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LTC9101-1/

LTC9102/LTC9103

Rev. 0

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APPLICATIONS INFORMATION

from a higher Class SS PD. Power limited IEEE 802.3bt

PSEs may issue three classification events to Class 5 and

higher SS PDs in order to demote those PDs to 25.5W.

Type 3 and 4 PSEs present four classification events (see

Figure 20) to Class 5 and 6 SS PDs if sufficient power is

available. Class 5 and 6 SS PDs present class signature

4 on the first two events. Class 5 and 6 SS PDs present

class signature 0 or 1, respectively, on the subsequent

events. Power limited PSEs may issue four events to

Class 7 and 8 SS PDs in order to demote those PDs to

51W.

Type 4 PSEs present five classification events (see

Figure 21) to Class 7 and 8 SS PDs if sufficient power is

available. Class 7 and 8 PDs present class signature 4 on

the first two events. Class 7 and 8 SS PDs present class

signature 2 or 3, respectively, on the subsequent events.

802.3bt Classification of Dual-Signature PDs

Classification and power allocations to each pairset of a

dual-signature (DS) PD are fully independent. For exam-

ple, a DS PD may request Class 1 (3.84W) on one pairset

and a Class 4 (25.5W) on the second pairset for a total

PD requested power of 29.3W. As such, all classification

is performed to the pairset entity as opposed to the PD.

The terms should be considered interchangeable for the

remainder of this section.

Type 3 and Type 4 PSEs issue three classification events

(see Figure 19) to all Class 1 through 4 DS PDs.

Power limited Type 3 and Type 4 PSEs may issue a class

reset to Class 4 and 5 DS PDs in order to demote those

PDs to 13W (see Understanding 4PID section).

Power limited Type 3 and Type 4 PSEs may issue only

three events to Class 5 DS PDs in order to demote those

PDs to 25.5W.

Type 4 PSEs present four classification events (see

Figure 20) to Class 5 DS PDs if sufficient power is avail-

able. Class 5 DS PDs present class signature 4 on the first

two events and class signature 3 on subsequent events.

classification supersede Type 1 and Type 2 classifica-

tion. Type 1 and Type 2 classification are described in

the preceding sections as a historical reference and to

define common terminology such as power demotion,

class events, mark events, and electrical parameters.

IEEE 802.3bt defines eight PD Classes for single-signature

PDs and five PD Classes for dual-signature PDs, as shown

in Table 11.

Classification treatment of single-signature and dual-

signature PDs differs. The following sections explain the

Physical Layer classification of each PD configuration

separately.

Table 11. Type 3 and Type 4 PD Classifications by

PD Configuration

SINGLE-SIGNATURE PDs

DUAL-SIGNATURE PDs

CLASS

PD AVAILABLE

POWER

CLASS

CHANNEL AVAILABLE

POWER*

Class 1

3.84W

Class 1

3.84W

Class 2

6.49W

Class 2

6.49W

Class 3

13W

Class 3

13W

Class 4

25.5W

Class 4

25.5W

Class 5

40W

Class 5

35.6W

Class 6

51W

Class 7

62W

Class 8

71.3W

*Dual-signature PD total available power is the sum of both channels

available power. Class signatures may differ between channels of a port,

e.g., Class 3 + Class 4 = 13W + 25.5W = 38.5W.

802.3bt Classification of Single-Signature PDs

Type 3 and Type 4 PSEs issue a single classification event

(see Figure 18) to Class 0 through 3 single-signature (SS)

PDs. A Class 0 through 3 SS PD presents its class signa-

ture to the PSE and is then powered on if sufficient power

is available. Power limited 802.3bt PSEs may also issue a

single classification event to Class 4 and higher SS PDs in

order to demote those PDs to 13W. See Figure 18.

Type 3 and 4 PSEs present three classification events

to Class 4 SS PDs (see Figure 19) if sufficient power is

available. Class 4 SS PDs present class signature 4 on

all events. The third event differentiates a Class 4 SS PD

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