1
LT1082
sn1082 1082fas
FEATURES
APPLICATIO S
U
DESCRIPTIO
U
1A High Voltage, Efficiency
Switching Voltage Regulator
LT1082C LT1072HV
V
IN
3V to 75V 3V to 60V
V
SW
100V 75V
Switch Current Limit 1A 1.25A
Quiescent Current 4.5mA 6mA
Operating Frequency 60kHz 40kHz
Flyback Reference Voltage 16.2 + 0.6 (35kΩ/R
FB
) 16 + 0.35 (7kΩ/R
FB
)
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.
■
Telecom 5V Supply at 0.7A from –48V
■
90V Supply at 120mA from 15V
■
All Applications Using LT1072 (See Below for
Specification Differences)
■
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
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.
Negative-to-Positive Telecom 5V Supply
INPUT VOLTAGE (V)
0
MAXIMUM OUTPUT CURRENT (A)
–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=550µH
L=450µH
L=350µH
L=250µH
L=150µH
L=100µH
f = 45kHz
I
SW
LIMIT = 1.07A
Telecom 5V Supply Maximum Output
Current vs Input Voltage
+
V
IN
V
SW
GND
FB
V
C
LT1082
4.7k
0.22µF
33µF
80V
CHEMI-CON
SXE SERIES
–20V
TO –70V
**250µH
3.83k
+
0.01µF
1.1k
Q1
2N5401
470µF
10V
CHEMI-CON
SXE SERIES
V
OUT
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 Mµ
OR MOLYPERMALLOY.
*
**
1082 TA01
NOTE: MAXIMUM OUTPUT
CURRENT IS A FUNCTION OF
INPUT VOLTAGE. SEE THE
GRAPH ON THE RIGHT.
TYPICAL APPLICATIO
U
, LTC and LT are registered trademarks of Linear Technology Corporation
