SI3452MS8-EVB Silicon Laboratories Inc, SI3452MS8-EVB Datasheet - Page 13

• Manufacturer Part Number: SI3452MS8-EVB
• Manufacturer: Silicon Laboratories Inc

Specifications of SI3452MS8-EVB

• Lead Free Status / Rohs Status: Supplier Unconfirmed

Si3452MS8-EVB
6. Operating the System
The RJ45 connector board has 8 LEDs for the 8 ports. The LEDs are driven by a comparator circuit with a
threshold of about 2 V. When the ports are in auto mode, the LEDs in the RJ45 connector board will flash,
indicating the detection cycle until a valid PD is connected. Once a valid PD is connected and the port is turned on,
the LEDs will glow steadily until the PD is disconnected. Once the PD is connected, the port current will be
displayed on the GUI.
The easiest way to get started is to put all of the ports in Auto mode. In Auto mode, detection, classification, power
management based on classification (Icut setting), disconnect (when enabled by "Dis Enable"), fault protection,
fault recovery, and port monitoring all happen without user intervention.
If the GUI is left in polling mode, the port status, port current, Vee voltage are all automatically updated by polling
the appropriate registers of the Si3452.
The Si3452 itself normally powers up as Alternative A, which means there is no detection back-off. This is the most
common usage for the Si3452. The RJ-45 connector board for the evaluation kit is configured to inject the power
on the "spare pairs" of the Ethernet cable, which is the Alternative B or "Midspan" connection. Detection back off is
helpful for insuring that a midspan and an endpoint do not compete with each other and result in a failure to provide
power. With detection back-off, the time between detection pulses is increased to just over two seconds so as not
to compete with the normal (approximately three times per second) detection of an endpoint. If detection back-off is
required, click the "Midspan" button to toggle this mode. You will see that the LEDs on the connector board now
flash at the slower detection speed. To toggle the mode back to standard detection timing, click the button again.
The Si3452 in auto mode is fully-compliant with the 802.3at standard (often called PoE+), which allows up to 30 W
to be delivered over the Ethernet cable. To enable the higher power support for a given port, click the "2x power"
check box for that port.
In 2x power mode, the Si3452 automatically performs the two-event classification and increases the cut-off current
if a class 4 PD is detected. The Si3401 evaluation board provided with the kit is configured to provide the Class 4
signature; so, if the 2x mode is enabled and the Si3401 PD is plugged in, the cut-off current is automatically set to
643 mA. The screen shot in Figure 13 shows the result of plugging in a class 4 PD (into Port1) with 2x power
enabled.
Figure 13. Result of Putting Port 1 into Auto and POE+ Mode
and Plugging in the Si3401 Class 4 PD with a 10  Load
Rev. 0.4
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