LINEAR TECHNOLOGY LT3080 Technical data

FEATURES

prop

LT3080

Adjustable1.1A Single

Resistor Low Dropout

Regulator

U

DESCRIPTIO

■

Outputs May be Paralleled for Higher Current and

Heat Spreading

■

Output Current: 1.1A

■

Single Resistor Programs Output Voltage

■

1% Initial Accuracy of SET Pin Current

■

Output Adjustable to 0V

■

Low Output Noise: 40μV

■

Wide Input Voltage Range: 1.2V to 36V

■

Low Dropout Voltage: 300mV

■

<1mV Load Regulation

■

<0.001%/V Line Regulation

■

Minimum Load Current: 0.5mA

■

Stable with 2.2μF Minimum Ceramic Output

(10Hz to 100kHz)

RMS

Capacitor

■

Current Limit with Foldback and Overtemperature

Protected

■

Available in 8-Lead MSOP, 3mm × 3mm DFN,

5-Lead TO-220 and 3-Lead SOT-223

U

APPLICATIO S

■

High Current All Surface Mount Supply

■

High Effi ciency Linear Regulator

■

Post Regulator for Switching Supplies

■

Low Parts Count Variable Voltage Supply

■

Low Output Voltage Power Supplies

The LT®3080 is a 1.1A low dropout linear regulator that can
be paralleled to increase output current or spread heat in
surface mounted boards. Architected as a precision cur­rent source and voltage follower allows this new regulator
to be used in many applications requiring high current,
adjustability to zero, and no heat sink. Also the device
brings out the collector of the pass transistor to allow low
dropout operation —down to 300 millivolts— when used
with multiple supplies.

A key feature of the LT3080 is the capability to supply a
wide output voltage range. By using a reference current
through a single resistor, the output voltage is programmed
to any level between zero and 36V. The LT3080 is stable
with 2.2μF of capacitance on the output, and the IC uses
small ceramic capacitors that do not require additional
ESR as is common with other regulators.

Internal protection circuitry includes current limiting and
thermal limiting. The LT3080 regulator is offered in the
8-lead MSOP (with an Exposed Pad for better thermal
characteristics), a 3mm × 3mm DFN, 5-lead TO-220 and
a simple-to-use 3-lead SOT-223 version.

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

trademarks are the

erty of their respective owners.

TYPICAL APPLICATIO

Variable Output Voltage 1.1A Supply

SET

LT3080

R

SET

V

OUT

+
–

V

1.2V TO 36V
V

CONTROL

1μF

IN

IN

= R

SET

U

• 10μA

OUT

3080 TA01a

V

OUT

2.2μF

Set Pin Current Distribution

N = 13792

9.80

9.90

SET PIN CURRENT DISTRIBUTION (μA)

10.00

10.10

3080 G02

10.20

3080f

1

LT3080

(

WW

W

ABSOLUTE AXI U RATI GS

V

CONTROL

Pin Voltage ..................................... 40V, –0.3V

U

(Note 1)(All Voltages Relative to V

IN Pin Voltage ................................................ 40V, –0.3V

SET Pin Current (Note 7) .....................................±10mA

SET Pin Voltage (Relative to OUT) .........................±0.3V

Output Short-Circuit Duration .......................... Indefi nite

PIN CONFIGURATION

TOP VIEW

1OUT

OUT

2

OUT

3

SET

4

8-LEAD

T

= 125°C, θJA = 64°C/W, θJC = 3°C/W

JMAX

EXPOSED PAD (PIN 9) IS OUT, MUST BE SOLDERED TO PCB

9

DD PACKAGE

3mm × 3mm) PLASTIC DFN

8
7

6
5

IN
IN
NC
V

CONTROL

)

OUT

Operating Junction Temperature Range

(Notes 2, 10) .......................................... –40°C to 125°C

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

Lead Temperature (Soldering, 10 sec)

