LTC4271 datasheet(18/32 Pages) LINER

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LTC4290/LTC4271

429071f

OPERATING MODES

The LTC4290/LTC4271 includes eight independent ports,

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

semi-auto, AUTO pin, or shutdown.

Table 1. 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

detectionissuccessful.AUTOpinmodewillautonomously

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

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

reset or power-up and remains high during operation.

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

or power a PD.

APPLICATIONS INFORMATION

Regardless of which mode it is in, the LTC4290/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.

Reset and the AUTO/MID Pins

The initial LTC4290/LTC4271 configuration depends on

the state of the AUTO and MID pins during reset. Reset

occurs at power-up, or whenever the RESET pin is pulled

low or the global Reset All bit is set. Changing the state of

AUTO or MID after power-up will not properly change the

portbehavioroftheLTC4290/LTC4271untilaresetoccurs.

Althoughtypicallyusedwithahostcontroller,theLTC4290/

LTC4271 can also be used in a standalone mode with no

connection to the serial interface. If there is no host pres-

ent, the AUTO pin must be tied high so that, at reset, all

portswillbeconfiguredtooperateautomatically.Eachport

will detect and classify repeatedly until a PD is discovered,

set ICUT and ILIM according to the classification results,

apply power to valid PDs, and remove power when a PD

is disconnected.

Table 2 shows the ICUT and ILIM values that will be auto-

matically set in standalone (AUTO pin) mode, based on

the discovered class.

Table 2. ICUT and ILIM Values in Standalone Mode

CLASS

ICUT

ILIM

Class 1

112mA

425mA

Class 2

206mA

425mA

Class 3 or 0

375mA

425mA

Class 4

638mA

850mA

The automatic setting of ICUT and ILIM values only occurs

if the LTC4290/LTC4271 is reset with the AUTO pin high.

Ifthestandaloneapplicationisamidspan,theMIDpinmust

be tied high to enable correct midspan detection timing.

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