Datasheet

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LT1072

1072fc

1.25A High Efficiency

Switching Regulator

■

Available in MiniDiP, TO-220, and TO-3 Packages

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Wide Input Voltage Range 3V to 60V

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Low Quiescent Current—6mA

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Internal 1.25A Switch

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Very Few External Parts Required

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Self-Protected Against Overloads

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Operates in Nearly All Switching Topologies

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Shutdown Mode Draws Only 50µA Supply Current

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Flyback-Regulated Mode has Fully Floating Outputs

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Can be Externally Synchronized

The LT

1072 is a monolithic high power switching

regulator. It can be operated in all standard switching

configurations including buck, boost, flyback, forward,

inverting and “Cuk”. A high current, high efficiency switch

is included on the die along with all oscillator, control, and

protection circuitry. Integration of all functions allows the

LT1072 to be built in a standard 5-pin TO-3 or TO-220

power package as well as the 8-pin miniDlP. This makes it

extremely easy to use and provides “bust proof” operation

similar to that obtained with 3-pin linear regulators.

The LT1072 operates with supply voltages from 3V to 60V,

and draws only 6mA quiescent current. It can deliver load

power up to 20 watts with no external power devices. By

utilizing current-mode switching techniques, it provides

excellent AC and DC load and line regulation.

The LT1072 has many unique features not found even on

the vastly more difficult to use low power control chips

presently available. It uses an adaptive anti-sat switch

drive to allow very wide ranging load currents with no loss

in efficiency. An externally activated shutdown mode

reduces total supply current to 50µA typical for standby

operation. Totally isolated and regulated outputs can be

generated by using the optional “flyback regulation mode”

built into the LT1072, without the need for optocouplers or

extra transformer windings.

USER NOTE:

This data sheet is only intended to provide specifications, graphs, and a general functional

description of the LT1072. Application circuits are included to show the capability of the LT1072.

A complete design manual (AN-19) 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 LT1072 by factoring in the lower switch current rating.

, LTC and LT are registered trademarks of Linear Technology Corporation.

FEATURES

DESCRIPTIO

Boost Converter (5V to 12V)

TYPICAL APPLICATIO

10.7k

1.24k

LT1072

GND V

1µF

–

470µF

12V, 0.25A

*REQUIRED IF INPUT LEADS ≥ 2”

**PULSE ENGINEERING 52626

220µH**

–

25µF*

–

LT1072 • TA01

Maximum Output Power*

LT1072 • TA02

INPUT VOLTAGE (V)

*ROUGH GUIDE ONLY. BUCK MODE P

OUT

= 1A x V

OUT

MINIDIP OUTPUT POWER MAY BE LIMITED BY PACKAGE TEMPERATURE

RISE AT HIGH INPUT VOLTAGES OR HIGH DUTY CYCLES

POWER (W)

30 40

BUCK-BOOST

= 5V

BUCK-BOOST

= 30V

FLYBACK

ISOLATED

BOOST

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Logic Supply 5V at 2.5A

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5V Logic to ±15V Op Amp Supply

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Offline Converter up to 50W

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Battery Upconverter

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Power lnverter (+ to –) or (– to +)

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Fully Floating Multiple Outputs

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Driver for High Current Supplies

APPLICATIO S

Summary of content (16 pages)

