LT4295 datasheet(19/50 Pages) AD

19 / 50 page

LTC9101-1/

LTC9102/LTC9103

Rev. 0

For more information www.analog.com

802.3at Mode

The LTC9101-1/LTC9102/LTC9103 may be configured as

a 2-pair (802.3at or 802.3bt) or 4-pair 802.3bt PSE. All

802.3bt-compliant PSEs are fully backwards compatible

with existing 802.3at Type 1 and Type 2 PDs as shown

in Table 1. In addition to full compatibility, 802.3bt PSEs

extend support for lower standby power, enhanced cur-

rent limit timing, and dynamic power management to all

PD Types (as supported by the PD application).

Table 1. PSE Maximum Delivered Power, Per-Port

DEVICE

PSE

STANDARD

802.3at

802.3bt

TYPE

802.3at

13W

13W*

25.5W

802.3bt

13W*

25.5W*

51W

13W*

25.5W*

51W*

71.3W

*Indicates PD allocated less power than requested.

The LTC9101-1 supports operation as an 802.3at com-

pliant PSE. This feature is available in both 2-pair and

4-pair modes.

Note that an 802.3at PSE will not pass an 802.3bt PSE

compliance test, and an 802.3bt PSE will not pass an

802.3at PSE compliance test. This is by design of the

respective standards. 802.3at and 802.3bt devices are

designed to be interoperable.

Table 2. 802.3at vs 802.3bt Features

FEATURE

802.3at

802.3bt

First Class Event

Short

Long

First Mark Event (15W Mode) No

Yes

Limit Timer

No (Uses Cutoff Timer) Yes

Connection Check

Yes

Active Alternative(s)

2-Pair: A

4-Pair: A and B

Maximum Class Events

Maximum Available Power

Class 4

2-Pair: Class 4

4-Pair: Class 8

Short MPS

Yes

Autoclass

Yes

PoE BASICS

Common Ethernet data connections consist of two or

four twisted pairs of copper wire (commonly known

as Ethernet cable), transformer-coupled at each end to

avoid ground loops. PoE systems take advantage of this

coupling arrangement by applying voltage between the

center-taps of the data transformers to transmit power

from the PSE to the PD without affecting data transmis-

sion. Figure 11 and Figure 12 show high level PoE system

schematics.

To avoid damaging legacy data equipment that does not

expect to see DC voltage, the PoE standard defines a

protocol that determines when the PSE may apply and

remove power. Valid PDs are required to have a specific

25k common-mode resistance at their input. When such

a PD is connected to the cable, the PSE detects this sig-

nature resistance and applies power. When the PD is

later disconnected, the PSE senses the open circuit and

removes power. The PSE also removes power in the event

of a current fault or short circuit.

When a PD is detected, the PSE looks for a classification

signature that tells the PSE the maximum power the PD

will draw. The PSE can use this information to allocate

power among several ports, to police the current con-

sumption of the PD, or to reject a PD that will draw more

power than the PSE has available.

New in 802.3bt

The 802.3bt specification introduces several new features:

Type 3 and Type 4 PSEs may provide power over all

four pairs (both pairsets), depending on connected PD

characteristics.

Type 3 and Type 4 PDs are required to be capable of

receiving power over all four pairs (both pairsets).

Type 3 and 4 PDs can be formed as either a single-

signature PD or dual-signature PD. A single-signature

PD presents the same valid signature resistor to both

pairsets simultaneously (see Figure 11). A dual-signa-

ture PD presents two fully independent valid detection

signatures, one to each pairset (see Figure 12).

APPLICATIONS INFORMATION

LT4295 датащи(PDF) 19 Page - Analog Devices

LT4295 датащи(HTML) 19 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

датащи скачать

ссылки URL