LTC4292 datasheet(21/40 Pages) AD

21 / 40 page

LTC4291-1/LTC4292

Rev 0

For more information www.analog.com

APPLICATIONS INFORMATION

Table 6. Port Detection Status

MEASURED PD SIGNATURE

(TYPICAL)

PORT DETECTION RESULT

Incomplete or Not Yet Tested

Detect Status Unknown

VPD < 1V

Short Circuit

RPD < 17k

RSIG Too Low

17k < RPD < 29k

Detect Good, Single-Signature PD

RPD > 29k

RSIG Too High

RPD > 50k

Open Circuit

VPD > 10V

Port Voltage Outside Detect Range

Connection Check = INVALID

Connection Check Invalid

Connection Check = DUAL or

Channel Detection Results Differ

Refer to Channel Detect Results

Table 7. Channel Detection Status

MEASURED PD SIGNATURE

(TYPICAL)

CHANNEL DETECTION RESULT

Incomplete or Not Yet Tested

Detect Status Unknown

VPD < 1V

Short Circuit

CPD > 2.7μF

CPD Too High

RPD < 17k

RSIG Too Low

17k < RPD < 29k

Detect Good, Dual-Signature PD

RPD > 29k

RSIG Too High

RPD > 50k

Open Circuit

VPD > 10V

Channel Voltage Outside Detect Range

Connection Check = INVALID

Connection Check Invalid

Connection Check = SINGLE or

Channel Detection Results Match

Refer to Port Detect Result

More on Operating Modes

The port’s operating mode determines when the

LTC4291-1/LTC4292 runs a detection cycle. In manual

mode, the port will idle until the host orders a detect cycle.

It will then run detection, report the result, and return to

idle to wait for another command.

In semi-auto mode the LTC4291-1/LTC4292 autono-

mously polls a port for PDs, but it will not apply power

until commanded to do so by the host. The Port Status

and Channel Status registers are updated at the end of

each detection/classification cycle.

In semi-auto mode, if a valid signature resistance is

detected and classification is enabled, the port will classify

the PD and report that result as well. The port will then

wait for at least 100ms, and will repeat the detection cycle

to refresh the data in the Port Status registers.

The port will not turn on in response to a power-on com-

mand unless the current detect result is Detect Good. Any

other detect result will generate a tSTART fault if a power-on

command is received.

Behavior in auto mode is similar to semi-auto; however,

after Detect Good is reported and the port is classified, it

is automatically powered on without host intervention. In

auto mode the ICUT-2P, ILIM-2P, and PCUT-4P thresholds are

automatically set; see the Reset and the AUTO Pin section

for more information.

Detection is disabled for a port when the LTC4291-1/

LTC4292 is initially powered up with AUTO low, when

the port is in shutdown mode, or when the corresponding

Detect Enable bit is cleared.

Detection of Legacy PDs

Proprietary PDs that predate the original IEEE 802.3af

standard are commonly referred to today as legacy PDs.

One type of legacy PD uses a large common-mode capaci-

tance (>10μF) as the detection signature. Note that PDs in

this range of capacitance are defined as invalid, so a PSE

that powers legacy PDs is noncompliant with the IEEE

standard. The LTC4291-1/LTC4292 can be configured to

detect this type of legacy PD. Legacy detection is disabled

by default, but can be manually enabled on a per-port

basis. When enabled, the port will report Detect Good

when it sees either a valid IEEE PD or a high-capacitance

legacy PD. With legacy mode disabled, only valid IEEE

PDs will be recognized.

If a nonstandard PD presents an invalid detection signa-

ture not included by legacy detection, the LTC4291-1/

LTC4292 may be configured to perform classification and/

or apply power regardless of detection result. To accom-

plish this, the LTC4291-1/LTC4292 introduces per-port

Force Power and Class Event overrides. These overrides

intentionally defeat compliance checks. See the LTC4291

Software Programming documentation for details.

LTC4292 датащи(PDF) 21 Page - Analog Devices

LTC4292 датащи(HTML) 21 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

датащи скачать

ссылки URL