IEEE 802.3af compliant single-port, powered device applications

Power over Ethernet (PoE) technology enables power sourcing equipment (PSE) such as switches/routers and midspan systems to deliver up to 15W of power over data cables. The system receiving power is called a powered device (PD). To meet the IEEE 802.3af standard, which specifies how the PSE and PD interact, the PSE must properly detect and classify the PD before supplying power. Once the PD is powered, the PSE must detect the PD's disconnection and rapidly de-energize the cable. The PSE must also protect cables and PDs from overcurrent and short-circuit conditions.

Single-port circuit for PSE systems

By integrating all necessary features, the MAX5922 makes designing PSE systems simple. The circuit illustrated in Figure 1 below is a complete PSE design.

Figure 1. MAX5922 feeder circuit diagram

The MAX5922A circuit has the following features:

• Compliant with IEEE 802.3af standard

• RJ-45 data input jack (J1)

• RJ-45 data and power output jack (J1)

• +32V to +60V wide operating input range

• 28V (±7%) turn-on voltage

• 0.45Ω integrated power switch

• Configurable powered device (PD), detection and classification

• 424mA (±6%) programmable current limit

• Configurable zero current detection with status output

• Classification status output

• Mid-span PSE application detection conflict avoidance feature; configurable for terminal PSE applications

• Power ready status output with green LED indicator (LED1)

• Overcurrent protection and overtemperature protection with status output

• Foldback current limiting with timeout setting and duty cycle control

• Selectable lockout or auto-restart fault management mode (JP1)

• Single button reset (SW1)

• Not affected by ESD and cable discharge