MS8E, T and ST Packages Only ........................ 300°C

TOP VIEW

8

OUT

1

OUT

2

OUT

SET

T

EXPOSED PAD (PIN 9) IS OUT, MUST BE SOLDERED TO PCB

8-LEAD PLASTIC MSOP

= 125°C, θJA = 60°C/W, θJC = 10°C/W

JMAX

9

3
4

MS8E PACKAGE

IN

7

IN

6

NC

5

V

CONTROL

FRONT VIEW

3

IN*

TAB IS

OUT

ST PACKAGE

3-LEAD PLASTIC SOT-223

AND IN TIED TOGETHER

CONTROL

= 125°C, θJA = 55°C/W, θJC = 15°C/W

JMAX

2

OUT

1

SET

TAB IS

OUT

FRONT VIEW

5
4
3
2
1

T PACKAGE

5-LEAD PLASTIC TO-220

T

= 125°C, θJA = 40°C/W, θJC = 3°C/W

JMAX

IN
V

CONTROL

OUT
SET
NC

*IN IS V

T

ORDER INFORMATION

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

LT3080EDD#PBF LT3080EDD#TRPBF LCBN 8-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
LT3080EMS8E#PBF LT3080EMS8E#TRPBF LTCBM 8-Lead Plastic MSOP –40°C to 125°C
LT3080ET#PBF LT3080ET#TRPBF LT3080ET 5-Lead Plastic TO-220 –40°C to 125°C
LT3080EST#PBF LT3080EST#TRPBF 3080 3-Lead Plastic SOT-223 –40°C to 125°C

LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE

LT3080EDD LT3080EDD#TR LCBN 8-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
LT3080EMS8E LT3080EMS8E#TR LTCBM 8-Lead Plastic MSOP –40°C to 125°C
LT3080ET LT3080ET#TR LT3080ET 5-Lead Plastic TO-220 –40°C to 125°C
LT3080EST LT3080EST#TR 3080 3-Lead Plastic SOT-223 –40°C to 125°C
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/

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

3080f

2

LT3080

The ● denotes the specifi cations which apply over the full operating

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifi cations are at T

PARAMETER CONDITIONS MIN TYP MAX UNITS

SET Pin Currrent I

Output Offset Voltage (V
V

= 1V, V

IN

CONTROL

= 2V, I

OUT

OUT

– V

= 1mA

SET

)

V

Load Regulation ΔI

ΔV

Line Regulation (Note 9)
DFN and MSOP Package

Line Regulation (Note 9)
SOT-223 and TO-220 Package

ΔI
ΔV

ΔI
ΔV

Minimum Load Current (Notes 3, 9) VIN = V

V

Dropout Voltage (Note 4) I

CONTROL

VIN Dropout Voltage (Note 4) I

CONTROL Pin Current I

Current Limit VIN = 5V, V
Error Amplifi er RMS Output Noise (Note 6) I
Reference Current RMS Output Noise (Note 6) 10Hz ≤ f ≤ 100kHz 1 nA
Ripple Rejection f = 120Hz, V

Thermal Regulation, I

SET

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 specifi ed, all voltages are with respect to V
The LT3080 is tested and specifi ed under pulse load conditions such that
T

≈ TA. The LT3080 is 100% tested at TA = 25°C. Performance at –40°C

J

and 125°C is assured by design, characterization and correlation with
statistical process controls.

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 LT3080, dropout is caused by either minimum control
voltage (V

) or minimum input voltage (VIN). Both parameters are

CONTROL

specifi ed with respect to the output voltage. The specifi cations represent the
minimum input-to-output differential voltage required to maintain regulation.

Note 5: The CONTROL pin current is the drive current required for the
output transistor. This current will track output current with roughly a 1:60
ratio. The minimum value is equal to the quiescent current of the device.

Note 6: Output noise is lowered by adding a small capacitor across the
voltage setting resistor. Adding this capacitor bypasses the voltage setting

VIN = 1V, V

SET

V

≥ 1V, V

IN

DFN and MSOP Package

OS

SOT-223 and T0-220 Package

ΔI

SET

SET

SET

OS

LOAD =

ΔI

OS

LOAD =

VIN = 1V to 25V, V
V

OS

IN

VIN = 1V to 26V, V
V

IN

V

IN

V

IN

LOAD

I

LOAD

LOAD

I

LOAD

LOAD

I

LOAD

LOAD

= 1V to 25V, V

= 1V to 26V, V

= V
= V

f = 10kHz
f = 1MHz

10ms Pulse 0.003 %/W

= 25°C. (Note 11)

A

CONTROL
CONTROL

= 2.0V, I
≥ 2.0V, 1mA ≤ I

= 1mA, TJ = 25°C

LOAD

1mA to 1.1A
1mA to 1.1A (Note 8)

=1V to 25V, I

CONTROL

=1V to 25V, I

CONTROL

=1V to 26V, I

CONTROL

=1V to 26V, I

CONTROL

= 10V

CONTROL

= 25V (DFN and MSOP Package)

CONTROL

= 26V (SOT-223 and TO-220 Package)

CONTROL

= 100mA
= 1.1A

= 100mA
= 1.1A

= 100mA
= 1.1A

CONTROL

= 5V, V

SET

= 0V, V

= 1.1A, 10Hz ≤ f ≤ 100kHz, C

RIPPLE

= 0.5V

P-P

, I

LOAD

= 0.2A, C

resistor shot noise and reference current noise; output noise is then equal
to error amplifi er noise (see Applications Information section).

