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PDF GM1937 Data sheet ( Hoja de datos )
| Número de pieza | GM1937 | |
| Descripción | WHITE LED STEP-UP CONVERTER | |
| Fabricantes | Gamma | |
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GM1937
WHITE LED STEP-UP CONVERTER
Description
Features
The GM1937 is a step-up DC/DC converter specifically High Efficiency: 84% Typical
designed to drive white LEDs with a constant current. 36V internal Switch
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
Fast 1.2MHz Switching Frequency
Drives Up to three LEDs from a 2.8V
Supply
Drives Up to six LEDs from a 5V
resistors.
Supply
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
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
VIN
3V to 5V
OFF ON
22µH
1µF VIN
SW
GM1937
CE FB
GND
0.22µF
R1
6.34Ω
Figure 1
Li-Ion Powered Driver for Three White LEDs
90
85
80 VIN = 3.0V
75
VIN = 3.6V
70
65
60 0 5 10 15 20
LED CURRENT (mA)
1
Free Datasheet http://www.datasheet4u.com/
1 page  
GM1937
WHITE LED STEP-UP CONVERTER
Application Information
Operation
GM1937 is designed with a constant frequency, current mode control scheme to provide excellent line
and load regulation. Operation can be best understood by referring to the block diagram in Figure 2. At
the start of each oscillator cycle, the SR latch is set, which turns on the power switch Q1. A voltage
proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the
positive terminal of the PWM comparator A2. When this voltage exceeds the level at the negative input of
A2, the SR latch is reset turning off the power switch. The level at the negative input of A2 is set by the
error amplifier A1, and is simply an amplified version of the difference between the feedback voltage and
the reference voltage of 95mV. In this manner, the error amplifier sets the correct peak current level to
keep the output in regulation. If the error amplifier’s output increases, more current is delivered to the
output; if it decreases, less current is delivered.
Minimum Output Current
GM 1937 can regulate three series LEDs connected a low output current. down to approximately 4mA
from a 4.2V supply, without pulse skipping, using the same external components as specified for 15mA
operation. As current is further reduced, the device will begin skipping pulses.This will result in some low
frequency ripple, although the LED current remains regulated on an average basis down to zero.
Inductor Selection
A 22mH inductor is recommended for most GM1937 applications. Although small size and high efficiency
are major concerns, the inductor should have low core losses at 1.2MHz and low DCR (copper wire
resistance). Some inductors in this category with small size are listed in Table 1.
Table 1. Recommended Inductors
Part Number
DCR (Ω)
Current Rating
(mA)
LQH3C220
0.71 250
ELJTC220KF
4.0 160
CDRH3D16-220
0.53
350
LB2023B220M
1.7
75
LEM2520-220
5.5 125
Manufacturer
Murata
Panasonic
Sumida
Taiyo Yuden
Taiyo Yuden
Capacitor Selection
The small size of ceramic capacitors makes them ideal for GM1937 applications. X5R and X7R types are
recommended because they retain their capacitance over wider voltage and temperature ranges than
other types such as Y5V or Z5U. A 1µF input capacitor and a 0.22µF output capacitor are sufficient for
most GM1937 applications.
5
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| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet GM1937.PDF ] | |
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