LTC4292 datasheet(24/40 Pages) AD

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LTC4291-1/LTC4292

Rev 0

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APPLICATIONS INFORMATION

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 18) 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).

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 19) 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 20) 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.

Figure 17. Type 3 or 4 PSE, 1-Event Class Sequence

42911 F17

VCLASSMIN

VMARKMAX

VSIGMIN

VRESET

DETECT

1ST

CLASS

1ST

MARK

POWER ON

Figure 18. Type 3 or 4 PSE, 3-Event Class Sequence

42911 F18

VCLASSMIN

VMARKMAX

VSIGMIN

VRESET

DETECT

1ST

CLASS

1ST

MARK

2ND

MARK

3RD

MARK

2ND

CLASS

3RD

CLASS

POWER ON

Figure 19. Type 3 or 4 PSE, 4-Event Class Sequence

42911 F19

VCLASSMIN

VMARKMAX

VSIGMIN

VRESET

DETECT

1ST

CLASS

1ST

MARK

2ND

MARK

3RD

MARK

4TH

MARK

2ND

CLASS

3RD

CLASS

4TH

CLASS

POWER ON

42911 F20

VCLASSMIN

VMARKMAX

VSIGMIN

VRESET

DETECT

1ST

CLASS

1ST

MARK

2ND

MARK

3RD

MARK

4TH

MARK

5TH

MARK

2ND

CLASS

3RD

CLASS

4TH

CLASS

5TH

CLASS

POWER ON

Figure 20. Type 4 PSE, 5-Event Class Sequence

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