LTC4292 datasheet(21/39 Pages) AD

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Data Sheet

LTC9101-2B/LTC9102

APPLICATIONS INFORMATION

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Rev. 0 | 21 of 39

New in 802.3bt

The 802.3bt specification introduces several new features:

►

Type 3 PSEs may be constructed as 2-pair or 4-pair devices.

Type 4 PSEs shall be constructed as 4-pair devices.

►

Type 3 and Type 4 PSEs may provide power over all four

pairs (both pairsets), depending on the PSE construction and

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 36). A dual-signature PD presents two fully independent

valid detection signatures, one to each pairset.

►

Type 3 single-signature PDs request exactly one of six possible

power levels: 3.84W, 6.49W, 13W, 25.5W, 40W, or 51W.

►

Type 3 dual-signature PDs request exactly one of four possible

power levels on each pairset: 3.84W, 6.49W, 13W, or 25.5W.

The total PD requested power is the sum of the requested power

on both pairsets.

►

Type 3 PD Classes overlap with Type 1 and 2 Classes in order to

provide additional Type 3 feature sets at lower power levels.

►

Type 4 single-signature PDs request exactly one of two possible

power levels: 62W or 71.3W.

►

Type 4 dual-signature PDs request exactly 35.6W on at least one

pairset and one of five possible power levels on the other pairset:

3.84W, 6.49W, 13W, 25.5W, or 35.6W. The total PD requested

power is the sum of the requested power on both pairsets.

►

Classification is extended to a possible maximum of five class

events. The additional events allow for unique identification of

existing and new PD Classes.

►

Type 3 and 4 PSEs issue a long first class event to advertise

Type 3 and 4 feature support to attached PDs.

►

Lower standby power is enabled by shortening the length of the

maintain power signature pulse (short MPS). The PD duty cycle

drops from ~23% to ~2%. A PD is allowed to present short MPS

if the PSE issues a long first class event.

►

Power management is augmented by Autoclass, an optional

feature for 802.3bt PSEs and PDs. In an Autoclass system the

maximum PD power is measured and reported to the PSE host,

enabling the PSE to reclaim output power not used by the PD

application and losses in the Ethernet cabling (Table 7). See the

Autoclass section and LTC9101-2B Software Interface guide for

details.

Table 7. IEEE-Specified Power Allocations, Single-Signature PD

CLASS

PSE OUTPUT

POWER

ALLOCATED CABLING

LOSS

PD INPUT POWER

0.16W

3.84W

6.7W

0.21W

6.49W

14W

13W

30W

4.5W

25.5W

45W

40W

60W

51W

75W

13W

62W

90W

18.7W

71.3W

DEVICE CONFIGURATION

An LTC9101-2B can control between one and four LTC9102. Each

LTC9102 controls 12 power channels. Thus, each LTC9101-2B can

control up to 48 power channels.

As described later in the Bus Addressing section, each group of

four channels occupies a single I2C address.

Table 8. Device Configuration Options

CFG[1:0]

NUMBER OF PORTS

NUM 9102s

I2C ADDRs

I2C ADDRESS OFFSET

0 (00b)

✓

1 (01b)

✓

2 (10b)

✓

3 (11b)

✓

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