Abstract: This reference design shows how to use a MAX5060 current-mode, step-down power-supply controller to implement lossless current sensing for high-current applications. In this design, the series resistance (DCR) of the inductor is used for current sensing to avoid power loss in the current-sense resistor. Introduction Today's data processing elements demand higher currents from power supplies to achieve higher speed. Lossless current sensing and ground bouncing are key challenges for accurate control of output voltage and current in these applications. The MAX5060 PWM buck power-supply controller uses an average-current-mode control technique to track the load current, and it employs differential sensing to accurately control the output voltage. In this reference design, the series resistance (DCR) of the inductor is used for current sensing to avoid power loss in the current-sense resistor. This design shows a solution for implementing a high-current (30A) power supply with high system efficiency and good load regulation. The complete schematic, bill of materials (BOM), efficiency measurements, and test results are included below. Specifications and Design Setup This reference design achieves the following specifications. Input voltage: 12V ±10% Output voltage: 1.5V Output current: 30A Output ripple: ±15mV Input ripple: ±250mV Efficiency: > 88% with half of full load (15A) Switching frequency: 275kHz Footprint size: 5cm × 3.3cm The schematic for this reference design is shown in Figure 1, and the BOM is given in Table 1. In this design, the MAX5060 is used in a buck configuration. More detailed image (PDF, 100kB) Figure 1. Schematic of the MAX5060 buck converter for FSW = 275kHz. Table 1. Bill of Materials Designator Description Comment Footprint Manufacturer Quantity Value C1, C20 Capacitor GRM1555C1H101JZ01D 402 Murata 2 100pF C2 Capacitor GRM155R71E223KA61D 402 Murata 1 22nF C3 Capacitor GRM155R71H682KA88D 402 Murata 1 6.8nF C4 Capacitor GRM1555C1H470JZ01D 402 Murata 1 47pF C5 Capacitor GRM155R61A224KE19D 402 Murata 1 0.22µF C6, C12 Capacitor GRM155R61A474KE15D 402 Murata 2 0.47µF C7, C8, C9, C18 Capacitor GRM188R71A105KA61D 402 Murata 4 1µF C10, C11 Capacitor GRM32ER71C226KE18L 1210 Murata 2 22µF/16V C13, C14 Capacitor GRM32ER60J107ME20L 1210 Murata 1 100µF/6.3V C15 Capacitor GRM31CR60J476KE19L 1206 Murata 1 47µF C16 Capacitor GRM155R71H103KA88D 402 Murata 1 10nF C17 SP Capacitor EEFSX0D471E4 7.3mm x 4.3mm SP CAP Panasonic 1 470µF/2V C19 Capacitor GRM155R71H102KA01D 402 Murata 1 1nF D1 Schottky Diode CMHSH5-2L SOD-123 Central Semiconductor 1 20V, 500mA Schottky D2 Schottky Diode UPS835LE3 POWERMITE3 Microsemi 1 35V, 8A Schottky Rectifier L Inductor T5060 (0.6µH) T5060_Falco_Inductor Falco 1 0.6µH Q1 N-Channel MOSFET Si7136DP PowerPAK SO8 Vishay 1 20V, 30A nMOSFET Q2, Q3 N-Channel MOSFET Si7866DP PowerPAK SO8 Vishay 2 20V, 40A nMOSFET Q4 NPN Transistor CMUT2222A SOT-523 Central Semiconductor 1 75V, 600mA NPN R1 Resistor Res1 402 Multisource 1 1.7kΩ R3, R16 Resistor Res1 402 Multisource 2 12.7kΩ R4, R21 Resistor Res1 402 Multisource 2 4.99kΩ R5, R20 Resistor Res1 402 Multisource 2 100kΩ R6 Resistor Res1 402 Multisource 1 226kΩ R7 Resistor Res1 402 Multisource 1 Open R8, R19 Resistor Res1 402 Multisource 2 10kΩ R9 Resistor Res1 402 Multisource 1 0 R10 Resistor Res1 402 Multisource 1 5.6kΩ R11 Resistor Res1 402 Multisource 1 1Ω R12 Resistor Res1 402 Multisource 1 2.2Ω R13, R22 Resistor Res1 402 Multisource 2 715Ω R14 Resistor Res1 402 Multisource 1 1.82Ω R15, R18 Resistor Res1 402 Multisource 2 22Ω R17 Resistor Res1 402 Multisource 1 8.45kΩ U1 PWM Controller MAX5060 28-TQFN-EP Maxim 1 — Efficiency Plots Figure 2 provides a plot of efficiency versus load current plots for this design, and Figure 3 presents load-regulation data. Figure 2. Load current versus converter efficiency for VIN = 12V. Figure 3. Load current versus converter output voltage for VIN = 12V. Experimental Results Converter output voltage and load current are shown in Figures 4–7 for different input excitations. Figure 4. Converter waveforms with VIN = 12V and IOUT = 30A. VIN = 12V and IOUT = 2 × 15A Ch1: Output current (2x) Ch2: Output voltage Ch3: Input voltage Ch4: High-side MOSFET gate drive Figure 5. Input and output ripple waveforms with VIN = 12V and IOUT = 30A. VIN = 12V and IOUT = 2 × 15A Ch2: Output voltage ripple Ch3: Input voltage ripple Figure 6. Line transient response. VIN = 0 to 12V and IOUT = 2 × 15A Ch2: Output voltage Ch3: Input voltage Figure 7. Load transient response. VIN = 12V and IOUT = 1A to 7A Ch1: Output current transient (1A to 7A) Ch2: Output voltage ripple The board developed for this application is shown in Figure 8. More detailed image (PDF, 16kB) Figure 8. Four-layer MAX5060 buck board. Related Parts   APP 4375: Apr 29, 2009 MAX5060 0.6V to 5.5V Output, Parallelable, Average-Current-Mode DC-DC 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 (167kB)  AN4375, AN 4375, APP4375, Appnote4375, Appnote 4375