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PDF AP5724 Data sheet ( Hoja de datos )
| Número de pieza | AP5724 | |
| Descripción | Step-up DC/DC Converter | |
| Fabricantes | Diodes | |
| Logotipo |  |
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Features
• Inherently Matched LED Current
• High Efficiency: 84% Typical
• Fast 1.2MHz Switching Frequency
• Current limit and UVLO Protections
• Internal Thermal Shutdown
• Internal Over Voltage Protection
• Integrated Soft-start Function
• SOT26 and DFN2020C-6: Available in “Green”
Molding Compound (No Br, Sb)
• Lead Free Finish/RoHS Compliant (Note 1)
AP5724
WHITE LED STEP-UP CONVERTER
General Description
The AP5724 is a step-up DC/DC converter specifically designed
to drive white LEDs with a constant current. The device can drive
2~6 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
AP5724 switches at 1.2MHz that allows the use of tiny external
components. A low 0.1V feedback voltage minimizes power loss
in the current setting resistor for better efficiency.
Applications
• Cellular Phones
• PDAs, Hand held Computers
• Digital Cameras
• MP3 Players
• GPS Receivers
Typical Application Circuit
VIN
ON OFF
PWM Dimming
L1
22uH
D1
C IN
1uF
VIN SW
AP5724 OVP
EN FB
GND
COUT
1uF
2~6 LEDs
RSET
5
Figure 1. Typical Application Circuit
AP5724 Rev. 1
1 of 16
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JUNE 2009
© Diodes Incorporated
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AP5724
WHITE LED STEP-UP CONVERTER
Typical Performance Characteristics (6 LEDs ; VIN = 3.6V ; IOUT = 25mA)
1
0.8
0.6
0.4
0.2
0
2.5
VIN vs. Shutdown Current
3 3.5 4 4.5 5
VIN (V)
5.5
VIN vs. Frequency
1.25
1.2
1.15
1.1
1.05
1
2.5 3 3.5 4 4.5 5 5.5
VIN (V)
0.12
0.11
0.1
0.09
0.08
0.07
0.06
2.5
VIN vs. Feedback Voltage
3 3.5 4 4.5 5
VIN (V)
5.5
700
600
500
400
300
200
100
0
2.5
VIN vs. Quiescent Current
3 3.5 4 4.5 5
VIN (V)
5.5
VIN vs. Max Duty
100
95
90
85
80
2.5 3 3.5 4 4.5 5 5.5
VIN(V)
0.12
0.11
0.1
0.09
0.08
0.07
0.06
0
IOUT vs. Feedback Voltage
10 20 30 40 50
IOUT (mA)
AP5724 Rev. 1
5 of 16
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JUNE 2009
© Diodes Incorporated
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AP5724
WHITE LED STEP-UP CONVERTER
Application 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 RSET 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 20mA.
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.
AP5724
FB
R3
100k
VDC
R2
5k
RSET
5
Figure 3. Dimming Control Using a DC Voltage
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 4. RSET sets the minimum LED current (when the NMOS is off). RSET sets how much the LED current
increases when the NMOS is turned on.
AP5724
Logic
Signal
FB
RINC
RSET
Figure 4. Dimming Control Using a Logic Signal
AP5724 Rev. 1
11 of 16
www.diodes.com
JUNE 2009
© Diodes Incorporated
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet AP5724.PDF ] | |
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