Si3462-EVB

Rev. 1.2

7

6. Detailed Description of the Si3462 PSE Controller

The Si3462 is a fully IEEE compliant PoE/PoE+ PSE power management controller. The Si3462 is specifically

designed and configured to work with an applications circuit (Si3462-EVB) with which it implements a single port

PSE solution for either Midspan or Endpoint PoE applications.

Refer to the detailed evaluation board schematics in "9. Si3462-EVB Schematics" on page 17 and "11.

Si3462-EVB PCB Layouts" on page 23; the overall functionality is described below. Representative waveforms are

shown in "8. Output Voltage and Load Current Waveforms" on page 13.

6.1. Initialization and Operating Mode Configuration

The Si3462 is initialized at powerup or whenever Pin 8 (RST) is held low and then allowed to transition high. Upon

reset (RST asserted low), the voltage at the STATUS pin (as determined by the DIP switch and the associated

resistor network) is sensed to determine the operating mode of the Si3462. The detection process begins

immediately after initialization.

The following operating mode parameters can be set with the DIP switches:



Endpoint or Midspan mode controls the back off timing per IEEE specifications.



Restart action on Fault or Overload determines whether the Si3462 automatically restarts after 2 s when a

fault or overload condition (e.g., input UVLO, output short-circuit event, classification power level

exceeded) is detected or waits to restart until an open-circuit condition is sensed.



Available power level (and PSE Type specifying the classification method used).

Table 2. Operating Modes1,2,3,4,5

DIP Switch

Configuration

Status Pin

Voltage (V)

Operating Mode

PSE

Type

Midspan/

Endpoint

Restart Action

on Fault or

Overload Event

Condition

Availab

le

Power

Classification

BOM5,6

Classification

Mark BOM5,7

< 0.122

2

Midspan

Restart after

disconnection

30 W

No

No

0.122 to 0.338

1

Midspan

Restart after

disconnection

7W

Yes

No

0.338 to 0.548

1

Midspan

Restart after

disconnection

15.4 W

No

No

0.548 to 0.756

2

Midspan

Restart after

disconnection

30 W

Yes

Yes

Notes:

1. After power-up, the STATUS pin drives the base of an NPN transistor that controls an LED.

2. There is a trade-off in selecting the mode setting resistor values between voltage step accuracy and additional

worst-case supply current. For high-value resistors, the base current will alter the voltage steps while low-value resistors

may place higher load on the STATUS pin while driving the LED. The suggested resulting parallel resistance used by the

Si3462-EVB is 2.0 k.

3. Each mode setting resistor should be connected either to GND or +3.3 V through the DIP switch. Care should be taken

not to short the +3.3 V supply to GND.

4. A reset is required after a DIP switch position change for the new mode to take effect.

5. Refer to the Si3462-EVB User Guide to understand the components required to support Classification and Mark.

6. Classification components are R14,R15,R16C8, D5, Q6, and Q17.

7. Classification mark components are Q2, R24, and R25.