AL8806EV4 USER GUIDE Performance • • • • • • Introduction This evaluation circuit demonstrates the AL8806 High Efficiency 30V 1.5A Buck LED Driver. For detailed information on the AL8806, please see the datasheet at: 9V to 30V DC input (with 2 LEDs) 1.5A LED current Drives 1 LED or several LEDs in series Brightness control using DC or PWM Inherent open circuit LED protection Ambient temperature range -40°C to +105°C http://www.diodes.com/datasheets/AL8806.pdf The evaluation board is preset to drive its maximum current of 1.5A into a single LED or multiple LEDs, the maximum number of which depends on their total forward voltage drop. EMC filtering is included to meet international standards including the radiated emission requirements of EN55015 and EN55022 Class B. Ordering Information Order Number AL8806EV4 The circuit operates in continuous switching mode at a frequency of approximately 170kHz when driving 2 LEDs each having a forward voltage drop of approximately 3.4V at 1.5A. Please note: Evaluation boards are subject to availability and qualified sales leads. The construction uses a double-sided FR4 printed circuit board, 63 x 40 x 1.7 mm with 2oz/sq ft copper (70µm). Components are mounted on one side only. Note: The evaluation board does not have reverse supply protection. Issue 2 – July 2011 www.diodes.com © Diodes Incorporated 2011 1 of 12 AL8806EV4 Quick Start Guide Suitable Test Equipment Count Description 1 Adjustable Power Supply, up to 30V 2A 2 Digital Multimeter 1 Digital Storage Oscilloscope 2 LED, high brightness, 2A, connected on suitable heat conducting PCB Manufacturer Part Number Thurlby Thandar CPX400A Fluke 179 Tektronix TDS2024B CAUTION: The LEDs are very bright. Ensure they are hidden from direct view, or covered with a dispersing filter. The lid from an aerosol can is convenient for this. Also the LEDs are very hot. Do not touch!! Lamp Operation 1. Set the power supply to 12.0V but do not switch on. Set the current limit to 2.0A. 2. Connect up the AL8806EV4 board to the equipment as in Figure 1 below. Set DMM1 and DMM2 to measure current up to 2A. Figure 1: Test Schematic 3. Cover the LEDs to avoid dazzling. 4. Switch on the power supply. This should illuminate the LEDs. Note that the input current (DMM1) depends on the LED volt drop. The input current is approximately 900mA if the total LED volt drop is about 6.9V. The output current (DMM2) is approximately 1.47A. The input voltage can be varied from approximately 8.5VDC to 30VDC and the current regulation observed is typically within ±2%. Issue 2 – July 2011 www.diodes.com © Diodes Incorporated 2011 2 of 12 AL8806EV4 Observe Switching Waveform 5. The switching waveform can be observed on an oscilloscope. 6. Set the oscilloscope as follows: Channel 1 sensitivity: Time base: Trigger Source: Trigger Mode: 2V/div (at probe tip) 2µs/div CH1 Auto 7. Connect the ground lead of a 10x probe to one of the plated fixing holes of the AL8806EV4, and touch the probe tip onto the anode of D1 as in Figure 2 below. On the oscilloscope, press RUN/STOP to capture the waveform. The cursor readout indicates a switching frequency of 170kHz approximately –see Figure 3. (This frequency is dependent on the LED volt drop.) Figure 2: Waveform Capture Dimming Both DC and PWM dimming can be achieved by driving the CTRL input pin. For DC dimming, the CTRL pin may be driven between 0.5V and 2.5V adjusting the output current from 25% to 100% of the maximum value of 1.5A nominal. Driving the CTRL pin below 0.4V will shut down the output current. A PWM signal (low level ≤ 0.4V and high level > 2.5V) allows the output current to be adjusted up to 1.5A. The PWM frequency can be around 100Hz to 1kHz, providing a resolution of 10 bits. In this case, C3 should be removed or reduced from the evaluation board (see AL8806EV4 schematic below) to give a more accurate control. Issue 2 – July 2011 www.diodes.com © Diodes Incorporated 2011 3 of 12 AL8806EV4 Figure 3: Oscilloscope Waveform Radiated EMI Performance, EN55022: Results of AL8806EV4 test at an independent EMC test facility. Input: 12VDC Load: 2 LEDS, 1.5A (By courtesy of Cass Industries, Limited) Issue 2 – July 2011 www.diodes.com © Diodes Incorporated 2011 4 of 12 AL8806EV4 R2 Vin Anode ANODE 0R2 C8 NOT FITTED C7 NOT FITTED Vin C6 NOT FITTED C9 NOT FITTED R1 0R1 C2 100nF 100V X7R 4 1 SET SW