Question
Are there any application hints for addressing EMC problems in order to pass CE
test? Are Ferrite chokes recommended for VCC?
Answer
ADuM5241 is extremely immune to EMI and can only be affected by extremely large
currents operated at high frequencies very close to the component. This is
because our transformers are so small (approx. 300 microns in diameter). If you
have not done so, read the section on pages 11 and 12 of the datasheet on
magnetic field immunity and on the recommendations for the correct PCB layout
in cases where EMI emission is a concern. Graphs are provided in the datasheet
for max allowable current for various current to ADuM524x spacings and for max
allowable external magnetic flux density.
You ask about ferrite chokes for Vcc, ferrites are recommended for both power
and ground traces, see details of this and other recommendations in the PCB
layout section of the datasheet. Be sure to use low inductance bypass
capacitors from power to ground, between the power supply and inductors. Try
using two in parallel, maybe 10nF and 200nF. Keep trace lengths as short as
possible. Make sure that the cabling in the emissions test board is shielded.
The shield in a standard coax can become an antenna adding to the radiation.