Abstract: This application note describes a compact-footprint, low-cost, 60A, two-phase solution for desktop motherboard applications using AMD K8 CPUs. Test data, schematics, and bill of materials are included. The regulator operates from a 12V input and delivers a peak efficiency of 90% with a four-layer, 1oz. copper PC board typically employed in desktop designs. It features a 5in x 1.3in regulator area footprint, and uses low-cost components. Adequate airflow is necessary to ensure that the board/component temperature rise is within acceptable limits for the required operating ambient-temperature range. The power supply is implemented using the MAX1937 Quick-PWM™ controller. The Quick-PWM architecture regulates the output voltage by driving the output inductor with a constant on-time pulse whenever the output-voltage ripple waveform falls below a reference voltage (Figure 1). The next pulse is applied to the inductor after a fixed minimum off-time, if the output voltage has fallen below the reference. Unlike fixed-frequency controllers that have to wait for the next clock pulse to service load transients, the Quick-PWM control architecture responds after the minimum off-time (350ns for the MAX1937) has elapsed. This ensures fast response under load-transient conditions. The steady-state switching frequency can still be low (180kHz in this design) to maximize efficiency. Load-transient response (Figure 2) and efficiency data (Figure 3) are shown, along with a bill of materials (Table 1) and schematics of a two-phase power supply for AMD K8 motherboards (Figures 4a and 4b). Figure 1. Quick-PWM operation. Figure 2. Load-transient response. Figure 3. Efficiency (VIN = 12V, VOUT = 1.5V). Table 1. Bill of Materials DESIGNATION QTY DESCRIPTION C1, C2, C20, C64 4 1500µF, 16V capacitors Rubycon 16VMBZ1500 C3, C9 2 10µF, 16V capacitors (1210) Taiyo Yuden CE EMK325 BJ106MN-T C4, C6 2 0.22µF, 10V X7R capacitors (0603) Taiyo Yuden CE LMK107 BJ334KA-T C5, C7 2 1000pF, 6.3V X7R capacitors (0603) Murata GRM39X7R102K C8 1 2.2µF, 6.3V capacitor (0603) Taiyo Yuden CE JMK107 BJ105MA-T C10 1 820pF, C0G capacitor (0603) Murata GRM39C0G821J050 C11, C14 1 0.22µF, 10V X7R capacitors (0603) Taiyo Yuden CE LMK107 BJ224KA-T C12, C13 2 2200pF, 6.3V X7R capacitors (0603) Murata GRM39X7R222K C15 1 47pF, 50V C0G capacitors (0603) Murata GRM39C0G470J050AD C16 1 Not used C17 1 0.47µF, 10V X5R capacitor (0603) Taiyo Yuden CE LMK107 BJ474KA-T C18, C19 2 0.0022µF, 50V capacitors (0805) Murata GRM39X7R222K50 C21 1 0.1µF, 25V X7R capacitor (0603) Murata GRM188R71E104KA01B C22-C27 6 3300µF, 6.3V capacitors Rubycon 6.3VMBZ3300, 12WMAX ESR C28-C33, C34-C39 12 10µF capacitors (1206) Taiyo Yuden CE JMK316 BJ106ML-T C40-C47, C48-C61 22 2.2µF capacitors (0603) Taiyo Yuden JMK107BJ225MA C62-C63, C67-C70 6 22µF X5R capacitors (1206) Taiyo Yuden JMK316BJ226ML R1 1 10 ±5% resistor (0603) R2, R5 2 3.3 ±5% resistors (0603) R3 1 10k ±5% resistor (0603) R4, R7, R8, R9 4 200 ±5% resistors (0603) R6 2 20k ±1% resistor (0603) R16, R17 2 68.1k ±5% resistors (0603) R8, R9 2 200 ±5% resistors (0603) R10 1 100k ±1% resistor (0603) R11 1 2k ±5% resistor (0603) R12 1 120k ±1% resistor (0603) R13 1 80.6k ±1% resistor (0603) R14, R15 2 200k ±1% resistors (0603) R18, R19 2 3.3 ±5% resistors (1206) R20 1 Open (0603) R21 1 390 ±1% resistor (0603) R22 1 1.5k ±1% resistor (0603) R29 1 2.2 ±5% resistor (0603) L1, L2 1 1.2µH, 30A toroidal inductors BI Technologies HM00-3583 L3 1 0.33µH, 10A toroidal inductor BI Technologies HM00-3661 D1 1 Dual Schottky diodes (SOT23) Central CMSSH-3A D2, D3 2 Diodes (SOT23) Central Semiconductor CMPD2836 J1-J6, J9 7 2-pin headers Q3, Q4, Q7, Q8 4 N-channel MOSFETs (D2-Pak) International Rectifier IRLR7833S Q1, Q2, Q5, Q6 4 N-channel MOSFETs (D-Pak), International Rectifier IRLR7821 Q9, Q10 2 N-channel MOSFETs (SOT23) Vishay 2N7002 U1 1 Maxim MAX1937EEI controller (QSOP) U2 1 National LM317 regulator (D-Pak) J7 1 4-pin ATX Molex connector J8 1 PGA socket 754 Foxconn PZ75403-2948-01 PC board 1 Maxim MAX1937 K8 evaluation kit, 8/03, compact footprint For Larger Image Figure 4a. 60A, Two-Phase Power Supply for AMD K8 Motherboards (VIN = 12V, VOUT = 1.5V at 60A) Figure 4b. 60A, Two-phase power supply for AMD K8 motherboards. We Want Your Feedback! 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™. More Information   APP 3499: May 11, 2005 MAX1937 Two-Phase Desktop CPU Core Supply Controllers with Controlled VID Change Full Data Sheet (PDF, 384kB) Free Samples   Download, PDF Format (103kB)  AN3499, AN 3499, APP3499, Appnote3499, Appnote 3499