LT8301 datasheet(20/46 Pages) AD

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Data Sheet

LTC4296-1

THEORY OF OPERATION

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Rev. 0 | 20 of 46

USAGE CASES

802.3cg-Compliant PSE

The primary usage case for the LTC4296-1 is an 802.3cg-compliant

PSE. With this case, the LTC4296-1 AUTO pin is pulled low and

a host operates the LTC4296-1 ports semimanually through the

states shown in Figure 46. In each state, the LTC4296-1 controls

the port output voltage accordingly.

From a system power-up or device reset, the LTC4296-1 starts in

the disabled state. An LTC4296-1 port is enabled by the host and

moves on to the idle state. The LTC4296-1 then awaits a command

from the host to move on to the next state.

When ready, the host configures the LTC4296-1 port to enter the

detection state. Note that the LTC4296-1 checks the port current

status before moving on to detection.

When the port is in the detection state, the host sets the LTC4296-1

to the classification state and performs the SCCP with a valid PD.

Once the host microcontroller determines that the class of the PD

is compatible, it can then command the port to enter the power-up

state.

During the power-up state, the LTC4296-1 controls inrush and mon-

itors the port output voltage to determine when inrush is complete.

After a successful power-up, the port enters the power-on state and

remains there until the LTC4296-1 detects a current overload fault

or an MFVS timeout, or the device is instructed by the host to exit

power-on when power is no longer available.

If the LTC4296-1 removes power to the port due to an invalid

MFVS, it monitors the port voltage discharge in the settle-sleep

state.

The LTC4296-1 enters the low power, sleep state after a successful

port discharge. In this state, the LTC4296-1 waits for the user, host,

or PD to initiate a wake-up before returning to the detection state.

While in the idle, power-on, settle-sleep, or sleep states, the

LTC4296-1 monitors the port for current overload fault conditions. If

a fault occurs, the LTC4296-1 turns off the port and waits a set time

in the overload state before entering the idle state.

A port that fails to exit either the detection or power-up states

successfully before the maximum allotted time enters the restart

state. The port then waits a set time before re-entering the idle

state.

Figure 46. Simplified 802.3cg-Compliant PSE State Sequence (Not to Scale)

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