PAGE 1
LT1072 1.25A High Efficiency Switching Regulator U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Available in MiniDiP, TO-220, and TO-3 Packages Wide Input Voltage Range 3V to 60V Low Quiescent Current—6mA Internal 1.
PAGE 2
LT1072 W W W AXI U U ABSOLUTE RATI GS (Note 1) Note 1: Minimum switch “on” time for the LT1072 in current limit is ≈ 0.7µsec. This limits the maximum input voltage during short-circuit conditions, in the buck and inverting modes only,to ≈ 40V. Normal (unshorted) conditions are not affected.
PAGE 3
LT1072 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range. Unless otherwise specified, VIN = 15V, VC = 0.5V, VFB = VREF, output pin open. SYMBOL PARAMETER CONDITlONS VREF Reference Voltage Measured at Feedback Pin VC = 0.8V IB Feedback Input Current ● MIN TYP MAX UNITS 1.224 1.214 1.244 1.244 1.264 1.
PAGE 4
LT1072 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Current Limit vs Duty Cycle Maximum Duty Cycle 4 Flyback Blanking Time 96 2.2 95 2.0 94 1.8 25°C 2 125°C TIME (µs) –55°C DUTY CYCLE (%) SWITCH CURRENT (A) 3 93 92 1.4 91 1.2 90 –75 –50 –25 0 25 50 75 100 125 150 JUNCTION TEMPERATURE (°C) 1.
PAGE 5
LT1072 U W TYPICAL PERFOR A CE CHARACTERISTICS Supply Current vs Supply Voltage (Shutdown Mode) Supply Current vs Input Voltage* 15 70 14 60 50 40 30 20 160 TJ = 25°C NOTE THAT THIS CURRENT DOES NOT 13 INCLUDE DRIVER CURRENT, WHICH IS A FUNCTION OF LOAD CURRENT AND 12 DUTY CYCLE. 90% DUTY CYCLE 11 10 50% DUTY CYCLE 9 8 10% DUTY CYCLE 7 10 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.
PAGE 6
LT1072 U W TYPICAL PERFOR A CE CHARACTERISTICS Transconductance of Error Amplifier VC Pin Characteristics 0 200 5000 30 4000 60 Gm 3000 90 TJ = 25°C 0 –100 1000 150 0 180 –300 –1000 210 10M –400 100k 1M FREQUENCY (Hz) 900 800 120 10k VFB = 1.5V (CURRENT INTO VC PIN) 100 2000 1k Switch “Off” Characteristics 1000 SWITCH CURRENT (µA) θ 300 PHASE (°) TRANSCONDUCTANCE (µmho) 6000 –30 VC PIN CURRENT (µA) 7000 –200 VFB = 0.
PAGE 7
LT1072 U LT1072 OPERATIO The LT1072 is a current mode switcher. This means that switch duty cycle is directly controlled by switch current rather than by output voltage. Referring to the block diagram, the switch is turned “on” at the start of each oscillator cycle. It is turned “off” when switch current reaches a predetermined level. Control of output voltage is obtained by using the output of a voltage sensing error amplifier to set current trip level. This technique has several advantages.
PAGE 8
LT1072 U LT1072 OPERATIO rough guide to calculate LT1072 power dissipation. For more details, the reader is referred to Application Note 19 (AN19), “Efficiency Calculations” section. Average supply current (including driver current) is: IIN ≈ 6mA + ISW(0.
PAGE 9
LT1072 U LT1072 OPERATIO Synchronizing with Bipolar Transistor Synchronizing with MOS Transistor VIN VIN LT1072 LT1072 VC GND C2 68pF R3 VC GND R1 3k R3 2N2369 C1 R2 2.2k VN2222* C1 FROM 5V LOGIC C2 200pF D1 1N4158 R2 2.2k D2 1N4158 FROM 5V LOGIC *SILICONIX OR EQUIVALENT LT1072 • OP01 LT1072 • OP02 U TYPICAL APPLICATIO S Totally Isolated Converter OPTIONAL OUTPUT FILTER 1:N R4 2.7k C3 0.
PAGE 10