Note 7: SET pin is clamped to the output with diodes. These diodes only
carry current under transient overloads.

.

OUT

Note 8: Load regulation is Kelvin sensed at the package.
Note 9: Current limit may decrease to zero at input-to-output differential

voltages (V
(SOT-223 and TO-220 package). Operation at voltages for both IN and
V

CONTROL

between input and output voltage is below the specifi ed differential (V
V

OUT

when the device is in current limit.
Note 10: This IC includes over-temperature protection that is intended

to protect the device during momentary overload conditions. Junction
temperature will exceed the maximum operating junction temperature
when over-temperature protection is active. Continuous operation above
the specifi ed maximum operating junction temperature may impair device
reliability.

Note 11: The SOT-223 package connects the IN and V
together internally. Therefore, test conditions for this pin follow the
V

CONTROL

≤ 1.1A (Note 9)

LOAD

●

●

●

9.90

9.801010
–2

–3.5

–5
–6

10.10

10.20
2

3.5
5

6

–0.1

LOAD
LOAD

LOAD
LOAD

=1mA
=1mA

=1mA
=1mA

●

●

●

●

●

●

0.6 1.3

0.1

0.003

0.1

0.003
300 500

0.5 nA/V

0.5 nA/V

1
1

1.2

OUT

= 10μF, C

OUT

= –0.1V

SET

= 0.1μF, C

SET

●

●

●

●

●

●

= 0.1μF 40 μV

= 2.2μF

OUT

1.35 1.6
100

350

17

200
500

4

6

30

1.1 1.4 A

75
55
20

) greater than 25V (DFN and MSOP package) or 26V

IN–VOUT

is allowed up to a maximum of 36V as long as the difference

) voltage. Line and load regulation specifi cations are not applicable

pins

CONTROL

conditions listed in the Electrical Characteristics Table.

μA
μA

mV
mV

mV
mV

nA

mV

mV/V

mV/V

μA
mA
mA

mV
mV

mA
mA

RMS

RMS

dB

dB

dB

–

IN

3080f

V
V

3

LT3080

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Set Pin Current

10.20

10.15

10.10

10.05

10.00

9.95

SET PIN CURRENT (μA)

9.90

9.85

9.80
–50

–25

0

50

25

TEMPERATURE (°C)

75

100

125

150

3080 G01

Offset Voltage Distribution

N = 13250

–2

–1

VOS DISTRIBUTION (mV)

Load Regulation Minimum Load Current

0

ΔI

= 1mA TO 1.1A

LOAD

– V

V

–0.1

IN

OUT

–0.2

–0.3

–0.4

–0.5

–0.6

–0.7

CHANGE IN OFFSET VOLTAGE WITH LOAD (mV)

–0.8

CHANGE IN REFERENCE CURRENT

CHANGE IN OFFSET VOLTAGE

–50

–25

0

0

= 2V

(V

– V

OUT

25

TEMPERATURE (°C)

)

SET

50

75

100

125

3080 G04

3080 G07

2

CHANGE IN REFERENCE CURRENT WITH LOAD (nA)

20

10

0

–10

–20

–30

–40

–50

–60

150

1

Set Pin Current Distribution Offset Voltage (V

N = 13792

9.80

9.90

SET PIN CURRENT DISTRIBUTION (μA)

Offset Voltage Offset Voltage

1.00
I

= 1mA

LOAD

0.75

0.50

0.25

0

–0.25

OFFSET VOLTAGE (mV)

–0.50

–0.75

–1.00

0.8

0.7

0.6

0.5

0.4

0.3

0.2

MINIMUM LOAD CURRENT (mA)

0.1

612 24

0

INPUT-TO-OUTPUT VOLTAGE (V)

*SEE NOTE 9 IN ELECTRICAL

CHARACTERISTICS TABLE

V

IN, CONTROL

V

IN, CONTROL

0

–50

–25

0

25

TEMPERATURE (°C)

*SEE NOTE 9 IN ELECTRICAL

CHARACTERISTICS TABLE

– V

– V

10.00

18

OUT

OUT

50

= 36V*

= 1.5V

75

10.10

100

– V

2.0

OUT

IL = 1mA

1.5

1.0

0.5

0

–0.5

OFFSET VOLTAGE (mV)

