PM8800ATR datasheet(20/35 Pages) STMICROELECTRONICS

Part #	PM8800ATR

Description	Integrated IEEE 802.3af compliant PoE-PD interface and PWM controller with support of external source

PDF	35 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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20 / 35 page

PD interface

PM8800A

20/35

In the following picture a typical start sequence that can be observed in real circuits.

Figure 11.

Typical start up sequence

Ch1 = 5 Vout, Ch2 = VSS - GND, Ch3 = Vcc, Ch4 = I input

Depending on the application, care must be put on the choice of the inrush current limit to

avoid that the voltage drop on the external Ethernet cable will cause UVLO conditions during

the charging phase of the bulk capacitor.

It is recommended to select this voltage drop (20

Ω max for 100 m of cable x I inrush) to be

lower than the UVLO hysteresis ( 7 V) in order to avoid hiccup turn on.

5.5

Continuos current limitation

PM8800A provide a default continuos current limitation of 440 mA. This is achieved by

leaving the pin DCCDL floating. A different DC current limit can be set by connecting a

resistor between DCCL and VSS whose value can be obtained by the following equation:

DC kΩ

[]

11200

DC mA

[]

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PM8800ATR Datasheet(PDF) 20 Page - STMicroelectronics