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

MP8020 Rev. 1.0

MonolithicPower.com

19

2/17/2022

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Table 3: PSE and Allocated Power Indicator

PSE Type

PD Class

PSE Allocated Power Number of Class Cycles

BT

TYP1 TYP2

Type 1

Type 2

Class 0

Class 1

Class 2

Class 3

12.95W

3.84W

6.49W

12.95W

1

High

High

High

Type 2

Class 4

25.5W

2

High

High

Low

Type 3

Type 4

Class 0

Class 1

Class 2

Class 3

12.95W

3.84W

6.49W

12.95W

1

Low

High

High

Class 4

25.5W

2, 3

Low

High

Low

Class 5

Class 6

40W

51W

4

Low

Low

High

Type 4

Class 7

Class 8

62W

71.3W

5

Low

Low

Low

Table 4: Power Demotion Cases

PSE Type

PD Class

PSE Allocated Power Number of Class Cycles

BT

TYP1 TYP2

Type 2

Class 4

12.95W

1

High

High

High

Type 3

Type 4

Classes 4~8

12.95W

1

Low

High

High

Type 3

Type 4

Classes 5~8

25.5W

2, 3

Low

High

Low

Type 3

Type 4

Classes 7~8

51W

4

Low

Low

High

Automatic Maintain Power Signature

To maintain the PSE power supply, the

MP8020 supports automatic maintain power

signature, and the current is configured by a

resistor on the R_MPS pin.

The MP8020 also has one DUTY pin to

configure the R_MPS pin’s voltage duty cycle,

which can compensate the effects of the long

cable and bulk bus capacitors. After VDD

reaches the UVLO rising threshold, the DUTY

pin sources one pulse current to detect the

maintain power signature function duty cycle

setting. Table 5 shows the DUTY pin’s

configuration options. Once VDD falls to the VDD

UVLO falling threshold, the DUTY signal resets.

Table 5: DUTY Configurations

DUTY to GND Resistance (kΩ)

R_MPS Duty

Cycle (%)

Min

Typ

Max

0

0

1.4

6

5.76

7.15

9.09

11.5

17.4

Float

Float

17

With type 1 and type 2 PSE inputs, the MP8020

generates a voltage on the R_MPS pin with a

fixed 37% duty cycle.

Wall Adapter Power Supply

For applications where an auxiliary power

source such as a wall adapter is used to power

the device, the MP8020 features wall power

adapter detection. Once the adapter voltage

(VADP) exceeds about 8.3V, the MP8020

enables wall adapter detection.

The resistor divider connected from VADP to

AUX detects the adapter status. Once the AUX

voltage exceeds the internal reference voltage,

the MP8020 switches the power source from

the PSE to the adapter if the adapter has higher

priority.

GATE2 drives the external N-channel MOSFET

and provides a smooth switch between the PSE

and auxiliary wall adapter with less power loss

than a traditional diode input. After the adapter

supply is enabled, the PG signal is high, the

TYP1 and TYP2 pins output low, and the BT pin

remains high.