AL8805 HIGH EFFICIENCY 36V 1A BUCK LED DRIVER Description Pin Assignments The AL8805 is a step-down DC/DC converter designed to drive LEDs (Top View) 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. SW 1 GND 2 CTRL 3 5 VIN 4 SET Maximum output current of AL8805 is set via an external resistor connected between the VIN and SET input pins. Dimming is achieved SOT25 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 Applications * LED Driving Current up to 1A * MR16 Lamps Better than 5% Accuracy * General Illumination Lamps * * 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) 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 (c) Diodes Incorporated AL8805 Pin Descriptions Pin Number Pin Name 1 SW 2 GND Function Switch Pin. Connect inductor/freewheeling diode here, minimizing track length at this pin to reduce EMI. GND Pin Dimming and On/Off Control Input. 3 CTRL 4 SET 5 VIN * Leave floating for normal operation. (VCTRL = VREF = 2.5V giving nominal average output current IOUTnom = 0.1/RS) * Drive to voltage below 0.4V to turn off output current * Drive with DC voltage (0.5V < VCTRL < 2.5V) to adjust output current from 20% to 100% of IOUTnom * A PWM signal (low level 0.4V and high level > 2.6; transition times less than 1us) allows the output current to be adjusted below the level set by the resistor connected to SET input pin. Set Nominal Output Current Pin. Configure the output current of the device. Input Supply Pin. Must be locally decoupled to GND with > 2.2F X7R ceramic capacitor - see applications section for more information. Absolute Maximum Ratings (@TA = +25C, unless otherwise specified.) Symbol Parameter Ratings Unit ESD HBM Human Body Model ESD Protection 2.5 kV ESD MM Machine Model ESD Protection 200 V VIN Continuous VIN Pin Voltage Relative to GND -0.3 to 40 V VSET SET Pin Voltage Relative to VIN Pin -5 to +0.3 V VSW SW Voltage Relative to GND -0.3 to 40 V VCTRL CTRL Pin Input Voltage -0.3 to 6 V ISW-DC DC or RMS Switch current 1.25 A ISW-PK Peak Switch Current (<10%) 2.5 A Junction Temperature 150 C TLEAD TJ Lead Temperature Soldering 300 C TST Storage Temperature Range -65 to +150 C Caution: Stresses greater than the 'Absolute Maximum Ratings' specified above, may cause permanent damage to the device. These are stress ratings only; functional operation of the device at these or any other conditions exceeding those indicated in this specification is not implied. Device reliability may be affected by exposure to absolute maximum rating conditions for extended periods of time. Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when handling and transporting these devices Recommended Operating Conditions (@TA = +25C, unless otherwise specified.) Symbol Min Max Operating Input Voltage relative to GND 6.0 36 V VCTRLH Voltage High for PWM Dimming Relative to GND 2.6 5.5 V VCTRLDC Voltage Range for 20% to 100% DC Dimming Relative to GND 0.5 2.5 V VCTRLL Voltage Low for PWM Dimming Relative to GND 0 0.4 V ISW Continuous Switch Current -- 1 A TJ Junction Temperature Range -40 125 C VIN Parameter AL8805 Document number: DS35030 Rev. 4 - 2 2 of 16 www.diodes.com Unit July 2012 (c) Diodes Incorporated AL8805 Electrical Characteristics (VIN = 12, @TA = +25C, unless otherwise specified.) Symbol Parameter Conditions VINSU Internal Regulator Start Up Threshold VINSH Internal Regulator Hysteresis Threshold VIN falling Quiescent Current Output not switching (Note 4) IS Input Supply Current CTRL pin floating f = 250kHz Set Current Threshold Voltage VTH-H Max Unit 5.9 V 300 mV 350 A 1.8 5 mA 100 105 mV 100 95 Set Threshold Hysteresis ISET Typ VIN rising IQ VTH Min 20 mV SET Pin Input Current VSET = VIN-0.1 16 RCTRL CTRL Pin Input Resistance Referred to internal reference 50 k VREF Internal Reference Voltage 2.5 V RDS(on) ISW_Leakage On Resistance of SW MOSFET ISW = 1A Switch Leakage Current VIN = 30V fOSC Switching Frequency JA Thermal Resistance Junction-to- JB Thermal Resistance Junction-to-Lead Notes: Ambient (Note 5) (Note 7) SOT25 (Note 6) 0.25 22 A 0.4 0.5 A 1 MHz 250 C/W SOT25 50 4. AL8805 does not have a low power standby mode but current consumption is reduced when output switch is inhibited: VSENSE = 0V. Parameter is tested with VCTRL 2.5V 5. Refer to figure 34 for the device derating curve. 