ADUM5242 EMI

Question

Hi

I have a question ADUM5242.

Ask about ADUM 5242ARZ-RL7.
Connect between the output pin (pin 8: Viso) - output GND (pin 5: GNDiso)
Although it is a capacitor, 0.1uF is connected in the recommended layout on page 13 in the specification sheet.
As a result of measuring EMI, when we set this capacitance value to 0.01 uF good result is obtained and we want to change capacitance value.
As the output load, 3 kohm is 10 kohm in parallel between the output power supply and output GND at maximum.

1. Is there a lower limit capacitance as output capacitor?
Is there any concerns such as defects when 2.0.01 uF is used?
3. By changing the output capacitor with the attached characteristics from 0.22 uF to 0.01 uF
EMI noise reduction is seen. Is there anything you can guess about this factor?

Best Regards

HOD

ADIApproved · Accepted Answer

HOD: 
 1. Bypass capacitors are recommended as 0.1uF to obtain the load regulation as shown in the datasheet spec tables and load transient response in figure 10. 
 2. Using 0.1uF value close to the VISO and GNDISO pins and a 0.01uF would ensure that good operation and load regulation. Have you tried a combination of 0.01uF and 0.1uF in parallel? 
 3. Using 0.01uF may have lower inductance and better impedance characteristics at the 300MHz switching frequency of the isoPower than the 0.1uF capacitor and may improve EMI emissions. Can you share the emissions data? 
 4. Layout and location of the bypass capacitors close to Viso and GNDiso may effect emissions. The datasheet also recommends: 
 In cases where EMI emission is a concern, series inductance may be added to critical power and ground traces. Discrete inductors should be added to the line such that the high frequency bypass capacitors are between the inductor and the ADuM524x device pin. Inductance can be added in the form of discrete inductors or ferrite beads added to both power and ground traces. The recommended value corresponds to impedance between 50 Ω and 100 Ω at approximately 300 MHz. 
 Regards, Brian