CTRL NC TAB 9 7 C3 100nF 100V X7R SW L1 Cathode Cathode 33uH 1k GND 5 SW 6 GND CTRL pin GND R3 U1 AL8806 C11 1.5nF 100V C0G C12 NOT FITTED 3 CTRL C4 1uF 25V X7R DFLS230LH GND CTRL GND D1 8 C1 C5 4.7uF 4.7uF 50V X7R 50V X7R GND GND 2 GND Vin GND C10 1.5nF 100V C0G GND GND GND AL8806EV4 Schematic Issue 2 – July 2011 www.diodes.com © Diodes Incorporated 2011 5 of 12 AL8806EV4 PCB Copper Layout & Silk Screen – Top PCB Copper Layout & Silk Screen –Bottom Issue 2 – July 2011 www.diodes.com © Diodes Incorporated 2011 6 of 12 AL8806EV4 Parts List Count Designator Description Package 2 C1 C5 Capacitor, 4.7µF 10% 50V X7R Manufacturer Part Number 1210 Kemet C1210X475K5RAC 2 C2 C3 Capacitor, 100nF 10% 100V X7R 0805 NIC Murata NMC0805X7R104K100PF GRM21BR71H104KA01L 1 C4 Capacitor, 1uF 10% 100V X7R 1206 generic NIC NMC1206X7R104K100 0 C6 – C9, C12 NOT FITTED 2 C10 C11 Capacitor, 1.5nF 100V COG 0805 generic 1 L1 Inductor, shielded, 33µH 20% 1 R1 Resistor, 0.1ohms 1% 1206 generic 1 R2 Resistor, 0.2ohms 1% 1206 generic 1 R3 Resistor, 1k 1% 0805 generic 1 D1 Diode, schottky, 30V 2A DFLS230LH PowerDi123 Diodes Inc DFLS230LH-7 1 U1 IC, LED Driver, AL8806 MSOP-8EP Diodes Inc AL8806MP8-13 Coilcraft NIC Würth MSS1038-333ML NPIS104F330MTRF 744-066-330 I/O Count Designator Description Function Manufacturer Part Number 1 VIN Loop terminal DC Supply + Input Hughes 100-108 1 GND Loop terminal DC Supply – Input Hughes 100-108 1 CTRL Loop terminal Dimming Control Input Hughes 100-108 1 LED A Loop terminal LED Anode Load Hughes 100-108 1 LED K Loop terminal LED Cathode load Hughes 100-108 Recommended Operating Conditions Symbol Parameter Min Max Units VDC Input Supply Voltage, VDC 8 30 V VOUT Load voltage 0 VDC-1.5 V TA Operating Ambient Temperature -40 +105 °C Issue 2 – July 2011 www.diodes.com © Diodes Incorporated 2011 7 of 12 AL8806EV4 Current Setting The LED current is set by the sense resistor value, RSENSE. On this PCB, there are two resistors in parallel. RSENSE = R1 * R2 / (R1 + R2) For the schematic values this gives a resistance of 0.1 * 0.2 (0.1 + 0.2) = 0.0667 ohms. The LED current flows through RSENSE. The sense voltage is 100mV, so the LED current is simply ILED = 0.1/ RSENSE For the schematic values this gives an LED current of 0.1/0.0667 = 1.500 A nominally. In practice there is a slight reduction in current partly due to the resistance of the PCB copper, depending on the PCB layout. At 1.5A this reduction is typically 1 to 2% using AL8806EV4. The following table gives commercially available resistor values for typical current requirements, allowing a current error of 3% maximum not including the effect of PCB copper. A power limit of 250mW is assumed for the 0805 size resistors with 50% de-rating. LED Current 150mA 300mA 380mA 500mA 660mA 1A 1.1A 1.5A R1, ohms 0.68 0.33 0.51 0.2 0.15 0.1 0.15 0.1 R2, ohms DO NOT FIT DO NOT FIT DO NOT FIT DO NOT FIT DO NOT FIT DO NOT FIT 0.22 0.2 Performance The performance of the AL8806EV4 demonstrated shows the capability to regulate LED current. The LED current of 1.5A is approximately 2% lower than the calculated value. This is partly due to copper resistance. With a load of 2 LEDs, the current changes by less than ±2% over the input voltage range from 9VDC to 30VDC. With 2 LEDs and a supply of 12VDC, the circuit operates in continuous mode with a switching frequency of approximately 170kHz. Power efficiency is approximately 95%. The radiated emission of AL8806EV4 is approximately 18dB below the limits of EN55015 and is also well within the limit of EN55022 Class B. (In the application of AL8806, the radiation depends very much upon PCB layout and filtering.) For further advice, please contact your local Diodes Field Applications Engineer, or one of our sales offices listed on the back page of this document. Issue 2 – July 2011 www.diodes.com © Diodes Incorporated 2011 8 of 12 AL8806EV4 INTENTIONALLY BLANK Issue 2 – July 2011 www.diodes.com © Diodes Incorporated 2011 9 of 12 AL8806EV4 INTENTIONALLY BLANK Issue 2 – July 2011 www.diodes.com © Diodes Incorporated 2011 10 of 12 AL8806EV4 INTENTIONALLY BLANK Issue 2 – July 2011 www.diodes.com © Diodes Incorporated 2011 11 of 12 AL8806EV4 IMPORTANT NOTICE DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD 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). 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