6. Test condition for SOT25: Device mounted on FR-4 PCB (25mm x 25mm 1oz copper, minimum recommended pad layout on top layer and thermal vias to bottom layer ground plane. For better thermal performance, larger copper pad for heat-sink is needed. 7. As SOT25 doesn't have an exposed tab or exposed pad the majority of heat flow is though pin 2 down to ground. AL8805 Document number: DS35030 Rev. 4 - 2 3 of 16 www.diodes.com July 2012 (c) Diodes Incorporated AL8805 Typical Performance Characteristics (@TA = +25C, unless otherwise specified.) 400 900 VCRTL = 0V VSET = VIN T A = 25C 350 700 FREQUENCY (kHz) 250 IIN (A) VIN = 12V 1 LED RSET = 150m TA = 25C 800 300 200 150 600 L = 68H 500 400 300 100 200 50 L = 100H 100 0 0 0 18 30 36 24 VIN (V) Figure 1 Supply Current (not switching) vs. Input Voltage 6 12 1 0.9 0.8 0 1 2 3 4 5 VCTRL (V) Figure 2 Switching Frequency vs. VCTRL 80 VIN = 12V 1 LED L = 68H T A = 25C VSET = VIN = 12V T A = 25C RSET = 100m 60 40 0.7 RSET = 150m 0.6 ICTRL (A) ILED (A) L = 33H 0.5 0.4 0.3 20 0 -20 RSET = 300m 0.2 -40 0.1 -60 0 0 1 2 3 4 VCTRL (V) Figure 3 LED Current vs. VCTRL 5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VCTRL (V) Figure 4 ICTRL vs. VCTRL 2.52 3 VCTRL = Open VSET = VIN = 12V 2.5 2.51 VCTRL (V) VCTRL (V) 2 1.5 2.50 1 2.49 VCTRL = Open VSET = VIN T A = 25C 0.5 0 0 3 6 9 12 15 18 21 24 27 30 33 36 VIN (V) Figure 5. VCTRL vs. Input Voltage (CTRL Pin Open Circuit) AL8805 Document number: DS35030 Rev. 4 - 2 4 of 16 www.diodes.com 2.48 -40 -15 10 35 60 85 AMBIENT TEMPERATURE (C) Figure 6 VCTRL vs. Temperature 110 July 2012 (c) Diodes Incorporated AL8805 4.5 0.9 4.0 0.8 3.5 0.7 3.0 0.6 2.5 0.5 2.0 0.4 1.5 0.3 1.0 0.2 0.5 0.1 0.0 0% 300 240 180 120 VCTRL = Open VSET = VIN TA = 25 C 60 0 40% 60% 80% 100% PWM DUTY CYCLE Figure 7 ILED vs. PWM Duty Cycle 0 20% 400 6 12 24 30 36 VIN (V) Figure 8 SW RDS(ON) vs. Input Voltage 130 R SET = 150m L = 68H VIN = 12V 1 LED Load 125 350 18 120 VSENSE VSW VSENSE (mV) RDS(ON) (m) 250 16 14 12 115 300 18 110 10 105 8 100 6 95 4 90 2 85 0 80 -2 200 VSW 1 RDS(ON) (m) 5.0 LED CURRENT (A) LED CURRENT ERROR (%) Typical Performance Characteristics (cont.) (@TA = +25C, unless otherwise specified.) 150 100 -40 -15 10 35 60 85 110 AMBIENT TEMPERATURE (C) Figure 9 SW RDS(ON) vs. Temperature RSET = 150m, L =68H, VIN = 12V, 1LED Load, T A =25C 20 0.9 18 ILED 16 0.8 0.7 14 VSW 0.6 12 0.5 10 0.4 8 0.3 6 0.2 4 VCTRL 0.1 0 0 50 100 150 Time (s) Figure 11 PWM Dimming AL8805 Document number: DS35030 Rev. 4 - 2 L = 33H RS = 150m TA = 25C 2 LED DUTY CYCLE Duty Cycle = 5% SWITCH and CTRL VOLTAGE (V) 1 LED CURRENT (A) TIME (s) Figure 10 SW Output Switching Characteristics 2 0 200 6 5 of 16 www.diodes.com 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 12 Duty Cycle vs. Input Voltage July 2012 (c) Diodes Incorporated AL8805 Typical Performance Characteristics (cont.) (@TA = +25C, unless otherwise specified.) 0.36 100% 6 LEDs 7 LEDs 98% 4 LEDs 96% 8 LEDs 5 LEDs 0.35 3 LEDs 2 LEDs EFFICIENCY 2 LEDs 92% 90% 88% 86% 3 LEDs LED CURRENT (A) 94% 1 LED 0.34 0.33 1 LED 0.30 6 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 13 Efficiency vs. Input Voltage 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 14 330mA LED Current vs. Input Voltage L = 100H RS = 150m TA = 25 C 300 0.710 0.700 250 LED CURRENT (A) SWITCHING FREQUENCY (kHz) 9 0.720 350 200 2 LEDs 150 1 LED 100 6 0.690 0.680 0.670 0.660 0.650 0.640 7 LEDs 6 LEDs 8 LEDs 5 LEDs 3 LEDs 4 LEDs 50 0 L = 68H R S = 300m TA = 25 C 0.31 L = 100H RS = 150m TA = 25C 80% 6 5 LEDs 6 LEDs 7 LEDs 8 LEDs 0.32 84% 82% 4 LEDs 0.630 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 15 Switching Frequency vs. Input Voltage 0.620 6 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 16 670mA LED Current vs. Input Voltage 1.10 LED CURRENT (A) 1.05 1.00 0.95 0.90 6 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 17 1A LED Current vs. Input Voltage AL8805 Document number: DS35030 Rev. 4 - 2 6 of 16 www.diodes.com July 2012 (c) Diodes Incorporated AL8805 Typical Performance Characteristics (cont.) (670mA LED Current) (@TA = +25C, unless otherwise specified.) 350 5% L = 100H RS = 150m TA = 25 C 4% 300 3% FREQUENCY (kHz) 2% % ERROR 1% 0% -1% -2% 250 200 150 2 LEDs 100 1 LED -3% 50 -4% -5% 6 5 LEDs 3 LEDs 4 LEDs 0 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 18 LED Current Deviation vs. Input Voltage 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 19 Switching Frequency vs. Input Voltage 8% 450 SWITCHING FREQUENCY (kHz) 500 4% % ERROR 6 10% 6% 2% 0% -2% -4% -6% 350 300 250 200 150 100 50 0 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 20 LED Current Deviation vs. Input Voltage 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 21 Switching Frequency vs. Input Voltage 900 8% 800 6% 9 700 FREQUENCY (kHz) 4% % ERROR 6 10% 2% 0% -2% -4% 600 500 400 300 -6% 200 -8% 100 -10% 6 9 400 -8% -10% 6 7 LEDs 6 LEDs 8 LEDs 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 22 LED Current Deviation vs. Input Voltage AL8805 Document number: DS35030 Rev. 4 - 2 7 of 16 www.diodes.com 0 6 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 23 Switching Frequency vs. Input Voltage July 2012 (c) Diodes Incorporated AL8805 Typical Performance Characteristics (cont.) (1A LED Current) (@TA = +25C, unless otherwise specified.) 250 10% 6% SWITCHING FREQUENCY (kHz) 8% 3 LEDs 5 LEDs 2 LEDs 4 LEDs 6 LEDs 7 LEDs 8 LEDs 4% % ERROR 2% 1 LED 0% -2% -4% -6% L = 100H RS = 100m TA = 25 C -8% -10% 6 150 100 50 0 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 25 Switching Frequency vs. Input Voltage 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 24 LED Current Deviation vs. Input Voltage 9 6% 3 LEDs 5 LEDs 2 LEDs 4 LEDs 6 LEDs 7 LEDs 4% SWITCHING FREQUENCY (kHz) 8% 8 LEDs 2% 0% 1 LED -2% -4% -6% L =68H RS = 100m TA = 25 C -8% 6 L = 68H R S = 100m TA = 25 C 250 200 150 100 1 LED 50 0 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 27 Switching Frequency vs. Input Voltage 9 6 8 LEDs 6 LEDs 7 LEDs 4 LEDs 2 LEDs 3 LEDs 5 LEDs 9 700 10% 2 LEDs 8% 4 LEDs SWITCHING FREQUENCY (kHz) 3 LEDs 6 LEDs 5 LEDs 6% 8 LEDs 4% % ERROR 9 300 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 26 LED Current Deviation vs. Input Voltage 2% 0% 6 350 10% % ERROR 200 1 LED -2% -4% -6% -8% -10% 6 L = 33H R S = 100m T A = 25 C 600 500 400 300 200 100 0 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 28 LED Current Deviation vs. Input Voltage AL8805 Document number: DS35030 Rev. 4 - 2 8 of 16 www.diodes.com 6 9 12 15 18 21 24 27 30 33 36 INPUT VOLTAGE (V) Figure 29 Switching Frequency vs. Input Voltage July 2012 (c) Diodes Incorporated AL8805 Application Information AL8805 Operation In normal operation, when voltage is applied at +VIN, the AL8805 internal switch is turned on. Current starts to flow through sense resistor R1, inductor L1, and the LEDs. The current ramps up linearly, and the ramp rate is determined by the input voltage +Vin and the inductor L1. This rising current produces a voltage ramp across R1. The internal circuit of the AL8805 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 internal switch is turned off. The inductor current continues to flow through R1, L1, the LEDs 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 AL8805. 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 internal switch is turned on again. This switch-on-and-off cycle continues to provide the average LED current set by the sense resistor R1. LED Current Control The LED current is controlled by the resistor R1 in Figure 30. Connected between VIN and SET the nominal average output current in the LED(s) is defined as: ILED = VTHD RSET If the CTRL pin is driven by an external voltage (higher than 0.4V and lower than 2.5V), the average LED current is: ILED = VCTRL VTHD VREF R SET For example for a desired LED current of 660mA and a default voltage VCTRL=2.5V the resulting resistor is: R SET = VTHD VCTRL 0 .1 2 .5 = 150m ILED VREF 0.66 2.5 VIN CTRL R1 SET 1 D1 C1 AL8805 C2 L1 GND SW Figure 30 Typical Application Circuit DC Dimming The CTRL pin can be driven by an external DC voltage (VCTRL), to adjust the output current to a value below the nominal average value defined by RSET. The LED current decreases linearly with the CTRL voltage when 0.5V VCTRL 2.5V, as in Figure 2 for 4 different current levels. When the CTRL voltage falls below the threshold, 0.4V, the output switch is turned off which allows PWM dimming. Note that 100% brightness setting corresponds to VCTRL = VREF, nominally 2.5V. For any voltage applied on the CTRL pin that is higher than VREF, the device will not overdrive the LED current and will still set the current according to the equation VCTRL = VREF. AL8805 Document number: DS35030 Rev. 4 - 2 9 of 16 www.diodes.com July 2012 (c) Diodes Incorporated AL8805 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. To achieve this resolution the PWM frequency has to be lower than 500Hz, however higher dimming frequencies can be used, at the expense of dimming dynamic range and accuracy. Typically, for a PWM frequency of 500Hz the accuracy is better than 1% for PWM ranging from 1% to 100%. 700 LED current [mA] 600 500 400 300 200 100 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 7% 8% 9% 10% PWM dimming [%] Figure 31 PWM Dimming at 500Hz 70 LED current [mA] 60 50 40 30 20 10 0 0% 1% 2% 3% 4% 5% 6% PWM dimming [%] Figure 32 Low Duty Cycle PWM Dimming at 500Hz The CTRL pin is designed to be driven by both 3.3V and 5V logic C levels directly from a logic output with either an open drain output AL8805 CTRL or push-pull output stage. GND AL8805 Document number: DS35030 Rev. 4 - 2 10 of 16 www.diodes.com July 2012 (c) Diodes Incorporated 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 1F 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 2.2F input capacitor is sufficient for most intended applications of AL8805; however a 4.7F input capacitor is suggested for input voltages approaching 36V. AL8805 Document number: DS35030 Rev. 4 - 2 11 of 16 www.diodes.com July 2012 (c) Diodes Incorporated AL8805 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. It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than the maximum output load current. In particular, it is recommended to have a diode voltage rating at least 15% higher than the operating voltage to ensure safe operation during the switching and a current rating at least 10% higher than the average diode current. The power rating is verified by calculating the power loss through the diode. Schottky diodes, e.g. B240 or B140, with their low forward voltage drop and fast reverse recovery, are the ideal choice for AL8805 applications. Thermal and Layout Considerations For continuous conduction mode of operation, the absolute maximum junction temperature must not be exceeded. The maximum power dissipation depends on several factors: the thermal resistance of the IC package JA, PCB layout, airflow surrounding the IC, and difference between junction and ambient temperature. The maximum power dissipation can be calculated using the following formula: PD(MAX) = (TJ(MAX) - TA) / JA where TJ(MAX) is the maximum operating junction temperature, TA is the ambient temperature, and JA is the junction to ambient thermal resistance. The recommended maximum operating junction temperature, TJ, is +125C and so maximum ambient temperature is determined by the AL8805's junction to ambient thermal resistance, JA. JA, is layout dependent and the AL8805's JA on a 25 x 25mm single layer PCB with 1oz copper standing in still air is approximately +250C/W (+160C/W on a four-layer PCB). The maximum power dissipation at TA = +25C can be calculated by the following formulas: PD(MAX) = (+125C - +25C) / (250C/W) = 0.4W for single-layer PCB PD(MAX) = (+125C - +25C) / (160C/W) = 0.625W for standard four-layer PCB Figure 34, shows the power derating of the AL8805 on two (one single-layer and four-layer) different 25x25mm PCB with 1oz copper standing in still air. Figure 34 Derating Curve for Different PCB AL8805 Document number: DS35030 Rev. 4 - 2 12 of 16 www.diodes.com July 2012 (c) Diodes Incorporated AL8805 Application Information (cont.) Thermal and Layout Considerations Figure 35 gives details about the PCB layout suggestions: 1. the capacitor C1 has to be placed as close as possible to VIN 2. The sense resistor R1 has to be placed as close as possible to VIN and SET 3. The D1 anode, the SW pin and the inductor have to be placed as close as possible to avoid ringing. Figure 35 Recommended PCB Layout Application Example Typical application example for the AL8805 is the MR16 lamp. They typically operate from 12VDC or 12VAC, using conventional electromagnetic transformers or electronic transformers. As a replacement in some halogen lamp applications LEDs offer a more energy efficient solution - providing no radiated heat and no Ultra Violet light. This application example is intended to fit into the base connector space of an MR16 style LED lamp. The design has been optimized for part count and thermal performance for a single 3W LED in the Lens section. AL8805 Figure 36 MR16 Schematic An inductor choice of 33H with saturation current higher than 1.1A, will limit the frequency variation between 230kHz and 350kHz over the whole input voltage variation (8V to 18V), and therefore represent the best choice for an MR16 solution also taking into account the size constraint of the lamp. The AL8805 guarantee high level of performance both with 12VAC and 12VDC power supply. The efficiency is generally higher than 81% and current regulation is better than 0.1mA/V in for a DC input voltage in the range from 8V to 18V. In table 1 can be found the bill of material of the MR16 application example. AL8805 Document number: DS35030 Rev. 4 - 2 13 of 16 www.diodes.com July 2012 (c) Diodes Incorporated AL8805 Application Information (cont.) In Figures 37 and 38 are displayed the top layer and the bottom layer of a typical PCB design for an MR16 solution. Figure 37 Top Layer Figure 38 Bottom Layer Table1 MR16 Application Example Bill of Material Quantity PCB Ident Value Description Sources 1 U1 AL8805 1 D1, DFLS240L freewheeling diode Diodes Zetex 4 D2, D3, D4, D5 SBR2A40 Input bridge Diodes Zetex 1 R1 0R15 1 C1 150uF 20V 0 C2 - 1 C3 100nF > = 25V 1 C4 1uF > = 25V 1 L1 33H AL8805 Document number: DS35030 Rev. 4 - 2 LED Driver IC Suggested Resistor, 0805, +/-1% <+/-300ppm Generic KOA SR732ATTDR150F SMD tantalum Kemet D case, T491X157K020AT Diodes Zetex Kemet Kemet Not fitted X7R 0805 Generic Kemet C0805C104K5RAC (50v) NIC NMC0805X7R104K50TRPF (50v) X7R 1206 Generic Kemet C1206105K5RAC7800 (50v) NIC NMC1206X7R105K50F (50v) LPS6235 - 333MLB 14 of 16 www.diodes.com Kemet NIC Components Kemet NIC Components Coilcraft July 2012 (c) Diodes Incorporated AL8805 Ordering Information AL 8805 W5 - 7 Device Package Code AL8805W5-7 W5 Note: Package Packing W5 :SOT25 7 : Tape & Reel 7" Tape and Reel Packaging (Note 6) Quantity Part Number Suffix SOT25 3000/Tape & Reel -7 8. Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at: http://www.diodes.com/datasheets/ap02001.pdf . Marking Information (Top View) 4 7 5 XX Y W X 1 2 3 XX : Identification code Y : Year 0~9 W : Week : A~Z : 1~26 week; a~z : 27~52 week; z represents 52 and 53 week X : A~Z : Internal code Part Number Package Identification Code AL8805W5-7 SOT25 A6 Package Outline Dimensions (All dimensions in mm.) A B C H K J M N D AL8805 Document number: DS35030 Rev. 4 - 2 L 15 of 16 www.diodes.com 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 July 2012 (c) Diodes Incorporated AL8805 Suggested Pad Layout C2 Z C2 Dimensions Value (in mm) Z 3.20 G 1.60 X 0.55 Y 0.80 C1 G C1 C2 Y 2.40 0.95 X 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. 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