DocID023640 Rev 2

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AN4160

Surge tests

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3.2

PLC circuit description

The PLC coupling circuit comprises three levels of protection, exploiting different protection

devices:

Direct power line protection: a Metal Oxide Varistor (MOV) is used as a first-line protection

to clamp most of the surge energy. The part number for the EVALKITST7580-1 is S14K320.

Line coupling primary side protection: it is implemented through a bidirectional TVS diode

put within the L-C series resonance. This position, thanks to the resonance, gives best

protection while limiting the current flowing through the TVS.

Secondary side protection at pin level: two pins of the PLC device are directly connected to

the line coupling:

•

PA_OUT: it is the line driver output of the PLC device forcing the transmission signal to

the power line. This is the most sensitive point to be protected. Two Schottky diodes

are used to clamp any residual disturbance exceeding VCC or going below ground.

The part number for the EVALKITST7580-1 is STPS1L30A.

•

RX_IN: it is the high-impedance receiving input of the PLC device. It is protected by a

bidirectional TVS diode put just before the dc-decoupling capacitor connected in series

with the pin.

The following tests and analysis will focus on the two TVS diodes included in the PLC

circuit.

Figure 8. PLC circuit schematic

Figure 8 shows PLC circuit used for the tests, based on the ST7580 power line modem TVS

and MOV highlighted.

Primary

TVS

MOV

Receiver

TVS