LT1932 Datasheet, PDF (1/16 Pages) Linear Technology – Constant-Current DC/DC LED Driver in ThinSOT

FEATURES
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 _{Regulates Current Even When VIN > VOUT}
s _{Operates with VIN as Low as 1V}
s _{Low Profile (1mm) ThinSOT}^TM _Package
U
APPLICATIO S
s _{Cellular Telephones}
s _{Handheld Computers}
s _{Digital Cameras}
s _{Portable MP3 Players}
s _Pagers
Final Electrical Specifications
LT1932
Constant-Current DC/DC
LED Driver in ThinSOT
July 2001
DESCRIPTIO
The LT^®1932 is a fixed frequency step-up DC/DC converter
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 1µA 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
Li-Ion Driver for Four White LEDs
V_IN
2.7V TO 4.2V
L1
6.8µH
D1
C1
4.7µF
PWM
DIMMING
CONTROL
6
1
V_IN
SW
LT1932
5
SHDN
3
LED
R_SET
GND
4
2
R_SET
1.50k
15mA
C1: TAIYO YUDEN JMK212BJ475
C2: TAIYO YUDEN EMK212BJ105
D1:ZETEX ZHCS400
L1: SUMIDA CLQ4D106R8 OR PANASONIC ELJEA6R8
C2
1µF
1932 TA01
Efficiency
85
80
V_IN = 4.2V
75
V_IN = 2.7V
70
65
60
55
0
5
10
15
20
LED CURRENT (mA)
1932 TA02
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.
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