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%. We Want Your Feedback! 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™. More Information   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   Download, PDF Format (128kB)  AN4151, AN 4151, APP4151, Appnote4151, Appnote 4151