33/42

AN1262 APPLICATION NOTE

must be placed in this region, except the above mentioned common mode suppression capacitor and any op-

tocoupler for secondary feedback.

Filling any unused space in the PCB with a ground plane helps reduce noise emission, but does not exempt

from using the above mentioned care in component placing and traces routing. For instance, if a signal ground

is connected to a ground plane along a pulsed current path between two components, (it is usually the most

direct one) noise will be injected into the signal circuitry.

Figure 20. Possible component placement.

19

TEST BOARD: DESIGN AND EVALUATION

In order to show how to proceed with the design of an application based on the L6590 family, the design of the

test board, used to evaluate the device's performance, will be illustrated in details. Finally, the resulting electrical

schematic and a bench evaluation of the test board will be presented. The electrical specifications of the test

board and some preliminary choices are listed in table 22. Table 23a) shows the results of some preliminary

calculations needed to go further with the design steps.

Table 22. Test board's electrical specification and pre-design choices

Electrical Specification

88 V

Minimum mains voltage

264 V

Maximum mains voltage

60 Hz

Mains frequency (@ min. mains)

0

Number of holdup cycles

5 V

Regulated output voltage

2 %

Percent output voltage tolerance

(±)

1 %

Percent output voltage ripple

10 W

Maximum output power

η

0,75

Expected converter efficiency

40 °

Maximum ambient temperature

+

to input

bridge

signal

ground

+

jumper

Transformer

Cin

C

Y

L6590

L6590D

Zener

clamp