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SI3401-X-GM Folha de dados(PDF) 10 Page - Silicon Laboratories |
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SI3401-X-GM Folha de dados(HTML) 10 Page - Silicon Laboratories |
10 / 20 page Si3400/Si3401 10 Rev. 0.9 3. Functional Description The Si3400 and Si3401 consist of two major functions: a hotswap controller/interface and a complete pulse- width-modulated switching regulator (controller and power FET). 3.1. Overview The hotswap interfaces of the Si3400 and Si3401 provide the complete front end of an 802.3-compliant PD. The Si3400 and Si3401 also include two full diode bridges, a transient voltage surge suppressor, detection circuit, classification current source, and dual-level hotswap current limiting switch. This high level of integration enables direct connection to the RJ-45 connector, simplifies system design, and provides significant advantages for reliability and protection. The Si3400 and Si3401 require only four standard external components (detection resistor, optional classification resistor, load capacitor, and input capacitor) to create a fully 802.3-compliant interface. For more information about supporting higher-power applications, see “AN313: Using the Si3400 and Si3401 in High Power Applications” and “AN314: Power Combining Circuit for PoE for up to 18.5 W Output”. The Si3400 and Si3401 integrate a complete pulse- width modulated switching regulator that includes the controller and power FET. The switching regulator utilizes a constant frequency pulse-width modulated controller optimized for all possible load conditions in PoE applications. The regulator integrates a low on- resistance (Ron) switching power MOSFET that minimizes power dissipation, increases overall regulator efficiency, and simplifies system design. An integrated error amplifier, precision reference, and programmable soft-start current source provide the flexibility of using a non-isolated buck regulator topology or an isolated flyback regulator topology. The Si3400 and Si3401 are designed to operate with both 802.3-compliant Power Sourcing Equipment (PSE) and pre-standard (legacy) PSEs that do not adhere to the 802.3 specified inrush current limits. The Si3400 and Si3401 are compatible with compliant and legacy PSEs because they use two levels for the hotswap current limits. By setting the initial inrush current limit to a low level, a PD based on the Si3400 or Si3401 minimizes the current drawn from either a compliant or legacy PSE during startup. After powering up, the Si3400 and Si3401 automatically switch to a higher- level current limit, thereby allowing the PD to consume up to 12.95 W (the max power allowed by the 802.3 specification). The inrush current limit specified by the 802.3 standard can generate high transient power dissipation in the PD. By properly sizing the devices and implementing on- chip thermal protection, the Si3400 and Si3401 can go through multiple turn-on sequences without overheating the package or damaging the device. The switching regulator power MOSFET has been conservatively designed and sized to withstand the high peak currents created when converting a high-voltage, low-current supply into a low-voltage, high-current supply. Excessive power cycling or short circuit faults will engage the thermal overload protection to prevent the onboard power MOSFETs from exceeding their safe and reliable operating ranges. 3.2. PD Hotswap Controller The Si3400 and Si3401 hotswap controllers change their mode of operation based on the input voltage applied to the CT1 and CT2 pins or the SP1 and SP2 pins, the 802.3-defined modes of operation, and internal controller requirements. Table 9 defines the modes of operation for the hotswap interface. Figure 3. Hotswap Block Diagram DIODE BRIDGES AND PROTECTION DETECTION CONTROL ON OFF VPOSF VNEG CT1/SP1 CT2/SP2 0V 12V RDET CLASSIFICATION CONTROL ON OFF 12V 22V RCL CENTRAL BIAS BANDGAP REF 10V 5V 1.32V CURRENT LIMIT HI/LO HOTSWAP CONTROL ON OFF 39V 32V SWITCHER STARTUP & BIAS IABS ITC VREF HSO POWER LOSS DETECTOR PLOSS SSFT VPOSS ISOSSFT |
Nº de peça semelhante - SI3401-X-GM |
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Descrição semelhante - SI3401-X-GM |
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