

Line Regulation ∆ISET

∆VOS

∆VIN = 2V to 36V, ILOAD = 5mA

1.5

0.001

nA/V

mV/V

Minimum Load Current (Note 3) 2V ≤ VIN ≤ 36V l1.1 5 mA

Dropout Voltage (Note 4) ILOAD = 100mA

ILOAD = 1.5A

1.21

1.23

1.5

Internal Current Limit VIN = 5V, VSET = 0V, VOUT = –0.1V l1.5 2 A

ILIM Programming Ratio l300 360 500 mA/kΩ

ILIM Minimum Output Current Resistance 450 Ω

IMON Full-Scale Output Current ILOAD = 1.5A 290 300 330 µA

IMON Scale Factor 100mA ≤ ILOAD ≤ 1.5A 200 µA/A

IMON Operating Range lVOUT – 40V VOUT + 0.4V V

LT3081

3081fc

For more information www.linear.com/LT3081

elecTrical characTerisTics

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TJ = 25°C. (Note 2)

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: Unless otherwise specified, all voltages are with respect to VOUT.

The LT3081 is tested and specified under pulse load conditions such

that TJ ≈ TA. The LT3081E is tested at TA = 25°C and performance is

guaranteed from 0°C to 125°C. Performance of the LT3081E over the

full –40°C and 125°C operating temperature range is assured by design,

characterization, and correlation with statistical process controls. The

LT3081I is guaranteed over the full –40°C to 125°C operating junction

temperature range. The LT3081MP is 100% tested and guaranteed

over the –55°C to 150°C operating junction temperature range. The

LT3081H is tested at 150°C operating junction temperature. High junction

temperatures degrade operating lifetimes. Operating lifetime is degraded at

junction temperatures greater than 125°C.

Note 3: Minimum load current is equivalent to the quiescent current of

the part. Since all quiescent and drive current is delivered to the output

of the part, the minimum load current is the minimum current required to

maintain regulation.

Note 4: For the LT3081, dropout is specified as the minimum input-to-

output voltage differential required supplying a given output current.

Note 5: Adding a small capacitor across the reference current resistor

lowers output noise. Adding this capacitor bypasses the resistor shot

noise and reference current noise; output noise is then equal to error

amplifier noise (see Applications Information section).

Note 6: Diodes with series 400Ω resistors clamp the SET pin to the

OUT pin. These diodes and resistors only carry current under transient

overloads.

Note 7: Load regulation is Kelvin sensed at the package.

Note 8: This IC includes overtemperature protection that protects the

device during momentary overload conditions. Junction temperature

exceeds the maximum operating junction temperature when

overtemperature protection is active. Continuous operation above the

specified maximum operating junction temperature may impair device

reliability.

Note 9: The TEMP pin output current represents the average die junction

temperature. Due to power dissipation and thermal gradients across the

die, the TEMP pin output current measurement does not guarantee that

absolute maximum junction temperature is not exceeded.

PARAMETER CONDITIONS MIN TYP MAX UNITS

TEMP Output Current (Note 9) TJ > 5°C 1 µA/°C

TEMP Output Current Absolute Error (Note 9) 0°C <TJ ≤ 125°C

125°C <TJ ≤ 150°C

–10

–15

µA

Reference Current RMS Output Noise (Note 5) 10Hz ≤ f ≤ 100kHz 5.7 nARMS

Error Amplifier RMS Output Noise (Note 5) ILOAD = 1.5A, 10Hz ≤ f ≤ 100kHz, COUT =10µF,

CSET = 0.1µF

27 µVRMS

Ripple Rejection

VRIPPLE = 0.5VP-P, ILOAD = 0.1A, CSET = 0.1µF,

COUT=10µF, VIN = VOUT(NOMINAL) + 3V

f = 120Hz

f = 10kHz

f = 1MHz

75 90

Thermal Regulation, ISET 10ms Pulse 0.003 %/W

LT3081

3081fc

For more information www.linear.com/LT3081

Typical perForMance characTerisTics

Offset Voltage Offset Voltage (VOUT – VSET) Offset Voltage (VOUT – VSET)

Load Regulation Minimum Load Current Dropout Voltage

SET Pin Current SET Pin Current

TJ = 25°C unless otherwise specified.

Offset Voltage (VOUT – VSET)

TEMPERATURE (°C)

–50

49.5

SET PIN CURRENT (µA)

49.6

49.8

49.9

50.0

50.5

50.2

050 75

3081 G01

49.7

50.3

50.4

50.1

–25 25 100 125 150

ILOAD = 5mA

SET PIN CURRENT DISTRIBUTION (µA)

N = 3195

49.5 50

3081 G02

50.5 51

TEMPERATURE (°C)

–50

OFFSET VOLTAGE (mV)

1.0

150

3081 G03

–1.0

–2.0 050 100

–25 25 75 125

2.0

–0.5

0.5

–1.5

1.5

ILOAD = 5mA

VOS DISTRIBUTION (mV)

–2

N = 3195

–1 0

3081 G04

1 2

INPUT-TO-OUTPUT DIFFERENTIAL (V)

–1.0

OFFSET VOLTAGE (mV)

–0.6

–0.2

0.2

612 18 24

3081 G05

0.6

1.0

–0.8

–0.4

0.4

0.8

ILOAD = 5mA

LOAD CURRENT (A)

OFFSET VOLTAGE (mV)

–0.6

3081 G06

–1.0

–1.4 0.5 1

0.25 0.75 1.25

–0.2

0.2

–0.8

–1.2

–0.4

1.5

TJ = 25°C

TJ = 125°C

TEMPERATURE (°C)

–50

SET PIN CURRENT LOAD REGULATION (nA)

OFFSET VOLTAGE LOAD REGULATION (mV)

100

150

200

0 50 100 150

3081 G07

250

300

–3.0

–2.5

–2.0

–1.5

–1.0

–0.5

–25 25 75 125

∆ILOAD = 5mA TO 1.5A

TEMPERATURE (°C)

–50

MINIMUM LOAD CURRENT (mA)

0.5

1.0

1.5

2.0

0 50 100 150

3081 G08

2.5

3.0

–25 25 75 125

VIN – VOUT = 36V

VIN – VOUT = 2V

LOAD CURRENT (A)

1.0

DROPOUT VOLTAGE (V)

1.1

1.2

1.3

1.4

1.5

0.25 0.5 0.75 1

3081 G09

1.25 1.5

TJ = –50°C

TJ = 25°C

TJ = 125°C

LT3081

3081fc

For more information www.linear.com/LT3081

TO-220 Package Maximum Power

Dissipation Programmable Current Limit Programmable Current Limit

Programmable Current Limit TEMP Pin Current IMON Pin Current

Dropout Voltage Internal Current Limit Internal Current Limit

TEMPERATURE (°C)

–50

DROPOUT VOLTAGE (V)

1.3

1.4

1.5

25 75 150

3081 G10

1.2

1.1

1.0 –25 0 50 100

ILOAD = 1.5A

ILOAD = 5mA

125

TEMPERATURE (°C)

–50

CURRENT LIMIT (A)

0.5

1.0

1.5

2.0

0 50 100 150

3081 G11

2.5

3.0

–25 25 75 125

VIN = 7V

VOUT = 0V

INPUT-TO-OUTPUT DIFFERENTIAL VOLTAGE (V)

CURRENT LIMIT (A)

0.4

0.8

1.2

612 18 24

3081 G12

1.6

2.0

0.2

0.6

1.0

1.4

1.8

TO-220 AND

DD-PAK

TSSOP

AND DFN

CASE TEMPERATURE (°C)

POWER (W)

150

3081 G13

070 90 110

60 80 100 120 130 140

VIN – VOUT = 20V

LIMITED BY FOLDBACK

CURRENT LIMIT

VIN – VOUT = 10V

VIN – VOUT = 5V

θJC = 3°C/W

RILIM (kΩ)

PROGRAMMED CURRENT LIMIT (A)

0.5

1.0

1.5

2.0

1 2 3 4

3081 G14

5 6

TJ = 25°C

VIN = 7V

VOUT = 0V

OUTPUT CURRENT (A)

OUTPUT VOLTAGE (V)

0.2

0.4

0.6

0.95

1.00

1.05

0.5 1 1.5 2

3081 G15

RILIM

1.5k

RILIM

3.01k

RILIM

4.53k

RSET = 20k

TEMPERATURE (°C)

–50

TEMP PIN CURRENT (µA)

120

150

3081 G16

0050 100

–25 25 75 125

160

100

140

LOAD CURRENT (A)

250

300

350

1.2

3081 G17

200

150

0.3 0.6 0.9 1.5

100

IMON PIN CURRENT (µA)

TEMPERATURE (°C)

–50

PROGRAMMED CURRENT LIMIT (A)

0.8

1.2

150

3081 G39

0.4

0050 100

–25 25 75 125

1.6

0.6

1.0

0.2

1.4 RILIM = 4.53k

RILIM = 3.01k

RILIM = 1.50k

VIN = 7V

VOUT = 0V

Typical perForMance characTerisTics

TJ = 25°C unless otherwise specified.

