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LTC4270/LTC4271

42701f

Extended Power LTPoE++

A-grade LTC4270/LTC4271 parts add the capability to

autonomously deliver up to 90W of power to the PD.

LTPoE++ PDs may forgoe 802.3 LLDP support and rely

solely on the LTPoE++ Physical Classification to negotiate

power with LTPoE++ PSEs; this greatly simplifies high-

power PD implementations.

LTPoE++ may be optionally enabled for A-grade LTC4270/

LTC4271s by setting both the High Power Enable and

LTPoE++ Enable bits.

The higher levels of LTPoE++ delivery impose additional

layout and component selection constraints. LTC4270 pin

selects allow the AUTO pin mode LTC4271 to autonomously

power up to supported power levels. If the AUTO pin is

high, the XIO1 and XIO0 pins are sampled at reset to de-

termine the maximum deliverable power. PDs requesting

more than the available power limits are not powered.

Table 1. LTPoE++ AUTO Pin Mode Maximum Delivered Power

Capabilities

POWER

XIO1

XIO0

35W

45W

70W

90W

BACKWARDS COMPATIBILITY

The LTC4270/LTC4271 chipset is designed to be backward

compatible with the LTC4266, operating in Type 2 mode,

without software changes; only minor layout changes

are required to implement a fully compliant IEEE 802.3at

design.

Some LTC4266 registers have been obsoleted in the

LTC4270/LTC4271 chipset. The obsoleted registers are not

required for 802.3at compliant PSE operation. For more

details about software differences between the LTC4266

and LTC4270/LTC4271, refer to the LTC4271 Software

Programming document.

Operation with high power mode disabled is obsoleted in

the LTC4270/LTC4271 chipset. All operations previously

available in low power mode are fully implemented as a

subset of the high power mode capabilities.

APPLICATIONS INFORMATION

OPERATING MODES

The LTC4270/LTC4271 includes 12 independent ports,

each of which can operate in one of four modes: manual,

semi-auto, AUTO pin, or shutdown.

Table 2. Operating Modes

MODE

AUTO

OPMD DETECT/

CLASS

POWER-UP

AUTOMATIC

ICUT/ILIM

ASSIGNMENT

AUTO Pin

11b

Enabled

at Reset

Automatically

Yes

Reserved

11b

N/A

Semi-auto

10b

Host

Enabled

Upon

Request

Manual

01b

Once

Upon

Request

Upon

Request

Shutdown

00b

Disabled

In manual mode, the port waits for instructions from the

host system before taking any action. It runs a single

detection or classification cycle when commanded to by

the host, and reports the result in its Port Status register.

The host system can command the port to turn on or off

the power at any time.

In semi-auto mode, the port repeatedly attempts to detect

and classify any PD attached to it. It reports the status of

these attempts back to the host, and waits for a command

from the host before turning on power to the port. The

host must enable detection (and optionally classification)

for the port before detection will start.

AUTO pin mode operates the same as semi-auto mode

except it will automatically turn on the power to the port if

detection is successful. AUTO pin mode will autonomously

set the ICUT and ILIM values based on the class result. This

operational mode is only valid if the AUTO pin is high.

In shutdown mode, the port is disabled and will not detect

or power a PD.

Regardless of which mode it is in, the LTC4270/LTC4271

will remove power automatically from any port that gener-

ates a current limit fault. It will also automatically remove

power from any port that generates a disconnect event if

disconnect detection is enabled. The host controller may

also command the port to remove power at any time.

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