LT1270A_15 [Linear]

8A and 10A High Efficiency Switching Regulators;


型号：	LT1270A_15
厂家：	Linear
描述：	8A and 10A High Efficiency Switching Regulators
文件：	总4页 (文件大小：136K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LT1270A/LT1270

8A and 10A High Efficiency

Switching Regulators

FEATURES

DESCRIPTIO

■

The LT1270A/LT1270 are monolithic high power switch-

ing regulators. Identical to the popular LT1070, except for

switching frequency (60kHz) and higher switch current,

they can be operated in all standard switching configura-

tions including buck, boost, flyback, and inverting. A high

current, high efficiency switch is included on the die along

with all oscillator, control, and protection circuitry. Inte-

gration of all functions allows the LT1270A/LT1270 to be

built in a standard TO-220 power package. This makes it

extremelyeasytouseandprovides“bustproof”operation

similar to that obtained with 3-pin linear regulators.

Wide Input Voltage Range: 3.5V to 30V

■

Low Quiescent Current: 7mA

■

Internal 8A Switch (10A for LT1270A)

Very Few External Parts Required

Self-Protected Against Overloads

Shutdown Mode Draws Only 100µA Supply Current

Flyback-Regulated Mode Has Fully Floating Outputs

Can be Externally Synchronized

(See LT1072 Data Sheet)

Comes in Standard 5-Pin TO-220 Package

■

APPLICATIO S

The LT1270A/LT1270 operate with supply voltages from

3.5V to 30V, and draw only 7mA quiescent current. By

utilizing current-mode switching techniques, they provide

excellent AC and DC load and line regulation.

■

High Efficiency Buck Converter

■

PC Power Supply with Multiple Outputs

■

Battery Upconverter

Negative-to-Positive Converter

■

TheLT1270A/LT1270useadaptiveanti-satswitchdriveto

allow very wide ranging load currents with no loss in

efficiency. An externally activated shutdown mode re-

duces total supply current to 100µA typical for standby

operation.

USER NOTE:

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

description of the LT1270A/LT1270. Application circuits are included to show the capability of the

LT1270A/LT1270. A complete design manual (AN-19) should be obtained to assist in developing

new designs. AN-19 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. AN-19 can also be used for the LT1270A/LT1270 by factoring in the higher switch

current rating and higher operating frequency.

A comprehensive CAD program called SwitcherCad is also available. Contact the local sales office

in your area or the factory direct.

TYPICAL APPLICATIO

Maximum Output Power*

High Efficiency^†Buck Converter

100

BOOST

^†EFFICIENCY IS ≈ 88% @ 2A, 86% @ 5A.

(8V TO 25V)

FOR µPOWER SHUTDOWN OPTION, CONSULT FACTORY.

BUCK-BOOST,

= 12V

*THESE COMPONENTS RATED CONSERVATIVELY TO

IMPROVE EFFICIENCY. MAXIMUM OUTPUT CURRENT

CAN BE 7A. FOR HIGH EFFICIENCY, THE INDUCTOR SHOULD

BE MOLYPERMALLOY OR FERRITE.

1N5819

LT1270*

(INVERTING)

FLYBACK^†

GND

1µF

0.047µF

35µH, 8A*

5V*

BUCK-BOOST, V = 5V

(INVERTING)

9.1k

10k

ANODE

LT1431CZ REF

CATHODE

470µF

35V

MBR1035*

2N3904

INPUT VOLTAGE (V)

LT1270 • TA02

1N4158

560Ω

1000µF

*MULTIPLY BY 1.2 FOR LT1270A.

360Ω

25V

BUCK MODE OUTPUT POWER ≈ (7.5A)(V

)

OUT

^†TRANSFORMER TURNS RATIO MUST BE

OPTIMUM TO ACHIEVE FULL POWER

LT1270 • TA01

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LT1270A/LT1270

W W W

ABS

OLU E

T A

U RATI GS

PACKAGE RDER I FOR ATIO

(Note 1)

Supply Voltage ....................................................... 30V

Switch Output Voltage ............................................ 60V

Feedback Pin Voltage (Transient, 1ms) ................ ±15V

Operating Junction Temperature Range

LT1270AC/LT1270C (Oper.)................ 0°C to 125°C

LT1270AC/LT1270C (Short-Ckt) ......... 0°C to 140°C

Storage Temperature Range ................ –65°c to 150°C

Lead Temperature (Soldering, 10 sec)................ 300°C

ORDER PART

FRONT VIEW

NUMBER

TAB

GND

LT1270CT

LT1270ACT

T PACKAGE

5-LEAD PLASTIC TO-220

T_JMAX= 100°C, θ_JA= 2°C/W, θ_JA= 50°C/W

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS ^The● denotes specifications which apply over the full operating tempera-

ture range, otherwise specifications are at T_A= 25°C. V_IN= 15V, V_C= 0.5V, V_FB= V_REF, switch pin open, unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Reference Voltage