LT3081

3081fc

For more information www.linear.com/LT3081

Linear Regulator

Load Transient Response

Linear Regulator

Line Transient Response

Current Source

Line Transient Response

Current Source

Line Transient Response

Linear Regulator

Turn-On Response

IMON Pin Line Regulation

Linear Regulator

Load Transient Response

Linear Regulator

Load Transient Response

Linear Regulator

Load Transient Response

INPUT-TO-OUTPUT DIFFERENTIAL VOLTAGE (V)

IMON PIN CURRENT (µA)

612 18 24

3791 TA02b

ILOAD = 200mA

TIME (µs)

OUTPUT VOLTAGE

DEVIATION (mV)

LOAD

CURRENT (mA)

–50

160 180

8081 G19

–100

400

040 80 120

20 200

60 100 140

200

150

100

VIN = 3V

VOUT = 1V

CSET = 0.1µF

COUT = 2.2µF

∆ILOAD = 100mA TO 500mA

TIME (µs)

OUTPUT VOLTAGE

DEVIATION (mV)

LOAD

CURRENT (mA)

–100

100

160 180

3081 G20

–200

2.0

040 80 120

20 200

60 100 140

1.0

300

200

VIN = 3V

VOUT = 1V

CSET = 0.1µF

COUT = 2.2µF

∆ILOAD = 500mA TO 1.5A

TIME (µs)

OUTPUT VOLTAGE

DEVIATION (mV)

LOAD

CURRENT (mA)

–200

–100

40 45

3081 G21

600

400

010 20 30

5 50

15 25 35

200

100

VIN = 3V

VOUT = 1V

CSET = 30pF

COUT = 0

∆ILOAD = 100mA TO 500mA

tr = tf = 1µs

TIME (µs)

OUTPUT VOLTAGE

DEVIATION (mV)

LOAD

CURRENT (mA)

–400

–200

40 45

3081 G22

1.5

1.0

010 20 30

5 50

15 25 35

0.5

400

200

VIN = 3V

VOUT = 1V

CSET = 30pF

COUT = 0

∆ILOAD = 500mA TO 1.5A

tr = tf = 1µs

TIME (µs)

OUTPUT VOLTAGE

DEVIATION (mV) INPUT VOLTAGE (V)

40 45

3081 G23

0.1

–0.2 10 20 30

5 50

15 25 35

–0.1

RSET = 20k

RLOAD = 0.67Ω

COUT = 2.2µF

CSET = 0.1µF

TIME (µs)

OUTPUT CURRENT (mA) INPUT VOLTAGE (V)

40 45

3081 G24

150

100

010 20 30

5 50

15 25 35

RSET = 6.04k

ROUT = 3.01Ω

COUT = 0

CSET = 30pF

100mA CURRENT SOURCE CONFIGURATION

TIME (µs)

OUTPUT CURRENT (A) INPUT VOLTAGE (V)

40 45

3081 G25

1.2

1.0

0.6 10 20 30

5 50

15 25 35

0.8

RSET = 6.04k

ROUT = 0.3Ω

COUT = 0

CSET = 30pF

1A CURRENT SOURCE CONFIGURATION

TIME (µs)

OUTPUT VOLTAGE (V) INPUT VOLTAGE (V)

40 45

3081 G26

1.0

0.5

–0.5 10 20 30

5 50

15 25 35

RSET = 20k

RLOAD = 0.67Ω

COUT = 2.2µF CERAMIC

CSET = 0

Typical perForMance characTerisTics

TJ = 25°C unless otherwise specified.

LT3081

3081fc

For more information www.linear.com/LT3081

Ripple Rejection Ripple Rejection

Output Impedance Ripple Rejection (120Hz)

Residual Output Voltage with

Less Than Minimum Load

Current Source

Turn-On Response

Current Source

Turn-On Response

TIME (µs)

OUTPUT CURRENT (mA) INPUT VOLTAGE (V)

160 180

3081 G28

150

100

040 80 120

20 200

60 100 140

RSET = 6.04k

ROUT = 3.01Ω

COUT = 0

CSET = 20pF

100mA CURRENT SOURCE CONFIGURATION

TIME (µs)

OUTPUT CURRENT (A) INPUT VOLTAGE (V)

160 180

3081 G29

1.5

1.0

040 80 120

20 200

60 100 140

0.5

RSET = 6.04k

ROUT = 0.3Ω

COUT = 0

CSET = 20pF

1A CURRENT SOURCE CONFIGURATION

RTEST (Ω)

OUTPUT VOLTAGE (mV)

400

500

600

2000

3081 G30

300

200

0500 1000 1500

100

800

700

VIN = 36V

VIN = 5V

VOUT

SET PIN = 0V

RTEST

VIN

FREQUENCY (Hz)

10 100

RIPPLE REJECTION (dB)

1k 10k 100k 1M 10M

3081 G31

100

ILOAD = 100mA

ILOAD = 500mA

ILOAD = 1.5A

COUT = 2.2µF CERAMIC

CSET = 0.1µF

VIN = VOUT(NOMINAL) + 2V

FREQUENCY (Hz)

10 100

RIPPLE REJECTION (dB)

1k 10k 100k 1M 10M

3081 G32

100

VIN = VOUT + 5V

VIN = VOUT + 2V

VIN = VOUT + 1.5V

COUT = 2.2µF CERAMIC

CSET = 0.1µF

ILOAD = 100mA

FREQUENCY (Hz)

OUTPUT IMPEDANCE (Ω)

100

10k

100k

10M

100 1k 10k 100k 1M 10M

3081 G33

ISOURCE = 10mA

ISOURCE = 100mA

ISOURCE = 1A

CURRENT SOURCE CONFIGURATION

TEMPERATURE (°C)

–50

RIPPLE REJECTION (dB)

050 75

3081 G34

–25 25 100 125 150

VIN = VOUT(NOMINAL) + 2V

RIPPLE = 500mVP-P

f = 120Hz

ILOAD = 0.1A

COUT = 2.2µF

CSET = 0.1µF

Linear Regulator

Turn-On Response

TIME (ms)

OUTPUT VOLTAGE (V) INPUT VOLTAGE (V)

16 18

3081 G27

1.0

0.5

–0.5 4812

2 20

610 14

RSET = 20k

RLOAD = 0.67Ω

COUT = 2.2µF CERAMIC

CSET = 0.1µF

Typical perForMance characTerisTics

TJ = 25°C unless otherwise specified.

LT3081

3081fc

For more information www.linear.com/LT3081

Noise Spectral Density

10Hz to 100kHz

Output Voltage Noise

Ripple Rejection (10kHz) Ripple Rejection (1MHz)

TEMPERATURE (°C)

–50

RIPPLE REJECTION (dB)

050 75

3081 G34

–25 25 100 125 150

VIN = VOUT(NOMINAL) + 2V

RIPPLE = 500mVP-P

f = 10kHz

ILOAD = 0.1A

COUT = 2.2µF

CSET = 0.1µF

TEMPERATURE (°C)

–50

RIPPLE REJECTION (dB)

150

3081 G36

10 050 100

–25 25 75 125

VIN = VOUT(NOMINAL) + 2V

RIPPLE = 200mVP-P

f = 1MHz

ILOAD = 0.1A

COUT = 2.2µF CERAMIC

CSET = 0.1µF

FREQUENCY (Hz)

ERROR AMPLIFIER NOISE

SPECTRAL DENSITY (nV/√Hz)

REFERENCE CURRENT NOISE

SPECTRAL DENSITY (pA/√Hz)

100

1000

100

1k100 10k 100k

3981 G37

TIME 1ms/DIV

VOUT

50µV/DIV

3081 G38

CSET = 0.1µF

COUT = 4.7µF

ILOAD = 1.5A

NOISE INDEPENDENT

OF OUTPUT VOLTAGE

Typical perForMance characTerisTics

TJ = 25°C unless otherwise specified.

LT3081

3081fc

For more information www.linear.com/LT3081

block DiagraM

–

50µA

IMON

TEMPERATURE

DEPENDENT

CURRENT SOURCE

1µA/°C

SET ILIM OUT

3081 BD

PROGRAMMABLE

CURRENT LIMIT

CURRENT

MONITOR

IMON = ILOAD/5000

TEMP

pin FuncTions

IN: Input. This pin supplies power to regulate internal

circuitry and supply output load current. For the device

to operate properly and regulate, the voltage on this pin

must be between the dropout voltage and 36V above the

OUT pin (depending on output load current, see Dropout

Voltage Specifications).

OUT: Output. This is the power output of the device. The

LT3081 requires a 5mA minimum load current for proper

output regulation.

TEMP: Temperature Output. This pin delivers a current

proportional to the internal average junction temperature.

