LT1082
1A High Voltage, Efficiency
Switching Voltage Regulator
DESCRIPTIO
The LT
®
1082 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 120µA 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
350µA, 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.
, LTC and LT are registered trademarks of Linear Technology Corporation
FEATURES
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Wide Input Voltage Range: 3V to 75V
High Switch Voltage: 100V
Low Quiescent Current: 4.5mA
Internal 1A Switch
Shutdown Mode Draws Only 120µA Supply Current
Isolated Flyback Regulation Mode for Fully Floating
Outputs
Can Be Externally Synchronized
Available in MiniDIP and TO-220 Packages
Same Pinout as LT1072
APPLICATIO S
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Telecom 5V Supply at 0.7A from –48V
90V Supply at 120mA from 15V
All Applications Using LT1072 (See Below for
Specification Differences)
LT1082 and LT1072 Major Specification Differences
LT1082C
LT1072HV
3V to 75V
3V to 60V
100V
75V
1A
1.25A
4.5mA
6mA
60kHz
40kHz
16.2 + 0.6 (35kΩ/R
FB
) 16 + 0.35 (7kΩ/R
FB
)
V
IN
V
SW
Switch Current Limit
Quiescent Current
Operating Frequency
Flyback Reference Voltage
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.
TYPICAL APPLICATIO
**250µH
*D1
Negative-to-Positive Telecom 5V Supply
3.83k
V
IN
33µF
80V
CHEMI-CON
SXE SERIES
V
SW
Q1
2N5401
+
MAXIMUM OUTPUT CURRENT (A)
V
OUT
5V, 0.7A
470µF
10V
CHEMI-CON
SXE SERIES
NOTE: MAXIMUM OUTPUT
CURRENT IS A FUNCTION OF
INPUT VOLTAGE. SEE THE
GRAPH ON THE RIGHT.
+
GND
LT1082
V
C
FB
1.1k
4.7k
0.01µF
0.22µF
* 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 Mµ
OR MOLYPERMALLOY.
–20V
TO –70V
1082 TA01
U
U
U
Telecom 5V Supply Maximum Output
Current vs Input Voltage
1.0
0.9
0.8
0.7
0.6
0.5
L=100µH
0.4
0 –10 –20 –30 –40 –50 –60 –70 –80 –90
INPUT VOLTAGE (V)
1082 TA02
f = 45kHz
I
SW
LIMIT = 1.07A
L=550µH
L=450µH
L=350µH
L=250µH
L=150µH
sn1082 1082fas
1
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
