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
s
s
s
s
s
s
s
s
s
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
s
s
s
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
LT1082
ABSOLUTE
AXI U
RATI GS
Supply Voltage ....................................................... 75V
Switch Output Voltage .......................................... 100V
Feedback Pin Voltage (Transient, 1ms) ................
±15V
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
PACKAGE/ORDER I FOR ATIO
TOP VIEW
GND 1
V
C
2
FB 3
NC 4
8
7
6
5
E2
V
SW
E1
V
IN
FRONT VIEW
5
4
3
2
1
Q PACKAGE
5-LEAD DD
T
JMAX
= 100°C,
θ
JA
= 40°C/ W (CQ)
T
JMAX
= 125°C,
θ
JA
= 40°C/ W (IQ)
NOTE:
θ
JA
VARIES FROM 25°C/W TO 50°C/W
DEPENDING ON BOARD COMPOSITION.
V
IN
V
SW
GND
FB
V
C
N8 PACKAGE
8-LEAD PLASTIC DIP
T
JMAX
= 100°C,
θ
JA
= 90°C/W (CN8)
T
JMAX
= 125°C,
θ
JA
= 90°C/W (IN8)
ORDER PART NUMBER
LT1082CN8
LT1082IN8
J8 PACKAGE
8-LEAD CERAMIC DIP
T
JMAX
= 150°C,
θ
JA
= 100°C/W (MJ8)
ORDER PART NUMBER
LT1082CQ
LT1082IQ
LT1082MJ8
OBSOLETE PACKAGE
Consider the Q Package for Alternate Source
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF
, output pin open, unless otherwise
specified.
SYMBOL
V
REF
I
B
g
m
PARAMETER
Reference Voltage
Feedback Input Current
Error Amplifier
Transconductance
Error Amplifier Source or
Sink Current
Error Amplifier Clamp
Voltage
Reference Voltage Line Regulation
A
V
Error Amplifier Voltage Gain
Minimum Input Voltage
CONDITIONS
Measured at Feedback Pin
V
C
= 0.8V
V
FB
= V
REF
q
q
ELECTRICAL CHARACTERISTICS
∆I
C
=
±25µA
q
V
C
= 1.5V
q
Hi Clamp, V
FB
= 1V
Lo Clamp, V
FB
= 1.5V
3V
≤
V
IN
≤
V
MAX
, V
C
= 0.8V
0.9V
≤
V
C
≤
1.4V
q
q
2
U
U
W
W W
U
W
(Note 1)
Operating Junction Temperature Range
LT1082M
(OBSOLETE) ...............
– 55°C to 150°C
LT1082I ........................................... – 40°C to 125°C
LT1082C ............................................... 0°C to 100°C
FRONT VIEW
5
4
3
2
1
T PACKAGE
5-LEAD TO-220
T
JMAX
= 100°C,
θ
JA
= 75°C/ W,
θ
JC
= 8°C/ W (CT)
T
JMAX
= 125°C,
θ
JA
= 75°C/ W,
θ
JC
= 8°C/ W (IT)
V
IN
V
SW
GND
FB
V
C
ORDER PART NUMBER
LT1082CT
LT1082IT
MIN
TYP
MAX
1.264
1.274
750
1100
6000
7000
400
400
2.3
0.36
0.03
UNITS
V
V
nA
nA
µmho
µmho
µA
µA
V
V
%/V
V/V
V
1.224 1.244
1.214 1.244
350
3000
2400
150
120
1.8
0.12
350
4400
200
0.22
650
2.6
3.0
sn1082 1082fas
LT1082
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF
, output pin open, unless otherwise
specified.
