Si3480MS8-KIT
E
VALUATION
K
IT
U
SER
’
S
G
UIDE FOR TH E
Si3480
POWER
MANAGEMENT CONTROLLER
1. Introduction
In Power over Ethernet (PoE) Power Sourcing Equipment (PSE), typically, not all PoE ports are connected to
loads, and the ports that are connected to loads draw substantially less than the maximum power defined in the
IEEE standard (30 W). For this reason, it is normal to use a power supply that is not capable of supplying full power
to all ports and to add a system-level power management function to deal with the rare situations in which the
system power supply becomes overloaded by selectively not granting power or by turning off ports in priority order.
In these situations, the system user can redistribute loads, add a larger power supply, or add more PSE systems as
needed.
The Si3480 works with the Si3452 PoE controllers and implements power management to enable the use of
smaller, lower-cost, and more efficiently-utilized power supplies in unmanaged PSE systems with up to eight ports.
The Si3480 also supports LED indication of port status and power supply consumption.
The Si3480MS8 evaluation board contains the Si3480 power manager, two Si3452 PoE controllers, a –50 V to
+3.3 V dc-to-dc converter based on an Si3500, status LEDs, and Ethernet coupling circuitry.
For demonstration purposes, Class 3 and Class 4 Powered Device (PD) loads are supplied with the evaluation
system. Various load resistors (also supplied) can be used to simulate normal and overload conditions.
2. Evaluation Board Overview
Figure 1 shows a photo of the evaluation board with highlights of the major functional blocks.
The PoE coupling circuit and Ethernet connectors are arranged as a “mid-span” power injector. Ethernet without
power is connected to the top row of connectors, and Ethernet with power injected is connected to the bottom row
of connectors. J300 is for the four ports connected to U1, and J301 is for the four ports connected to U2. If only the
PSE function is being evaluated, only the bottom row of connectors needs to be used. Table 1 lists the contents of
the Si3480MS8 evaluation kit.
Table 1. Si3480MS8 Evaluation Kit Contents
Part Number
Si3480-EVB
Si3402ISO-EVB
Si3402ISO-C4-EVB
Quantity
1
2
1
3
3
Description
The Si3480 evaluation board shown in Figure 1.
A powered device with Class 3 signature (15.4 W maximum).
A powered device with Class 4 signature (30 W maximum).
Ethernet cables for connecting the powered devices.
Load board with three 5
loads. Each resistor that is connected will
draw about 6.5 W of input power from the PSE.
Rev. 0.2 10/10
Copyright © 2010 by Silicon Laboratories
Si3480MS8-KIT
Si3480MS8-KIT
J1
Si3480
JP1
J2
J3
Si3500 –50 to + 3.3 V
Converter
Power
Programming
Power
Meter
Si3452 Controllers
Port Status LEDs
PoE Coupling Circuit
RJ45 Connectors
Port 1
Port 2
Port 3
Port 4
Port 5
Port 6
Port 7
Port 8
Figure 1. Si3480 Evaluation Board Functional Blocks
2
Rev. 0.2
Si3480MS8-KIT
3. Using the Si3480 Evaluation Board
3.1. Board Power
A nominal 50 V power supply is connected to J101. For high-power (PoE+) support according to the IEEE
standard, the supply voltage should be between 51 and 57 V. For normal power levels, the power supply can be 45
to 57 V. The total power supply wattage is normally in the range of 30 to 150 W. The large diode, D100, will be
forward-biased in case of accidental wrong input polarity. It is recommended that the power supply be connected to
the board and then turned on so as to prevent large inrush current from charging the two 33 µF filter capacitors on
the board.
3.2. Jumper Settings
Jumper JP1 sets the timing configuration. Since the board implements Alterative B wiring, the normal setting of JP1
is tied high (+3.3 V side). The Si3482 can support Alternative A timing by setting JPI low.
Jumpers J1, J2, and J3 set the voltage on the Si3480 programming pins. The voltage is set by a resistor ladder as
shown in Figure 2.
Figure 2. Si3480 Programming Jumpers
The silk-screen numbers 1, 2, 4, 8 refer to the resistor weighting; so, the jumper near the “1” is the MSB, and the
jumper near the “8” is the LSB. The voltage on the output pin (MD in Figure 2) as well as the way in which this is
interpreted by the Si3480 is shown in Table 2.
