PCB layout

AN3978

10/19

Doc ID 022179 Rev 1

2.1

Supply voltage filter layout

It is important to place the supply voltage filter components in the right order and make the

routes accordingly. A correct reference is visible in Figure 7.

Figure 7.

Supply voltage filter PCB design

The power supply is connected to CN3. The first component on the track should always be

a Transil diode (D1) in order to ensure a low-impedance path to the supply connector and to

minimize loop which may create electromagnetic disturbances. The next component is

a large bulk capacitor (C1). Its function is to cover energetic peaks during output current

transients and optimize EMI performance. The last stage of the filter is a ~100 nF ceramic

capacitor (C2). Points TP1 and TP2 are central reference points for power (Vs and GND)

distribution for the application.

2.2

Earth coupling

The board is equipped with a connection to earth protection line. Two high voltage coupling

capacitors - C3 and C4 (4.7 nF / 3 kV) are assembled on the board. It is recommended to

lead their connection tracks directly to power supply connector CN3 to suppress

charge/discharge current intervention of application reference supply points (TP1, TP2).

The charge/discharge currents are generated, for instance, by burst or surge noise in the

environment or during EMC tests.