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AL8807

Document number: DS35281 Rev. 5 - 2

1 of 20

www.diodes.com

March 2013

L8807

HIGH EFFICIENCY LOW 36V 1A BUCK LED DRIVER

Description

The AL8807 is a step-down DC/DC converter designed to drive LEDs

with a constant current. The device can drive up to 9 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 AL8807 switches at frequency up to

1MHz with controlled rise and fall times to reduce EMI. This allows

the use of small size external components, hence minimizing the PCB

area needed.

Maximum output current of AL8807 is set via an external resistor

connected between the V

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.

Features

 LED Driving Current up to 1.3A (MSOP-8EP)

 Better Than 5% Accuracy

 High Efficiency up to 96%

 Optimally Controlled Switching Speeds

 Operating Input Voltage from 6V to 36V

 PWM/DC Input for Dimming Control

 Built-In Output Open-Circuit Protection

 SOT25, MSOP-8EP: Available in “Green” Molding Compound

(No Br, Sb)

 Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)

 Halogen and Antimony Free. “Green” Device (Note 3)

Pin Assignments

SOT25

(Top View)

GND

CTRL

SET

(Top View)

MSOP-8EP

SET

GND

CTRL

N/C

Applications

 MR16 Lamps

 General Illumination Lamps

 12V Powered LED Lamps

 24V Powered LED 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/quality/lead_free.html 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



100 nF

1µF

DFLS2100

DFLS 2100

DFLS2100

GND

CTRL

SET

AL8807

0R15

33µH

100nFC5

150µF

NODE

CATHODE

Summary of content (20 pages)

