Abstract: This applicaTIon note shows a reference design using the MAX15026 low-cost, high-efficiency synchronous buck converter in an auxiliary power supply for LCD TVs or set-top boxes. This reference design generates a 5V, 5A power supply from a wide, 6.5V to 24V input voltage range.

Key specificaTIons for the reference design are listed below, along with a detailed schemaTIc (Figure 1) and the bill of materials (Table 1) needed for this applicaTIon.

Specifications

• Input Voltage Range: 6.5V to 24V
• Output Voltage: 5V
• Output Current: 5A
• Output Voltage Ripple (pk-pk): 50mV
• Switching Frequency of Converter: 300kHz
• Overcurrent Protection Limit: 6A
• Efficiency: > 90% for Normal Operation

Figure 1. Schematic of the MAX15026 synchronous buck converter for a 300kHz switching frequency.

Table 1. Bill of Materials Designator Value Description Part Footprint Manufacturer Quantity C1 220µF, 35V Capacitor EEVFK1V221P 8mm x 10.2mm Panasonic 1 C2, C3 4.7µF, 50V Capacitor GRM31CR71H475KA12L 1206 Murata 2 C4 0.1µF, 50V Capacitor GRM188R71H104KA93D 0603 Murata 1 C5 4.7µF, 6.3V Capacitor GRM188R60J475KE19D 0603 Murata 1 C6 2.2µF, 6.3V Capacitor GRM188R60J225KE19D 0603 Murata 1 C7 1µF, 50V Capacitor GRM21BR71H105KA12L 0805 Murata 1 C8 0.47µF, 16V Capacitor GRM188R71C474KA88D 0603 Murata 1 C9, C16 1200pF, 50V Capacitor GRM1885C1H122JA01D 0603 Murata 2 C10, C11 47µF, 10V Capacitor GRM32ER71A476KE15L 1210 Murata 2 C12, C13, C14 22µF, 10V Capacitor GRM31CR71A226KE15L 1206 Murata 3 C15 560pF, 50V Capacitor GRM1885C1H561JA01D 0603 Murata 1 C17 22pF, 50V Capacitor GRM1885C1H220JA01D 0603 Murata 1 R1 10Ω Resistor SMD 1% Resistor 0603 Vishay 1 R2 10kΩ Resistor SMD 1% Resistor 0603 Vishay 1 R3, R6 2.2Ω Resistor SMD 1% Resistor 0603 Vishay 2 R4 15kΩ Resistor SMD 1% Resistor 0603 Vishay 1 R5 56.2kΩ Resistor SMD 1% Resistor 0603 Vishay 1 R7 3.57Ω Resistor SMD 1% Resistor 1206 Vishay 1 R8 102kΩ Resistor SMD 1% Resistor 0603 Vishay 1 R9 13.7kΩ Resistor SMD 1% Resistor 0603 Vishay 1 R10 2.74kΩ Resistor SMD 1% Resistor 0603 Vishay 1 R11 47.5kΩ Resistor SMD 1% Resistor 0603 Vishay 1 L1 10µH ±20%, 5.5A Inductor SLF12575T-100M5R4-PF 12.5mm x 12.5mm x 7.5mm TDK 1 N1 30V, 6.3A, 35.5mΩ—Q1;
30V, 8.6A, 16.5mΩ—Q2 Dual MOSFET FDS6982AS 8-SO Fairchild 1 U1 PWM Controller Low-Cost, DC-DC Synchronous Buck Controller with a 4.5V to 28V Operating Range MAX15026BETD+ 14-TDFN-EP Maxim 1

Performance Data

Figure 2. Steady-state output voltage, input voltage, and switching-node voltage at VIN = 24V, VOUT = 5V.
Ch1: VOUT; Ch2: VIN; Ch3: Lx Node Voltage



Figure 3. Enable, soft-start, soft-stop and PGOOD sequence waveforms.
Ch1: Enable; Ch2: VOUT; Ch3: PGOOD



Figure 4. Output and input ripples at VIN = 24V, VOUT = 5V and IOUT = 5A.
Ch1: Output Voltage Ripple; Ch2: Input Voltage Ripple



Figure 5. Converter load transient response with a 2A step change in load current.
Ch1: Output Voltage Dip; Ch2: Load-Step Change (1A/div)

Test Conditions

VIN = 12V, VOUT = 5V
Load Current Step Change: 1A to 3A
Load Current Slew Rate: 2A/µs


Figure 6.Hiccup-mode overcurrent protection with output shorted.
CH1: Output Voltage; CH2: Gate Pulses



Figure 7. Efficiency vs. load current plots.