Linear Technology LT3081 User manual

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

reverseinputandreverseoutput-to-inputvoltageswithout

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

nExtended Safe Operating Area

nMaximum Output Current: 1.5A

nStable with or without Input/Output Capacitors

nWide Input Voltage Range: 1.2V to 36V

nSingle Resistor Sets Output Voltage

nOutput Current Monitor: IMON = IOUT/5000

nJunction Temperature Monitor: 1µA/°C

nOutput Adjustable to 0V

n50µA SET Pin Current: 1% Initial Accuracy

nOutput Voltage Noise: 27µVRMS

nParallel Multiple Devices for Higher Current or

Heat Spreading

nProgrammable Current Limit

nReverse-Battery and Reverse-Current Protection

n<1mV Load Regulation Typical Independent of VOUT

n<0.001%/V Line Regulation Typical

nAvailable in Thermally-Enhanced 12-Lead 4mm ×4mm

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

TO-220

nAll Surface Mount Power Supply

nRugged Industrial Power Supply

nPost Regulator for Switching Supplies

nLow Output Voltage Supply

nIntrinsic 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 ldenotes 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 ldenotes 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.

Table of contents

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