Current output is 1µA/°C for temperatures above 5°C. The

TEMP pin output current typically equals 25µA at 25°C.

The output of the TEMP pin is valid for voltages from VOUT

+ 0.4V to VOUT – 40V. If unused, connect this pin to OUT.

ILIM: Current Limit Program. A resistor between this pin

and OUT programs output current limit to a level propor-

tional to resistor value. Connect this resistor directly to

OUT at the pins of the package. The typical ratio of current

limit to resistor value is 360mA/kΩ with a 450Ω offset.

If programmable current limit is not used, leave this pin

open; the internal current limit of the LT3081 is still active,

keeping the device inside safe operating limits. External

voltage drops between the current limit resistor and VOUT

will affect the current limit. Keep drops below 1mV.

IMON: Output Current Monitor. The IMON pin sources a

current typically equal to ILOAD/5000 or 200µA per amp of

output current. Terminating this pin with a resistor to GND

produces a voltage proportional to ILOAD. For example,

at ILOAD = 1.5A, IMON typically sources 300µA. With a

1k resistor to GND, this produces 300mV. The output

of the IMON pin is valid for voltages from VOUT + 0.4V to

VOUT – 40V. If unused, connect this pin to OUT.

SET: Set. This pin is the error amplifier’s noninverting

input and also sets the operating bias point of the circuit.

A fixed 50μA current source flows out of this pin. A single

external resistor programs VOUT. Output voltage range is

0V to 34.5V.

Exposed Pad/Tab: Output. The exposed pad of the DF and

FE packages and the tab of the R and T7 packages are tied

internally to OUT. As such, tie them directly to OUT (Pins

1-4/Pins 1-5, 8, 9, 16/Pin 4/Pin 4) at the PCB. The amount

of copper area and planes connected to OUT determine

the effective thermal resistance of the packages.

NC: No Connection. No connect pins have no connection

to internal circuitry and may be tied to IN, OUT, GND or

floated.

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Introduction

The LT3081 regulator is easy to use and has all the pro-

tection features expected in high performance regulators.

Included are short-circuit protection, reverse-input protec-

tion and safe operating area protection, as well as thermal

shutdown with hysteresis. Safe operating area (SOA) for

the LT3081 is extended, allowing for use in harsh indus-

trial and automotive environments where sudden spikes

in input voltage lead to high power dissipation.

The LT3081 fits well in applications needing multiple rails.

This new architecture adjusts down to zero with a single

resistor, handling modern low voltage digital ICs as well

as allowing easy parallel operation and thermal manage-

ment without heat sinks. Adjusting to zero output allows

shutting off the powered circuitry.

A precision “0” TC 50μA reference current source connects

to the noninverting input of a power operational amplifier.

The power operational amplifier provides a low impedance

buffered output to the voltage on the noninverting input.

A single resistor from the noninverting input to ground

sets the output voltage. If this resistor is set to 0Ω, zero

output voltage results. Therefore, any output voltage can

be obtained between zero and the maximum defined by

the input power supply is obtainable.

The benefit of using a true internal current source as the

reference, as opposed to a bootstrapped reference in older

regulators, is not so obvious in this architecture. A true

reference current source allows the regulator to have gain

and frequency response independent of the impedance on

the positive input. On older adjustable regulators, such as

the LT1086 loop gain changes with output voltage and

bandwidth changes if the adjustment pin is bypassed to

ground. For the LT3081, the loop gain is unchanged with

output voltage changes or bypassing. Output regulation

is not a fixed percentage of output voltage, but is a fixed

fraction of millivolts. Use of a true current source allows

all of the gain in the buffer amplifier to provide regulation,

and none of that gain is needed to amplify up the reference

to a higher output voltage.

The LT3081 has many additional features that facilitate

monitoring and control. Current limit is externally pro-

grammable via a single resistor between the ILIM pin and

OUT. Shorting this resistor out disables all output current

to the load, only bias currents remain.

The IMON pin produces a current output proportional to

load current. For every 1A of load current, the IMON pin

sources 200µA of current. This can be sensed using an

external resistor to monitor load requirements and detect

potential faults. The IMON pin can operate at voltages above

OUT, so it operates even during a short-circuit condition.

One additional monitoring function is the TEMP pin, a cur-

rent source that is proportional to average die temperature.

For die temperatures above 0°C, the TEMP pin sources a

current equal to 1µA/°C. This pin operates normally during

output short-circuit conditions.

Programming Linear Regulator Output Voltage

The LT3081 generates a 50μA reference current that flows

out of the SET pin. Connecting a resistor from SET to

ground generates a voltage that becomes the reference

point for the error amplifier (see Figure 1). The reference

voltage equals 50µA multiplied by the value of the SET

pin resistor. Any voltage can be generated and there is

no minimum output voltage for the regulator.

3081 F01

SET OUT

–

LT3081

50µA

RLOAD

CSET RSET

CIN

VOUT = 50µA • R

SET

COUT

Figure 1. Basic Adjustable Regulator

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Table 1 lists many common output voltages and the clos-

est standard 1% resistor values used to generate that

output voltage.

Regulation of the output voltage requires a minimum load

current of 5mA. For true zero voltage output operation,

return this 5mA load current to a negative output voltage.

Table 1. 1% Resistors for Common Output Voltages

VOUT (V) RSET (kΩ)

1 20

1.2 24.3

1.5 30.1

1.8 35.7

2.5 49.9

3.3 66.5

5 100

With the 50µA current source used to generate the reference

voltage, leakage paths to or from the SET pin can create

errors in the reference and output voltages. High quality

insulation should be used (e.g., Teflon, Kel-F); cleaning of

all insulating surfaces to remove fluxes and other residues

is required. Surface coating may be necessary to provide

a moisture barrier in high humidity environments.

Minimize board leakage by encircling the SET pin and

circuitry with a guard ring operated at a potential close

to itself. Tie the guard ring to the OUT pin. Guarding both

sides of the circuit board is required. Bulk leakage reduction

depends on the guard ring width. 50nA of leakage into or

out of the SET pin and its associated circuitry creates a

0.1% reference voltage error. Leakages of this magnitude,

coupled with other sources of leakage, can cause signifi-

cant offset voltage and reference drift, especially over the

possible operating temperature range. Figure 2 depicts an

example guard ring layout.

If guard ring techniques are used, this bootstraps any

stray capacitance at the SET pin. Since the SET pin is

a high impedance node, unwanted signals may couple

into the SET pin and cause erratic behavior. This will

be most noticeable when operating with minimum

output capacitors at full load current. The easiest way

to remedy this is to bypass the SET pin with a small

amount of capacitance from SET to ground, 10pF to

20pF is sufficient.

Configuring the LT3081 as a Current Source

Setting the LT3081 to operate as a 2-terminal current

source is a simple matter. The 50µA reference current from

the SET pin is used with one resistor to generate a small

voltage, usually in the range of 100mV to 1V (200mV is a

level that rejects offset voltage, line regulation, and other

errors without being excessively large). This voltage is

then applied across a second resistor that connect from

OUT to the first resistor. Figure 3 shows connections and

formulas to calculate a basic current source configuration.

3081 F02

SET PIN

GND

OUT

Figure 2. Guard Ring Layout Example of DF Package Figure 3. Using the LT3081 as a Current Source

IOUT ≥5mA

VSET =50µA •RSET

IOUT =VSET

OUT

=50µA •RSET

OUT

SET OUT

–

LT3081

50µA

IOUT

VSET RSET

3081 F03

–

ROUT

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Again, the lower current levels used in the LT3081 neces-

sitate attention to board leakages as error sources (see the

Programming Linear Regulator Output Voltage section).

In a current source configuration, programmable cur-

rent limit and current monitoring functions are often

unused. When not used, tie IMON to OUT and leave ILIM

open. The TEMP pin is still available for use, if unused tie

TEMP to OUT.

Selecting RSET and ROUT in Current Source Applications

In Figure 3, both resistors RSET and ROUT program the

value of the output current. The question now arises: the

ratio of these resistors is known, but what value should

each resistor be?

The first resistor to select is RSET. The value selected should

generate enough voltage to minimize the error caused by

the offset between the SET and OUT pins. A reasonable

starting level is ~200mV of voltage across RSET (RSET equal

to 4.02k). Resultant errors due to offset voltage are a few

percent. The lower the voltage across RSET becomes, the

higher the error term due to the offset.

From this point, selecting ROUT is easy, as it is a straight-

forward calculation from RSET. Take note, however, resistor

errors must be accounted for as well. While larger voltage

drops across RSET minimize the error due to offset, they

also increase the required operating headroom.

Obtaining the best temperature coefficient does not require

the use of expensive resistors with low ppm temperature

coefficients. Instead, since the output current of the LT3081

is determined by the ratio of RSET to ROUT, those resis-

tors should have matching temperature characteristics.

Less expensive resistors made from the same material

provide matching temperature coefficients. See resistor

manufacturers’ data sheets for more details.

