National Instruments LM1085 User Manual

LM1085
3A Low Dropout Positive Regulators

LM1085 3A Low Dropout Positive Regulators

June 2005

General Description

The LM1085 is a series of low dropout positive voltage
regulators with a maximum dropout of 1.5V at 3A of load
current. It has the same pin-out as National Semiconductor’s
industry standard LM317.

The LM1085 is available in an adjustable version, which can
set the output voltage with only two external resistors. It is
also available in three fixed voltages: 3.3V, 5.0V and 12.0V.
The fixed versions integrate the adjust resistors.

The LM1085 circuit includes a zener trimmed bandgap ref­erence, current limiting and thermal shutdown.

The LM1085 series is available in TO-220 and TO-263 pack­ages. Refer to the LM1084 for the 5A version, and the
LM1086 for the 1.5A version.

Connection Diagrams

TO-220

10094702

Top View

TO-263

Features

n Available in 3.3V, 5.0V, 12V and Adjustable Versions
n Current Limiting and Thermal Protection
n Output Current 3A
n Line Regulation 0.015% (typical)
n Load Regulation 0.1% (typical)

Applications

n High Efficiency Linear Regulators
n Battery Charger
n Post Regulation for Switching Supplies
n Constant Current Regulator
n Microprocessor Supply

Application Circuit

1.2V to 15V Adjustable Regulator

10094704

Top View

10094752

Basic Functional Diagram, Adjustable Version

10094765

© 2005 National Semiconductor Corporation DS100947 www.national.com

Ordering Information

LM1085

3-lead TO-263 −40˚C to +125˚C LM1085IS-ADJ Rails

3-lead TO-220 −40˚C to + 125˚C LM1085IT-ADJ Rails

Package Temperature Range Part Number Transport Media NSC Drawing

LM1085ISX-ADJ Tape and Reel

LM1085IS-12 Rails

LM1085ISX-12 Tape and Reel

LM1085IS-3.3 Rails

LM1085ISX-3.3 Tape and Reel

LM1085IS-5.0 Rails

LM1085ISX-5.0 Tape and Reel

LM1085IT-12 Rails

LM1085IT-3.3 Rails

LM1085IT-5.0 Rails

Simplified Schematic

TS3B

T03B

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10094734

LM1085

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Junction Temperature (TJ)(Note 3) 150˚C

Storage Temperature Range -65˚C to 150˚C

Lead Temperature 260˚C, to 10 sec

ESD Tolerance (Note 4) 2000V

Maximum Input to Output Voltage Differential

LM1085-ADJ 29V

Operating Ratings (Note 1)

LM1085-12 18V

LM1085-3.3 27V

LM1085-5.0 25V

Power Dissipation (Note 2) Internally Limited

Junction Temperature Range (T

Control Section −40˚C to 125˚C

Output Section −40˚C to 150˚C

) (Note 3)

J

Electrical Characteristics

Typicals and limits appearing in normal type apply for TJ= 25˚C. Limits appearing in Boldface type apply over the entire junc­tion temperature range for operation.

Symbol Parameter Conditions

V

REF

Reference Voltage LM1085-ADJ

= 10mA, VIN−V

I

OUT

10mA ≤I

OUT

≤ I

FULL LOAD

=3V

OUT

,1.5V ≤ (VIN−V

(Note 7)

V

OUT

Output Voltage
(Note 7)

LM1085-3.3

= 0mA, VIN=5V

I

OUT

0 ≤ I

OUT≤IFULL LOAD

, 4.8V≤ VIN≤15V

LM1085-5.0

= 0mA, VIN=8V

I

OUT

0 ≤ I

OUT

≤ I

FULL LOAD

, 6.5V ≤ VIN≤ 20V

LM1085-12

= 0mA, VIN= 15V

I

OUT

∆V

OUT

Line Regulation
(Note 8)

OUT

≤ I

FULL LOAD

0 ≤ I

LM1085-ADJ

=10mA, 1.5V≤ (VIN-V

I

OUT

, 13.5V ≤ VIN≤ 25V

OUT

LM1085-3.3

= 0mA, 4.8V ≤ VIN≤ 15V

I

OUT

LM1085-5.0
I

= 0mA, 6.5V ≤ VIN≤ 20V

OUT

LM1085-12

=0mA, 13.5V ≤ VIN≤ 25V

I

OUT

∆V

OUT

Load Regulation
(Note 8)

LM1085-ADJ
(V

IN-VOUT

) = 3V, 10mA ≤ I

OUT

LM1085-3.3

= 5V, 0 ≤ I

V

IN

OUT

≤ I

FULL LOAD

LM1085-5.0

= 8V, 0 ≤ I

V

IN

OUT

≤ I

FULL LOAD

LM1085-12

Dropout Voltage
(Note 9)

