VIPER20DIP-E datasheet(22/31 Pages) STMICROELECTRONICS

22 / 31 page

7 Layout

VIPer20-E/DIP-E

22/31

Layout

7.1

Layout Considerations

Some simple rules insure a correct running of switching power supplies. They may be

classified into two categories:

–

Minimizing power loops: The switched power current must be carefully analysed and

the corresponding paths must be as small an inner loop area as possible. This avoids

radiated EMC noises, conducted EMC noises by magnetic coupling, and provides a

better efficiency by eliminating parasitic inductances, especially on secondary side.

–

Using different tracks for low level and power signals: Interference due to mixing of

signal and power may result in instabilities and/or anomalous behaviour of the device

in case of violent power surge (Input overvoltages, output short circuits...).

In case of VIPer, these rules apply as shown on (see Figure 24).

–

Loops C1-T1-U1, C5-D2-T1, and C7-D1-T1 must be minimized.

–

C6 must be as close as possible to T1.

–

Signal components C2, ISO1, C3, and C4 are using a dedicated track connected

directly to the power source of the device.

Figure 24. Recommended Layout

VIPerXX0

13V

OSC

COMP

SOURCE

DRAIN

VDD

ISO1

From input

diodes bridge

To secondary

filtering and load

FC00500

VIPER20DIP-E Datasheet(PDF) 22 Page - STMicroelectronics