Table 2. Possible Jumper Settings
Jumper
1
0
0
0
0
0
0
0
2
0
0
0
0
1
1
1
4
0
0
1
1
0
0
1
8
0
1
0
1
0
1
0
J1
Pin Voltage
(V
DD
= 3.3 V) System Power
0.00 V
0.22 V
0.44 V
0.66 V
0.88 V
1.10 V
1.32 V
0
13.3 W
26.7 W
40 W
53.3 W
66.7 W
80 W
Ports 1–3
Ports 1–3 high priority
Ports 1,2
Ports 1,2 high priority
J2
PoE+ Enable
No ports PoE+
Port 1
J3
Port Priority
All same
Port 1 high priority
Rev. 0.2
3
Si3480MS8-KIT
Table 2. Possible Jumper Settings (Continued)
Jumper
1
0
1
1
1
1
1
1
1
1
2
1
0
0
0
0
1
1
1
1
4
1
0
0
1
1
0
0
1
1
8
1
0
1
0
1
0
1
0
1
J1
Pin Voltage
(V
DD
= 3.3 V) System Power
1.54 V
1.76 V
1.98 V
2.20 V
2.42 V
2.64 V
2.86 V
3.08 V
3.30 V
93.3 W
106.7 W
120 W
133.3 W
146.7 W
160 W
173.3 W
186.7 W
200 W
All ports PoE+
All same
Ports 1–7
Ports 1–7 high priority
Ports 1–6
Ports 1–6 high priority
Ports 1–5
Ports 1–5 high priority
J2
PoE+ Enable
Ports 1–4
J3
Port Priority
Ports 1–4 high priority
In a system where the voltage at the pin will be fixed, the jumper arrangement can be replaced with a simple
resistor divider. The A/D reference voltage for the Si3480 is V
DD
; so, as V
DD
varies, the Si3480 is only sensitive to
the ratio of resistors.
3.3. LEDs
Upon power application or reset (by SW1 in the upper left corner), the Si3480 probes to see whether there are one
or two Si3452 ICs connected (4 or 8 ports). The Si3480 then controls the LED display in the startup sequence
described and automatically starts managing the power among the ports as determined by the jumper settings.
After startup, the power meter and port status LEDs give a visual indication of the Si3480 operation.
3.3.1. Start-Up LED Sequence
During startup, the LEDs are lit in the sequence listed in Table 3 (1 second for each step).
Table 3. Startup Sequence
Step
1
2
3
4
5
All LEDs on.
Port 1 LED and either four or eight power meter LEDs to indicate the number of 4-port controllers
found by the Si3480 (no LEDs if no controllers are found).
Port 2 LED and zero to eight power meter LEDs to indicate the provided power as determined by
reading the voltage at the PWRCFG pin in 25 W steps (For example, two LEDs is 50 W).
Port 3 LED and zero to eight power meter LEDs to indicate the number of PoE+ ports as determined
by reading the voltage at the POECFG pin.
Port 4 LED and zero to eight power meter LEDs to indicate the number of high-priority ports as deter-
mined by reading the voltage at the PRIOCFG pin.
Action
4
Rev. 0.2
Si3480MS8-KIT
3.3.2. Port Status LEDs
After the startup sequence, the port status LEDs display the patterns listed in Table 4 to indicate port status.
Table 4. Port LED Pattern Definitions
Port LED Pattern
Flashing once every two seconds
Continuously lit
Blinks off once every two seconds
Flashing five times per second
Flashing twice every two seconds
PoE port is on.
PoE+ port is on with a class 4 PD load (30 W granted).
Port overloaded.
Power denied due to lack of power.
Meaning
Detection and Classification in process.
For a port overload, an open circuit must be seen before the port is re-enabled; that is, the PD must be unplugged,
and the overload must be cleared.
Ports are turned off in priority order if more than the available power is being consumed. If the amount of power
consumed is >10% more than the available power, all low priority ports are shut off immediately.
Ports are not granted power unless there is enough power available to grant the requested power (based on
classification) with 15% margin. The 15% margin generally avoids situations where a port is granted power and
then later turned off due to lack of power.
If a port is turned off or denied power due to a lack of available power, the LED continues flashing twice every two
seconds until enough power is available to turn the port on or the PD is unplugged.
3.3.3. Power Meter LEDs
The power meter LEDs light consecutively, indicating the amount of power that is being consumed. There are eight
LEDs in the power meter. The LEDs will light in bar graph fashion:
Number_LEDs_Lit = 8 x Total_Power_Consumed / (0.85 x Provided_Power – 4 W) (rounded down)
The eighth power meter LED is generally a red LED. If this LED is lit, it means that there is not enough power
available to grant even a Class 1 load power and maintain a 15% margin. The eighth LED is flashed five times per
second if the Si3452 controllers report a power supply undervoltage.
3.4. Demonstration Using the Supplied Loads
The Si3480MS8-KIT ships with three powered devices based on the Si3402 with loads for up to approximately
18 W of input power. The loads are arranged as one to three 5
resistors, which draw 5 W each at the PD output
voltage of 5 V. Due to the PD input diode bridge and the dc-to-dc conversion efficiency, each resistor causes
approximately 6.5 W of power to be drawn from the PSE. This means that the PD will draw 6.5, 13, or 19.5 W from
the PSE, depending on the number of load resistors connected.
The Si3402 loads and resistors can be used to demonstrate most of the operation of the Si3480. In the following
example, it is assumed that the Si3480 board is connected to a 50 V power supply with a capacity of at least 40 W.
Step 1: Set the Jumpers.
Table 5. Jumper Settings
J1
J2
J3
System Power
PoE+ enable
Port priority
0011
0001
0001
40 W of power provided.
Only port 1 is PoE+.
Only port 1 is high priority.
Because the system power is set to 40 W, the power meter display during normal operation is:
Number_LEDs_Lit = 8 x Total_Power_Consumed / (0.85 x 40 W – 4 W) (rounded down)
= Total_Power_Consumed/3.75 W (rounded down)
Rev. 0.2
5
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