Power Electronics

MOSFET Module Saves Space in PoE Designs

International Rectifier has introduced the IRF4000, a 100-V-rated device integrating four HEXFET MOSFETs into a single Power MLP package for Power-over-Ethernet (PoE) applications. The new device complies with the IEEE 802.3af specification for networking and communications infrastructure systems, such as Ethernet switches, routers and hubs, delivering up to 15 W per port. The device replaces four individual SOT-223-packaged MOSFETs.

The IEEE 802.3af specification outlines power delivery requirements from the power sourcing equipment (PSE) through the LAN cable to the powered device (PD) in a networking system. The MOSFET operates like a hot-swap FET, transferring power from the PSE to the PD in a controlled fashion. It must operate in the linear region and requires an extremely robust safe operating area (SOA).

The low-transconductance silicon technology used in the IRF4000 combines with a 1°C/W package thermal resistance to enable efficient removal of heat while operating in the linear region. The device has been fully electrically and thermally characterized under worst-case IEEE 802.3af operating conditions. The IRF4000 guarantees a 56% higher device safe operating area compared to individual SOT-223 MOSFETs, improving system reliability and thermal margin.

In addition to 48-port systems, the device is suitable for 96-port applications or for smaller PoE “jack companion” modules using 12 ports where, in each case, four ports can be addressed with a single IRF4000 device. The new device is qualified to industrial moisture sensitivity level (MSL) 3.

In addition to the IEEE 802.3af specification, the IRF4000 is compliant with the upcoming PoE Plus architecture for high power loads. The new part is available now, and pricing is $2 each in 10,000-unit quantities. Data sheets are posted on the International Rectifier Web site. Selected parameters for the part are shown in the table below:

Part Number Package VDSS RDS(on) max @ VGS = 12 V RDS(on) max @ VGS = 10 V IDSS @ 100 V RTH (J to LEAD)
IRF4000 10 mm (l) × 5 mm (w) × 1.85 mm (h) Power MLP 100 V 270 mΩ 350 mΩ 1.5 µA 1.5°C/W max

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