1

LT1932

Constant-Current DC/DC

LED Driver in ThinSOT

July 2001

The LT

designed to operate as a constant-current source. Be-

cause it directly regulates output current, the LT1932 is

ideal for driving light emitting diodes (LEDs) whose light

intensity is proportional to the current passing through

them, not the voltage across their terminals.

With an input voltage range of 1V to 10V, the device works

from a variety of input sources. The LT1932 accurately

regulates LED current even when the input voltage is

higher than the LED voltage, greatly simplifying battery-

powered designs. A single external resistor sets LED

current between 5mA and 40mA, which can then be easily

adjusted using either a DC voltage or a pulse width

modulated (PWM) signal. When the LT1932 is placed in

shutdown, the LEDs are disconnected from the output,

ensuring a quiescent current of under 1

µA for the entire

circuit. The device’s 1.2MHz switching frequency permits

the use of tiny, low profile chip inductors and capacitors to

minimize footprint and cost in space-conscious portable

applications.

s

Up to 80% Efficiency

s

Inherently Matched LED Current

s

Drives Five White LEDs from 2V

s

Drives Six White LEDs from 2.7V

s

Drives Eight White LEDs from 3V

s

Precise, Adjustable Control of LED Current

s

Disconnects LEDs In Shutdown

s

1.2MHz Fixed Frequency Switching

s

Uses Tiny Ceramic Capacitors

s

Uses Tiny 1mm-Tall Inductors

s

s

s

Low Profile (1mm) ThinSOT

s

Cellular Telephones

s

Handheld Computers

s

Digital Cameras

s

Portable MP3 Players

s

Pagers

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 represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

Li-Ion Driver for Four White LEDs

Efficiency

Final Electrical Specifications

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

SW

D1

15mA

1932 TA01

L1

6.8

µH

2.7V TO 4.2V

LT1932

SHDN

C1: TAIYO YUDEN JMK212BJ475

C2: TAIYO YUDEN EMK212BJ105

D1:ZETEX ZHCS400

L1: SUMIDA CLQ4D106R8 OR PANASONIC ELJEA6R8

61

4

1.50k

PWM

DIMMING

CONTROL

C1

4.7

µF

C2

1

µF

2

3

5

LED

GND

LED CURRENT (mA)

0

55

60

65

70

75

80

85

510

15

20

1932 TA02

ThinSOT is a trademark of Linear Technology Corporation.