Abstract: This reference design is a complete application design for an automotive LED application. It utilizes the MAX15005 current-mode controller to boost a standard lead-acid car battery to 21V for driving a string of automotive LEDs. The reference design below provides a reference design for an automotive LED application. The MAX15005 is used to boost a standard, 8V to 16V car battery to 21V in order to drive a string of 6 to 8 LEDs. Key specifications for this reference design are listed below, along with a detailed schematic (Figure 1) and the bill of materials (Table 1) needed for this application. Specifications VIN: 8V to 16V (Continuous), 40V (Transient) VLED+ Supply Voltage: 21V ±5% at 80mA (max) VLED+ Load Range: 10V to 20V at 70mA ILED: 70mA ±5% Dimming Input: 400Hz, 50Ω, Open Collector Dimming Resolution: 3µs Switching Frequency: 385kHz Operating Temperature: -40°C to +125°C More detailed image (PDF, 92kB) Figure 1. MAX15005 reference design. Table 1. Bill of Materials Designator Value Description Part Footprint Manufacturer Quantity C1, C5, C6, C8, C10 1µF/50V Capacitors GCM31MR71H105KA55L 1206 Murata 5 C2 200pF/100V Capacitor GRM2165C2A201JA01D 0805 Murata 1 C3, C13, C14 100nF/100V Capacitors GCM21BR72A104KA37L 0805 Murata 3 C4, C7, C9 100pF/50V Capacitors GRM2165C1H101JA01D 0805 Murata 3 C11 10nF/50V Capacitor GRM216R71H103KA01D 0805 Murata 1 C12 10µF/50V Capacitor UUD1H100MCL1GS SMD Nichicon 1 D1 1A/400V Diode S1G SMA Fairchild 1 D2 200mA/100V Schottky diode BAT41ZFILM SOD123 STM 1 D3 200mA/30V Schottky diode STM SOT23 STM 1 L1 470µF/0.86A Inductor MSD1260-474 SMD Coilcraft 1 Q1 1A/100V n-FET ZXMN10A07Z SOT89 Zetex 1 Q2 2A/55V n-FET IRLL014NTRPBF SOT223 International Rectifier 1 Q3 220mA/50V n-FET BSS138 SOT23 Fairchild 1 R1 22.1kΩ Resistor SMD, 1%, 0.125W 0805 Vishay 1 R2, R4, R6 100kΩ Resistors SMD, 1%, 0.125W 0805 Vishay 3 R3 26.7kΩ Resistor SMD, 1%, 0.125W 0805 Vishay 1 R5 6.19kΩ Resistor SMD, 1%, 0.125W 0805 Vishay 1 R7 3.65kΩ Resistor SMD, 1%, 0.125W 0805 Vishay 1 R8 210kΩ Resistor SMD, 1%, 0.125W 0805 Vishay 1 R9, R16 2kΩ Resistors SMD, 1%, 0.125W 0805 Vishay 2 R10 10Ω Resistor SMD, 1%, 0.125W 0805 Vishay 1 R11 100Ω Resistor SMD, 1%, 0.125W 0805 Vishay 1 R12 8.66kΩ Resistor SMD, 1%, 0.125W 0805 Vishay 1 R13 0.51Ω Resistor Sense resistor SL1 Vishay 1 R14 1.4kΩ Resistor SMD, 1%, 0.125W 0805 Vishay 1 R15 100Ω Resistor SMD, 1%, 0.125W 0805 Vishay 1 R17 10Ω Resistor SMD, 1%, 0.205W 1206 Vishay 1 IC1 MAX15005A Boost controller MAX15005AAUE+ 16-TSSOP-EP Maxim 1 IC2 MAX4400 Single op-amp MAX4400AXK+ 5-SC70 Maxim 1 The oscilloscope photos in Figures 2, 3, and 4 show the switching waveforms for this reference design at three different dimming conditions. Figure 2. Waveform measurements for ILED at VIN = 14V with dimming at 50.0%. Figure 3. Waveform measurements for ILED at VIN = 14V with dimming at 0.1%. Figure 4. Waveform measurements for ILED at VIN = 14V with dimming at 99.9%. Related Parts   APP 4151: Dec 21, 2007 MAX15005 4.5V to 40V Input Automotive Flyback/Boost/SEPIC Power-Supply Controllers Full Data Sheet (PDF, 536kB) Free Samples Automatic Updates Would you like to be automatically notified when new application notes are published in your areas of interest? Sign up for EE-Mail™. We Want Your Feedback!   Download, PDF Format (128kB)  AN4151, AN 4151, APP4151, Appnote4151, Appnote 4151