PAGE 1
AL8807 HIGH EFFICIENCY LOW 36V 1A BUCK LED DRIVER Description Pin Assignments The AL8807 is a step-down DC/DC converter designed to drive LEDs (Top View) with a constant current. The device can drive up to 9 LEDs, depending on the forward voltage of the LEDs, in series from a SW voltage source of 6V to 36V. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating VIN GND the need for ballast resistors.
PAGE 2
AL8807 Pin Descriptions Pin Name SW GND CTRL SET VIN Pin Number Function SOT25 MSOP-8EP 1 5, 6 Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI. 2 2, 3 GND Pin Dimming and On/Off Control Input.  Leave floating for normal operation. (VCTRL = VREF = 2.5V giving nominal average output current IOUTnom = 0.1/RS) 3 4  Drive to voltage below 0.4V to turn off output current  Drive with DC voltage (0.5V < VCTRL < 2.
PAGE 3
AL8807 Electrical Characteristics (@VIN = 12, TA = +25°C, unless otherwise specified.
PAGE 4
AL8807 Typical Performance Characteristics 400 900 350 800 700 FREQUENCY (kHz) 300 IIN (µA) 250 200 150 100 0 3 600 L = 68µH 500 400 300 200 VCTRL = 0V VSET = VIN TA = 25°C 50 0 0 6 9 12 15 18 21 24 27 30 33 36 VIN (V) Figure 1. Supply Current (not switching) vs. Input Voltage 90 60 70 40 ICTRL (µA) 80 60 40 L = 100µH 100 100 LED CURRENT (A) VIN = 12V 1 LED RSET = 150m TA = 25°C L = 33µH 0 1 2 3 4 5 VCTRL Figure 2. Switching Frequency vs.
PAGE 5
AL8807 Typical Performance Characteristics (cont.) 7 240 6 0.5 LED Current Error 0.4 LED Current 4 270 0.7 0.6 5 300 0.3 3 210 RDS(ON) (m) 8 LED CURRENT ERROR (%) 0.8 L = 68H, RS = 150m TA = 25C, VIN = 12V CTRL = PWM, fPWM = 500Hz 1 LED LED CURRENT (A) 9 150 120 90 0.2 2 180 VCTRL = Open VSET = VIN TA = 25°C 60 0.1 1 0 0 20 40 60 80 PWM DUTY CYCLE Figure 7. ILED vs. PWM Duty Cycle 30 0 100 0 6 9 12 15 18 21 24 27 30 33 36 VIN (V) Figure 8. SW RDS(ON) vs.
PAGE 6
AL8807 Typical Performance Characteristics (cont.) (670LED Current) 350 10 6 4 2 0 -2 -4 -6 -8 -10 300 SWITCHING FREQUENCY (kHz) LED CURRENT ERROR (%) 8 200 150 100 50 0 6 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 13. LED Current Deviation vs. Input Voltage 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 14. Switching Frequency vs.
PAGE 7
AL8807 Typical Performance Characteristics (cont.) (1A LED Current MSOP-8EP) 10 350 L = 100µH RS = 100m TA = 25°C VCTRL = Open SWITCHING FREQUENCY (kHz) LED CURRENT ERROR (%) 8 6 4 2 0 -2 -4 -6 300 250 200 150 1 LED 100 50 -8 -10 4 LEDs 5 LEDs 6 LEDs 2 LEDs3 LEDs 0 6 6 7 LEDs 8 LEDs 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 20. Switching Frequency vs. Input Voltage 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 19. LED Current Deviation vs.
PAGE 8
AL8807 Typical Performance Characteristics (cont.) (1.3A LED Current MSOP-8EP) 250 10 L = 100µH RS = 77m TA = 25°C VCTRL = Open SWITCHING FREQUENCY (kHz) LED CURRENT ERROR (%) 8 6 4 2 0 -2 -4 -6 200 150 100 1 LED 50 -8 -10 2 LEDs 3 LEDs 5 LEDs 6 LEDs7 LEDs 8 LEDs 4 LEDs 0 6 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 25. LED Current Deviation vs. Input Voltage 6 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 26. Switching Frequency vs.
PAGE 9
AL8807 Application Information The AL8807 is a hysteretic (also known as equal ripple) LED driver with integrated power switch. It is available in two packages that provide a PCB area-power dissipation capability compromise. It is recommended that at higher LED currents/smaller PCBs that the MSOP-8EP version is used to maximize the allowable LED current over a wider ambient temperature range. AL8807 Operation In normal operation, when voltage is applied at +VIN, the AL8807 internal switch is turned on.
PAGE 10
AL8807 Application Information (cont.) PWM Dimming LED current can be adjusted digitally, by applying a low frequency Pulse Width Modulated (PWM) logic signal to the CTRL pin to turn the device on and off. This will produce an average output current proportional to the duty cycle of the control signal. In particular, a PWM signal with a max resolution of 10bit can be applied to the CTRL pin to change the output current to a value below the nominal average value set by resistor RSET.
PAGE 11
AL8807 Application Information (cont.) Soft Start The AL8807 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.
PAGE 12
AL8807 Application Information (cont.) Diode Selection For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode with low reverse leakage at the maximum operating voltage and temperature. The Schottky diode also provides better efficiency than silicon PN diodes, due to a combination of lower forward voltage and reduced recovery time.
PAGE 13
AL8807 Application Information (cont.) The following equations can be used as a guide, with reference to Figure 1 - Operating waveforms. Switch ‘On’ time Switch ‘Off’ time L I tON  VIN  VLED  IAVG x RS  rL  RSW  tOFF  LI VLED  VD  IAVG x RS  rL  Where: L is the coil inductance (H) rL is the coil resistance (Ω)RS is the current sense resistance (Ω) Iavg is the required LED current (A) ΔI is the coil peak-peak ripple current (A) {Internally set to 0.
PAGE 14
AL8807 Application Information (cont.) EMI and Layout Considerations The AL8807 is a switching regulator with fast edges and measures small differential voltages; as a result of this care has to be taken with decoupling and layout of the PCB.To help with these effects the AL8807 has been developed to minimise radiated emissions by controlling the switching speeds of the internal power MOSFET.
PAGE 15
AL8807 Application Information (cont.) Recommendations for minimising radiated EMI and other transients and thermal considerations are: 1. The decoupling capacitor (C1) has to be placed as close as possible to the VIN pin and D1 Cathode 2. The freewheeling diode’s (D1) anode, the SW pin and the inductor have to be placed as close as possible to each other to avoid ringing. 3. 4.
PAGE 16
AL8807 Application Information (cont.) The associated EMI measurements for this board using the AL8807 is shown in figure 40. Figure 40 AL8807EV2 Radiated EMI Performance The EMI performance was measured at 12VDC driving two white LEDs (VF = 3.1V at 660mA) on the AL8807EV2. The red bold line is for EN55022 class B used for domestic equipment including lighting. The bottom magenta line is the noise floor of the test chamber.
PAGE 17
AL8807 Ordering Information AL8807 XX - XX Package Packing W5 : SOT25 MP : MSOP-8EP 7 : 7” Tape & Reel 13 : 13” Tape & Reel Part Number Status Package Code Packaging AL8807W5-7 AL8807MP-13 New Product New Product W5 MP SOT25 MSOP-8EP 7” Tape and Reel Quantity Part Number Suffix 3000/Tape & Reel -7 2500/Tape & Reel -13 Marking Information (1) SOT25 (Top View) 4 7 5 XX Y W X 1 2 Part Number AL8807W5-7 (2) 3 XX : Identification code Y : Year 0~9 W : Week : A~Z : 1~26 week; a~z : 27~52
PAGE 18
AL8807 Package Outline Dimensions (All dimensions in mm.) Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version. (1) SOT25 A SOT25 Dim Min Max Typ A 0.35 0.50 0.38 B 1.50 1.70 1.60 C 2.70 3.00 2.80 D   0.95 H 2.90 3.10 3.00 J 0.013 0.10 0.05 K 1.00 1.30 1.10 L 0.35 0.55 0.40 M 0.10 0.20 0.15 N 0.70 0.80 0.75 0° 8°   All Dimensions in mm B C H K J (2) M N D L MSOP-8EP D 4X 10 ° 0.
PAGE 19
AL8807 Suggested Pad Layout Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version. (1) SOT25 C2 Z C2 Dimensions Value (in mm) Z 3.20 G 1.60 X 0.55 Y 0.80 C1 2.40 C2 0.95 C1 G Y X (2) MSOP-8EP X C Dimensions C G X X1 Y Y1 Y2 Y G Y2 Y1 X1 AL8807 Document number: DS35281 Rev. 5 - 2 19 of 20 www.diodes.com Value (in mm) 0.650 0.450 0.450 2.000 1.350 1.700 5.
PAGE 20
AL8807 IMPORTANT NOTICE DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION). Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes without further notice to this document and any product described herein.