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PDF AP1521W Data sheet ( Hoja de datos )
| Número de pieza | AP1521W | |
| Descripción | White LED Step-Up Converter | |
| Fabricantes | ETC | |
| Logotipo |  |
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White LED Step-Up Converter
AP1521
Features
- Inherently Matched LED Current
- Drives Up to Four LEDs from a 3.2V Supply
- Drives Up to Six LEDs from a 5V Supply
- High Efficiency: 84% Typical
- Fast 1MHz Switching Frequency
- 36V Rugged Bipolar Switch
- Low Profile SOT23-5 Pb-Free Packaging
Applications
- Cellular Phones
- PDAs, Hand-held Computers
- Digital Cameras
- MP3 Players
- GPS Receivers
Pin Assignments
Top View
VIN SHDN
SW VSS FB
SOT23-5L
General Description
The AP1521 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
eliminates the need for ballast resistors. The
AP1521 switches at 1MHz that allows the use of
tiny external components. A low 300mV feedback
voltage minimizes power loss in the current setting
resistor for better efficiency.
Pin Descriptions
Name
SW
VSS
FB
SHDN
VIN
Description
Switch Pin. Connect inductor/diode
here. Minimize trace area at this pin
to reduce EMI.
GND pin
Feedback Pin. Reference voltage is
310mV. Connect cathode of lowest
LED and resistor here. Calculate
resistor value according to the
formula： RFB = 310mV / ILED
Shutdown Pin. Tie to 1.5V or higher
to enable the device；0.4V or less to
disable the device.
Input Supply Pin. Must be locally
bypassed.
Ordering Information
AP1521 X X
Package
W: SOT23-5L
Packing
Blank : Tube
A : Taping
This datasheet contains new product information. Anachip Corp. reserves the rights to modify the product specification without notice. No liability is assumed as a result of the use of
this product. No rights under any patent accompany the sale of the product.
Rev. 0.1 Apr. 27, 2004
1/8
1 page  
White LED Step-Up Converter
AP1521
Applications Information (Continued)
2. Using a DC Voltage
For some applications, the preferred method of
brightness control is a variable DC voltage to adjust
the LED current. The dimming control using a DC
voltage is shown in Figure 3. As the DC voltage
increases, the voltage drop on R2 increases and
the voltage drop on R1 decreases. Thus, the LED
current decreases. The selection of R2 and R3
will make the current from the variable DC source
much smaller than the LED current and much larger
than the FB pin bias current. For VDC range from
0V to 2V, the selection of resistors in Figure 3 gives
dimming control of LED current from 0mA to 15mA.
3. Using a Filtered PWM Signal
The filtered PWM signal can be considered as an
adjustable DC voltage. It can be used to replace
the variable DC voltage source in dimming control.
The circuit is shown in Figure 4.
4. Using a Logic Signal
For applications that need to adjust the LED current
in discrete steps, a logic signal can be used as
shown in Figure 5. R1 sets the minimum LED
current (when the NMOS is off). RSET sets how
much the LED current increases when the NMOS is
turned on.
Start-up and Inrush Current
To achieve minimum start-up delay, no internal
soft-start circuit is included in AP1521. When first
turned on without an external soft-start circuit,
inrush current is about 200mA. If soft-start is
desired, the recommended circuit and the
waveforms are shown in Figure 6. If both
soft-start and dimming are used, a 10kHz PWM
signal on SHDN is not recommended. Use a lower
frequency or implement dimming through the FB pin
as shown in Figures 3, 4 or 5.
AP1521
AP1521
FB
R3
90k
VDC
R2
5k
R1
15Ω
Figure 3. Dimming Control Using a DC Voltage
AP1521
10k
PWM
FB
R3 R2
90k 5k
0.1uF
R1
15Ω
Figure 4. Dimming Control Using a Filtered PWM
Signal
Logic
Signal
FB
RSET
R1
Figure 5. Dimming Control Using a Logic Signal
D1
2.2nF
D2
AP1521
FB
R2
1k COUT
5k
R1
15Ω
D2:MMBT
Figure 6. Recommended Soft-Startup Circuit
Anachip Corp.
www.anachip.com.tw
Rev. 0.1 Apr. 27, 2004
5/8
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet AP1521W.PDF ] | |
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