= 15V, 0 ≤ I

V

IN

LM1085-ADJ, 3.3, 5, 12

, ∆V

∆V

REF

OUT

OUT

= 1%, I

≤ I

FULL LOAD

=3A 1.3 1.5 V

OUT

) ≤ 15V

≤ I

FULL LOAD

OUT

) ≤ 15V

Min

(Note 6)

1.238

1.225

3.270

3.235

4.950

4.900

11.880

11.760

Typ

(Note 5)

1.250

1.250

3.300

3.300

5.000

5.000

12.000

12.000

0.015

0.035

0.5

1.0

0.5

1.0

1.0

2.0

0.1

0.2

3

7

5

10

12

24

Max

(Note 6)

1.262

1.270

3.330

3.365

5.050

5.100

12.120

12.240

0.2

0.2

6

6

10

10

25

25

0.3

0.4

15

20

20

35

36

72

Units

V
V

V
V

V
V

V
V

%
%

mV
mV

mV
mV

mV
mV

%
%

mV
mV

mV
mV

mV
mV

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Electrical Characteristics (Continued)

Typicals and limits appearing in normal type apply for TJ= 25˚C. Limits appearing in Boldface type apply over the entire junc-

LM1085

tion temperature range for operation.

Symbol Parameter Conditions

I

LIMIT

Current Limit LM1085-ADJ

V

IN−VOUT

V

IN−VOUT

=5V
= 25V

LM1085-3.3
VIN=8V 3.2 5.5 A

LM1085-5.0

= 10V 3.2 5.5 A

V

IN

LM1085-12
VIN= 17V 3.2 5.5 A

Minimum Load
Current (Note 10)

LM1085-ADJ
V

IN−VOUT

= 25V 5.0 10.0 mA

Quiescent Current LM1085-3.3

VIN≤ 18V 5.0 10.0 mA

LM1085-5.0

≤ 20V 5.0 10.0 mA

V

IN

LM1085-12

≤ 25V 5.0 10.0 mA

V

IN

Thermal Regulation T

Ripple Rejection f

= 25˚C, 30ms Pulse .004 0.02 %/W

A

= 120Hz, C

RIPPLE

LM1085-3.3, V

LM1085-5.0, V

LM1085-12 V

IN

IN

IN

= 25µF Tantalum, I

OUT

= 25µF, (VIN−VO)=3V

ADJ

= 6.3V 60 72 dB

=8V 60 68 dB

= 15V 54 60 dB

Adjust Pin Current LM1085 55 120 µA

Adjust Pin Current

10mA ≤ I

OUT

≤ I

FULL LOAD

, 1.5V ≤ VIN−V

Change

Temperature
Stability

Long Term Stability T

RMS Output Noise

OUT

)

(% of V

Thermal Resistance
Junction-to-Case

=125˚C, 1000Hrs 0.3 1.0 %

A

10Hz ≤ f≤ 10kHz 0.003 %

3-Lead TO-263: Control Section/Output Section
3-Lead TO-220: Control Section/Output Section

OUT

OUT

Min

(Note 6)

3.2

0.2

=3A

60 75 dBLM1085-ADJ, C

≤ 25V

Typ

(Note 5)

(Note 6)

5.5

0.5

0.2 5 µA

0.5 %

0.7/3.0

0.7/3.0

Max

Units

A
A

˚C/W
˚C/W

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.

Note 2: Power dissipation is kept in a safe range by current limiting circuitry. Refer to Overload Recovery in Application Notes.

Note 3: The maximum power dissipation is a function of T

P

=(T

D

J(max)–TA

Note 4: For testing purposes, ESD was applied using human body model, 1.5kΩ in series with 100pF.

Note 5: Typical Values represent the most likely parametric norm.

Note 6: All limits are guaranteed by testing or statistical analysis.

Note 7: I

dissipation for the LM1085 is only achievable over a limited range of input-to-output voltage.

Note 8: Load and line regulation are measured at constant junction temperature, and are guaranteed up to the maximum power dissipation of 30W. Power
dissipation is determined by the input/output differential and the output current. Guaranteed maximum power dissipation will not be available over the full input/output
range.

Note 9: Dropout voltage is specified over the full output current range of the device.

Note 10: The minimum output current required to maintain regulation.

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)/θJA. All numbers apply for packages soldered directly into a PC board. Refer to Thermal Considerations in the Application Notes.

FULL LOAD

is defined in the current limit curves. The I

, θJA, and TA. The maximum allowable power dissipation at any ambient temperature is

J(max)

FULL LOAD

Curve defines the current limit as a function of input-to-output voltage. Note that 30W power