Linear Technology Electronic Components Datasheet

LT1959 Datasheet

4.5A/ 500kHz Step-Down Switching Regulator

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LT1959

4.5A, 500kHz Step-Down

Switching Regulator

FEATURES

s Operates with Input as Low as 4V

s Output Range Down to 1.21V

s Constant 500kHz Switching Frequency

s Uses All Surface Mount Components

s Inductor Size Reduced to 1.8µH

s Saturating Switch Design: 0.07Ω

s Shutdown Current: 20µA

s Easily Synchronizable

s Cycle-by-Cycle Current Limiting

s 4.5A Switch

s Current Mode Control

APPLICATIO S

s Portable Computers

s Battery-Powered Systems

s Battery Chargers

s Distributed Power

s 5V to 3.3V Conversion

s 5V to 2.5V Conversion

s 5V to 1.8V Conversion

DESCRIPTIO

The LT®1959 is a 500kHz monolithic buck mode switching

regulator functionally identical to the LT1506 but optimized

for lower output voltage applications. It will operate down

to 1.21V output compared to 2.42V for the LT1506. A 4.5A

switch is included on the die along with all the necessary

oscillator, control and logic circuitry. High switching fre-

quency allows a considerable reduction in the size of ex-

ternal components. The topology is current mode for fast

transient response and good loop stability.

A special high speed bipolar process and new design tech-

niques achieve high efficiency at high switching frequency.

Efficiency is maintained over a wide output current range

by keeping quiescent supply current to 4mA and by utiliz-

ing a supply boost capacitor to saturate the power switch.

The LT1959 fits into standard 7-pin DD and fused lead

SO-8 packages. Full cycle-by-cycle short-circuit protection

and thermal shutdown are provided. Standard surface

mount external parts are used, including the inductor and

capacitors. There is the optional function of shutdown or

synchronization. A shutdown signal reduces supply current

to 20µA. Synchronization allows an external logic level sig-

nal to increase the internal oscillator from 580kHz to 1MHz.

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

TYPICAL APPLICATION

INPUT

10µF

50µF

CERAMIC

5V to 1.8V Down Converter

1N914

OPEN

HIGH

= ON

BOOST

VIN VSW

LT1959

SHDN

GND VC

1.5nF

0.68µF

5µH

1.21k

OUTPUT

1.8V

R2 +

D1 2.49k

MBRS330T3

100µF, 10V

SOLID

TANTALUM

1959 TA01

Efficiency vs Load Current

VOUT = 3.3V

VIN = 5V

L = 10µH

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

LOAD CURRENT (A)

1959 TA02

Linear Technology Electronic Components Datasheet

LT1959 Datasheet

4.5A/ 500kHz Step-Down Switching Regulator

No Preview Available !

LT1959

ABSOLUTE MAXIMUM RATINGS (Note 1)

Input Voltage .......................................................... 16V

BOOST Voltage ........................................................ 30V

BOOST Pin Above Input Voltage ............................. 15V

SHDN Pin Voltage ..................................................... 7V

FB Pin Voltage ....................................................... 3.5V

FB Pin Current ....................................................... 1mA

SYNC Pin Voltage ..................................................... 7V

Operating Junction Temperature Range

LT1959C ................................................ 0°C to 125°C

LT1959I ........................................... – 40°C to 125°C

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

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

PACKAGE/ORDER INFORMATION

FRONT VIEW

7 FB

6 BOOST

TAB 5 VIN

IS 4 GND

GND

3 VSW

2 SHDN

1 VC

R PACKAGE

7-LEAD PLASTIC DD

TJMAX = 150°C, θJA = 30°C/W

WITH PACKAGE SOLDERED TO 0.5 SQUARE INCH

COPPER AREA OVER BACKSIDE GROUND PLANE OR

INTERNAL POWER PLANE. θJA CAN VARY FROM 20°C/W

TO > 40°C/W DEPENDING ON MOUNTING TECHNIQUES

ORDER PART

NUMBER

LT1959CR

LT1959IR

TOP VIEW

VIN 1

BOOST 2

FB 3

GND** 4

8 VSW

7 SYNC

6 SHDN

5 VC

S8 PACKAGE

8-LEAD PLASTIC SO

TJMAX = 150°C, θJA = 80°C/W

**WITH (FUSED GND) GROUND PIN

CONNECTED TO GROUND PLANE OR

LARGE LANDS

ORDER PART

NUMBER

LT1959CS8

LT1959IS8

S8 PART MARKING

1959

1959I

ELECTRICAL CHARACTERISTICS The q denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C, TJ = 25°C, VIN = 5V, VC = 1.5V, Boost = VIN + 5V, switch open, unless

otherwise noted.

PARAMETER

Feedback Voltage (Adjustable)

Reference Voltage Line Regulation

Feedback Input Bias Current

Error Amplifier Voltage Gain

Error Amplifier Transconductance

CONDITIONS

All Conditions

4.3V ≤ VIN ≤ 15V

(Note 2)

∆I (VC) = ±10µA

VC Pin to Switch Current Transconductance

Error Amplifier Source Current

Error Amplifier Sink Current

VC Pin Switching Threshold

VC Pin High Clamp

Switch Current Limit

Slope Compensation

VFB = 1.05V

VFB = 1.35V

Duty Cycle = 0

VC Open, VFB = 1.05V, DC ≤ 50%

DC = 80%

MIN TYP MAX

q 1.19 1.21 1.23

0.01 0.03

q –0.5 0 0.5

200 400

1500 2000 2700

q 1000

3100

5.3

q 140 225 320

0.9

2.1

q 4.5 6 8.5

0.8

UNITS

%/ V

µA

µMho

A/ V

µA

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LT1959 Datasheet

4.5A/ 500kHz Step-Down Switching Regulator

LT1959 Datasheet

4.5A/ 500kHz Step-Down Switching Regulator

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