Compact-Footprint, 60A, Two-Phase Power Supply for AMD K8 Motherboards
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, 12ΩWMAX 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 | 10Ω ±5% resistor (0603) |
| R2, R5 | 2 | 3.3Ω ±5% resistors (0603) |
| R3 | 1 | 10kΩ ±5% resistor (0603) |
| R4, R7, R8, R9 | 4 | 200Ω ±5% resistors (0603) |
| R6 | 2 | 20kΩ ±1% resistor (0603) |
| R16, R17 | 2 | 68.1kΩ ±5% resistors (0603) |
| R8, R9 | 2 | 200Ω ±5% resistors (0603) |
| R10 | 1 | 100kΩ ±1% resistor (0603) |
| R11 | 1 | 2kΩ ±5% resistor (0603) |
| R12 | 1 | 120kΩ ±1% resistor (0603) |
| R13 | 1 | 80.6kΩ ±1% resistor (0603) |
| R14, R15 | 2 | 200kΩ ±1% resistors (0603) |
| R18, R19 | 2 | 3.3Ω ±5% resistors (1206) |
| R20 | 1 | Open (0603) |
| R21 | 1 | 390Ω ±1% resistor (0603) |
| R22 | 1 | 1.5kΩ ±1% resistor (0603) |
| R29 | 1 | 2.2Ω ±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.
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