PM8805 datasheet(18/45 Pages) STMICROELECTRONICS

18 / 45 page

PM8805 overview

PM8805

18/45

DS12813 Rev 1

Figure 4. DET internal circuitry

4.2

Boot and reset

When the voltage at the input rises above about Voff_det (11.5 V typ.), the PM8805 turns on

its internal circuitries (bandgap reference, bias reference, regulators and control logic) and

enters into the so-called mark range, waiting for the voltage entering into the Classification

range.

When the voltage falls below Vrst_cls (5.2 V typ.), the PM8805 turns off its control logic and

analog circuitries and turns the detection circuitry on again, resetting the results of previous

classifications.

The current consumption when VDD is in the mark range (IDD_mark) acts as a pull-down of

the input voltage and allows a fast reset of the control logic if the cable is disconnected.

4.3

PoE classification

The classification allows the PSE-PD mutual identification, and it is used by PSE to allocate

the power to the PD. The PD also understands which type of PSE is connected, and adapts

its behavior accordingly.

PM8805 complies with both IEEE802.3-2015 1-event and 2-event classification schemes,

and is also capable of multiple event-classification as specified by IEEE802.3bt.

1-event classification in IEEE802.3-2015 is performed by Type1 PSEs capable of powering

PDs up to 12.95 W. They can be classified into 4 classes (class 0 to class 3).

2-event classification is performed by Type2 PSEs and class 4 identifies Type2 PDs

requiring up to 25.5 W.

PM8805 데이터시트(PDF) 18 Page - STMicroelectronics