–1.0

–1.5

36*

–2.0

–50

0.25

0

–0.25

–0.50

–0.75

–1.00

OFFSET VOLTAGE (mV)

–1.25

–1.50

–1.75

–25

0

TEMPERATURE (°C)

TJ = 125°C

0.2 0.4 0.8

0

LOAD CURRENT (A)

25

TJ = 25°C

50

0.6

10.20

3080 G02

30

3080 G05

)

SET

75

100

1.0

125

150

3080 G03

1.2

3080 G06

Dropout Voltage (Minimum IN
Voltage)

400

350

125

3080 G08

150

) (mV)

OUT

300

– V

250

IN

200

150

100

50

MINIMUM IN VOLTAGE (V

0

0.2 0.4 0.8

0

OUTPUT CURRENT (A)

TJ = 125°C

0.6

TJ = 25°C

1.0

1.2

3080 G09

4

3080f

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LT3080

Dropout Voltage (Minimum IN
Voltage)

400

350

) (mV)

OUT

300

– V

IN

250

I

200

150

100

50

MINIMUM IN VOLTAGE (V

0

–25

–50

0

TEMPERATURE (°C)

LOAD

I

LOAD

50

25

Current Limit

1.6

1.4

1.2

VIN = 7V

1.0

0.8

0.6

CURRENT LIMIT (A)

0.4

0.2

0

–50

V

–25

OUT

= 0V

0

50

25

TEMPERATURE (°C)

I

LOAD

= 500mA

= 100mA

75

75

= 1.1A

100

100

125

125

3080 G10

3080 G13

150

150

Dropout Voltage (Minimum

Pin Voltage)

TJ = –50°C

TJ = 25°C

0.2 0.4 0.8

0.6

OUTPUT CURRENT (A)

) (V)

1.6

OUT

1.4

– V

1.2

CONTROL

1.0

0.8

0.6

0.4

0.2

0

MINIMUM CONTROL VOLTAGE (V

V

CONTROL

0

Current Limit

1.6

1.4

1.2

1.0

0.8

0.6

CURRENT LIMIT (A)

MSOP

0.4

0.2

0

612 24

0

INPUT-TO-OUTPUT DIFFERENTIAL (V)

*SEE NOTE 9 IN ELECTRICAL

CHARACTERISTICS TABLE

SOT-223
AND
TO-220

AND

DFN

18

TJ = 125°C

TJ = 25°C

1.0

30

3080 G11

3080 G14

1.2

36*

Dropout Voltage (Minimum

) (V)

1.6

OUT

1.4

– V

1.2

CONTROL

1.0

0.8

0.6

0.4

0.2

0

MINIMUM CONTROL VOLTAGE (V

–50

V

CONTROL

–25

0

Pin Voltage)

I

= 1mA

LOAD

50

25

TEMPERATURE (°C)

Load Transient Response

75

50

25

0

–25

–50

OUTPUT VOLTAGE DEVIATION (mV)LOAD CURRENT (mA)

400

300

200

100

C

OUT

0

105

0

C

OUT

= 2.2μF CERAMIC

2015

25

TIME (μs)

I

= 1.1A

LOAD

75

100

V

= 1.5V

OUT

= 0.1μF

C

SET

= V

V

IN

CONTROL

= 10μF CERAMIC

30 35 45

40

125

150

3080 G12

= 3V

50

3080 G15

Load Transient Response Line Transient Response

150

100

50

0

–50

–100

OUTPUT VOLTAGE DEVIATION (mV)LOAD CURRENT (A)

1.2

0.9

0.6

0.3

0

105

0

VIN = V
V
C
C

2015

25

TIME (μs)

CONTROL

= 1.5V

OUT

= 10μF CERAMIC

OUT

= 0.1μF

SET

30 35 45

40

= 3V

50

3080 G16

75

50

25

0

–25

–50

6

5

4

3

2

2010

0

IN/CONTROL VOLTAGE (V) OUTPUT VOLTAGE DEVIATION (mV)

4030

50

TIME (μs)

V

= 1.5V

OUT

= 10mA

I

LOAD

= 2.2μF

C

OUT

CERAMIC

= 0.1μF

C

SET

CERAMIC

60 70 90

80

3080 G17

100

Turn-On Response

5

4

3

2

1

0

2.0

1.5

1.0

0.5

0

OUTPUT VOLTAGE (V) INPUT VOLTAGE (V)

