L1937 Datasheet, PDF (1/7 Pages) Unisonic Technologies – WHITE LED STEP-UP CONVERTER

UTC L1937
LINEAR INTEGRATED CIRCUIT
WHITE LED STEP-UP
CONVERTER
DESCRIPTION
The UTC L1937 is a step-up DC/DC converter
specifically designed to drive white LEDs with a
constant current. The device can drive two, three or
four LEDs in series from a Li-Ion cell. Series
connection of the LEDs provides identical LED
currents resulting in uniform brightness and
eliminating the need for ballast resistors. The UTC
LT1937 switches at 1.2MHz, allowing the use of tiny
external components. The output capacitor can be as
small as 0.22 DŽF, saving space and cost versus
alternative solutions. A low 95mV feedback voltage
minimizes power loss in the current setting resistor for
better efficiency.
FEATURES
* Inherently Matched LED Current
* High Efficiency: 84% Typical
* Drives Up to Four LEDs from a 3.2V Supply
* Drives Up to Six LEDs from a 5V Supply
* 36V Rugged Bipolar Switch
* Fast 1.2MHz Switching Frequency
* Uses Tiny 1mm Tall Inductors
* Requires Only 0.22DŽF Output Capacitor
APPLICATIONS
* Marking code: LTCG
* Cellular Phones
* PDAs, Handheld Computers
* Digital Cameras
* MP3 Players
* GPS Receivers
1
2
3
5
4
SOT-25
1
SOT-363


*Pb-free plating product number: L1937L
PIN FUNCTION
PIN NO. PIN NO. _{PIN NAME}
(SOT-25) (SOT-363).
1
Switch
2
Ground
3
Feedback
4
5
6
5
Shutdown
Input Supply
Ground
SYMBOL
FUNCTION
SW
GND
FB
SHDN
VIN
GND
Connect inductor/diode here. Minimize trace area at this pin to
reduce EMI.
Connect directly to local ground plane.
Reference voltage is 95mV. Connect cathode of lowest LED and
resistor here. Calculate resistor value according to the formula:
R_FB = 95mV/I_LED
Connect to 1.5V or higher to enable device;0.4V or less to
disable device.
Input Supply Pin. Must be locally bypassed.
Connect to Pin 2 and to local ground plane
UTC UNISONIC TECHNOLOGIES CO., LTD. 1
QW-R103-021,A