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PDF AL8805 Data sheet ( Hoja de datos )
| Número de pieza | AL8805 | |
| Descripción | HIGH EFFICIENCY 30V 1A BUCK LED DRIVER | |
| Fabricantes | Diodes Incorporated | |
| Logotipo |  |
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AL8805
HIGH EFFICIENCY 36V 1A BUCK LED DRIVER
Description
The AL8805 is a step-down DC/DC converter designed to drive LEDs
with a constant current. The device can drive up to 8 LEDs,
depending on the forward voltage of the LEDs, in series from a
voltage source of 6V to 36V. Series connection of the LEDs provides
identical LED currents resulting in uniform brightness and eliminating
the need for ballast resistors. The AL8805 switches at frequency up to
1MHz. This allows the use of small size external components, hence
minimizing the PCB area needed.
Maximum output current of AL8805 is set via an external resistor
connected between the VIN and SET input pins. Dimming is achieved
by applying either a DC voltage or a PWM signal at the CTRL input
pin. An input voltage of 0.4V or lower at CTRL switches off the output
MOSFET simplifying PWM dimming.
Pin Assignments
(Top View)
SW 1
GND 2
CTRL 3
5 VIN
4 SET
SOT25
Features
• LED Driving Current up to 1A
• Better than 5% Accuracy
• High Efficiency up to 98%
• Operating Input Voltage from 6V to 36V
• High Switching Frequency up to 1MHz
• PWM/DC Input for Dimming Control
• Built-In Output Open-Circuit Protection
• SOT25: Available in “Green” Molding Compound (No Br,Sb) with
lead Free Finish/ RoHS Compliant
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
Applications
• MR16 Lamps
• General Illumination Lamps
Notes:
1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.
2. See http://www.diodes.com for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green" and Lead-free.
3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and
<1000ppm antimony compounds.
Typical Applications Circuit
AL8805
Document number: DS35030 Rev. 4 - 2
1 of 16
www.diodes.com
July 2012
© Diodes Incorporated
1 page  
AL8805
Typical Performance Characteristics (cont.) (@TA = +25°C, unless otherwise specified.)
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0%
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
20% 40% 60% 80%
PWM DUTY CYCLE
Figure 7 ILED vs. PWM Duty Cycle
0
100%
400
350
300
250
200
150
100
-40
-15 10 35 60 85 110
AMBIENT TEMPERATURE (°C)
Figure 9 SW RDS(ON) vs. Temperature
300
240
180
120
60
VCTRL = Open
VSET = VIN
TA = 25°C
0
6 12 18 24 30 36
VIN (V)
Figure 8 SW RDS(ON) vs. Input Voltage
130
125
120
115
VSENSE
110
105
100
95
RSET = 150mΩ
L = 68µH
VIN = 12V
1 LED Load
18
16
14
12
VSW
10
8
6
4
90 2
85 0
80 -2
TIME (µs)
Figure 10 SW Output Switching Characteristics
RSET = 150mΩ, L =68µH, VIN = 12V, 1LED Load, TA =25°C
1 20
Duty Cycle = 5%
0.9 ILED 18
0.8 16
0.7 VSW 14
0.6 12
0.5 10
0.4 8
0.3 6
0.2 4
VCTRL
0.1 2
00
0 50 100 150 200
Time (µs)
Figure 11 PWM Dimming
L = 33µH
RS = 150mΩ
TA = 25°C
2 LED
6 9 12 15 18 21 24 27 30 33 36
INPUT VOLTAGE (V)
Figure 12 Duty Cycle vs. Input Voltage
AL8805
Document number: DS35030 Rev. 4 - 2
5 of 16
www.diodes.com
July 2012
© Diodes Incorporated
5 Page 
AL8805
Application Information (cont.)
Soft Start
The AL8805 does not have in-built soft-start action – this provides very fast turn off of the output the stage improving PWM dimming accuracy;
nonetheless, adding an external capacitor from the CTRL pin to ground will provide a soft-start delay. This is achieved by increasing the time
taken for the CTRL voltage to rise to the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the
comparator. Adding a capacitor increases the time taken for the output to reach 90% of its final value, this delay is 0.1ms/nF, but will impact on
the PWM dimming accuracy depending on the delay introduced.
Figure 33 Soft Start with 22nF Capacitor on CTRL Pin (VIN = 36V, ILED = 667mA, 1 LED)
Reducing Output Ripple
Peak to peak ripple current in the LED(s) can be reduced, if required, by shunting a capacitor C2 across the LED(s) as shown already in the
circuit schematic.
A value of 1μF will reduce the supply ripple current by a factor three (approx.). Proportionally lower ripple can be achieved with higher capacitor
values. Note that the capacitor will not affect operating frequency or efficiency, but it will increase start-up delay, by reducing the rate of rise of
LED voltage. By adding this capacitor the current waveform through the LED(s) changes from a triangular ramp to a more sinusoidal version
without altering the mean current value.
Capacitor Selection
The small size of ceramic capacitors makes them ideal for AL8805 applications. X5R and X7R types are recommended because they retain their
capacitance over wider voltage and temperature ranges than other types such as Z5U.
A 2.2μF input capacitor is sufficient for most intended applications of AL8805; however a 4.7μF input capacitor is suggested for input voltages
approaching 36V.
AL8805
Document number: DS35030 Rev. 4 - 2
11 of 16
www.diodes.com
July 2012
© Diodes Incorporated
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet AL8805.PDF ] | |
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