21

0

C

= 2.2μF CERAMIC

OUT

43

5

TIME (μs)

R

= 100k

SET

= 0

C

SET

= 1Ω

R

LOAD

67 9

8

3080 G27

3080f

5

10

LT3080

UW

TYPICAL PERFOR A CE CHARACTERISTICS

V

CONTROL

25

20

15

10

CONTROL PIN CURRENT (mA)

5

0

0

*SEE NOTE 9 IN ELECTRICAL

CHARACTERISTICS TABLE

Pin Currrent

I

= 1.1A

LOAD

DEVICE IN
CURRENT LIMIT

I

= 1mA

LOAD

12 18 24

6

INPUT-TO-OUTPUT DIFFERENTIAL (V)

Ripple Rejection - Single Supply

100

VIN = V

90

80

70

60

50

40

30

RIPPLE REJECTION (dB)

20

10

= 2.2μF CERAMIC

C

OUT

0

CONTROL

I

= 1.1A

LOAD

FREQUENCY (Hz)

= V

OUT (NOMINAL)

RIPPLE = 50mV

10k 100k10010 1k 1M

I

LOAD

30 36*

+ 2V

= 100mA

3080 G18

P–P

3080 G21

V

CONTROL

30

V
V

25

20

15

10

CONTROL PIN CURRENT (mA)

5

0

0

Ripple Rejection - Dual Supply

- V

100

90

80

70

60

50

40

VIN = V
V

30

RIPPLE REJECTION (dB)

C

20

10

0

Pin Current

– V

CONTROL

– V

= 1V

IN

OUT

0.4 0.6 0.8

0.2
LOAD CURRENT (A)

Pin

CONTROL

I

LOAD

OUT (NOMINAL)

= V

CONTROL

= 2.2μF CERAMIC

OUT

RIPPLE = 50mV

= 2V

OUT

TJ = –50°C

= 125°C

T

J

= 1.1A

+ 1V

OUT (NOMINAL)

P–P

FREQUENCY (Hz)

+2V

10k 100k10010 1k 1M

I

LOAD

T

J

= 25°C

1.0 1.2

3080 G19

= 100mA

3080 G22

Residual Output Voltage with
Less Than Minimum Load

0.8
SET PIN = 0V

0.7

0.6

0.5

0.4

0.3

OUTPUT VOLTAGE (V)

0.2

0.1

0

V

IN

V

= 10V

IN

0

V

OUT

R

TEST

= 5V

V

IN

R

(Ω)

TEST

Ripple Rejection - Dual Supply

- IN Pin

100

90

80

70

60

50

VIN = V

40

30

RIPPLE REJECTION (dB)

20

10

V

CONTROL

RIPPLE = 50mV

C

= 2.2μF CERAMIC

OUT

= 1.1A

I

LOAD

0

OUT (NOMINAL)

= V

+ 1V

OUT (NOMINAL)

P–P

FREQUENCY (Hz)

+2V

10k 100k10010 1k 1M

VIN = 20V

2k1k

3080 G20

3080 G23

6

Ripple Rejection (120Hz)

80

79

78

77

76

75

74

73

RIPPLE REJECTION (dB)

72

71

70

–50

SINGLE SUPPLY OPERATION

= V

V

IN

RIPPLE = 500mV

= 1.1A

I

LOAD

= 0.1μF, C

C

SET

–25 25

0

TEMPERATURE (°C)

OUT(NOMINAL)

REFERENCE CURRENT NOISE SPECTRAL DENSITY (pA/ √Hz)

Noise Spectral Density

10k

1k

100

+ 2V

, f=120Hz

P-P

= 2.2μF

OUT

125

50

100

75

150

3080 G24

10

1

ERROR AMPLIFIER NOISE SPECTRAL DENSITY (nV/√Hz)

FREQUENCY (Hz)

10k 100k10010 1k

1k

100

10

1.0

0.1

3080 G25

3080f

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LT3080

Output Voltage Noise

V

OUT

100μV/DIV

3080 G26

V

OUT

R

SET

C

SET

C

OUT

I

LOAD

= 1V

TIME 1ms/DIV

= 100k
= O.1μF

= 10μF

= 1.1A

UUU

PI FU CTIO S

V

CONTROL

pin for the control circuitry of the device. The current fl ow
into this pin is about 1.7% of the output current. For the
device to regulate, this voltage must be more than 1.2V
to 1.35V greater than the output voltage (see Dropout
specifi cations).

