AL8807QEV1 User Guide General Description The AL8807QEV1, Figure 1, is a double sided evaluation board for the AL8807Q step‐ down, or ‘buck’, LED driver with internal switch. The evaluation board is preset to drive 1A into a single LED, or multiple LEDs, the maximum number of which depends on their total forward voltage drop and the supply voltage. The operating voltage is nominally 30 volts, but it can be reduced to a minimum of 6 volts. The 68uH inductor used in the circuit is based on this nominal supply. The evaluation board should be connected as in Figure 1 below. Terminal CTRL provides a connection point for DC or PWM dimming and shutdown. AL8807QEV1 Specifications Parameter Value Input Voltage LED Current LED Current Accuracy Switching Frequency Efficiency Number of LEDs 6VDC to 30VDC 1A (Adjustable) XY Dimension ±5% 100kHz 95% 2 LEDs in series (Under Tested) 2.48 ” x 1.57” EVB (Rev 1.0) Key Features • • • • • • • Automotive Grade with AEC‐Q100 Qualification 6V to 30V DC input (with 2 LEDs) 1A 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 +125°C Applications • • • Automotive LED Lamps Illuminated signs High Power LED driving AL8807QEV1 Rev1 June 2014 www.diodes.com Figure 1: Top View (Single Side Board) Connection Instructions Input Voltage: 6VDC to 30VDC (VIN, GND) LED Outputs: LED A (+), LED K (‐) Page 1 of 6 AL8807QEV1 User Guide Evaluation Board Schematic Figure 2: Evaluation Board Schematic Evaluation Board Layout Figure 3: Top View Figure 4: Bottom View AL8807QEV1 Rev1 June 2014 www.diodes.com Page 2 of 6 AL8807QEV1 User Guide Bill of Material # 1 2 3 4 5 6 7 8 9 Name U1 D1 L1 R1 R2 R3 C1, C5 C2, C3 C4 C6, C7, C8, C9, 10 C12 C10, 11 C11 VIN, GND, CTRL, LEDA, 12 LEDK Quantity 1 1 1 1 1 1 2 2 1 Part number Manufacturer Diodes Inc Diodes Inc Coilcraft generic AL8807QMP-13 DFLS260 MSS1038‐683ML - Description IC, LED Driver (MSOP‐8EP) Schottky diode, 60V/2A Inductor, shielded, 68µH 20% 0.1Ω Resistor 1/8W 1% 1206 SMD NOT FITTED C1210X475K5RAC NMC0805X7R104K100PF NMC1206X7R104K100 generic Kemet NIC NIC 1kΩ Resistor 1/8W 1% 0805 SMD 4.7µF Cap 50V 10% X7R 1210 100nF Cap 100V 10% X7R 0805 1µF Cap 100V 10% X7R 1206 0 - - 2 - generic 1.5nF Cer Cap 100V COG 0805 Hughes 2.15mm Test Loop Terminal 5 100-108 NOT FITTED Quick Start Guide Basic Operation at full voltage 1. Connect Vin and GND Warning: The board does not feature reverse battery/supply protection. 2. Set the PSU to 30V 3. Turn on the PSU and the LED will illuminate and the current should be approximately 680mA. Warning: Do not stare at the LED directly. Switching the output current off Shorting the CTRL pin to GND will cause the LED current to go to zero. Soft start Adding a C2 capacitor will create a soft‐start power‐up sequence (0.1ms/nF). This delay will reduce the PWM dimming performance. AL8807QEV1 Rev1 June 2014 www.diodes.com Page 3 of 6 AL8807QEV1 User Guide Changing the LED current 1. Remove R1. 2. Calculate and replace sense resistor, R1, the value of which is based on the required LED current without dimming. R1 can be calculated using following equation: R1 = 0.1V/IOUT where IOUT = the LED current. R1 = the sense resistor value in ohms. 0.1V is the nominal sense voltage with ‘CTRL’ open circuit or set to 2.5V. The device calculator at the address below can be used to speed up the redesign phase: http://www.diodes.com/destools/calculators.html Performance The system efficiency depends on the sense resistor, supply voltage, switching frequency and the number of LEDs. With a 12V supply and two LEDs, the switching frequency is typically 102kHz, and the efficiency level is 88%. AL8807Q Operation In normal operation, when a voltage is applied at +Vin, the AL8807Q internal NDMOS switch is turned on. Current starts to flow through sense resistor R1, inductor L1, and the LED. The current ramps up linearly, the ramp rate being determined by the input voltage +Vin and the inductor L1. This rising current produces a voltage ramp across R1. The internal circuit of the AL8807Q senses the voltage across R1 and applies a proportional voltage to the input of the internal comparator. When this voltage reaches an internally set upper threshold, the NDMOS switch is turned off. The inductor current continues to flow through R1, L1, the LED and the Schottky diode D1, and back to the supply rail, but it decays, with the rate of decay determined by the forward voltage drop of the LEDs and the Schottky diode. This decaying current produces a falling voltage at R1, which is sensed by the AL8807Q. A voltage proportional to the sense voltage across R1 is applied at the input of the internal comparator. When this voltage falls to the internally set lower threshold, the NDMOS switch is turned on again. This switch‐on‐and‐off cycle continues to provide the average LED current set by the sense resistor R1. Please refer to the datasheets for the threshold limits, AL8807Q internal circuits, electrical characteristics and AL8807QEV1 Rev1 June 2014 www.diodes.com Page 4 of 6 AL8807QEV1 User Guide parameters. AL8807QEV1 Evaluation Board Reference Design The AL8807QEV1 is configured to the reference design in Figure 2. The operating voltage is up to 30V. The nominal current is set at 1A with a 0R1 sense resistor R1. The circuit operates in continuous mode between approximately 40kHz and 130kHz, depending on the input voltage, and with a 68uH inductor and one LED. Both DC and PWM dimming can be achieved by driving the CTRL 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 ILED. Driving the CTRL pin below 0.4V will shut down the output current. A PWM signal (low level ≤ 0.4V and high level > 2.5) allows the output current to be adjusted above or below the level set by the resistor connected to SET input pin. The PWM frequency can be around 100Hz to 1kHz, providing a resolution of 10 bits. For low frequency PWM, C2 should be removed from the evaluation board, to give a more accurate duty cycle. Shorting R2 will connect the test pin CTRL to device pin CTRL, if required. For further advice, please contact your local Diodes Field Applications Engineer. AL8807QEV1 Rev1 June 2014 www.diodes.com Page 5 of 6 AL8807QEV1 User Guide 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. Diodes Incorporated does not assume any liability arising out of the application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or trademark rights, nor the rights of others. Any Customer or user of this document or products described herein in such applications shall assume all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated website, harmless against all damages. Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales channel. Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify and hold Diodes Incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized application. Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and markings noted herein may also be covered by one or more United States, international or foreign trademarks. This document is written in English but may be translated into multiple languages for reference. Only the English version of this document is the final and determinative format released by Diodes Incorporated. LIFE SUPPORT Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein: A. Life support devices or systems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems. Copyright © 2014, Diodes Incorporated www.diodes.com AL8807QEV1 Rev1 June 2014 www.diodes.com Page 6 of 6