Test results

AN2052

4/13

DocID10909 Rev 2

Figure 3. FM configuration “B”, time average at 200 kHz, 43.92 dBuV/m

As shown in Figure 1, 2 and 3, using the FM technique, an improvement is obtained.

When frequencies are lower than 1 MHz, the device switching is the primary noise

generator. Using the configuration “A” or “B”, a 5 dBuV/m drop is obtained for

frequencies lower than 200 kHz.

Between 1 MHz and 10 MHz, both configurations “A” and “B” make a dramatic drop

bigger than 15 dBuV/m. Above 10 MHz, FM technique benefits are reduced and

capacitive coupling between copper tracks in PCB is dominant.

Table 1. EMI comparison between original “A” and “B” configurations

<1 MHz

1 MHz to10 MHz

>10 MHz

Original

Marginally pass

Pass

Enough margin

“A”

Pass

More margin

Enough margin

“B”

More margin

More margin

Enough margin