GM1937
WHITE LED STEP-UP CONVERTER
Description
The GM1937 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 output capacitor can be as small as 0.22µF,
saving space versus alternative solutions. A low 95mV
feedback voltage minimizes power loss for better
Features
High Efficiency: 84% Typical
36V internal Switch
Fast 1.2MHz Switching Frequency
Drives Up to three LEDs from a 2.8V
Supply
Drives Up to six LEDs from a 5V
Supply
External Matched LED Current
Uses Tiny 1mm height inductor
Requires Only 0.22
F Output
Capacitor
Low profile TSOT package
Application
Cellular Phones
PDA, Handheld Computers
Digital Cameras
MPS3 Players
GPS Receivers
Typical Application Circuits
V
IN
3V to 5V
1µF
V
IN
22µH
90
EFFICIENCY (%)
SW
0.22µF
85
80
75
70
65
60
0
5
10
15
LED CURRENT (mA)
20
V
IN
= 3.0V
V
IN
= 3.6V
OFF ON
GM1937
FB
CE
GND
R1
6.34Ω
Figure 1
Li-Ion Powered Driver for Three White LEDs
1
GM1937
V2.00
GAMMA [ GAMMA MICROELECTRONICS INC. ]
