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LM1085
3A Low Dropout Positive Regulators
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 ref-
erence, current limiting and thermal shutdown.
The LM1085 series is available in TO-220 and TO-263 pack-
ages. Refer to the LM1084 for the 5A version, and the
LM1086 for the 1.5A version.
Connection Diagrams
Top View
Top View
Basic Functional Diagram,
Adjustable Version
© 2005 National Semiconductor Corporation
TO-220
10094702
TO-263
10094704
10094765
DS100947
Features
n Available in 3.3V, 5.0V, 12V and Adjustable Versions
n Current Limiting and Thermal Protection
n Output Current
n Line Regulation
n Load Regulation
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
June 2005
3A
0.015% (typical)
0.1% (typical)
10094752
www.national.com
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Table of Contents
Summary of Contents for National Semiconductor LM1085 Series
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Page 1: General Description
The LM1085 circuit includes a zener trimmed bandgap ref- erence, current limiting and thermal shutdown. The LM1085 series is available in TO-220 and TO-263 pack- ages. Refer to the LM1084 for the 5A version, and the LM1086 for the 1.5A version. -
Page 2: Ordering Information
Ordering Information Package Temperature Range 3-lead TO-263 −40˚C to +125˚C 3-lead TO-220 −40˚C to + 125˚C Simplified Schematic www.national.com Part Number Transport Media LM1085IS-ADJ Rails 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... -
Page 3: Absolute Maximum Ratings
Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Maximum Input to Output Voltage Differential LM1085-ADJ LM1085-12 LM1085-3.3 LM1085-5.0 Power Dissipation (Note 2) Electrical Characteristics Typicals and limits appearing in normal type apply for T tion temperature range for operation. - Page 4 Electrical Characteristics Typicals and limits appearing in normal type apply for T tion temperature range for operation. Symbol Parameter Current Limit LM1085-ADJ LIMIT −V −V LM1085-3.3 LM1085-5.0 LM1085-12 Minimum Load LM1085-ADJ Current (Note 10) Quiescent Current LM1085-3.3 LM1085-5.0 LM1085-12 Thermal Regulation = 25˚C, 30ms Pulse Ripple Rejection RIPPLE...
- Page 5 Typical Performance Characteristics Dropout Voltage vs. Output Current Short-Circuit Current vs. Input/Output Difference 10094768 10094763 Percent Change in Output Voltage vs. Temperature Adjust Pin Current vs. Temperature 10094798 10094799 Maximum Power Dissipation vs. Temperature Ripple Rejection vs. Frequency (LM1085-Adj.) 10094743 10094770 www.national.com...
- Page 6 Typical Performance Characteristics (Continued) Ripple Rejection vs. Output Current (LM1085-Adj.) Line Transient Response 10094744 10094772 Load Transient Response 10094771 www.national.com...
- Page 7 Application Note GENERAL Figure 1 shows a basic functional diagram for the LM1085- Adj (excluding protection circuitry) . The topology is basically that of the LM317 except for the pass transistor. Instead of a Darlingtion NPN with its two diode voltage drop, the LM1085 uses a single NPN.
- Page 8 Application Note (Continued) Figure 3 shows a typical application using a fixed output regulator. Rt1 and Rt2 are the line resistances. V than the V by the sum of the voltage drops along the line resistances. In this case, the load regulation seen at the would be degraded from the data sheet specification.
- Page 9 Application Note (Continued) must be added, one for case to heat-sink (θ heatsink to ambient (θ ). The junction temperature can be predicted as follows: + θ + θ (θ ) = T is junction temperature, T is ambient temperature, and is the power consumption of the device.
- Page 10 Typical Applications 10094767 5V to 3.3V, 1.5A Regulator 10094754 Battery Charger 10094750 Adjustable 10094755 Adjustable Fixed Regulator 10094756 Regulator with Reference 10094752 1.2V to 15V Adjustable Regulator 10094757 High Current Lamp Driver Protection 10094753 5V Regulator with Shutdown www.national.com...
- Page 11 Typical Applications (Continued) 10094761 Automatic Light control 10094759 Battery Backup Regulated Supply 10094762 Generating Negative Supply voltage 10094760 Ripple Rejection Enhancement 10094758 Remote Sensing www.national.com...
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Page 12: Physical Dimensions
Physical Dimensions inches (millimeters) unless otherwise noted 3-Lead TO-263 NS Package Number TS3B 3-Lead TO-220 NS Package Number T03B www.national.com... - Page 13 National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR...