AL8806QEV1 User Guide Issue 1

AL8806QEV1 User Guide
General Description This evaluation circuit demonstrates the AL8806Q High Efficiency 30V 1.5A Buck LED Driver. 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. 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. AL8806QEV1 Specifications Parameter
Value Input Voltage LED Current LED Current Accuracy Switching Frequency Efficiency Number of LEDs 6VDC to 30VDC 1.5A (Adjustable) XY Dimension ±5% ~170kHz ~98% 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) 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 +125°C Applications •
Automotive LED Lamps Multi‐Die LED Driver Figure 1: Top View (Single Side Board) Connection Instructions Input Voltage: 6VDC to 30VDC (VIN, GND) LED Outputs: LED A (+), LED K (‐) Evaluation Board Schematic AL8806QEV1 Rev1
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Figure 2: Evaluation Board Schematic Evaluation Board Layout
Figure 3: Top View Figure 4: Bottom View Bill of Material AL8806QEV1 Rev1
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1 2 3 4 5 6 7 8 9 Name
U1 D1 L1 R1
C1, C5
C2, C3
C6, C7,
C8, C9,
10 C12
11 C11
1 1 1 1 1 1 2 2 1 Part number
DFLS230LH‐7 MSS1038‐333ML C1210X475K5RAC
Diodes Inc Diodes Inc Coilcraft generic generic
Kemet NIC NIC Description
IC, LED Driver (MSOP‐8EP) Schottky diode, 30V/2A (PDI123) Inductor, shielded, 33µH 20% 0.1Ω Resistor 1/8W 1% 1206 SMD
0.2Ω Resistor 1/8W 1% 1206 SMD
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
Quick Start Guide Test Equipment Count
Adjustable Power Supply, up to
30V 2A
Digital Multimeter
Digital Storage Oscilloscope
LED, high brightness, 2A,
connected on suitable heat
conducting PCB
Part Number
Thurlby Thandar
CAUTION: The LEDs are very bright. Ensure they are
hidden from direct view, or covered with a dispersing filter.
Also the LEDs are very hot. Do not touch!!
LED Operation AL8806QEV1 Rev1
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1. Set the power supply to 12.0V but do not switch on. Set the current limit to 2.0A. 2. Connect up the AL8806QEV1 board to the equipment as in Figure 5 below. Set DMM1 and DMM2 to measure current up to 2A. Figure 5: 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 6VDC to 30VDC and the current regulation observed is typically within ±2%. Observe Switching Waveform 5. The switching waveform can be observed on an oscilloscope. 6. Set the oscilloscope as follows: Channel 1 sensitivity: 2V/div (at probe tip) Time base: 2µs/div Trigger Source: CH1 Trigger Mode: Auto 7. Connect the ground lead of a 10x probe to one of the plated fixing holes of the AL8806QEV1, and touch the probe tip onto the anode of D1 as in Figure 6 below. On the oscilloscope, press RUN/STOP to capture the waveform. The cursor readout AL8806QEV1 Rev1
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indicates a switching frequency of 170kHz approximately –see Figure 7. (This frequency is dependent on the LED volt drop.) Figure 6: Waveform Capture Figure 7: Oscilloscope Waveform AL8806QEV1 Rev1
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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 (Refer to AL8806QEV1 schematic) to give a more accurate control. 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 AL8806QEV1. 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 AL8806QEV1 Rev1
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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 Page 6 of 8
AL8806QEV1 User Guide
Performance The performance of the AL8806QEV1 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 6VDC 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%. For further advice, please contact your local Diodes Field Applications Engineer. AL8806QEV1 Rev1
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