ANALOG DEVICES LT1082CN8PBF Datasheet

Switching Voltage Regulator

FEATURES

■

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

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APPLICATIO 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

V

IN

V

SW

Switch Current Limit 1A 1.25A
Quiescent Current 4.5mA 6mA
Operating Frequency 60kHz 40kHz
Flyback Reference Voltage 16.2 + 0.6 (35kΩ/RFB) 16 + 0.35 (7kΩ/RFB)

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.

3V to 75V 3V to 60V

100V 75V

LT1082

1A High Voltage, Efficiency

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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 quies­cent current. It can deliver load power up to 20W with no
external power devices. By utilizing current-mode switch­ing 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

TYPICAL APPLICATIO

Negative-to-Positive Telecom 5V Supply

*D1

V

SW

2N5401

0.01µF

33µF

80V
CHEMI-CON
SXE SERIES

–20V

TO –70V

**250µH

V

IN

+

GNDFBV

LT1082

C

4.7k

0.22µF

U

+

3.83k

Q1

1.1k

1082 TA01

470µF
10V
CHEMI-CON
SXE SERIES

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.

V

OUT

5V, 0.7A

NOTE: MAXIMUM OUTPUT
CURRENT IS A FUNCTION OF
INPUT VOLTAGE. SEE THE
GRAPH ON THE RIGHT.

Telecom 5V Supply Maximum Output

Current vs Input Voltage

1.0
f = 45kHz

LIMIT = 1.07A

I

SW

0.9

0.8

0.7

0.6

0.5

MAXIMUM OUTPUT CURRENT (A)

0.4

–10 –30

0

–20

–40

INPUT VOLTAGE (V)

L=550µH
L=450µH
L=350µH

L=250µH

L=150µH

L=100µH

–70

–60

–80

1082 TA02

sn1082 1082fas

–50 –90

1

LT1082

A

W

O

LUTEXI TIS

S

A

WUW

U

(Note 1)

ARB

G

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

GND

1

V

2

C

FB

3

NC

4

8-LEAD PLASTIC DIP

T

= 100°C, θJA = 90°C/W (CN8)

JMAX

T

= 125°C, θJA = 90°C/W (IN8)

JMAX

ORDER PART NUMBER

/

O

RDER I FOR ATIO

TOP VIEW

E2

8

V

7

SW

E1

6

V

5

IN

N8 PACKAGE

WU

T

JMAX

T

JMAX

VARIES FROM 25°C/W TO 50°C/W

NOTE: θ

JA

DEPENDING ON BOARD COMPOSITION.

U

FRONT VIEW

Q PACKAGE

5-LEAD DD

= 100°C, θJA = 40°C/W (CQ)

= 125°C, θJA = 40°C/W (IQ)

LT1082CN8
LT1082IN8

J8 PACKAGE

8-LEAD CERAMIC DIP

T

= 150°C, θJA = 100°C/W (MJ8)

JMAX

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.

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

V
4
3
2
1

IN

V

SW

GND

FB

V

C

= 100°C, θJA = 75°C/W, θJC = 8°C/W (CT)

T

JMAX

= 125°C, θJA = 75°C/W, θJC = 8°C/W (IT)

T

JMAX

5
4
3
2
1

T PACKAGE

5-LEAD TO-220

ORDER PART NUMBER

LT1082CT
LT1082IT

V

IN

V

SW

GND
FB
V

C

LECTRICAL C CHARA TERIST

E

temperature range, otherwise specifications are at TA = 25°C.

The ● denotes the specifications which apply over the full operating

ICS

VIN = 15V, VC = 0.5V, VFB = V

, output pin open, unless otherwise

REF

specified.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

REF

I

B

g

m

A

V

Reference Voltage Measured at Feedback Pin 1.224 1.244 1.264 V

VC = 0.8V ● 1.214 1.244 1.274 V

Feedback Input Current VFB = V

Error Amplifier ∆IC = ±25µA 3000 4400 6000 µmho
Transconductance ● 2400 7000 µmho

Error Amplifier Source or VC = 1.5V 150 200 400 µA
Sink Current ● 120 400 µA

Error Amplifier Clamp Hi Clamp, VFB = 1V 1.8 2.3 V
Voltage Lo Clamp, VFB = 1.5V 0.12 0.22 0.36 V

Reference Voltage Line Regulation 3V ≤ VIN ≤ V
Error Amplifier Voltage Gain 0.9V ≤ VC ≤ 1.4V 350 650 V/V
Minimum Input Voltage ● 2.6 3.0 V

REF

● 1100 nA

, VC = 0.8V ● 0.03 %/V

MAX

350 750 nA

sn1082 1082fas

2

LT1082

LECTRICAL C CHARA TERIST

E

ICS

temperature range, otherwise specifications are at TA = 25°C.

