MP8020 – IEEE 802.3af/at/bt, PoE, POWERED DEVICE INTERFACE

MP8020 Rev. 1.0

MonolithicPower.com

16

2/17/2022

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© 2022 MPS. All Rights Reserved.

OPERATION

The MP8020 is an IEEE802.3af/at/bt-compliant,

Power over Ethernet (PoE), powered device

(PD). The device includes all the functions of

IEEE

802.3af/at/bt,

including

detection,

classification, input current (IIN) control, a 100V

hot-swap MOSFET, and automatic maintain

power signature functionality.

Detection

The MP8020 integrates an internal detection

resistor. When the power-sourcing equipment

(PSE) applies two safe voltages between 2.7V

and 10.1V to the MP8020, the MP8020 typically

shows a 25kΩ resistance between the VDD and

GND pins.

Classification

The PSE distributes power to the PDs based on

the classification results. Classification mode is

active between 14.5V and 20.5V. The MP8020

presents different currents in classification

mode (see Table 1).

Table 1: Different Classification Power Rating and Setting with the MP8020

PD

Class

Power

Rating (W)

Class Cycle with

Max Power

CLSA

Signature

CLSB

Signature

CLSA

Resistor

CLSB

Resistor

0

0.44 to 12.95

1

0

0

578

578

1

0.44 to 3.84

1

1

1

110

110

2

3.84 to 6.49

1

2

2

62

62

3

6.49 to 12.95

1

3

3

41.2

41.2

4

12.95 to 25.5

2, 3

4

4

28.7

28.7

5

25.5 to 40

4

4

0

28.7

578

6

40 to 51

4

4

1

28.7

110

7

51 to 62

5

4

2

28.7

62

8

62 to 71.3

5

4

3

28.7

41.2

IEEE802.3bt supports an 8-level class power

rating, with up to 5 classification cycle

operations. These classification cycles have the

below functions:

 All PSEs perform one cycle classification for

the class 0, class 1, class 2, and class 3

PDs.

 Type 2 PSEs perform 2-cycle classification

if a class 4 signature is detected during the

first class cycle.

 Type 3 and type 4 PSEs start their third

cycle classification if a class 4 signature is

detected during the first and second class-

cycle. Based on the third cycle classification

result, the Type 3 and Type 4 PSEs follow

one of the operations listed below:

o If the third classification result is a class

4 signature, classification stops and

there is a class 4 PD.

o If the third classification results in a

class 0 or class 1 signature, the devices

continue

to

the

fourth

cycle

classification.

o If the third classification result is class 2

or class 3 signature, the type 4 PSE

performs a fourth and fifth cycle

classification.

The MP8020 performs a class signature signal

with the CLSA pin during the first and second

class cycles. The device performs a class

signature signal with the CLSB pin in the

remaining class cycles, unless VDD drops to the

mark event reset threshold.

Both CLSA and CLSB use the same output

voltage (VOUT) for classification. The maximum

output current (IOUT) is limited for self-protection.

Under-Voltage Lockout (UVLO) and the

Power Supply Voltage

The MP8020 integrates one under-voltage

lockout (UVLO) circuit with a large hysteresis.

The UVLO block ensures that the MP8020

starts up when VDD exceeds 40V and shuts

down when VDD drops below 30V.

The MP8020 also has an inrush current limit

function during start-up. This current is about

1/7 of the steady state current limit, which is

configured by the ILIM pin.