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Reference Design for a High-Current Power Supply with Lossless Current Sensing Using the MAX5060

筆者: Surya Prakash

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.

Figure 1. Schematic of the MAX5060 buck converter for FSW = 275kHz.
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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
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 2. Load current versus converter efficiency for VIN = 12V.

Figure 3. Load current versus converter output voltage 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 47 for different input excitations.

Figure 4. Converter waveforms with VIN = 12V and IOUT = 30A.
VIN = 12V and IOUT = 2 × 15A
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
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
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
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.

Figure 8. Four-layer MAX5060 buck board.
More detailed image
(PDF, 16kB)
Figure 8. Four-layer MAX5060 buck board.

関連製品
MAX5060 0.6V~5.5V出力、並列接続可能、平均電流モードDC-DCコントローラ 無料
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APP 4375: Apr 29, 2009
リファレンス回路4375, AN4375, AN 4375, APP4375, Appnote4375, Appnote 4375