SYMBOL
I
Q
PARAMETER
Supply Current
Control Pin Threshold
Normal/Flyback Threshold
on Feedback Pin
f
Switching Frequency
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
3V
≤
V
IN
≤
V
MAX
, V
C
= 0.6V
Duty Cycle = 0
q
MIN
TYP
4.5
MAX
7.0
1.1
1.25
0.8
70
75
UNITS
mA
V
V
V
kHz
kHz
kHz
V
A/V
0.7
0.5
0.58
50
45
100
0.9
0.67
60
12
800µA
≥
I
FB
≥
450µA
BV
Output Switch Breakdown Voltage
Control Voltage to Switch
Current Transconductance
V
FB
Flyback Reference Voltage
Change in Flyback Reference Voltage
Flyback Reference Voltage Line Regulation
Flyback Amplifier Transconductance (g
m
)
Flyback Amplifier Source
and Sink Current
V
SAT
I
LIM
Output Switch “On” Resistance (Note 2)
Switch Current Limit
(LT1082C)
Switch Current Limit
(LT1082I)
Switch Current Limit
(LT1082M)
∆I
IN
∆I
SW
DC
MAX
Supply Current Increase
During Switch-On Time
Maximum Switch Duty Cycle
Flyback Sense Delay Time
Shutdown Mode Supply Current
Shutdown Mode
Threshold Voltage
3V
≤
V
IN
≤
V
MAX
, V
C
= 0.05V
3V
≤
V
IN
≤
V
MAX
q
3V
≤
V
IN
≤
V
MAX
, I
SW
= 1.5mA
q
115
1.5
I
FB
= 60µA
q
17
16
3.5
150
18.6
4.6
0.01
300
32
50
0.8
20.5
21.5
6.5
0.03
500
70
90
1.2
2.6
2.6
2.4
2.8
2.8
2.6
3.0
3.0
2.8
V
V
V
%/V
µmho
µA
µA
Ω
A
A
A
A
A
A
A
A
A
mA/A
%
µs
µA
mV
mV
60µA
≤
I
FB
≤
200µA
I
FB
= 60µA, 3V
≤
V
IN
≤
V
MAX
∆I
C
=
±10µA
V
C
= 0.6V Source
I
FB
= 60µA Sink
I
SW
= 0.7A (LT1082C), I
SW
= 0.5A (LT1082M)
Duty Cycle = 20%
Duty Cycle
≤
50%
Duty Cycle = 80% (Note 3)
Duty Cycle = 20%
Duty Cycle
≤
50%
Duty Cycle = 80% (Note 3)
Duty Cycle = 20%
Duty Cycle
≤
50%
Duty Cycle = 80% (Note 3)
q
q
q
q
q
q
q
q
q
q
q
q
15
30
1.07
1.0
0.8
0.85
0.8
0.65
0.75
0.7
0.6
35
85
92
1.5
70
50
120
150
45
97
350
250
300
Note 1:
Absolute Maximum Ratings are those values beyond which the
life of a device may be impaired.
Note 2:
Measured with V
C
in hi clamp, V
FB
= 0.8V.
Note 3:
For duty cycles (DC) between 50% and 80%, minimum
guaranteed switch current decreases linearly.
sn1082 1082fas
3
LT1082
TYPICAL PERFOR A CE CHARACTERISTICS
Suggested Core Size and
Inductance for Telecom
5V Supply
LOAD
CURRENT
100mA
200mA
400mA
600mA
800mA
TYPE 52
POWDERED
IRON
T38 250µH
T50 250µH
T60 250µH
T60 250µH
T80 350µH
KOOL Mµ
OR MOLY-
PERMALLOY
T38 200µH
EFFICIENCY (%)
79
76
73
70
67
64
61
58
55
0
1
2
3
4
POWER OUTPUT (W)
NOTE: THIS GRAPH IS BASED ON LOW CORE LOSS
PERMALLOY INDUCTOR. IF POWDERED IRON CORE
INDUCTOR IS USED, THE CORE LOSS IS TYPICALLY
100mW HIGHER.
