Users Guide

76 Switch Feature Overview
• In AF mode, the classification mechanism is based on a single event, and
the device is classified as a Type 1 PD.
• In AT mode, the classification mechanism is based on two events as
defined in IEEE802.3AT-2009, and the device is classified as a Type 1 or a
Type 2 PD.
Port Start Up
Upon a successful detection and classification process, power is applied to the
load using a controlled Start Up mechanism. During this period, inrush
current is limited to 425 milliampere (mA) for a typical duration of 65
milliseconds (ms), which allows PD load to charge to a steady state power
condition.
Overload Detection and Port Shutdown
After power up, the switch automatically initializes its internal protection
mechanisms. These are utilized to monitor and disconnect power from the
PD in the cases where extreme conditions occur, as specified in the
IEEE802.3AF/AT standard. These conditions include over-current or short
ports terminals scenarios.
Disconnect Detection
The PoE switches support a DC Disconnect Function, per the
IEEE802.3AF/AT standard. This mechanism continuously monitors load
current and disconnects power in cases where the load current is below 7.5mA
(typical) for more than 324 ms.
IC Thermal Monitoring
The PoE IC contains a thermal sensor that is sampled every 20ms so the die
temperature is monitored at all times. In case the die exceeds the 150°C, the
system ports will be disconnected to protect the ICs.
Over-Temperature Protection
In addition to the die thermal sensor, there are thermal sensors on each
MOSFET that continuously monitor per port main MOSFETs junction
temperature and will shut down the port load power in cases where the
temperature exceeds 200°C.