SI3461-KIT Silicon Laboratories Inc, SI3461-KIT Datasheet - Page 11

• Manufacturer Part Number: SI3461-KIT
• Description: BOARD EVAL FOR SI3461
• Manufacturer: Silicon Laboratories Inc
• Type: Controllers & Processorsr

Specifications of SI3461-KIT

• Main Purpose: Special Purpose DC/DC, Power Over Ethernet
• Board Type: Fully Populated
• Utilized Ic / Part: Si3461
• Ethernet Connection Type: 10/100 Base-T, IEEE 802.3
• Interface Type: Ethernet
• Operating Voltage: 12 V to 15 V
• Operating Current: 10 mA
• Product: Modules
• For Use With/related Products: Si3460
• Lead Free Status / RoHS Status: Lead free / RoHS non-compliant
• Current - Output: -
• Voltage - Output: -
• Voltage - Input: -
• Power - Output: -
• Frequency - Switching: -
• Outputs And Type: -
• Regulator Topology: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 336-1843

Si3461-EVB
7. Design and Layout Considerations
7.1. General Recommendations
The Si3461-EVB schematic and layout are intended to be used as a reference for all customer designs. The
Si3461-EVB has been tested by the University of New Hampshire Interoperability Lab (UNH IoL) to comply with the
relevant
IEEE
802.3
Clause
33
specifications.
UNH
test
reports
can
be
downloaded
from
http://www.silabs.com/PoE. Since the Si3461's performance in an application depends on external components
and PCB layout, customers are ultimately responsible for validating their design's conformance to all relevant
industry, safety, and customer-specific requirements. For applications support, visit the Silicon Labs Technical
Support web page: https://www.silabs.com/support/pages/contacttechnicalsupport.aspx.
7.2. Isolation
The IEEE 802.3 specification requires that the PSE output power be isolated from earth ground*. To accomplish
this, the input power source must be isolated from earth ground. Also, do not connect the Si3461's ground
connection (Pin #11) to earth ground because this pin serves only as a circuit reference point in the Si3461-EVB.
*Note: If the input power supply is referenced to earth ground and if one of the output pads is connected to ground, it can
create a high-current fault condition that will not be protected.
7.3. SELV-Compliant Output Voltage
Since the output of the Si3461-EVB reference design is designed to be less than 57 Vdc under all conditions, it is
considered an SELV circuit.
7.4. Surge Protection
The Si3461-EVB applications design includes a clamp diode, D6, to protect against 50 µs intra-building lightning
surges as specified in IEEE 802.3. Additional protection, such as a 1 A fuse in the output circuit, may be required
for applications in which the Ethernet cabling is not intra-building.
7.5. Thermal Considerations
The pass FET needs a cooling surface of adequate size. The Si3461 controller itself implements over-temperature
protection, but this alone cannot effectively protect the pass FET in case of a sudden overload. Nevertheless,
relatively tight thermal coupling between the two devices may be a good idea.
Some of the resistors, such as the current sensor and the series resistors of the shunt regulator (if used), also
dissipate relatively large amounts of power. Care should be taken to select resistors with proper power ratings.
Using a high-efficiency external 3.3 V supply instead of the onboard shunt regulator can save almost 1 W of power.
Rev. 0.5
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