Hi team.
My customer wants to use this Isolator.
they wants to need more creepage is over 9mm in 450Vrms.
However it clear the voltage of 450Vrms, but the creepage is short of 9mm in recommend layout.
Would you tell me the advice if you have good way?
I checked the "Digital Isolator Design Guide", is it only the way it is listed here?
Best regards
Hayashi
Hi Hayashi,
I understand customer's concern. Let me try to explain using a diagram.
Creepage distance between side one and side two of the isolator can be through 2 paths as shown in figure.
1) Surface of IC -> Packaging Material (creepage >8mm fixed for specific package size)
2) Surface of board -> PCB Material (can be increased to >9mm with notch/cut on the board)
The electrical breakdown of different materials can be defined using a parameter called Comparative Tracking Index (CTI).
The packaging material used for our digital isolator belongs to the highest CTI Material Group (CTI-1).
Usually, PCB materials belong to CTI-2 category which is lower strength than the CTI-1 material group. Presence of dirt particles on the board can further degrade this rating.
A creepage distance through the CTI-1 material is much stronger than the same creepage distance through CTI-2 material. Hence a cut on the board as shown in the figure below will increase the creepage distance through the PCB material and help with the rating of the end system if the PCB material had been the weakest path (which is usually the case).
Please note that the creepage distance still remains the same 8mm, but it is now through the packaging material which is much stronger in surface electrical breakdown than the PCB material. This should still help in strengthening the effective electrical breakdown voltage.
Could you please check and let me know if customer requires >9mm creepage along the board or whether he requires the creepage distance through the package of the device?
Regards,
Anand Reghunathan