LT1072 U TYPICAL APPLICATIO S Flyback Converter L2 10µH C4 200µF OPTIONAL FILTER D1 VIN 20 TO 30V R4 1k ** + N* = 1 3 b 0V VOUT + Vf c C4 + 25µF* N • VIN SECONDARY VOLTAGE AREA “c” = AREA “d” TO MAINTAIN ZERO DC VOLTS ACROSS SECONDARY 0V d C1 500µF ∆I IPRI D2 VIN R1 3.74k VSW PRIMARY CURRENT 0 LT1072 IPRI SECONDARY CURRENT N 0 IPRI VC FB GND + Vf V PRIMARY FLYBACK VOLTAGE = OUT N LT1072 SWITCH VOLTAGE AREA “a” = AREA “b” TO MAINTAIN ZERO DC VOLTS ACROSS PRIMARY a VIN VOUT 5V 1.
PAGE 11
LT1072 U TYPICAL APPLICATIO S Positive to Negative Buck-Boost Converter D3† 1N4001 R5† 470Ω, 1W C5 100µF* VIN C4 5µF + *REQUIRED IF INPUT LEADS ≥ 2" **PULSE ENGINEERING 92113 VIN 10 TO 30V † VSW LT1072 D2 1N914 R1 10.7k FB VC GND R4 47Ω TO AVOID START-UP PROBLEMS FOR INPUT VOLTAGES BELOW 10V, CONNECT ANODE OF D3 TO VIN, AND REMOVE R5. C1 MAY BE REDUCED FOR LOWER OUTPUT CURRENTS. C1 ≈ (500µF)(IOUT). FOR 5V OUTPUTS, REDUCE R3 TO 1.5k, INCREASE C2 TO 0.3µF, AND REDUCE R6 TO 100Ω R3 5k R2 1.
PAGE 12
LT1072 U TYPICAL APPLICATIO S Driving High Voltage FET (for Offline Applications, See AN-25) G D Q1 D1 VIN VSW + 10 TO 20V LT1072 GND LT1072 • TA10 Negative Buck Converter C2 500µF D1 VIN C3 25µF* + VSW GND R1 4.64k LOAD –5.2V AT 1A L1** 220µH Q1 2N3906 LT1072 OPTIONAL INPUT FILTER + VC FB C1 L3 R3 OPTIONAL + OUTPUT FILTER R2 1.24k VIN –20V C4 200µF L2 4µH *REQUIRED IF INPUT LEADS ≥ 2" **PULSE ENGINEERING 52626 LT1072 • TA11 Positive Buck Converter VIN D3 L2 VIN C3 2.
PAGE 13
LT1072 U TYPICAL APPLICATIO S Negative Boost Regulator D2 VIN VSW R1 27k LT1072 C4 470µF* + + + R0 (MINIMUM LOAD) C1 1000µF VC FB GND R3 3.3k C2 0.22µF L1 200µH VIN –15V C3 10µF R2 1.24k D1 VOUT –28V AT 0.25A *REQUIRED IF INPUT LEADS ≥ 2" LT1072 • TA13 U PACKAGE DESCRIPTIO J8 Package 8-Lead CERDIP (Narrow .300 Inch, Hermetic) (Reference LTC DWG # 05-08-1110) CORNER LEADS OPTION (4 PLCS) .023 – .045 (0.584 – 1.143) HALF LEAD OPTION .045 – .068 (1.143 – 1.650) FULL LEAD OPTION .005 (0.
PAGE 14
LT1072 U PACKAGE DESCRIPTIO K Package 4-Lead TO-3 Metal Can (Reference LTC DWG # 05-08-1311) 0.320 – 0.350 (8.13 – 8.89) 0.760 – 0.775 (19.30 – 19.69) 0.060 – 0.135 (1.524 – 3.429) 0.420 – 0.480 (10.67 – 12.19) 0.038 – 0.043 (0.965 – 1.09) 1.177 – 1.197 (29.90 – 30.40) 0.655 – 0.675 (16.64 – 19.05) 0.470 TP P.C.D. 0.151 – 0.161 (3.84 – 4.09) DIA 2 PLC 0.167 – 0.177 (4.24 – 4.49) R 0.490 – 0.510 (12.45 – 12.95) R 72° 18° K4(TO-3) 1098 OBSOLETE PACKAGE N8 Package 8-Lead PDIP (Narrow .
PAGE 15
LT1072 U PACKAGE DESCRIPTIO S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 7 8 5 6 N N .245 MIN .160 ±.005 1 .030 ±.005 TYP .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT 1 .010 – .020 × 45° (0.254 – 0.508) 3 2 4 .053 – .069 (1.346 – 1.752) .008 – .010 (0.203 – 0.254) .004 – .010 (0.101 – 0.254) 0°– 8° TYP .016 – .050 (0.
PAGE 16
LT1072 U PACKAGE DESCRIPTIO T Package 5-Lead Plastic TO-220 (Standard) (Reference LTC DWG # 05-08-1421) .165 – .180 (4.191 – 4.572) .147 – .155 (3.734 – 3.937) DIA .390 – .415 (9.906 – 10.541) .045 – .055 (1.143 – 1.397) .230 – .270 (5.842 – 6.858) .460 – .500 (11.684 – 12.700) .570 – .620 (14.478 – 15.748) .620 (15.75) TYP .330 – .370 (8.382 – 9.398) .700 – .728 (17.78 – 18.491) SEATING PLANE .152 – .202 .260 – .320 (3.861 – 5.131) (6.60 – 8.13) .095 – .115 (2.413 – 2.921) .155 – .195* (3.