IN (Pins 7, 8/Pins 7, 8/Pin 5/Pin 3): This is the collector
to the power device of the LT3080. The output load current
is supplied through this pin. For the device to regulate, the
voltage at this pin must be more than 0.1V to 0.5V greater
than the output voltage (see Dropout specifi cations).

(Pin 5/Pin 5/Pin 4/NA): This pin is the supply

(DD/MS8E/T/ST)

Error Amplifi er Gain and Phase

3080 G28

300

250

200

PHASE (DEGREES)

150

100

50

0

–50

–100

–150

–200

20

15

10

5

0

–5

GAIN (dB)

–10

–15

–20

–25

–30

FREQUENCY (Hz)

10k 100k10010 1k 1M

IL = 1.1A

= 100mA

I

L

IL = 1.1A

IL = 100mA

OUT (Pins 1-3/Pins 1-3/Pin 3/Pin 2): This is the power
output of the device. There must be a minimum load cur­rent of 1mA or the output may not regulate.

SET(Pin 4/Pin 4/Pin 2/Pin 1): This pin is the input to the
error amplifi er and the regulation set point for the device.
A fi xed current of 10μA fl ows out of this pin through a
single external resistor, which programs the output voltage
of the device. Output voltage range is zero to the absolute
maximum rated output voltage. Transient performance
can be improved by adding a small capacitor from the
SET pin to ground.

NC (Pin 6/Pin 6/Pin 1/NA): No Connection. No Connect
pins have no connection to internal circuitry and may be
tied to V

IN

, V

CONTROL

, V

, GND, or fl oated.

OUT

Exposed Pad (Pin 9/Pin 9/NA/NA): OUT on MS8E and
DFN packages.

TAB: OUT on TO-220 and SOT-223 packages.

3080f

7

LT3080

BLOCK DIAGRA

W

V

CONTROL

IN

10μA

+

–

3080 BD

OUTSET

U

WUU

APPLICATIO S I FOR ATIO

The LT3080 regulator is easy to use and has all the pro­tection features expected in high performance regulators.
Included are short-circuit protection and safe operating
area protection, as well as thermal shutdown.

The LT3080 is especially well suited to applications needing
multiple rails. The new architecture adjusts down to zero
with a single resistor handling modern low voltage digital
IC’s as well as allowing easy parallel operation and thermal
management without heat sinks. Adjusting to “zero” output
allows shutting off the powered circuitry and when the
input is pre-regulated – such as a 5V or 3.3V input supply
– external resistors can help spread the heat.

A precision “0” TC 10μA internal current source is con­nected to the non-inverting input of a power operational
amplifi er. The power operational amplifi er provides a low
impedance buffered output to the voltage on the non-invert­ing input. A single resistor from the non-inverting input to
ground sets the output voltage and if this resistor is set
to zero, zero output results. As can be seen, any output
voltage can be obtained from zero up to the maximum
defi ned by the input power supply.

What is not so obvious from this architecture are the ben­efi ts of using a true internal current source as the reference
as opposed to a bootstrapped reference in older regulators.
A true current source allows the regulator to have gain
and frequency response independent of the impedance on
the positive input. Older adjustable regulators, such as the

LT1086 have a change in loop gain with output voltage
as well as bandwidth changes when the adjustment pin
is bypassed to ground. For the LT3080, the loop gain is
unchanged by changing the output voltage or bypassing.
Output regulation is not fi xed at a percentage of the output
voltage but is a fi xed fraction of millivolts. Use of a true
current source allows all the gain in the buffer amplifi er
to provide regulation and none of that gain is needed to
amplify up the reference to a higher output voltage.

The LT3080 has the collector of the output transistor
connected to a separate pin from the control input. Since
the dropout on the collector (IN pin) is only 300mV, two
supplies can be used to power the LT3080 to reduce dis­sipation: a higher voltage supply for the control circuitry
and a lower voltage supply for the collector. This increases
effi ciency and reduces dissipation. To further spread the
heat, a resistor can be inserted in series with the collector
to move some of the heat out of the IC and spread it on
the PC board.

The LT3080 can be operated in two modes. Three terminal
mode has the control pin connected to the power input pin
which gives a limitation of 1.35V dropout. Alternatively,
the “control” pin can be tied to a higher voltage and the
power IN pin to a lower voltage giving 300mV dropout
on the IN pin and minimizing the power dissipation. This
allows for a 1.1A supply regulating from 2.5V
or 1.8V

to 1.2V

IN

with low dissipation.

OUT

IN

to 1.8V

OUT

3080f

8