Si3454-KIT
Confidential Rev. 0.1
15
6. Operating the System
Each RJ45 connector board has eight LEDs for the eight ports. Each LED is driven by a comparator circuit which
detects when a voltage is forced to the load at the PoE output. When the ports are in auto mode, the LEDs in the
RJ45 connector board 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. Note that the comparator circuits load the ports slightly,
and the LEDs dissipate power from the 3.3 V rail. If performing calibrated tests, it may be desirable to isolate the
comparator circuitry and eliminate any loading. This may be done by removing all jumpers from the connector
board.
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 “Disconnect Enable”), fault
protection, fault recovery, and port monitoring all happen without user intervention. Figure 15 shows the result of
putting Port 1 in Auto mode. Circles indicate the required settings, and the squares indicate that a PD connected to
the port has been detected, classified, and powered. Auto mode may also be enabled on all ports by configuring
J10 and resetting the board by pressing SW1 or cycling power.
The Si3454 normally operates in manual or semi-automatic mode with the AUTO pin is held low. If a positive
voltage is applied to the AUTO pin, the Si3454 enters into fully autonomous operation, independent of a host. The
Si3454 also features dc disconnect detection algorithms to determine when a PD device is disconnected from any
of the eight independent ports. The AUTO mode can be set via the AUTO pin or from the host via I
2
C. At power-up,
the Si3454 reads the voltage on the AUTO pin (which can be set by a resistor divider from VDD to GND). If a
positive voltage is applied, the Si3454 enters into AUTO mode (all ports operate fully autonomously). The AUTO
pin voltage level configures the Si3454’s behavior to register default values. For additional detail on Auto Pin
Configurations, refer to Section 3.2 Operating Modes in the Si3454 data sheet.
If the GUI is left in polling mode, the port status, port current, port voltage are all automatically updated by polling
the appropriate registers of the Si3454.
The Si3454 itself normally powers up as Alternative A, with no detection back-off, meaning the detect function
cycles at its highest rate. This is the most common usage for the Si3454. 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 intended to ensure 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 Si3454 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. In host-controlled mode, to enable the higher power support for a given
port, it is necessary to make multiple selections as described in "5.5.2. Port Configuration" on page 10. When Auto
mode is selected by the Auto jumper, the Si3454 automatically performs the two-event classification and increases
the cut-off current if a Class 4 PD is detected. The Si3402 evaluation board provided with the kit is configured to
provide the Class 4 signature; so, if the PoE+ mode is enabled and the Si3402 is plugged in, the cut-off current is
automatically set to 643.2 mA. Figure 16 shows the result of plugging in a Class 4 PD (into Port1) with PoE+ power
enabled. Class 4-specific settings and results are highlighted.
Summary of Contents for Si3454-KIT
Page 22: ...Si3454 KIT 22 Confidential Rev 0 1 Figure 21 Evaluation Board Top Side ...
Page 23: ...Si3454 KIT Confidential Rev 0 1 23 Figure 22 Evaluation Board Ground Layer ...
Page 24: ...Si3454 KIT 24 Confidential Rev 0 1 Figure 23 Evaluation Board Power Layer ...
Page 25: ...Si3454 KIT Confidential Rev 0 1 25 Figure 24 Evaluation Board Bottom Side ...
Page 35: ...Si3454 KIT Confidential Rev 0 1 35 Figure 32 Connector Board Bottom Side ...
