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PDF EUP2571 Data sheet ( Hoja de datos )
| Número de pieza | EUP2571 | |
| Descripción | White LED Step-Up Converter | |
| Fabricantes | Eutech Microelectronics | |
| Logotipo |  |
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EUP2571
White LED Step-Up Converter
In Tiny SOT-23 Package
DESCRIPTION
The EUP2571 is a constant current step-up converter
specifically designed to drive white LEDs. The Step-up
converter topology allows series connection of the
white LEDs so the LED currents are identical for
uniform brightness. The EUP2571 switches at 1.1MHz,
allowing the use of tiny external components. The
input and output capacitor can be as small as 1µF,
saving space and cost versus alternative solutions. A
low 0.25V feedback voltage minimizes power loss in
the current setting resistor for better efficiency.
www.DTahtaeShEeUet4PU2.5co7m1 is available in low profile SOT23-5,
SOT23-6 package.
FEATURES
z 2.6V to 5.5V Input Range
z 26V Output with Over Voltage Protection
z High Efficiency :85 % Typical
z PWM Dimming Control
z Internal High Power 30V MOSFET Switch
z Fast 1.1MHz Switching Frequency
z Small, Low-Profile Inductors and Capacitors
z SOT23-5,SOT23-6 Package
z RoHS Compliant and 100% Lead (Pb)-Free
APPLICATIONS
z Mobile Phone
z Digital Still Camera
z PDAs, Handheld Computers
z MP3 Players
z GPS Receivers
Typical Application Circuit
DS2571 Ver1.1 May. 2007
Figure 1. White LED Application
1
1 page  
Typical Operating Characteristics
Efficiency vs. Vin (Driving 1WLED)
EUP2571
Efficiency vs. Vin (Driving 2WLEDs)
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Efficiency vs. Vin (Driving 3WLEDs)
Efficiency vs. Vin (Driving 5WLEDs)
Efficiency vs. Vin (Driving 7WLEDs)
DS2571 Ver1.1 May. 2007
5
5 Page 
c. Using a Filtered PWM signal
Another common application is using a filtered PWM
signal as an adjustable DC voltage for LED dimming
control. A filtered PWM signal acts as the DC voltage
to regulate the output current. The recommended
application circuit is shown in the Figure 7. In this
circuit, the output ripple depends on the frequency of
PWM signal. For smaller output voltage ripple
(<100mV), the recommended frequency of 2.8V PWM
signal should be above 2kHz. To fix the frequency of
PWM signal and change the duty cycle of PWM signal
can get different output current. According to the
application circuit of Figure 7, output current is from
20.5mA to 5.5mA by adjusting the PWM duty cycle
from 10% to 90%.
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EUP2571
Constant Output Voltage for Backlight of Main
Panel and Flashlight
Figure 8 is an application of EUP2571 for backlight of
main panel and flashlight. Setting the divider-resistors
(R1 & R2) is to get a constant output voltage that
depends on the forward voltage and the numbers of
series-LEDs. There are three kinds of mode controlled
by the switches - backlight mode /flashlight mode
/backlight + flashlight mode. It can turn on backlight or
flashlight at one time or both at the same time.
Applying different duty cycle of PWM signal above
22kHz to backlight's switch can also control the
brightness. The following formula (2)(3) can determine
R3 and R4.
R3 = VOUT − 3VFb − VDS --------------------------(2)
Ib
R4 = VOUT − 3VFf − VDS --------------------------(3)
If
VDS = Ib× R DS(ON) ---------------------------------(4)
Figure 7. Filtered PWM Signal for LED
Dimming Control
Figure 8. Constant Output Voltage for Backlight
and Flashlight
DS2571 Ver1.1 May. 2007
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet EUP2571.PDF ] | |
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