The ● denotes the specifications which apply over the full operating

VIN = 15V, VC = 0.5V, VFB = V

, output pin open, unless otherwise

REF

specified.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

Q

f Switching Frequency 50 60 70 kHz

BV Output Switch Breakdown Voltage 3V ≤ VIN ≤ V

V

FB

V

SAT

I

LIM

∆I

IN

∆I

SW

DC

MAX

Supply Current 3V ≤ VIN ≤ V
Control Pin Threshold Duty Cycle = 0 0.7 0.9 1.1 V

Normal/Flyback Threshold 0.58 0.67 0.8 V
on Feedback Pin

800µA ≥ IFB ≥ 450µA 12 kHz

Control Voltage to Switch 1.5 A/V
Current Transconductance

Flyback Reference Voltage IFB = 60µA 17 18.6 20.5 V

Change in Flyback Reference Voltage 60µA ≤ IFB ≤ 200µA 3.5 4.6 6.5 V
Flyback Reference Voltage Line Regulation IFB = 60µA, 3V ≤ VIN ≤ V
Flyback Amplifier Transconductance (gm) ∆IC = ±10µA 150 300 500 µmho
Flyback Amplifier Source V

and Sink Current IFB = 60µA Sink ● 30 50 90 µA
Output Switch “On” Resistance (Note 2) ISW = 0.7A (LT1082C), ISW = 0.5A (LT1082M) ● 0.8 1.2 Ω

Switch Current Limit Duty Cycle = 20% ● 1.07 2.6 A
(LT1082C) Duty Cycle ≤ 50%

Switch Current Limit Duty Cycle = 20%
(LT1082I) Duty Cycle ≤ 50%

Switch Current Limit Duty Cycle = 20%
(LT1082M) Duty Cycle ≤ 50%

Supply Current Increase 35 45 mA/A
During Switch-On Time

Maximum Switch Duty Cycle 85 92 97 %
Flyback Sense Delay Time 1.5 µs
Shutdown Mode Supply Current 3V ≤ VIN ≤ V
Shutdown Mode 3V ≤ V

Threshold Voltage ● 50 300 mV

= 0.6V Source ● 15 32 70 µA

C

Duty Cycle = 80% (Note 3) ● 0.8 2.4 A

Duty Cycle = 80% (Note 3) ● 0.65 2.6 A

Duty Cycle = 80% (Note 3) ● 0.6 2.8 A

IN

, VC = 0.6V 4.5 7.0 mA

MAX

● 0.5 1.25 V

● 45 75 kHz

, ISW = 1.5mA ● 100 115 V

MAX

● 16 21.5 V

MAX

● 1.0 2.6 A

● 0.85 2.8 A

● 0.8 2.8 A

● 0.75 3.0 A

● 0.7 3.0 A

, VC = 0.05V 120 350 µA

MAX

≤ V

MAX

0.01 0.03 %/V

70 150 250 mV

Note 1: Absolute Maximum Ratings are those values beyond which the
life of a device may be impaired.

Note 2: Measured with V

in hi clamp, VFB = 0.8V.

C

Note 3: For duty cycles (DC) between 50% and 80%, minimum
guaranteed switch current decreases linearly.

sn1082 1082fas

3

LT1082

TEMPERATURE (°C)

–75

DUTY CYCLE (%)

97

96

95

94

93

92

91

90

–50

50

100

1082 G05

25

150

175

–25

0

75 125

LPER

Suggested Core Size and
Inductance for Telecom
5V Supply

LOAD
CURRENT

100mA
200mA
400mA
600mA
800mA

Short-Circuit Frequency
Shift-Down vs Feedback Current

70

TA = 0°C

60

TA = 150°C

50

F

TYPE 52
POWDERED
IRON

T38 250µH
T50 250µH
T60 250µH
T60 250µH
T80 350µH

TA = –55°C

R

O

KOOL Mµ
OR MOLY­PERMALLOY

T38 200µH
T38 150µH
T50 150µH
T50 200µH
T80 350µH

ATYPICA

1082 GA

UW

CCHARA TERIST

E

C

Telecom 5V Supply Efficiency

79

76

VIN = –20V

73

VIN = –40V

70

67

VIN = –60V

64

EFFICIENCY (%)

61

VIN = –70V

58

55

0

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.

Switch Current Limit

4

3

1

ICS

2

POWER OUTPUT (W)

L = 250µH
R = 0.08Ω

3

1082 G01

Telecom 5V Supply Short-Circuit
Frequency Shift-Down

80

TA = 25°C

70

60

50

40

30

FREQUENCY (kHz)

20

10

4

0

6

54 32

OUTPUT VOLTAGE (V)

10

1082 G02

Maximum Duty Cycle

40

30

FREQUENCY (kHz)

20

10

0

100 200 800

0 300

FEEDBACK CURRENT (µA)

Flyback Blanking Time

2.2

2.0

1.8

1.6

TIME (µs)

1.4

1.2

1.0
–75

–50

–25

JUNCTION TEMPERATURE (°C)

400 500 600 700

0

50

25

1082 G03

100

75 125

1082 G06

150

2

TJ = –55°C

SWITCH CURRENT (A)

0

1

0

TJ = 150°C

102030

40

DUTY CYCLE (%)

Minimum Input Voltage

2.9

2.8

2.7

2.6

2.5

MINIMUM INPUT VOLTAGE (V)

2.4

2.3
–75

–50

0

–25

25

TEMPERATURE (°C)

TJ = 25°C

50 60 70 80 90 100

1082 G04

ISW = 1A

ISW = 0A

100

50

75 125

150

1082 G07

Switch Saturation Voltage

2.00

1.75

1.50

1.25

1.00

0.75

0.50

SWITCH SATURATION VOLTAGE (V)

0.25

0

0.50

0

0.25
SWITCH CURRENT (A)

TJ = 150°C

TJ = 100°C

TJ = 25°C

TJ = –50°C

1.00 1.25 1.75

0.75

1.50

sn1082 1082fas

2.00

1082 G08

4