Abstract: The MAX5066 high performance dual buck regulator provides outstanding performance. The reference design in this application note depicts a detailed solution with complete schematic, bill of materials, and load-transient-response scope photos. In many networking and telecom applications, there are multiple regulated power rails. Many of these power rails need to provide high current, reasonable size and efficiency, and outstanding load-transient response. This article shows a detailed reference design solution using the MAX5060 dual buck controller operating at a switching frequency of 300kHz. 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 = 5.15V (-0.4V, +0.4V) VOUT1 = 1.2V ±48mV/IOUT1 = 0 to 8.5A (Including Transients) Converter 1 Output-Voltage Ripple: 12mVP-P Converter 1 Load-Transient Response: 18mVP-P for 10% to 60% Variation of the Load VOUT2 = 3.3V ±132mV/IOUT2 = 0 to 4.4A (Including Transients) Converter 2 Output-Voltage Ripple: 27mVP-P Converter 2 Load-Transient Response: 40mVP-P for 10% to 60% Variation of the Load Composite Efficiency of Converters 1 and 2: 93.38% at Full Load Temperature Range: -40°C to +85°C Figure 1. MAX5066 reference design showing DC-DC converters of 1.2V/8.5A and 3.3V/4.4A from 5.1V; fSW = 295kHz. Table 1. Bill of Materials Designator Value Description Part Footprint Manufacturer Quantity C50, C71 4.7µF/6.3V Capacitors JMK107BJ475MA-T 0603 Taiyo Yuden 2 C60 470µF/6.3V Capacitor APXA6R3ARA471MHC0G 3.1mm x 4.2mm x 2.2mm Nippon Chemi-Con 1 C61, C62, C64, C72, C74, C75, C76, C77 10µF/10V Capacitors LMK212BJ106M 0805 Taiyo Yuden 8 C63, C73, C86, C87 1.0µF/16V Capacitors EMK107BJ105KA-T 0603 Taiyo Yuden 4 C65, C79 220nF/16V Capacitors EMK107BJ224MA-T 0603 Taiyo Yuden 2 C66, C80 4.7nF/16V Capacitors TMK105BJ472KV-F 0402 Taiyo Yuden 2 C67, C68, C81, C83, C84 100nF/16V Capacitors EMK105BJ104KV-FR 0402 Taiyo Yuden 5 C69 18pF Capacitor UMK105CH180JW 0402 Taiyo Yuden 1 C70, C85 1.0µF/6.3V Capacitors JMK105BJ105KV 0402 Taiyo Yuden 2 C78, C88 470µF/2.5V Capacitors APXE2R5ARA471MF80G 1.9mm x 3.5mm x 1.6mm Nippon Chemi-Con 2 C82 OPEN Capacitor OPEN 0402 OPEN 1 L60, L61 2.3µH Inductors MVR1278 7.8mm x 11.5mm Coilcraft 2 Q60, Q61 n-channel 30V nMOSFETs SI7114DN PowerPAK 1212-8 Vishay-Siliconix 2 Q62, Q63, Q64 n-channel 20V nMOSFETs SI7106DN PowerPAK 1212-8 Vishay-Siliconix 3 R60, R72 1Ω Resistors SMD, 1%, 63mW 0402 Vishay 2 R62, R63, R74, R75, R76, R77 0.01Ω Resistors RL1220T, 250mW 0805 Susumu 6 R64 0.039Ω Resistor RL1220T, 250mW 0805 Susumu 1 R65 1.2kΩ Resistor SMD, 1%, 63mW 0402 Vishay 1 R66 3.3kΩ Resistor SMD, 1%, 63mW 0402 Vishay 1 R67, R83 1MΩ Resistors SMD, 1%, 63mW 0402 Vishay 2 R68, R84, R85 1kΩ Resistors SMD, 1%, 63mW 0402 Vishay 3 R69 43kΩ Resistor SMD, 1%, 63mW 0402 Vishay 1 R70 4.7kΩ Resistor SMD, 1%, 63mW 0402 Vishay 1 R71 41.2Ω Resistor SMD, 1%, 63mW 0402 Vishay 1 R78 0.027Ω Resistor RL1220T, 250mW 0805 Susumu 1 R79 910Ω Resistor SMD, 1%, 63mW 0402 Vishay 1 R80 22kΩ Resistor SMD, 1%, 63mW 0402 Vishay 1 R81 20kΩ Resistor SMD, 1%, 63mW 0402 Vishay 1 R82 100Ω Resistor SMD, 1%, 63mW 0402 Vishay 1 D60, D61 30V/200mA Schottky diodes RB521S30T1 SOD-523 ON Semiconductor 2 D62, D63 30V/30mA Schottky diodes RB751 SOD-523 ON Semiconductor 2 U60 MAX5066 PWM controller MAX5066AUI 28-TSSOP-EP Maxim 1 Efficiency data for each regulator is summarized in Table 2, showing high efficiency for both outputs, as shown in Figure 2. Table 2. Efficiency Data VIN (V) IIN (A) VOUT1 (V) IOUT1 (A) VOUT2 (V) IOUT2 (A) Efficiency (%) 5.1402 5.0780 1.1814 8.5008 3.2558 4.4016 93.38% 5.1347 4.5728 1.1853 7.6491 3.2636 3.9652 93.73% 5.1361 4.0605 1.1891 6.8012 3.2713 3.5244 94.06% 5.1500 3.5440 1.1928 5.9558 3.2791 3.0836 94.32% 5.1441 3.0423 1.1967 5.1030 3.2870 2.6435 94.54% 5.1497 2.5398 1.2005 4.2507 3.2948 2.2086 94.65% 5.1522 2.0337 1.2044 3.3988 3.3030 1.7608 94.57% 5.1490 1.5407 1.2083 2.5557 3.3111 1.3232 94.15% 5.1465 1.0441 1.2122 1.7073 3.3194 0.8815 92.97% 5.1380 0.5472 1.2163 0.8455 3.3279 0.4419 88.88% Figure 2. Global efficiency is shown as a function of total output power. In Figures 3 and 4, the output voltages of the controllers are shown versus their output load currents. Figure 3. The first controller's output voltage versus its output load current. Figure 4. The second controller's output voltage versus its output load current. Load-transient-response performance for each regulated output is shown in Figures 5 and 6. Figure 5. A transient of 1.2V with a load varying between 0.85A and 5.1A in 18mV steps over a period of 10µs. Figure 6. A transient of 3.3V with a load varying between 0.44A and 2.64A in 40mV steps over a period of 10µs. Related Parts   APP 4150: Dec 21, 2007 MAX5066 Configurable, Single-/Dual-Output, Synchronous Buck Controller for High-Current Applications Full Data Sheet (PDF, 376kB) 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 (117kB)  AN4150, AN 4150, APP4150, Appnote4150, Appnote 4150