PM8803

PD interface

Doc ID 018559 Rev 2

19/34

Figure 6.

PM8803: reference schematic of the PoE classification logic

The classification resistor can be disconnected for the following reasons:

–

the classification has been successfully completed

–

an auxiliary power source has been connected

–

the device is in thermal protection

Designers can set the current by changing the value of the external resistor according to the

following table.

4.3

Indication of successful 2-event classification

The PM8803 is capable of recognizing whether it is connected to a PSE performing 1-event

or 2-event physical layer classification by asserting the T2P signal.

T2P is an open-drain, active-low signal which is asserted in case a successful 2-event

classification event is completed.

T2P will be asserted as soon as the high-voltage startup regulator output is stable. ( see

Figure 7 and Figure 8 for timing sequences). If the PM8803 sees a 1-event classification or

no classification, T2P is pulled up and the main circuit in the PD can try to establish an

LLDP connection to negotiate the power. No LLDP response from the PSE means that the

PD is connected to a Type1 PSE, and only 13 W input power will be available.

Table 7.

Value of the external classification resistor for the different PD classes of

power

Class

PD max average power (W)

013

2k

13.84

150

26.49

80.6

313

51.1

425.5

35.6

VDD

VSS

+

-

1.4V

CLS

EN

Thermal_alarm

Class_enable

Aux_enabled

PM8803

AM045096v1