si3480 Silicon Laboratories, si3480 Datasheet - Page 7

• Manufacturer Part Number: si3480
• Description: Si3480 Power Management Controller
• Manufacturer: Silicon Laboratories

4. 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 start-up sequence
described and automatically starts managing the power among the ports as determined by the configuration pins.
After start-up, the Si3480 controls the power meter and port status LEDs give a visual indication of the status.
4.1. Start-Up LED Sequence
During start-up, the LEDs are lit in the sequence listed in Table 4 (1 second for each step).
4.2. Port Status LEDs
After the start-up sequence, the port status LEDs display the patterns listed in Table 5 to indicate port status.
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.
4.3. 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.
Flashing once every two seconds
Continuously lit
Blinks off once every two seconds
Flashing five times per second
Flashing twice every two seconds
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 volt-
age at the PWRCFG pin in 25 W steps (e.g. 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 determined by
reading the voltage at the PRIOCFG pin.
Port LED Pattern
Table 5. Port LED Pattern Definitions
Table 4. LED Sequence
Detection and Classification in process
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
Rev. 1.0
Action
Meaning
Si3480
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