Ver: 1.1
Nov 17, 2005
TEL: 886-3-5788833
http://www.gmt.com.tw
1

G5121
Global Mixed-mode Technology Inc.
Fixed Frequency White LED Step-Up Converter
Features
„ Inherently Matched LED Current
„ High Efficiency: 87%
„ Drives Up to Five LEDs from 2.5V Supply
„ 24V Internal Power Switch
„ Fast 1MHz Switching Frequency
„ Uses Tiny 1mm Tall Inductors
„ Requires Only 1µF Output Capacitors
„ 19.5V Over Voltage Protection
„ SOT-23-6 Package
Applications
„ White LED Backlight Display for PDA
„ Pocket PC
„ Smart Phones
„ Handheld Devices
„ Cellular Phones

General Description
The G5121 is a step-up DC/DC converter specifically
designed to drive up to 5 series white LEDs with con-
stant current. Series connection of the LEDs provides
identical LED currents resulting in uniform brightness
and eliminates the need for ballast resistors. The
G5121 switches at 1MHz, allowing the use of tiny ex-
ternal components. A low 0.254V feedback voltage
minimizes power loss in the current setting resistor for
high efficiency. The OVP pin monitors the output volt-
age and turns off the converter whenever the LEDs
are open.
The G5121 is available in low profile SOT-23-6 pack-
age.
Ordering Information
ORDER
NUMBER
MARKING
TEMP.
RANGE
PACKAGE
(Pb free)
G5121TB1U 5121x -40°C ~ +85°C SOT-23-6



Note: TB : SOT23-6
U: Tape & Reel
Pin Configuration Typical Application Circuit

VCC
SHDN
SOT-23-6
G5121
6
4
1SW
2
3
GND
FB
5 OVP
VCC SW
SHDN FB
GND
G5121
L1
V
IN
2.7V to 4.2V
D1
OVP
5 LEDs
PWM Dimming
Waveform
RS
C1
4.7µF/6.3V
4.7µH
C2
1µF/25V
C1:TAIYO YUDEN, JMK212BJ475KD
C2:TAIYO YUDEN, TMK316BJ105KD