In many networking and telecom applications, there are multiple regulated power rails. Many of these power rails need to provide high current, reasonable size and efficiency, and outstanding load-transient response. This article shows a detailed reference design solution using the MAX5060 dual buck controller operating at a switching frequency of 300kHz. Key specifications for this reference design are listed below, along with a detailed schematic (Figure 1) and the bill of materials (Table 1) needed for this application.
Specifications:
- VIN = 5.15V (-0.4V, +0.4V)
- VOUT1 = 1.2V ±48mV/IOUT1 = 0 to 8.5A (Including Transients)
- Converter 1 Output-Voltage Ripple: 12mVP-P
- Converter 1 Load-Transient Response: 18mVP-P for 10% to 60% Variation of the Load
- VOUT2 = 3.3V ±132mV/IOUT2 = 0 to 4.4A (Including Transients)
- Converter 2 Output-Voltage Ripple: 27mVP-P
- Converter 2 Load-Transient Response: 40mVP-P for 10% to 60% Variation of the Load
- Composite Efficiency of Converters 1 and 2: 93.38% at Full Load
- Temperature Range: -40°C to +85°C
Figure 1. MAX5066 reference design showing DC-DC converters of 1.2V/8.5A and 3.3V/4.4A from 5.1V; fSW = 295kHz
| Designator | Value | Description | Part | Footprint | Manufacturer | Quantity |
| C50, C71 | 4.7µF/6.3V | Capacitors | JMK107BJ475MA-T | 0603 | Taiyo Yuden | 2 |
| C60 | 470µF/6.3V | Capacitors | APXA6R3ARA471MHC0G | 3.1mm x 4.2mm x 2.2mm | Nippon Chemi-Con | 1 |
| C61, C62, C64, C72, C74, C75, C76, C77 | 10µF/10V | Capacitors | LMK212BJ106M | 0805 | Taiyo Yuden | 8 |
| C63, C73, C86, C87 | 1.0µF/16V | Capacitors | EMK107BJ105KA-T | 0603 | Taiyo Yuden | 4 |
| C65, C79 | 220nF/16V | Capacitors | EMK107BJ224MA-T | 0603 | Taiyo Yuden | 2 |
| C67, C68, C81, C83, C84 | 100nF/16V | Capacitors | EMK105BJ104KV-FR | 0402 | Taiyo Yuden | 5 |
| C69 | 100pF | Capacitor | UMK105CH180JW | 0402 | Taiyo Yuden | 1 |
| C70, C85 | 1.0µF/6.3V | Capacitors | JMK105BJ105KV | 0402 | Taiyo Yuden | 2 |
| C82 | OPEN | Capacitor | OPEN | 0402 | OPEN | 1 |
| L60, L61 | 2.3µH | Inductors | MVR1278 | 7.8mm x 11.5mm | Coilcraft | 2 |
| Q60, Q61 | n-channel 30V | nMOSFETs | SI7114DN | PowerPAK 1212-8 | Vishnay-Siliconix | 2 |
| Q62, Q63, Q64 | n-channel 20V | nMOSFETs | SI7114DN | PowerPAK 1212-8 | Vishnay-Siliconix | 3 |
| R60, R72 | 1Ω | Resistors | SMD, 1%, 63mW | 0402 | Vishay | 2 |
| R62, R73, R74, R75, R76, R77 | 0.01Ω | Resistors | RL1220T, 250mW | 0805 | Susumu | 6 |
| R62, R73, R74, R75, R76, R77 | 0.01Ω | Resistors | RL1220T, 250mW | 0805 | Susumu | 6 |
| R64 | 0.039Ω | Resistor | RL1220T, 250mW | 0805 | Susumu | 1 |
| R65 | 1.2kΩ | Resistor | SMD, 1%, 63mW | 0402 | Vishay | 1 |
| R66 | 3.3kΩ | Resistor | SMD, 1%, 63mW | 0402 | Vishay | 1 |
| R67, R83 | 1MΩ | Resistors | SMD, 1%, 63mW | 0402 | Vishay | 2 |
| R69 | 43kΩ | Resistor | SMD, 1%, 63mW | 0402 | Vishay | 1 |
| R70 | 4.7kΩ | Resistor | SMD, 1%, 63mW | 0402 | Vishay | 1 |
| R71 | 41.2Ω | Resistor | SMD, 1%, 63mW | 0402 | Vishay | 1 |
| R78 | 0.027Ω | Resistor | RL1220T, 250mW | 0805 | Susumu | 1 |
| R79 | 910Ω | Resistor | SMD, 1%, 63mW | 0402 | Vishay | 1 |
| R80 | 22kΩ | Resistor | SMD, 1%, 63mW | 0402 | Vishay | 1 |
| R81 | 20kΩ | Resistor | SMD, 1%, 63mW | 0402 | Vishay | 1 |
| R82 | 100kΩ | Resistor | SMD, 1%, 63mW | 0402 | Vishay | 1 |
| D60, D61 | 30V/200mA | Schottky Diodes | RB521S30T1 | SOD-523 | ON Semiconductor | 2 |
| D62, D63 | 30V/30mA | Schottky Diodes | RB751 | SOD-523 | ON Semiconductor | 2 |
| U60 | MAX5066 | PWM Controller | MAX5066AUI | 28-TSSOP-EP | Maxim | 1 |
Efficiency data for each regulator is summarized in Table 2, showing high efficiency for both outputs, as shown in Figure 2.
| VIN(V) | IIN(A) | VOUT1(V) | IOUT1(A) | VOUT2(v) | IOUT2(A) | Efficiency (%) |
| 5.1402 | 5.0780 | 1.1814 | 8.5008 | 3.2558 | 4.4016 | 93.38% |
| 5.1347 | 4.5728 | 1.1853 | 72.6491 | 3.2636 | 3.96 | 95.73% |
| 5.361 | 4.0605 | 1.1891 | 6.8012 | 3.2713 | 3.5244 | 95.06% |
| 5.1500 | 3.5440 | 1.1928 | 5.9558 | 3.2791 | 3.0836 | 94.32% |
| 5.1441 | 3.0432 | 1.1967 | 5.1030 | 3.2870 | 2.6435 | 94.54% |
| 5.1497 | 2.5398 | 1.2005 | 4.2507 | 3.2948 | 2.2086 | 94.65% |
| 5.1522 | 2.0337 | 1.2044 | 3.3988 | 3.3030 | 1.7608 | 94.57% |
| 5.1490 | 1.5407 | 1.2083 | 4.2557 | 3.3111 | 1.3232 | 94.15% |
| 5.1465 | 1.0441 | 1.2122 | 1.7073 | 3.3194 | 0.8815 | 92.97% |
| 5.380 | 0.5472 | 1.2163 | 0.8455 | 3.3279 | 0.4419 | 88.88% |
Figure 2. Global efficiency is shown as a function of total output power
In Figures 3 and 4, the output voltages of the controllers are shown versus their output load currents.
Figure 3. The first controller's output voltage versus its output load current
Figure 4. The second controller's output voltage versus its output load current
Load-transient-response performance for each regulated output is shown in Figures 5 and 6.
Figure 5. A transient of 1.2V with a load varying between 0.85A and 5.1A in 18mV steps over a period of 10µs
Figure 6. A transient of 3.3V with a load varying between 0.44A and 2.64A in 40mV steps over a period of 10µs
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