PD77728 datasheet(7/44 Pages) MICROCHIP

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PD77728

Functional Descriptions

Data Sheet

DS00003920E - 7

1.3

Digital Processing and Control Block

The digital block communicates with the integrated PoE controller and controls the analog front-end

block. It consists of the following blocks:

• Ports ON/OFF control block

• ILIM and ICLASS control blocks

• IINRUSH control and protection block

• Detection and RPORT control block

• Port voltage and temperature measurement post-processing module

• Port current post-processing module

• RTP module

1.4

PoE Controller

The integrated PoE controller controls both port-level and device-level PoE tasks. The firmware is

pre-programmed into the integrated controller with field-upgradable capability through the I2C host

interface.

The integrated PoE controller provides the following features:

• Host communication interface (Fast-Mode Plus I2C interface, INT_OUT signal)

• OSS fast shut-down control

• Device-level data processing

• Supports PoE firmware download capability from host

• Manages one device 2p and 4p ports configuration

• Device-Level power budgeting and power assignment

1.5

Power

The PD77728 device is designed for low power consumption and low power dissipation, using

cutting-edge process technology and proprietary port’s MOSFET design.

The following two parameters allow a total power dissipation of equal to or less than 2W at TJ = 125

°C:

• Very low channel (port) resistance (typically, 160 mΩ at 25 °C)

• Very low VMAIN quiescent current

The PD77728 device supports any power rail sequencing of the VMAIN and VDD rails.

1.6

Real-Time Protection (RTP)

This section describes the RTP blocks included in the PD77728 device. The device supports multi-

level and real-time support mechanisms. All RTP mechanisms are configured by the PoE controller,

implemented in the digital domain, and directly control the port analog front-end. Each port has its

own RTP protection blocks. This type of design ensures fast-acting protection under all conditions.

1.6.1

Current Overload (TLIM/ILIM) Protection

The configurable ILIM and TLIM parameters are based on the IEEE 802.3bt standard. TLIM and ILIM

threshold levels are selected by firmware based on the assigned class. The port shuts down if it

enters current limit (ILIM) and maintains ILIM for a period of TLIM. Current overload RTP also protects

against repetitive overload conditions, where the port repetitively enters current limit for a duration

less than TLIM, which might result in a device damage due to accumulated overheating. The PD77728

overload protection mechanism disconnects the port if the accumulated power poses danger to the

Safe Operating Area (SOA) of the MOSFET.

PD77728 Datasheet(PDF) 7 Page - Microchip Technology

PD77728 Datasheet(HTML) 7 Page - Microchip Technology

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