PM8805 datasheet(8/45 Pages) STMICROELECTRONICS

8 / 45 page

Pin description and connection diagram

PM8805

8/45

DS12813 Rev 1

13, 14

GND12

System low potential; it is the return of the first active bridge and it is

connected to the Source of the IN12 low-side MOSFET. It must be

connected to the system AGND, together with the other bridges'

grounds.

17, 18, 29,

38, 39

VOB

System high potential; it is the positive potential of the active bridges

and it is connected to the drain of the internal bridge, high-side

MOSFETs.

Protect the rectified voltage with a TVS and a 100nF X7R 100V

rated ceramic capacitor as per IEEE802.3 standard.

19, 20, 23

IN36

Input for the signals connected to "Tx and Rx" pairs. This signal

along with IN12 signals is used to feed the 1st internal bridge.

21,22

GND36

System low potential; it is the return of the first active bridge and it is

connected to the Source of the IN36 low-side MOSFET. It must be

connected to the system AGND, together with the other bridges'

grounds.

CTRL

Protected replica of the internal gate driver for an external hot swap

MOSFET.

To slow down the rising edge of this signal a small value ceramic

capacitor may be added between this pin and GND.

PGD

High-voltage rating, open drain output signal to be used as Enable

for a DC/DC converter feed with VOUT voltage.

It is pulled down until the PoE voltage is below UVLO, or FAUX is

asserted, and the hot swap MOSFET is completely closed.

A 85ms delay typ. is required when receiving power from a PSE

before this signal is asserted.

PGD is also asserted as soon as an RAUX configuration is set.

High-voltage rating spare pin. At the moment its function is

undefined.

27, 28

VOUT

Source of the high side, hot swap MOSFET.

This voltage can be used as input voltage for a DC/DC converter.

VDD

High-voltage rating pin, it is the supply voltage input for the PM8805

controller. It must be connected to VOB.

DET

Detection resistor, high-voltage rating pin.

Connect the signature resistance between DET pin and VOB.

Current flows through the resistor only during the detection phase; a

typical value for it is 26.1KΩ.

This pin has negligible resistance with respect to the external

resistance.

VCP

High-voltage rating pin, output of the internal charge pump.

Connect a 0.5A fast switching diode and a 10nF, 50V X7R ceramic

capacitor between this pin and VDD to filter this pin.

33, 36, 37

IN45

Input for the signals connected to "Spare" pairs. This signal along

with IN78 signals is used to feed the 2nd internal bridge.

Table 2. Pin description (continued)

Pin#

Name

Function

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