Measured at Feedback Pin

1.224

1.214

1.244

1.264

1.274

REF

V = 0.8V

●

Feedback Input Current

= V

REF

350

4400

200

750

1100

Error Amplifier

Transconductance

∆l = ±25µA

3000

2400

6000

7000

µmho

●

Error Amplifier Source of

Sink Current

V = 1.5V

150

120

350

400

µA

Error Amplifier Clamp Voltage

Hi Clamp, V = 1V

1.80

0.25

2.30

0.52

Lo Clamp, V = 1.5V

0.38

Reference Voltage Line Regulation

Error Amplifier Voltage Gain

Minimum Input Voltage

Supply Current

3V ≤ V ≤ V

, V = 0.8V

●

0.03

%/V

V/V

MAX

0.9V ≤ V ≤ 1.4V

500

800

2.8

3.0

3V ≤ V ≤ V

, V = 0.6V

MAX

Control Pin Threshold

Duty Cycle = 0

0.70

0.50

0.90

1.08

1.25

●

Normal/Flyback Threshold

on Feedback Pin

0.40

0.45

16.3

6.8

0.54

Flyback Reference Voltage

= 50µA

15.0

14.0

17.6

18.0

Change in Flyback Reference

Voltage

0.05 ≤ I ≤ 1mA

4.5

8.5

0.03

650

Flyback Reference Voltage

Line Regulation

= 50µA

0.01

300

%/V

3V ≤ V ≤ V

MAX

Flyback Amplifier

Transconductance (gm)

∆l = ±10µA

150

µmho

Flyback Amplifier Source

and Sink Current

V = 0.6V Source

●

µA

= 50µA Sink

Output Switch Breakdown

Voltage

3V ≤ V ≤ V

●

0.12

MAX

= 1.5mA

Output Switch ON

Resistance (Note 2, 4)

T ≤ 100°C

0.18

0.22

Ω

SAT

T ≤ 125°C

Control Voltage to Switch

Current Transconductance

A/V

Switch Current Limit (LT1270)

(Note 4)

Duty Cycle = 50%, T ≤ 100°C

●

LIM

Duty Cycle = 80%, T ≤ 100°C

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LT1270A/LT1270

ELECTRICAL CHARACTERISTICS ^The● denotes specifications which apply over the full operating tempera-

ture range, otherwise specifications are at T_A= 25°C. V_IN= 15V, V_C= 0.5V, V_FB= V_REF, switch pin open, unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

Duty Cycle = 50%, T ≤ 100°C

MIN

TYP

MAX

UNITS

Switch Current Limit (LT1270A)

(Note 4)

●

10.0

7.5

16.0

14.0

LIM

Duty Cycle = 80%, T ≤ 100°C

∆I

Supply Current Increase

During Switch-ON Time

mA/A

∆I

Switching Frequency

kHz

●

MAX

Maximum Switch Duty Cycle

Flyback Sense Delay Time

1.5

µs

µA

Shutdown Mode Supply Current

Shutdown Mode Threshold Voltage

3V ≤ V ≤ V

, V = 0.05V

100

150

400

MAX

3V ≤ V ≤ V

100

250

300

●

Note 1: Absolute Maximum Ratings are those values beyond which the life

of a device may be impaired.

switch current is given by I

= 6.67 (1.7 – DC) for the LT1270 and I

LIM

8.33 (1.7 – DC) for the LT1270A.

Note 4: Minimum current limit is reduced by 0.5A at 125°C. 100°C test

limits are guaranteed by correlation to 125°C tests.

Note 2: Measured with V in Hi Clamp, V = 0.8V.

Note 3: For duty cycles (DC) between 50% and 80%, minimum guaranteed

U W

TYPICAL PERFOR A CE CHARACTERISTICS

Switch Current Limit vs Duty Cycle

Switch Saturation Voltage

1.6

1.2

0.8

0.4

T = 25°C

25°C

–55°C

125°C

100

DUTY CYCLE (%)

SWITCH CURRENT (A)

LT1270 • TA03

LT1270 • TA04

TYPICAL APPLICATIO S

Boost Converter (5V to 12V)

55µH*

MBR1020

12V, 2A

LT1270

10.7k

25V

GND

1000µF

1.24k

1µF

PULSE ENGINEERING #PE-92116

LT1270 • TA05

1270afc

Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However,

no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the

interconnection of circuits as described herein will not infringe on existing patent rights.

LT1270A/LT1270

TYPICAL APPLICATIO S

Negative-to-Positive Buck-Boost Converter

Negative Buck Converter

OPTIONAL

OUTPUT

55µH**

FILTER

1000µF

100µH**

4.64k

LOAD

OUT

12V, 3A

–5.2V, 7.5A

11.3k

2000µF

12k

LT1270

100µF*

200µF*

OPTIONAL

INPUT FILTER

OPTIONAL

INPUT

FILTER

GND

OPTIONAL

OUTPUT

FILTER

10µH

2.2k

1.24k

200µF

0.22µF

4µF

–12V

–20V

LT1270 • TA06

LT1270 • TA07

*REQUIRED IF INPUT LEADS ≥ 2"

**PULSE ENGINEERING #PE-92116

**PULSE ENGINEERING #PE-92115

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)

.570 – .620

(14.478 – 15.748)

.620

(15.75)

TYP

.460 – .500

(11.684 – 12.700)

.330 – .370

(8.382 – 9.398)

.700 – .728

(17.78 – 18.491)

.095 – .115

(2.413 – 2.921)

SEATING PLANE

.152 – .202

(3.861 – 5.131)

.155 – .195*

(3.937 – 4.953)

.260 – .320

(6.60 – 8.13)

.013 – .023

(0.330 – 0.584)

.067

BSC

.135 – .165

(3.429 – 4.191)

.028 – .038

(0.711 – 0.965)

(1.70)

* MEASURED AT THE SEATING PLANE

T5 (TO-220) 0801

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LT/TP 1203 1K REV C • PRINTED IN USA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

●

LINEAR TECHNOLOGY CORPORATION 1992

(408) 432-1900 FAX: (408) 434-0507 www.linear.com

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