Higher output currents necessitate the use of higher watt-

age resistors for ROUT. There may be a difference between

the resistors used for ROUT and RSET. A better method to

maintain consistency in resistors is to use multiple resis-

tors in parallel to create ROUT, allowing the same wattage

and type of resistor as RSET.

Programming Current Limit Externally

A resistor placed between ILIM and OUT on the LT3081

externally sets current limit to a level lower than the internal

current limit. Connect this resistor directly at the OUT pins

for best accuracy. The value of this resistor calculates as:

RILIM = ILIMIT/360mA/kΩ + 450Ω

The resistor for a 1.3A current limit is: RILIM = 1.3A/360mA/

kΩ + 450Ω = 4.06k. Tolerance over temperature is ±15%,

so current limit is normally set 20% above maximum load

current. The 450Ω offset resistance built in to the pro-

grammable current limit allows for lowering the maximum

output current to only bias currents (see curve of Minimum

Load Current in Typical Performance Characteristics) us-

ing external switches.

The LT3081’s internal current limit overrides the pro-

grammed current limit if the input-to-output voltage dif-

ferential in the power transistor is excessive. The internal

current limit is ≈2A with a foldback characteristic dependent

on input-to-output differential voltage, not output voltage

per se (see Typical Performance Characteristics).

Stability and Input Capacitance

The LT3081 does not require an input capacitor to main-

tain stability. Input capacitors are recommended in linear

regulator configurations to provide a low impedance input

source to the LT3081. If using an input capacitor, low

ESR, ceramic input bypass capacitors are acceptable for

applications without long input leads. However, applica-

tions connecting a power supply to an LT3081 circuit’s

IN and GND pins with long input wires combined with

low ESR, ceramic input capacitors are prone to voltage

spikes, reliability concerns and application-specific board

oscillations. The input wire inductance found in many

battery-powered applications, combined with the low ESR

ceramic input capacitor, forms a high Q LC resonant tank

circuit. In some instances this resonant frequency beats

against the output current dependent LDO bandwidth and

interferes with proper operation. Simple circuit modifica-

tions/solutions are then required. This behavior is not

indicative of LT3081 instability, but is a common ceramic

input bypass capacitor application issue.

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The self-inductance, or isolated inductance, of a wire is

directly proportional to its length. Wire diameter is not a

major factor on its self-inductance. For example, the self-

inductance of a 2-AWG isolated wire (diameter = 0.26") is

about half the self-inductance of a 30-AWG wire (diameter

= 0.01"). One foot of 30-AWG wire has about 465nH of

self inductance.

One of two ways reduces a wire’s self-inductance. One

method divides the current flowing towards the LT3081

between two parallel conductors. In this case, the farther

apart the wires are from each other, the more the self-

inductance is reduced; up to a 50% reduction when placed

a few inches apart. Splitting the wires basically connects

two equal inductors in parallel, but placing them in close

proximity gives the wires mutual inductance adding to

the self-inductance. The second and most effective way

to reduce overall inductance is to place both forward and

return current conductors (the input and GND wires) in

very close proximity. Tw o 30-AWG wires separated by

only 0.02", used as forward and return current conduc-

tors, reduce the overall self-inductance to approximately

one-fifth that of a single isolated wire.

If wiring modifications are not permissible for the applica-

tions, including series resistance between the power supply

and the input of the LT3081 also stabilizes the application.

As little as 0.1Ω to 0.5Ω, often less, is effective in damp-

ing the LC resonance. If the added impedance between

the power supply and the input is unacceptable, adding

ESR to the input capacitor also provides the necessary

damping of the LC resonance. However, the required ESR

is generally higher than the series impedance required.

Stability and Frequency Compensation for Linear

Regulator Configurations

The LT3081 does not require an output capacitor for

stability. LT C recommends an output capacitor of 10μF

with an ESR of 0.5Ω or less to provide good transient

performance in linear regulator configurations. Larger

values of output capacitance decrease peak deviations and

provide improved transient response for larger load current

changes. Bypass capacitors, used to decouple individual

components powered by the LT3081, increase the effec-

tive output capacitor value. For improvement in transient

performance, place a capacitor across the voltage setting

resistor. Capacitors up to 1μF can be used. This bypass

capacitor reduces system noise as well, but start-up time

is proportional to the time constant of the voltage setting

resistor (RSET in Figure 1) and SET pin bypass capacitor.

Stability and Frequency Compensation for Current

Source Configurations

The LT3081 does not require input or output capacitors

for stability in many current-source applications. Clean,

tight PCB layouts provide a low reactance, well controlled

operating environment for the LT3081 without requiring

capacitors to frequency compensate the circuit. Figure 3

highlights the simplicity of using the LT3081 as a current

source.

Some current source applications use a capacitor con-

nected in parallel with the SET pin resistor to lower the

current source’s noise. This capacitor also provides a

soft-start function for the current source. See Quieting the

Noise section for further details. When operating without

output capacitors, the high impedance nature of the SET

pin as the input of the error amplifier allows signal from

the output to couple in, showing as high frequency ring-

ing during transients. Bypassing the SET resistor with a

capacitor in the range of 20pF to 30pF dampens the ringing.

Depending on the pole introduced by a capacitor or other

complex impedances presented to the LT3081, external

compensation may be required for stability. Techniques

are discussed to achieve this in the following paragraphs.

Linear Technology strongly recommends testing stability

in situ with final components before beginning production.

Although the LT3081’s design strives to be stable without

capacitors over a wide variety of operating conditions, it is

not possible to test for all possible combinations of input

and output impedances that the LT3081 will encounter.

These impedances may include resistive, capacitive, and

inductive components and may be complex distributed

networks. In addition, the current source’s value will dif-

fer between applications and its connection may be GND

referenced, power supply referenced, or floating in a signal

line path. Linear Technology strongly recommends that

stability be tested in situ for any LT3081 application.

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In LT3081 applications with long wires or PCB traces, the

inductive reactance may cause instability. In some cases,

adding series resistance to the input and output lines (as

shown in Figure 4) may sufficiently dampen these possible

high-Q lines and provide stability. The user must evaluate

the required resistor values against the design’s headroom

constraints. In general, operation at low output current

levels (<20mA) automatically requires higher values of

programming resistors and may provide the necessary

damping without additional series impedance.

If the line impedances in series with the LT3081 are

complex enough such that series damping resistors are

not sufficient, a frequency compensation network may be

necessary. Several options may be considered.

Figure 5 depicts the simplest frequency compensation

networks as a single capacitor across the two terminals

of the current source. Some applications may use the

capacitance to stand off DC voltage but allow the transfer

of data down a signal line.

For some applications, pure capacitance may be unac-

ceptable or present a design constraint. One circuit

example typifying this is an “intrinsically-safe” circuit in

which an overload or fault condition potentially allows the

capacitor’s stored energy to create a spark or arc. For ap-

plications where a single capacitor is unacceptable, Figure

5 alternately shows a series RC network connected across

the two terminals of the current source. This network has

the added benefit of limiting the discharge current of the

capacitor under a fault condition, preventing sparks or

arcs. In many instances, a series RC network is the best

solution for stabilizing the application circuit. Typical resis-

tor values will range from 100Ω to 5k. Once again, Linear

Technology strongly recommends testing stability in situ

for any LT3081 application across all operating conditions,

especially ones that present complex impedance networks

at the input and output of the current source.

If an application refers the bottom of the LT3081 current

source to GND, it may be necessary to bypass the top

of the current source with a capacitor to GND. In some

cases, this capacitor may already exist and no additional

capacitance is required. For example, if the LT3081 was

used as a variable current source on the output of a power

supply, the output bypass capacitance would suffice to

provide LT3081 stability. Other applications may require

the addition of a bypass capacitor. A series RC network

may also be used as necessary, and depends on the ap-

plication requirements.

SET OUT

–

LT3081

50µA

RSET ROUT

RSERIES

LONG LINE

REACTANCE/INDUCTANCE

3081 F04

LONG LINE

REACTANCE/INDUCTANCE

Figure 4. Adding Series Resistance Decouples

and Dampens Long Line Reactances

Figure 5. Compensation from Input to Output

of Current Source Provides Stability

3081 F05

SET OUT

–

LT3081

50µA CCOMP OR

RSET ROUT

RCOMP

CCOMP

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In some extreme cases, capacitors or series RC networks

may be required on both the LT3081’s input and output to

stabilize the circuit. Figure 6 depicts a general application

using input and output capacitor networks rather than

an input-to-output capacitor. As the input of the current

source tends to be high impedance, placing a capacitor

on the input does not have the same effect as placing a

capacitor on the lower impedance output. Capacitors in the

range of 0.1µF to 1µF usually provide sufficient bypassing

on the input, and the value of input capacitance may be

increased without limit. Pay careful attention to using low

ESR input capacitors with long input lines (see the Stabil-

ity and Input Capacitance section for more information).

