UG324: Non-Isolated Buck Evaluation Board for the Si3404 The Si3404 non-isolated Buck evaluation board is a reference de- KEY FEATURES sign for a power supply in a Power over Ethernet (PoE) Powered Device (PD) application. IEEE 802.03af compliant Very small application PCB surface This Si3404-Buck EVB provides a simple and low-cost solution with different output vol- High efficiency tages and power levels. High integration The Si3404-Buck-5V EVB board is shown below. The Si3404 IC integrates an IEEE Low-profile 4 x 4 mm 20-pin QFN 802.03af compatible PoE interface as well as a current control-based dc/dc converter. Integrated thermal shutdown protection Low BOM cost The Si3404 PD integrates a detection circuit, classification circuit, dc/dc switch, hotswap switch, TVS overvoltage protection, dynamic soft-start circuit, cycle-by-cycle current lim- Integrated transient overvoltage protection it, thermal shutdown, and inrush current protection. The switching frequency is set to 220 kHz by installing R10 = 88.7 k. Si3404- Si3404- Si3404- Si3404- Parameter Condition BUCK-3.3V BUCK-5V BUCK-12V BUCK-24V PSE Input Voltage Range Connector J1 37 V to 57 V PoE Type/Class IEEE 802.3af Type 1/Class 2 Type 1/Class 3 Output Voltage/Current Connectors J2J3 3.3 V / 2.1 A 5 V / 1.4 A 12 V / 1.25 A 24 V / 0.625 A V = 50 V, Schottky bridge Efficiency, End-to-End 71.2 % 77.7 % 85.9 % 89.3 % IN Efficiency, End-to-End V = 50 V, Silicon bridge 70.8 % 77.1 % 85.3 % 88.6 % IN R (R10) = 88.7 k Switching Frequency 220 kHz FREQ Conducted EMI EN55032, average detector Passed Conducted EMI EN55032, peak detector Passed Radiated EMI EN55032 Class B Passed silabs.com Building a more connected world. Rev. 0.3 Table of Contents 1. Selector Guide...............................4 2. Powering Up the Si3404-Buck Board ......................5 3. Si3404-Buck EVB: 3.3 V, Class 2 Configuration ..................6 3.1 Si3404-Buck EVB Schematic: 3.3 V, Class 2, 7 W..................6 3.2 End-to-End EVB Efficiency..........................7 3.3 Thermal Measurements...........................8 3.4 SIFOS PoE Compatibility Test Results......................9 3.5 Adjustable EVB Current Limit.........................9 3.6 Feedback Loop Phase and Gain Measurement Results (Bode Plots)............10 3.7 Load Step Transient Measurement Results ....................11 3.8 Output Voltage Ripple ...........................11 3.9 Soft-Start Protection ............................12 3.10 Output Short Protection ..........................13 3.11 Pulse Skipping at No-Load Condition......................14 3.12 Discontinuous (DCM) and Continuous (CCM) Current Modes..............14 3.13 Radiated Emissions Measurement Results....................15 3.14 Conducted Emissions Measurement Results ...................16 3.15 Bill of Materials .............................17 4. Si3404-Buck EVB: 5 V, Class 2 Configuration .................. 19 4.1 Si3404-Buck EVB Schematic: 5V, Class 2, 7 W...................19 4.2 End-to-End EVB Efficiency..........................20 4.3 Thermal Measurements...........................21 4.4 SIFOS PoE Compatibility Test Results......................22 4.5 Adjustable EVB Current Limit.........................22 4.6 Feedback Loop Phase and Gain Measurement Results (Bode Plots)............23 4.7 Load Step Transient Measurement Results ....................24 4.8 Output Voltage Ripple ...........................24 4.9 Soft-Start Protection ............................25 4.10 Output Short Protection ..........................26 4.11 Pulse Skipping at No-Load Condition......................27 4.12 Discontinuous (DCM) and Continuous (CCM) Current Modes..............27 4.13 Radiated Emissions Measurement Results....................28 4.14 Conducted Emissions Measurement Results ...................29 4.15 Bill of Materials .............................30 5. Si3404-Buck EVB: 12 V, Class 3 Configuration.................. 32 silabs.com Building a more connected world. Rev. 0.3 2