1

LT1082

1A High Voltage, Efficiency

Switching Voltage Regulator

LT1082C

LT1072HV

3V to 75V

3V to 60V

100V

75V

Switch Current Limit

1A

1.25A

Quiescent Current

4.5mA

6mA

Operating Frequency

60kHz

40kHz

Flyback Reference Voltage

16.2 + 0.6 (35k

LT1082 and LT1072 Major Specification Differences

USER NOTE: This data sheet is only intended to provide specifications, graphs, and a general

functional description of the LT1082. Application circuits are included to show the capability of the

LT1082. A complete design manual (AN19) and Switcher CAD (LTC Switching Power Supply Design

Program) should be obtained to assist in developing new designs. This manual contains a

comprehensive discussion of both the LT1070 and the external components used with it, as well as

complete formulas for calculating the values of these components. The manual can also be used for

the LT1082 by factoring in the lower switch current rating.

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Telecom 5V Supply at 0.7A from –48V

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90V Supply at 120mA from 15V

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All Applications Using LT1072 (See Below for

Specification Differences)

S

APPLICATI

S

FEATURE

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Wide Input Voltage Range: 3V to 75V

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High Switch Voltage: 100V

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Low Quiescent Current: 4.5mA

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Internal 1A Switch

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Shutdown Mode Draws Only 120

µA Supply Current

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Isolated Flyback Regulation Mode for Fully Floating

Outputs

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Can Be Externally Synchronized

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Available in MiniDIP and TO-220 Packages

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Same Pinout as LT1072

The LT1082 is a monolithic high voltage switching

regulator. It can be operated in all standard switching

configurations including buck, boost, flyback, forward,

and inverting. A 1A high efficiency switch is included on

the die along with all oscillator, control, and protection

circuitry.

The LT1082 operates with supply voltages from 3V to 75V,

switch voltage up to 100V and draws only 4.5mA quies-

cent current. It can deliver load power up to 20W with no

external power devices. By utilizing current-mode switch-

ing techniques, it provides excellent AC and DC load and

line regulation.

An externally activated shutdown mode reduces total

supply current to 120

µA typical for standby operation.

Totally isolated and regulated outputs can be generated by

using the optional “isolated flyback regulation mode” built

into the LT1082, without the need for optocouplers or

extra transformer windings.

The LT1082 has a unique feature to provide high voltage

short-circuit protection. When the FB pin is pulled down to

0.6V and the current out of the pin reaches approximately

350

µA, the switching frequency will shift down from

60kHz to 12kHz.

The LT1082 is nearly identical to the lower voltage LT1072.

For the major differences in specifications, see the table on

the left.

DESCRIPTIO

Negative-to-Positive Telecom 5V Supply

INPUT VOLTAGE (V)

0

–20

–40 –50

–90

1082 TA02

–10

–30

–60 –70 –80

1.0

0.9

0.8

0.7

0.6

0.5

0.4

L=550

µH

L=450

µH

L=350

µH

L=250

µH

L=150

µH

L=100

µH

f = 45kHz

Telecom 5V Supply Maximum Output

Current vs Input Voltage

+

GND

FB

LT1082

4.7k

0.22

µF

33

µF

80V

CHEMI-CON

SXE SERIES

–20V

TO –70V

**250

µH

3.83k

+

0.01

µF

1.1k

Q1

2N5401

470

µF

10V

CHEMI-CON

SXE SERIES

5V, 0.7A

*D1

MOTOROLA MUR110 (100V, 1A)

69 TURNS OF #28 AWG WIRE ON A

MICROMETALS T60 TYPE 52 CORE.

NOTE: THIS CORE IS LOW COST, BUT

HAS HIGHER CORE LOSS AND IS LARGER

THAN NECESSARY FOR LOWER CURRENT

APPLICATIONS. FOR SMALLER INDUCTORS

OR HIGHER EFFICIENCY, USE A LOW LOSS

CORE SUCH AS MAGNETICS INC. KOOL M

µ

OR MOLYPERMALLOY.

*

**

1082 TA01

NOTE: MAXIMUM OUTPUT

CURRENT IS A FUNCTION

OF INPUT VOLTAGE. SEE

THE GRAPH ON THE RIGHT.