Using Ceramic Capacitors

Give extra consideration to the use of ceramic capacitors.

Ceramic capacitors are manufactured with a variety of di-

electrics, each with different behavior across temperature

and applied voltage. The most common dielectrics used

are specified with EIA temperature characteristic codes of

Z5U, Y5V, X5R and X7R. The Z5U and Y5V 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 7 and 8. 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 temperature 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 available 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 capacitance

change over temperature. Capacitance change due to DC

bias with X5R and X7R capacitors is better than Y5V and

Z5U capacitors, but can still be significant enough to drop

capacitor values below appropriate levels. Capacitor DC

bias characteristics tend to improve as component case

size increases, but expected capacitance at operating

voltage should be verified.

Figure 8. Ceramic Capacitor DC Bias CharacteristicsFigure 7. Ceramic Capacitor Temperature Characteristics

Figure 6. Input and/or Output Capacitors May

Be Used for Compensation

3081 F06

SET OUT

–

LT3081

50µA

IOUT

RSET ROUT

COUT OR

VIN

COUT

ROUT

CIN

RIN

TEMPERATURE (°C)

–50

–20

–40

–60

–80

–100 25 75

3081 F07

–25 0 50 100 125

Y5V

CHANGE IN VALUE (%)

X5R

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10µF

DC BIAS VOLTAGE (V)

CHANGE IN VALUE (%)

3081 F08

–20

–40

–60

–80

–100 04810

2 6 12 14

X5R

Y5V

BOTH CAPACITORS ARE 16V,

1210 CASE SIZE, 10µF

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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. In a

ceramic capacitor, the stress can be induced by vibrations

in the system or thermal transients.

Paralleling Devices

Higher output current is obtained by paralleling multiple

LT3081s together. Tie the individual SET pins together and

tie the individual IN pins together. Connect the outputs in

common using small pieces of PC trace as ballast resistors

to promote equal current sharing. PC trace resistance in

milliohms/inch is shown in Table 2. Ballasting requires

only a tiny area on the PCB.

Table 2. PC Board Trace Resistance

WEIGHT (oz) 10mil WIDTH 20mil WIDTH

1 54.3 27.1

2 27.1 13.6

Trace resistance is measured in mΩ/in.

The worst-case room temperature offset, only ±1.5mV

between the SET pin and the OUT pin, allows the use of

very small ballast resistors.

As shown in Figure 9, each LT3081 has a small 10mΩ

ballast resistor, which at full output current gives better

than 80% equalized sharing of the current. The external

resistance of 10mΩ (5mΩ for the two devices in parallel)

only adds about 15mV of output regulation drop at an

output of 3A. Even with an output voltage as low as 1V,

this only adds 1.5% to the regulation. Of course, paralleling

more than two LT3081s yields even higher output current.

Spreading the devices on the PC board also spreads the

heat. Series input resistors can further spread the heat if

the input-to-output difference is high.

If the increase in load regulation from the ballast resis-

tors is unacceptable, the IMON output can be used to

compensate for these drops (see Using IMON Cancels

Ballast Resistor Drop in the Typical Applications section).

Regulator paralleling without the use of ballast resistors is

accomplished by comparing the IMON outputs of regula-

tors (see Load Current Sharing Without Ballasting in the

Typical Applications section).

Quieting the Noise

The LT3081 offers numerous noise performance advan-

tages. Every linear regulator has its sources of noise. In

general, a linear regulator’s critical noise source is the

reference. In addition, consider the error amplifier’s noise

contribution along with the resistor divider’s noise gain.

Many traditional low noise regulators bond out the voltage

reference to an external pin (usually through a large value

resistor) to allow for bypassing and noise reduction. The

LT3081 does not use a traditional voltage reference like

other linear regulators. Instead, it uses a 50µA reference

current. The 50µA current source generates noise current

levels of 18pA/√Hz (5.7nARMS over a 10Hz to 100kHz

bandwidth). The equivalent voltage noise equals the RMS

noise current multiplied by the resistor value.

The SET pin resistor generates spot noise equal to √4kTR

(k = Boltzmann’s constant, 1.38 • 10–23J/°K, and T is abso-

lute temperature) which is RMS summed with the voltage

noise. If the application requires lower noise performance,

bypass the voltage setting resistor with a capacitor to GND.

Note that this noise-reduction capacitor increases start-up

time as a factor of the RC time constant.

SET

–

LT3081

50µA

10mΩ

VIN

4.8V TO 40V

VOUT

3.3V

OUT

10µF

1µF

33k

3081 F09

SET

–

LT3081

50µA

OUT

Figure 9. Parallel Devices

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The LT3081 uses a unity-gain follower from the SET pin

to the OUT pin. Therefore, multiple possibilities exist

(besides a SET pin resistor) to set output voltage. For

example, using a high accuracy voltage reference from

SET to GND removes the errors in output voltage due to

reference current tolerance and resistor tolerance. Active

driving of the SET pin is acceptable.

The typical noise scenario for a linear regulator is that the

output voltage setting resistor divider gains up the reference

noise, especially if VOUT is much greater than VREF. The

LT3081’s noise advantage is that the unity-gain follower

presents no noise gain whatsoever from the SET pin to the

output. Thus, noise figures do not increase accordingly.

Error amplifier noise is typical 85nV/√Hz(27µVRMS over

a 10Hz to 100kHz bandwidth). The error amplifier’s noise

is RMS summed with the other noise terms to give a final

noise figure for the regulator.

Paralleling of regulators adds the benefit that output noise

is reduced. For n regulators in parallel, the output noise

drops by a factor of √n.

Curves in the Typical Performance Characteristics sec-

tion show noise spectral density and peak-to-peak noise

characteristics for both the reference current and error

amplifier over a 10Hz to 100kHz bandwidth.

Load Voltage Regulation

The LT3081 is a floating device. No ground pin exists on

the packages. Thus, the IC delivers all quiescent current

and drive current to the load. Therefore, it is not possible

to provide true remote load sensing. The connection re-

sistance between the regulator and the load determines

load regulation performance. The data sheet’s load

regulation specification is Kelvin sensed at the package’s

pins. Negative-side sensing is a true Kelvin connection by

returning the bottom of the voltage setting resistor to the

negative side of the load (see Figure 10).

Connected as shown, system load regulation is the sum

of the LT3081’s load regulation and the parasitic line

resistance multiplied by the output current. To minimize

load regulation, keep the positive connection between the

regulator and load as short as possible. If possible, use

large diameter wire or wide PC board traces.

TEMP Pin Operation (Die Temperature Monitor)

The TEMP pin of the LT3081 outputs a current proportional

to average die temperature. At 25°C, the current from the

TEMP pin is 25µA, with a slope of 1µA/°C. The current out

of the TEMP pin is valid for junction temperatures above

0°C (absent initial offset considerations). Below 0°C, the

TEMP pin will not sink current to indicate die temperature.

The TEMP pin output current is valid for voltages up to

40V below and 0.4V above the OUT pin allowing operation

even during short-circuit conditions.

Connecting a resistor from TEMP to ground converts the

TEMP pin current into a voltage to allow for monitoring

by an ADC. With a 1k resistor, 0mV to 150mV indicates

0°C to 150°C.

It should be noted that the TEMP pin current represents an

average temperature and should not be used to guarantee

that maximum junction temperature is not exceeded.

Instantaneous power along with thermal gradients and

time constants may cause portions of the die to exceed

maximum ratings and thermal shutdown thresholds. Be

sure to calculate die temperature rise for steady state (>1

minute) as well as impulse conditions.

IMON Pin Operation (Current Monitor)

The LT3081’s IMON pin outputs a current proportional to

the load current supplied at a ratio of 1:5000. The IMON

pin current is valid for voltages up to 40V below and 0.4V

above the OUT pin, allowing operation even during short-

circuit conditions.

applicaTions inForMaTion

Figure 10. Connections for Best Load Regulation

SET

–

LT3081

50µA

3081 F10

OUT

RSET

PARASITIC

RESISTANCE

LOAD

LT3081

3081fc

For more information www.linear.com/LT3081

Connecting a resistor from IMON to ground converts the

IMON pin current into a voltage to allow for monitoring by

an ADC. With a 1k resistor, 0mV to 300mV indicates 0A

to 1.5A of load current.

Compensating for Cable Drops with IMON

The IMON pin can compensate for resistive drops in wires

or cables between the LT3081 and the load. Breaking the

SET resistor into two pieces adjusts the output voltage as a

function of load current. The ratio of the output wire/cable

impedance to the bottom resistor should be 1:5000. The

sum total of the two SET resistor values determines the

initial output voltage. Figure 11 shows a typical application

and formulas for calculating resistor values.

PC board, copper traces and planes. Surface mount heat

sinks, plated through-holes and solder-filled vias can also

spread the heat generated by power devices.

