Reference Design for a High-Cu

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

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 detai led 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
D1	Schottky Diode	CMHSH5-2L	SOD123	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
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.

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LO(39370) LO(39370)
MAX5060(6079) MAX5060(6079)

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Reference Design for a High-Cu

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