1082 G01
V
IN
= –70V
L = 250µH
R = 0.08Ω
V
IN
= –40V
FREQUENCY (kHz)
T38 150µH
T50 150µH
T50 200µH
T80 350µH
1082 GA
Short-Circuit Frequency
Shift-Down vs Feedback Current
70
60
T
A
= 0°C
T
A
= 150°C
T
A
= – 55°C
SWITCH CURRENT (A)
FREQUENCY (kHz)
DUTY CYCLE (%)
50
40
30
20
10
0
0
100 200 300 400 500 600 700 800
FEEDBACK CURRENT (µA)
1082 G03
Flyback Blanking Time
2.2
2.0
1.8
SWITCH SATURATION VOLTAGE (V)
MINIMUM INPUT VOLTAGE (V)
TIME (µs)
1.6
1.4
1.2
1.0
–75 –50 –25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (°C)
1082 G06
4
U W
Telecom 5V Supply Efficiency
80
V
IN
= –20V
Telecom 5V Supply Short-Circuit
Frequency Shift-Down
T
A
= 25°C
70
60
50
40
30
20
10
0
6
5
4
3
2
OUTPUT VOLTAGE (V)
1
0
1082 G02
V
IN
= –60V
Switch Current Limit
4
97
96
Maximum Duty Cycle
3
95
94
93
92
91
2
T
J
= –55°C
T
J
= 150°C
T
J
= 25°C
1
0
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
1082 G04
90
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1082 G05
Minimum Input Voltage
2.9
2.8
2.7
I
SW
= 0A
2.6
2.5
2.4
2.3
–75 –50 –25
2.00
1.75
Switch Saturation Voltage
I
SW
= 1A
T
J
= 150°C
1.50
1.25
1.00
0.75
0.50
0.25
0
0
0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00
SWITCH CURRENT (A)
1082 G08
T
J
= 100°C
T
J
= 25°C
T
J
= –50°C
0 25 50 75 100 125 150
TEMPERATURE (°C)
1082 G07
sn1082 1082fas
LT1082
TYPICAL PERFOR A CE CHARACTERISTICS
Isolated Mode Flyback
Reference Voltage
25
24
23
FLYBACK VOLTAGE (V)
70
R
FB
= 3k
FREQUENCY (kHz)
65
V
REF
FREQ
1.245
REFERENCE VOLTAGE CHANGE (mV)
22
21
20
19
18
17
16
15
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1082 G09
R
FB
= 6k
R
FB
= 10k
Feedback Bias Current vs
Temperature
800
700
750
FEEDBACK BIAS CURRENT (nA)
675
650
625
600
575 FEEDBACK PIN CURRENT
(AT THRESHOLD)
550
525
–18
–16
–14
–12
–10
–8
–6
SUPPLY CURRENT (µA)
V
C
PIN VOLTAGE (mV)
600
500
400
300
200
100
0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1082 G12
Supply Current vs Supply Voltage
(Shutdown Mode)
200
100
90
160
SUPPLY CURRENT (µA)
DRIVER CURRENT (mA)
120
V
C
= 50mV
70
60
50
40
30
20
10
SUPPLY CURRENT (mA)
80
V
C
= 0V
40
0
0
10
20 30 40 50 60
SUPPLY VOLTAGE (V)
70
80
U W
1082 G15
Reference Voltage and Switching
Frequency vs Temperature
1.250
5
4
3
2
1
0
–1
–2
–3
–4
–5
Line Regulation
REFERENCE VOLTAGE (V)
60
1.240
T
J
= –55°C
55
1.235
T
J
= 150°C
T
J
= 25°C
50
1.230
45
1.225
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1082 G11
0
10
20
30 40 50 60
INPUT VOLTAGE (V)
70
80
1082 G10
Normal/Feedback Mode
Threshold on Feedback Pin
–24
–22
–20
V
C
PIN CURRENT (µA)
Shutdown Mode Supply Current
200
180
160
140
120
100
80
60
40
20
0
0
10 20 30 40 50 60 70 80 90 100
V
C
PIN VOLTAGE (mV)
1082 G17
725 FEEDBACK PIN VOLTAGE
(AT THRESHOLD)
700
–55°C
≤
T
J
≤
125°C
T
J
= 150°C
500
–4
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1082 G16
Driver Current* vs Switch Current
14
13
12
11
10
9
8
7
6
5
4
3
2
Supply Current vs Input Voltage**
80
90% DUTY CYCLE
50% DUTY CYCLE
10% DUTY CYCLE
0% DUTY CYCLE
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
SWITCH CURRENT (A)
0
10
20
60
40 50
30
INPUT VOLTAGE (V)
70
80
* AVERAGE SUPPLY CURRENT
= I
Q
+ DC(2.9 + 10
–2
I
SW
+ 10
–5
I
SW
2
)
I
Q
= QUIESCENT CURRENT, DC = DUTY CYCLE,
1082 G13
I
SW
= SWITCH CURRENT
**UNDER VERY LOW OUTPUT CURRENT CONDITIONS,
DUTY CYCLE FOR MOST CIRCUITS WILL APPROACH
1082 G14
10% OR LESS.
sn1082 1082fas
5
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