Silicon Laboratories Si3460 User Manual

Si3460 E
VALUATION
1. Introduction
This document is intended to be used in conjunction with the Si3460 data sheet for designers interested in:
 An introduction to Power-over-Ethernet (PoE) and Power Sourcing Equipment (PSE) design
considerations
 How the Si3460 PSE controller operates in the Si3460-EVB reference design
 Configuring and operating the Si3460-EVB
2. Overview of the Si3460 and Evaluation Board
The Si3460 is a single-port –48 V power management controller for IEEE 802.3af compliant Power Sourcing
Equipment (PSE). The Si3460 operates directly from a 12 or 15 V isolated input supply and integrates a digital
PWM-based dc-dc converter for generating the –48 V PSE output supply. The negative polarity on the PSE supply
provides safety-extra-low-voltage (SELV) compatibility with telephony ports in the same system. The complete
Si3460 reference design (i.e., the Si3460-EVB) also provides full IEEE-compliant classification and detection as
well as a robust disconnect algorithm. Intelligent protection circuitry includes input under-voltage lockout (UVLO),
current limiting, and output short-circuit protection.
The Si3460 is designed to operate completely independently of host processor control. A reset input and an
optional LED status signal is provided to indicate the port status, including detect, power good and output fault
event information for use within the host system.
The Si3460 is pin programmable to support:
 Endpoint and midspan applications, with support for either 10/100BASE-T or 10/100/1000BASE-T
 All four classification power levels specified by the IEEE 802.3 standard
 Classification-based current limiting
 Automatic or manual restart after various fault events are detected
3. Introduction to PoE
IEEE 802.3-2005 clause 33 (formerly IEEE 802.3af) is the standard for providing power to a remote Ethernet
device on the same cable that is carrying data. The power is either carried common mode on one of the data pairs
(for 10/100/1000BASE-T) or on the spare pairs for 10/100BASE-T only applications.
Figures 1 and 2 show the possible connections for the power. The connections shown in Figure 1 should be used
for power injection in an Ethernet midspan, and the connections shown in Figure 2 can be used for either midspan
or endpoint (switch) applications. Designed for use on the PSE side for providing power to a single Ethernet PD
port, the Si3460 can be configured to operate in either midspan or endpoint applications. Although at this time the
existing IEEE specification doesn't specifically allow or prohibit gigabit (10/100/1000BASE-T) midspans, in
midspan mode, the Si3460-EVB is designed to operate in 10/100BASE-T mode, as the power is carried on the
spare pairs. However, the Si3460 controller can also be designed into gigabit endpoints with the power connected
to either the data or spare pairs.
Rev. 1.2 3/13
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Copyright © 2013 by Silicon Laboratories
Si3460- EVB
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Si3460-EVB