Junction-to-case thermal resistance is specified from the

IC junction to the bottom of the case directly, or the bot-

tom of the pin most directly in the heat path. This is the

lowest thermal resistance path for heat flow. Only proper

device mounting ensures the best possible thermal flow

from this area of the packages to the heat sinking material.

Note that the exposed pad of the DFN and TSSOP pack-

ages and the tab of the DD-Pak and TO-220 packages

are electrically connected to the output (VOUT).

Tables 3 through 5 list thermal resistance as a function

of copper areas on a fixed board size. All measurements

were taken in still air on a 4-layer FR-4 board with 1oz

solid internal planes and 2oz external trace planes with a

total finished board thickness of 1.6mm.

Table 3. DF Package, 12-Lead DFN

COPPER AREA

BOARD AREA

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)TOPSIDE* BACKSIDE

2500mm22500mm22500mm218°C/W

1000mm22500mm22500mm222°C/W

225mm22500mm22500mm229°C/W

100mm22500mm22500mm235°C/W

*Device is mounted on topside

Table 4. FE Package, 16-Lead TSSOP

COPPER AREA

BOARD AREA

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)TOPSIDE* BACKSIDE

2500mm22500mm22500mm216°C/W

1000mm22500mm22500mm220°C/W

225mm22500mm22500mm226°C/W

100mm22500mm22500mm232°C/W

*Device is mounted on topside

Table 5. R Package, 7-Lead DD-Pak

COPPER AREA

BOARD AREA

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)TOPSIDE* BACKSIDE

2500mm2 2500mm2 2500mm2 13°C/W

1000mm2 2500mm2 2500mm2 14°C/W

225mm2 2500mm2 2500mm2 16°C/W

*Device is mounted on topside

applicaTions inForMaTion

Figure 11. Using IMON to Compensate for Cable Drops

Thermal Considerations

The LT3081’s internal power and thermal limiting circuitry

protects itself under overload conditions. For continuous

normal load conditions, do not exceed the 125°C (E- and

I-grades) or 150°C (H- and MP-grades) maximum junc-

tion temperature. Carefully consider all sources of thermal

resistance from junction-to-ambient. This includes (but is

not limited to) junction-to-case, case-to-heat sink inter-

face, heat sink resistance or circuit board-to-ambient as

the application dictates. Consider all additional, adjacent

heat generating sources in proximity on the PCB.

Surface mount packages provide the necessary heat

sinking by using the heat spreading capabilities of the

LT3081

CIN

1µF

COUT

10µF

3081 F11

OUT

SET

RSET

29.8k

RCOMP = 5000 • RCABLE(TOTAL)

VOUT(LOAD) = 50µA (RSET + RCOMP)

RCABLE2

0.02Ω

RCABLE

0.02Ω

RCOMP

200Ω

IMON

LOAD

LT3081

3081fc

For more information www.linear.com/LT3081

applicaTions inForMaTion

T7 Package, 7-Lead TO-220

Thermal Resistance (Junction-to-Case) = 3°C/W

For further information on thermal resistance and using

thermal information, refer to JEDEC standard JESD51,

notably JESD51-12.

PCB layers, copper weight, board layout and thermal vias

affect the resultant thermal resistance. Tables 3 through 5

provide thermal resistance numbers for best-case 4-layer

boards with 1oz internal and 2oz external copper. Modern,

multilayer PCBs may not be able to achieve quite the same

level performance as found in these tables. Demo circuit

1870A’s board layout using multiple inner VOUT planes

and multiple thermal vias achieves 16°C/W performance

for the FE package.

Calculating Junction Temperature

Example: Given an output voltage of 0.9V, an IN voltage

of 2.5V ±5%, output current range from 10mA to 1A

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

the maximum junction temperature for the DD-Pak on a

2500mm2 board with topside copper of 1000mm2?

The power in the circuit equals:

PTOTAL = (VIN – VOUT)(IOUT)

The current delivered to the SET pin is negligible and can

be ignored.

VIN(MAX_CONTINUOUS) = 2.625V (2.5V + 5%)

VOUT = 0.9V, IOUT = 1A, TA = 50°C

Power dissipation under these conditions equals:

PTOTAL = (VIN – VOUT)(IOUT)

PTOTAL = (2.625V – 0.9V)(1A) = 1.73W

Junction Temperature equals:

TJ = TA + PTOTAL • θJA (using tables)

TJ = 50°C + 1.73W • 14°C/W = 74.2°C

In this case, the junction temperature is below the maxi-

mum rating, ensuring reliable operation.

Reducing Power Dissipation

In some applications it may be necessary to reduce the

power dissipation in the LT3081 package without sacrificing

output current capability. Tw o techniques are available. The

first technique, illustrated in Figure 12, employs a resis-

tor in series with the regulator’s input. The voltage drop

across RS decreases the LT3081’s IN-to-OUT differential

voltage and correspondingly decreases the LT3081’s

power dissipation.

As an example, assume: VIN = 7V, VOUT = 3.3V and IOUT(MAX)

= 1.5A. Use the formulas from the Calculating Junction

Temperature section previously discussed.

Without series resistor RS, power dissipation in the

LT3081 equals:

PTOTAL = (7V – 3.3V) • 1.5A = 5.55W

If the voltage differential (VDIFF) across the LT3081 is

chosen as 1.5V, then RS equals:

RS=

7V – 3.3V – 1.5V

1.5A

=1.5Ω

Power dissipation in the LT3081 now equals:

PTOTAL = 1.5V • 1.5A = 2.25W

The LT3081’s power dissipation is now only 40% compared

to no series resistor. RS dissipates 3.3W of power. Choose

appropriate wattage resistors or use multiple resistors in

parallel to handle and dissipate the power properly.

3081 F12

VIN′

SET OUT

–

LT3081

50µA

RSET

VOUT

VIN

Figure 12. Reducing Power Dissipation Using a Series Resistor

LT3081

3081fc

For more information www.linear.com/LT3081

applicaTions inForMaTion

The second technique for reducing power dissipation,

shown in Figure 13, uses a resistor in parallel with the

LT3081. This resistor provides a parallel path for current

flow, reducing the current flowing through the LT3081.

This technique works well if input voltage is reasonably

constant and output load current changes are small. This

technique also increases the maximum available output

current at the expense of minimum load requirements.

RP dissipates 1.52W of power. As with the first technique,

choose appropriate wattage resistors to handle and dis-

sipate the power properly. With this configuration, the

LT3081 supplies only 0.86A. Therefore, load current can

increase by 0.64A to a total output current of 2.14A while

keeping the LT3081 in its normal operating range.

High Temperature Operation

Care must be taken when designing the LT3081H/

LT3081MP applications to operate at high ambient tem-

peratures. The LT3081H/LT3081MP operates at high

temperatures, but erratic operation can occur due to un-

foreseen variations in external components. Some tantalum

capacitors are available for high temperature operation, but

ESR is often several ohms; capacitor ESR above 0.5Ω is

unsuitable for use with the LT3081H/LT3081MP. Multiple

ceramic capacitor manufacturers now offer ceramic capaci-

tors that are rated to 150°C using an X8R dielectric. Check

each passive component for absolute value and voltage

ratings over the operating temperature range.

Leakages in capacitors or from solder flux left after insuf-

ficient board cleaning adversely affects low current nodes,

such as the SET, IMON, and TEMP pins. Consider junction

temperature increase due to power dissipation in both

the junction and nearby components to ensure maximum

specifications are not violated for the LT3081H/LT3081MP

or external components.

Protection Features

The LT3081 incorporates several protection features ideal

for harsh industrial and automotive environments, among

other applications. In addition to normal monolithic regula-

tor protection features such as current limiting and thermal

limiting, the LT3081 protects itself against reverse-input

voltages, reverse-output voltages, and large OUT-to-SET

pin voltages.

Current limit protection and thermal overload protection

protect the IC against output current overload conditions.

For normal operation, do not exceed the rated absolute

maximum junction temperature. The thermal shutdown

circuit’s temperature threshold is typically 165°C and

incorporates about 5°C of hysteresis.

3081 F13

SET OUT

–

LT3081

50µA

RSET VOUT

VIN

Figure 13. Reducing Power Dissipation Using a Parallel Resistor

As an example, assume: VIN = 5V, VIN(MAX) = 5.5V, VOUT

= 3.3V, VOUT(MIN) = 3.2V, IOUT(MAX) = 1.5A and IOUT(MIN)

= 0.7A. Also, assuming that RP carries no more than 90%

of IOUT(MIN) = 630mA.

