Datasheet

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LT1082

sn1082 1082fas

FEATURES

APPLICATIO S

DESCRIPTIO

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 (35kΩ/R

) 16 + 0.35 (7kΩ/R

)

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)

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

LIMIT = 1.07A

Telecom 5V Supply Maximum Output

Current vs Input Voltage

GND

LT1082

4.7k

0.22µF

33µF

80V

CHEMI-CON

SXE SERIES

–20V

TO –70V

**250µH

3.83k

0.01µF

1.1k

2N5401

470µF

10V

CHEMI-CON

SXE SERIES

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

, LTC and LT are registered trademarks of Linear Technology Corporation

Summary of content (12 pages)

PAGE 1
LT1082 1A High Voltage, Efficiency Switching Voltage Regulator DESCRIPTIO U 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 The LT®1082 is a monolithic high voltage switching regulator.
PAGE 2
LT1082 W W W AXI U U ABSOLUTE RATI GS (Note 1) 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 Operating Junction Temperature Range LT1082M (OBSOLETE) ............... – 55°C to 150°C LT1082I .....................................
PAGE 3
LT1082 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 15V, VC = 0.5V, VFB = VREF, output pin open, unless otherwise specified. SYMBOL IQ PARAMETER CONDITIONS MIN Supply Current 3V ≤ VIN ≤ VMAX, VC = 0.6V Control Pin Threshold Duty Cycle = 0 ● Normal/Flyback Threshold on Feedback Pin f Switching Frequency ● Output Switch Breakdown Voltage 3V ≤ VIN ≤ VMAX, ISW = 1.
PAGE 4
LT1082 U W TYPICAL PERFOR A CE CHARACTERISTICS Suggested Core Size and Inductance for Telecom 5V Supply Telecom 5V Supply Short-Circuit Frequency Shift-Down Telecom 5V Supply Efficiency KOOL Mµ OR MOLYPERMALLOY 100mA T38 250µH T38 200µH 200mA T50 250µH T38 150µH 400mA T60 250µH T50 150µH 600mA T60 250µH T50 200µH 800mA T80 350µH T80 350µH 80 79 TA = 25°C 76 70 VIN = –20V 60 73 1082 GA FREQUENCY (kHz) TYPE 52 POWDERED IRON EFFICIENCY (%) LOAD CURRENT VIN = –40V 70 67 VIN = –
PAGE 5
LT1082 U W TYPICAL PERFOR A CE CHARACTERISTICS Reference Voltage and Switching Frequency vs Temperature Isolated Mode Flyback Reference Voltage Line Regulation 1.250 5 24 RFB = 3k FREQUENCY (kHz) 21 RFB = 6k 19 RFB = 10k 18 FREQ 60 17 1.245 1.240 55 1.235 50 1.230 16 45 1.
PAGE 6
LT1082 U W TYPICAL PERFOR A CE CHARACTERISTICS gm = 4000 400 –400 10 350 –350 9 CURRENT (OUT OF VC PIN) 300 VC VOLTAGE (mV) 3500 3000 2500 2000 1500 –300 250 –250 200 –200 VOLTAGE AT VC PIN 150 –150 100 –100 50 –50 VC CURRENT (µA) TRANSCONDUCTANCE (µmho) 4500 ∆I (VC PIN) ∆V (FB PIN) IDLE SUPPLY CURRENT (mA) 5000 Idle Supply Current vs Temperature Shutdown Thresholds Error Amplifier Transconductance 1000 500 0 –75 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 8 7 6 5 VI
PAGE 7
LT1082 W BLOCK DIAGRA VIN 16.2V SWITCH OUT FLYBACK ERROR AMP 2.3V REG OSC 60kHz 14kHz LOGIC DRIVER ANTI-SAT MODE SELECT COMP – FB + ERROR + AMP VC CURRENT AMP GAIN ≈ 5 – E1* E2 SHUTDOWN CIRCUIT 1.24V REF 0.2Ω 0.2Ω 0.15V GND * ALWAYS CONNECT E1 TO GROUND PIN ON MiniDIP PACKAGE. EMITTERS TIED TO GROUND ON TO-220 PACKAGE. 1082 BD U OPERATIO The LT1082 is a current mode switcher. This means that switch duty cycle is directly controlled by switch current rather than by output voltage.
PAGE 8
LT1082 U OPERATIO disconnect the main error amplifier output and connects the output of the flyback amplifier to the comparator input. The LT1082 will then regulate the value of the flyback pulse with respect to the supply voltage. This flyback pulse is directly proportional to output voltage in the traditional transformer coupled flyback topology regulator. By regulating the amplitude of the flyback pulse, the output voltage can be regulated with no direct connection between input and output.
PAGE 9
LT1082 U OPERATIO Total power dissipation is the sum of supply current times input voltage plus switch power: PTOT = (IIN)(VIN) + PSW In a typical example, using negative-to-positive converter to generate 5V at 0.5A from a – 45V input, duty cycle is approximately 12%, and switch current is about 0.5A, yielding: IIN = 4.5mA + 0.5(0.004 + DC/28) = 8.7mA PSW = (0.5)2 • 1.2Ω • (0.12) = 0.036W LT1082 Synchronizing The LT1082 can be externally synchronized in the frequency range of 75kHz to 90kHz.
PAGE 10
LT1082 UO TYPICAL APPLICATI S Totally Isolated Converter MUR110 1.24:1 25V MUR110 15V AT 0.3A + 200µF 1 LPRI 500µH COM 1 + 200µF VIN + VIN 30V to 70V –15V AT 0.3A VSW 25µF MUR110 LT1082 FB GND VC 3k 0.01µF MINIMUM LOAD OF 0.15A IS REQUIRED FOR EACH OUTPUT. (SEE AN19) 7k 1082 TA03 Boost Converter 1mH, 1A VIN 15V VIN MUR110 VOUT 90V AT 120mA 78.8k VSW LT1082 + + FB 25µF GND 100µF VC 4.7k 0.033µF 1.1k 0.
PAGE 11
LT1082 U PACKAGE DESCRIPTIO N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) 0.300 – 0.325 (7.620 – 8.255) 0.130 ± 0.005 (3.302 ± 0.127) 0.045 – 0.065 (1.143 – 1.651) 0.065 (1.651) TYP 0.009 – 0.015 (0.229 – 0.381) ( 0.400* (10.160) MAX 8 7 6 5 1 2 3 4 0.255 ± 0.015* (6.477 ± 0.381) +0.035 0.325 –0.015 +0.889 8.255 –0.381 ) 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003 0.100 (2.54) BSC (0.457 ± 0.
PAGE 12
LT1082 U PACKAGE DESCRIPTIO T Package 5-Lead Plastic TO-220 (Standard) (Reference LTC DWG # 05-08-1421) 0.165 – 0.180 (4.191 – 4.572) 0.147 – 0.155 (3.734 – 3.937) DIA 0.390 – 0.415 (9.906 – 10.541) 0.045 – 0.055 (1.143 – 1.397) 0.230 – 0.270 (5.842 – 6.858) 0.570 – 0.620 (14.478 – 15.748) 0.460 – 0.500 (11.684 – 12.700) 0.620 (15.75) TYP 0.330 – 0.370 (8.382 – 9.398) 0.700 – 0.728 (17.78 – 18.491) 0.095 – 0.115 (2.413 – 2.921) SEATING PLANE 0.152 – 0.202 0.260 – 0.320 (3.861 – 5.131) (6.60 – 8.