LT8607 datasheet(8/20 Pages) AD

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LTC9111

Rev. 0

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that the connected PD is compatible, it proceeds to apply

full operating voltage to the PD. In order to stay fully

powered, the PD is required to present a valid Maintain

Full Voltage Signature (MFVS). If the PD is disconnected

or goes to sleep, the PSE detects the absence of MFVS

and removes full operating voltage. The PSE also removes

full operating voltage in the event of a fault.

After removing the full operating voltage, the PSE pro-

vides a very low power standby voltage (3.3V). The

PD can request wakeup in this condition by presenting

a wakeup current signature to the PSE. Thereafter, the

PSE may begin the sequence again to re-establish full

operating voltage.

PORT STATE MACHINE SEQUENCE

The LTC9111 implements a voltage-driven PD state

machine as defined by the IEEE 802.3cg standard. Figure 2

illustrates the time-domain sequence of powering up after

the initial application of power.

In a compliant PoDL system, the PSE will initially apply

voltage in the range of VSLEEP (typical 3.3V). When power is

first applied to the LTC9111, it enters the WAKEUP state. In

the WAKEUP state, the LTC9111 alerts the PSE to its presence

with a wakeup signature, IWAKEUP_PD (typically 1.55mA).

An IEEE 802.3cg compliant PSE and PD perform the

classification step using the Serial Communication

Classification Protocol (see Power Class and SCCP) and

the PSE evaluates if the PD is compatible. If it is, the PSE

proceeds to ramp the port voltage.

The LTC9111 monitors the port voltage as it ramps. Once

the port voltage crosses a threshold of VON, and after

a mandated delay of tPWRDLY, the LTC9111 enters the

MDI_POWER2 state. The LTC9111 ramps up the GATE

pin, turning on the external MOSFET and inrushing the

application capacitance. After inrush, the EN pin is pulled

high to enable the PD application.

WAKEUP

CLASSIFICATION

MDI_POWERDELAY

TIME

9111 F02

MDI_POWER2

MDI_POWER1

DISCONNECT

3.3V

1.55mA

VEN

VOUT

VGATE

VPD

IPD

tPWRDLY

VSIG_DIS

VON

IINRUSH

IOPERATING

VOFF

VSIG_EN

VGATE

VOUT

3.3V

SCCP

• • •

Figure 2. LTC9111 State Machine Sequence (Not to Scale)

OPERATION

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