Calculating RP yields:

RP=

5.5V – 3.2V

0.63A

=3.65Ω

(5% Standard value = 3.6Ω)

The maximum total power dissipation is:

(5.5V – 3.2V) • 1.5A = 3.5W

However, the LT3081 supplies only:

1.5A –

5.5V – 3.2V

3.6Ω

=0.86A

Therefore, the LT3081’s power dissipation is only:

PDISS = (5.5V – 3.2V) • 0.86A = 1.98W

LT3081

3081fc

For more information www.linear.com/LT3081

applicaTions inForMaTion

Typical applicaTions

Paralleling Regulators Using IMON Cancels Ballast Resistor Drop

SET

RSET

30.1k

TEMP

IMON ILIM

10mΩ

OUT

–

LT3081

ISET

50µA

VOUT

VIN

SET

TEMP

IMON ILIM

10mΩ

OUT

–

LT3081

ISET

50µA

3.01k

3081 TA03

SET

RSET

15k

TEMP

IMON ILIM

OUT

–

LT3081

ISET

50µA

VOUT

1.5V

VIN

SET

TEMP

IMON ILIM

RBALLAST

10mΩ

OUT

–

LT3081

ISET

50µA

3081 TA04

RCOMP

25Ω

RBALLAST

10mΩ

The LT3081’s IN pin withstands ±40V voltages with respect

to the OUT and SET pins. Reverse current flow, if OUT is

greater than IN, is less than 1mA (typically under 100µA),

protecting the LT3081 and sensitive loads.

Clamping diodes and 400Ω limiting resistors protect the

LT3081’s SET pin relative to the OUT pin voltage. These

protection components typically only carry current under

transient overload conditions. These devices are sized to

handle ±10V differential voltages and ±25mA crosspin

current flow without concern. Relative to these applica-

tion concerns, note the following two scenarios. The first

scenario employs a noise-reducing SET pin bypass ca-

pacitor while OUT is instantaneously shorted to GND. The

second scenario follows improper shutdown techniques

in which the SET pin is reset to GND quickly while OUT

is held up by a large output capacitance with light load.

LT3081

3081fc

For more information www.linear.com/LT3081

Typical applicaTions

Load Sharing Without Ballast Resistors

Load Current Sharing Without Ballasting

22µF

20k

OUT

VIN

3V TO 18V

IMON

SET

LT3081

0.1µF

22µF

1k 5.1k

20k

OUT

IMON

SET

LT3081

100k

0.47µF

5.1k

0.1µF 1k

IN OUT

IMON

SET

LT3081

–

20k

VOUT

4.5A

100k

0.47µF

5.1k

0.1µF 1k

3081 TA05

–

1/2 LT1638 1/2 LT1638

4.7µF

20k

OUT

VIN

3V TO 36V

IMON

SET

ILIM

LT3081

0.1µF

2.2µF

VOUT

0.1µF

3081 TA05

100Ω

1k1k

20k

= 2N3904

OUT IN

IMON SET

ILIM

LT3081

3081fc

For more information www.linear.com/LT3081

Typical applicaTions

Constant-Voltage, Constant-Current 20V/3A Lab Supply

www.linear.com/product/LT3081#demoboards

BSTVIN

EN/UV

SYNC

INTVCC

TR/SS

LT8612

GND

PGND

BIAS

1µF

10µF

VIN

30V

10µH

49.9k

4.99k

100k

60.4k

22µF

47µF

TPO610T

ARDUINO

A2 PORT

ARDUINO

GND PORT

10µF

×2

SET OUT

–

LT3092

10µA

49.9K 562Ω

SET TEMP

IMON ILIM

10mΩ

OUT

–

LT3081

ISET

50µA

VOUT

0V TO

20V

SET TEMP

IMON ILIM

10mΩ

OUT

–

LT3081

ISET

50µA

3081 TA07

B140

10k

1µF

0.1µF

10nF

ARDUINO

A3 PORT

10k

20k

249Ω 9.09k

CURRENT LIMIT 0A TO 3A

ARDUINO

A4 PORT

4.99k

0.01µF

×2

ARDUINO

A5 PORT

10k

22µF

×2

ARDUINO

A1 PORT

4.99k

LT3081

3081fc

For more information www.linear.com/LT3081

Typical applicaTions

Boosting Fixed Output Regulators

Reference Buffer

Adding Soft-Start

8.2Ω*

3.3VOUT

47µF

*4mV DROP ENSURES LT3081 IS OFF WITH NO LOAD

MULTIPLE LT3081s CAN BE USED

SET TEMP

IMON ILIM

20mΩ

OUT

–

LT3081

ISET

50µA

3081 TA08

6.2k

10µF

LT1963-3.3

47µF

20mΩ

1k 1k*1k

LT1019

VOUT

*MIN LOAD 5mA

SET TEMP

IMON ILIM

OUT

–

LT3081

ISET

50µA

3081 TA09

1µF

OUTPUT

GND

47µF

INPUT

VIN

1k1k

VOUT

3.3V

1.5A

SET TEMP

IMON ILIM

OUT

–

LT3081

ISET

50µA

3081 TA10

0.1µF

10µF

IN4148

VIN

4.8V TO 38V

66.5k

10µF

LT3081

3081fc

For more information www.linear.com/LT3081

Typical applicaTions

Using a Lower Value Set Resistor

Using an External Reference Current

20k

SET

TEMP

IMON ILIM

OUT

–

LT3081

ISET

50µA

1µF

3081 TA12

SET OUT

–

LT3092

10µA

1mA

VIN

VOUT

0V TO 20V

20k 215Ω

1µF

RSET

2k VOUT = 0.2V + 5mA • RSET

SET

TEMP

IMON ILIM

OUT

–

LT3081

ISET

50µA

4.7µF

3081 TA11

1k 4.02k 40.2Ω

VIN

12V

VOUT

0.2V TO 10V

4.7µF

LT3081

3081fc

For more information www.linear.com/LT3081

package DescripTion

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

4.00 ±0.10

(4 SIDES)

NOTE:

1. PACKAGE OUTLINE DOES NOT CONFORM TO JEDEC MO-229

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION

ON THE TOP AND BOTTOM OF PACKAGE

PIN 1

TOP MARK

(NOTE 6)

0.40 ±0.10

127

BOTTOM VIEW—EXPOSED PAD

2.65 ±0.10

0.75 ±0.05

R = 0.115

TYP

0.25 ±0.05

0.50 BSC

2.50 REF

3.38 ±0.10

0.200 REF

0.00 – 0.05

(DF12) DFN 1112 REV A

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

0.70 ±0.05

0.25 ±0.05

0.50 BSC

3.10 ±0.05

4.50 ±0.05

PACKAGE OUTLINE

PIN 1 NOTCH

R = 0.20 TYP OR

0.35 × 45°

CHAMFER

2.65 ±0.05

3.38 ±0.05

2.50 REF

DF Package

12-Lead Plastic DFN (4mm × 4mm)

(Reference LTC DWG # 05-08-1733 Rev A)

LT3081

3081fc

For more information www.linear.com/LT3081

package DescripTion

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

FE16 (BB) TSSOP REV K 0913

0.09 – 0.20

(.0035 – .0079)

0° – 8°

0.25

REF

0.50 – 0.75

(.020 – .030)

4.30 – 4.50*

(.169 – .177)

1 3 4 5678

10 9

4.90 – 5.10*

(.193 – .201)

16 1514 13 12 11

1.10

(.0433)

MAX

0.05 – 0.15

(.002 – .006)

0.65

(.0256)

BSC

2.94

(.116)

0.195 – 0.30

(.0077 – .0118)

TYP

RECOMMENDED SOLDER PAD LAYOUT

0.45 ±0.05

0.65 BSC

4.50 ±0.10

6.60 ±0.10

1.05 ±0.10

2.94

(.116)

3.05

(.120)

3.58

(.141)

3.58

(.141)

4.70

(.185)

MILLIMETERS

(INCHES)

NOTE:

1. CONTROLLING DIMENSION: MILLIMETERS

2. DIMENSIONS ARE IN

3. DRAWING NOT TO SCALE

4. RECOMMENDED MINIMUM PCB METAL SIZE

FOR EXPOSED PAD ATTACHMENT

SEE NOTE 4

NOTE 5

6.40

(.252)

BSC

FE Package

16-Lead Plastic TSSOP (4.4mm)

(Reference LTC DWG # 05-08-1663 Rev K)

Exposed Pad Variation BB

5. BOTTOM EXPOSED PADDLE MAY HAVE METAL PROTRUSION

IN THIS AREA. THIS REGION MUST BE FREE OF ANY EXPOSED

TRACES OR VIAS ON PBC LAYOUT

*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH

SHALL NOT EXCEED 0.150mm (.006") PER SIDE

DETAIL A

DETAIL A IS THE PART OF THE

LEAD FRAME FEATURE FOR

REFERENCE ONLY

NO MEASUREMENT PURPOSE

0.56

(.022)

REF

0.53

(.021)

REF

DETAIL A

LT3081

3081fc

For more information www.linear.com/LT3081

package DescripTion

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

.050

(1.27)

.026 – .036

(0.660 – 0.914)

T7 (TO-220) 0801

.135 – .165

(3.429 – 4.191)

.700 – .728

(17.780 – 18.491)

.045 – .055

(1.143 – 1.397)

