DocID018573 Rev 2

19/32

UM1063

Power-up sequence

6

Power-up sequence

It is recommended to apply power at PoE input first, slowly increasing the voltage to verify

the absence of abnormal input current levels.

From about 2 V to about 12 V input, the demonstration kit performs the detection signature.

At 10 V input the current drawn is about 400 µA.

In the range of 14 V to 23 V, the demonstration kit performs a class-4 classification, and the

current drawn is about 40 mA.

After those two steps are verified, the voltage can be increased to 48 V typical. The PoE

converter starts operations at about 36 V input.

Three green LEDs indicate proper operation of the PoE and DC-DC section of the PM8803

demonstration kit:

•

D44 is the T2P LED and is ON when the PM8803 has successfully recognized a type 2

PSE or a 802.3at compliant injector; using a bench power supply to power up the

PM8803 demonstration board, this LED is OFF.

•

D26 indicates the presence of the output voltage.

•

D20 is the AUX LED and indicates the presence of an auxiliary voltage applied to the

converter; proper selection of the auxiliary voltage is done with jumper JM1 and JM2:

put a short between pin 1 and 2 when SA auxiliary source on J1 connector is used; put

the short between pin 2 and 3 when SP auxiliary source on J2 connector is used.

Note:

Set the R73 trimmer at a value around 10 k

Ω

Adjust this value for best converter performances in terms of efficiency over its actual load

range.

Note:

In the case of SA external auxiliary source tests, it is strongly recommended to change the

position of the 100 nF, 100 V from C18, at the input filter, where it is soldered to C60, across

the internal hot-swap MOSFET. This change of position, that has no impact on the standard

compliance, permits an optimal behavior of the PM8803 device during the change of ground

reference consequent to the power jack insertion/removal.