Sifos Technologies PowerSync PSA100, Technical Reference Manual, Page: 11 / 147

PowerSync Analyzer Reference Manual
March 9, 2010 Sifos Technologies page 11
Minimum Current Maximum Current Units Classification
0 5 mA Class 0
8 13 mA Class 1
16 21 mA Class 2
25 31 mA Class 3
35 45 mA Class 4
The PSE is free to make decisions regarding current
measurements that fall between the above bands.
Classification must be completed in 75 mSec, so typically
classification involves a short duration pulse with amplitude
between 15.5 and 20.5 Volts. A “single-event” class pulse
(see Figure 2.2) may return to zero or may hold its value (or
anything in between) following completion of classification.
The 802.3at specification requires that all compliant PSE’s
perform classification and it adds an expanded classification
measurement option that allows PSE’s to “signal” their
802.3at high power capability to a powered device while
reading the power demand of the powered device. The “2-
event” classification (see Figure 2.2) involves 2 successive
classification current measurements separated by a “mark” region. The 802.3at PD must be capable of discharging the
class voltage in order to “see” this mark region and thereby detect the presence of an 802.3at capable PSE. The 2-event
classification cannot ever drop below 2.8V, or the PD will reset and forget that the PSE is 802.3at capable.
802.3at PSE’s may use either single-event or 2-event PD classification. Those that use single event method are
required to us MAC layer LLDP protocol to negotiate power with an 802.3at PD following initial PD power-up.
2.1.4. Power-Up
Following classification, assuming the PSE performs
this step, the PSE will apply power (voltage and
current) to the PD. A PSE is required to furnish
between 44 V (50 V for Type-2 PSE’s) and 57 V to
at the PSE interface. There are two timing criteria of
interest: Time from end-of-detection until power-up
is complete and the rise time of the PoE voltage.
The first parameter includes classification time and
must be under 400 mSec. The power-on rise time is
required to be longer than 15
μ
sec.
Other parameters of interest during the power-on
event are the initial (in-rush) current and the peak-to-
peak ripple and noise amplitude. PSE’s are required
to clamp in-rush current to 450 mA regardless of the
transient load provided by a PD. AC ripple
(including AC MPS signals) under 500 Hz in frequency should not exceed 500 mVpp. AC noise in the region below
150 KHz should not exceed 200 mVpp.
While the PSE is furnishing power to the PD, the PSE is responsible for regulating total power delivered to the PD.
802.3af compliant PSE ports must have capability of furnishing a minimum of 15.4 watts given connection to a “Class
0” PD. High Power 802.3at compliant PSE ports must have capability to furnish at least 30 watts given connection to a
“Class 4” PD. The maximum power capacity of a PSE port is limited by a current ceiling defined as
Icut
in the 802.3
specification. Given the ceilings specified, an 802.3af compliant PSE might theoretically furnish a maximum of 22.7
watts while a 2-pair, high power, 802.3at compliant PSE might theoretically supply up to 38.9 watts continuous power.
Practically speaking, typical port power capacity will be relatively close to the minimum required values.
802.3 Classification Pulses
15.5
20.5
Volts
DC
Vclass
Tpdc
Single Event
Class Pulse 2-Event
Class Pulse
10.0
7.0
Vmark
Tcle
Tme
802.3 Classification Pulses
15.5
20.5
Volts
DC
Vclass
Tpdc
Single Event
Class Pulse 2-Event
Class Pulse
10.0
7.0
Vmark
Tcle
Tme
Figure 2.2
802.3af & 802.3at Classification
Figure 2.3
802.3af Power-Up
802.3 Power-Up
20
44
Detection
Vol
ts
DC
10
Classification
Tpon
57
Vport
Inrush Load
Vpp
Trise
802.3 Power-Up
20
44
Detection
Vol
ts
DC
10
Classification
Tpon
57
Vport
Inrush Load
Vpp
Trise