.165 – .180

(4.191 – 4.572)

.095 – .115

(2.413 – 2.921)

.013 – .023

(0.330 – 0.584)

.620

(15.75)

TYP

.155 – .195*

(3.937 – 4.953)

.152 – .202

(3.860 – 5.130)

.260 – .320

(6.604 – 8.128)

.147 – .155

(3.734 – 3.937)

DIA

.390 – .415

(9.906 – 10.541)

.330 – .370

(8.382 – 9.398)

.460 – .500

(11.684 – 12.700)

.570 – .620

(14.478 – 15.748)

.230 – .270

(5.842 – 6.858)

BSC

SEATING PLANE

*MEASURED AT THE SEATING PLANE

T7 Package

7-Lead Plastic TO-220 (Standard)

(Reference LTC DWG # 05-08-1422)

LT3081

3081fc

For more information www.linear.com/LT3081

package DescripTion

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

R (DD7) 0212 REV F

.026 – .035

(0.660 – 0.889)

TYP

.143 +.012

–.020

( )

3.632+0.305

–0.508

.050

(1.27)

BSC

.013 – .023

(0.330 – 0.584)

.095 – .115

(2.413 – 2.921)

.004 +.008

–.004

( )

0.102+0.203

–0.102

.050 ±.012

(1.270 ±0.305)

.059

(1.499)

TYP

.045 – .055

(1.143 – 1.397)

.165 – .180

(4.191 – 4.572)

.330 – .370

(8.382 – 9.398)

.060

(1.524)

TYP

.390 – .415

(9.906 – 10.541)

15° TYP

.420

.350

.585

.090

.035

.050

.325

.205

.080

.585

RECOMMENDED SOLDER PAD LAYOUT

FOR THICKER SOLDER PASTE APPLICATIONS

RECOMMENDED SOLDER PAD LAYOUT

.090

.035.050

.420

.276

.320

NOTE:

1. DIMENSIONS IN INCH/(MILLIMETER)

2. DRAWING NOT TO SCALE

.300

(7.620)

.075

(1.905)

.183

(4.648)

.060

(1.524)

.060

(1.524)

.256

(6.502)

BOTTOM VIEW OF DD PAK

HATCHED AREA IS SOLDER PLATED

COPPER HEAT SINK

R Package

7-Lead Plastic DD Pak

(Reference LTC DWG # 05-08-1462 Rev F)

DETAIL A

0° – 7° TYP0° – 7° TYP

LT3081

3081fc

For more information www.linear.com/LT3081

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

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

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

revision hisTory

REV DATE DESCRIPTION PAGE NUMBER

A 11/13 Modified Typical Application circuit for more detail

Added H- and MP-grade references

Changed TJMAX to 150°C on the FE and T7 packages

Changed specs to TEMP Output Current Absolute Error

Modified Block Diagram

Modified Paralleling Regulators Circuit

Modified Arduino Supply Circuit

Added new Typical Application circuits

Modified High Efficiency Adjustable Supply circuit

Updated Related Parts Table

Throughout

25, 26

B 7/14 Updated the Typical Application circuit.

Changed T7 diagram to 'Standard’ package drawing.

C 3/15 Updated Typical Values for External ILIM Programming

Corrected ILIM Text in Pin Functions

Corrected Formula and Text in Programming Current Limit Section

LT3081

3081fc

For more information www.linear.com/LT3081

 LINEAR TECHNOLOGY CORPORATION 2014

LT 0315 REV C • PRINTED IN USA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LT3081

relaTeD parTs

Typical applicaTion

High Efficiency Adjustable Supply

PART NUMBER DESCRIPTION COMMENTS

LT1185 3A Negative Low Dropout Regulator VIN: –4.5V to –35V, 0.8V Dropout Voltage, DD-Pak and TO-220 Packages

LT1764/

LT1764A

3A, Fast T

ransient Response,

Low Noise LDO

340mV Dropout Voltage, Low Noise: 40µVRMS, VIN = 2.7V to 20V, TO-220, TSSOP and DD-Pak,

LT1764A Version Stable Also with Ceramic Capacitors

LT1963/

LT1963A

1.5A Low Noise, Fast T

ransient

Response LDO

340mV Dropout Voltage, Low Noise: 40µVRMS, VIN = 2.5V to 20V, LT1963A Version Stable with

Ceramic Capacitors, TO-220, DD, TSSOP, SOT-223 and SO-8 Packages

LT1965 1.1A, Low Noise, Low Dropout

Linear Regulator

290mV Dropout Voltage, Low Noise: 40µVRMS, VIN: 1.8V to 20V, VOUT: 1.2V to 19.5V, Stable with

Ceramic Capacitors, TO-220, DD-Pak, MSOP and 3mm × 3mm DFN Packages

LT3022 1A, Low Voltage, VLDO Linear

Regulator

VIN: 0.9V to 10V, Dropout Voltage: 145mV Typical, Adjustable Output (VREF = VOUT(MIN) = 200mV),

Stable with Low ESR, Ceramic Output Capacitors, 16-Pin DFN (5mm × 3mm) and 16-Lead

MSOP Packages

LT3070 5A, Low Noise, Programmable

VOUT, 85mV Dropout Linear

Regulator with Digital Margining

Dropout Voltage: 85mV, Digitally Programmable VOUT: 0.8V to 1.8V, Digital Output Margining: ±1%,

±3% or ±5%, Low Output Noise: 25µVRMS (10Hz to 100kHz), Parallelable: Use Tw o for a 10A Output,

Stable with Low ESR Ceramic Output Capacitors (15µF Minimum), 28-Lead 4mm × 5mm QFN Package

LT3071 5A, Low Noise, Programmable

VOUT, 85mV Dropout Linear

Regulator with Analog Margining

Dropout Voltage: 85mV, Digitally Programmable VOUT: 0.8V to 1.8V, Analog Margining: ±10%,

Low Output Noise: 25µVRMS (10Hz to 100kHz), Parallelable: Use Tw o for a 10A Output, IMON Output

Current Monitor, Stable with Low ESR Ceramic Output Capacitors (15µF Minimum) 28-Lead

4mm × 5mm QFN Package

LT3080/

LT3080-1

1.1A, Parallelable, Low Noise,

Low Dropout Linear Regulator

300mV Dropout Voltage (2-Supply Operation), Low Noise: 40µVRMS, VIN: 1.2V to 36V, VOUT: 0V to 35.7V,

Current-Based Reference with 1-Resistor VOUT Set; Directly Parallelable (No Op Amp Required),

Stable with Ceramic Capacitors, TO-220, DD-Pak, SOT-223, MS8E and 3mm × 3mm DFN-8 Packages;

LT3080-1 Version Has Integrated Internal Ballast Resistor

LT3082 200mA, Parallelable, Single

Resistor, Low Dropout Linear

Regulator

Outputs May Be Paralleled for Higher Output, Current or Heat Spreading, Wide Input Voltage

Range: 1.2V to 40V Low Value Input/Output Capacitors Required: 2.2µF, Single Resistor Sets Output

Voltage 8-Lead SOT-23, 3-Lead SOT-223 and 8-Lead 3mm × 3mm DFN Packages

LT3085 500mA, Parallelable, Low Noise,

Low Dropout Linear Regulator

275mV Dropout Voltage (2-Supply Operation), Low Noise: 40µVRMS, VIN: 1.2V to 36V,

VOUT: 0V to 35.7V, Current-Based Reference with 1-Resistor VOUT Set; Directly Parallelable

(No Op Amp Required), Stable with Ceramic Capacitors, MS8E and 2mm × 3mm DFN-6 Packages

LT3092 200mA 2-Terminal Programmable

Current Source

Programmable 2-Terminal Current Source, Maximum Output Current = 200mA, Wide Input Voltage

Range: 1.2V to 40V, Resistor Ratio Sets Output Current, Initial Set Pin Current Accuracy = 1%, Current

Limit and Thermal Shutdown Protection, Reverse-Voltage Protection, Reverse-Current Protection,

8-Lead SOT-23, 3-Lead SOT-223 and 8-Lead 3mm × 3mm DFN Packages.

LT3083 Adjustable 3A Single Resistor

Low Dropout Regulator

Low Noise: 40µVRMS, 50µA Set Pin Current, Output Adjustable to 0V, Wide Input Voltage Range: 1.2V to 23V

(DD-Pak and TO-220), Low Dropout Operation: 310mV (2 Supplies)

RUN/SS

0.47µF

47µF

1µF

1000pF

VIN

6.3V TO

36V

6.8µH

VIN BD

LT3680

15k 590k

10k

3081 TA13

2N3904

MTD2955

CMDSH-4E

MBRA340T3

GND

BOOST

IN OUT

IMON ILIM

1k 1k

VCSW

63.4k

SYNC

15k

6.04k

LT3081

500k

22µF

VOUT

0V TO

25V,

1.5A

TEMP SET

0.1µF