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Anoop Varma m , 01-22-2026, 10:02 AM

Dear team
We have designed an isolated –48 V DC-DC power input stage and would like your guidance on the PCB routing approach with respect to EMI performance and surge immunity.
System Overview
• Input supply: –48 V DC
• DC-DC converters:
• –48 V to +48 V (isolated)
• –48 V to +12 V (isolated)
• Maximum input current: 20 A
• PCB: 14-layer stack-up, compact board size
Routing Strategy
• From input to filter output:
• LINE and RTN are routed on the same layer
• Traces are maintained 2 mm clearance
From Filter output to DC-DC modules:
• 7 layers used for LINE and 7 layers for RTN
• Layer sequence arranged as RTN / LINE / RTN / LINE
• Via stitching provided near DC-DC module input through-hole pins for current sharing
Stack-up and Copper Details
• Dielectric thickness between adjacent layers: 0.153 mm
• Copper thickness:
• Top and bottom layers: 1 oz
• Inner layers: 0.5 oz
Isolation and Earth Clearance
• Isolation of Earth and primary are kept separate
• Primary to earth clearance on top layer: 2 mm
• Primary to earth clearance on inner layers: 0.5 mm
Clarifications Required
• Is this routing approach effective for differential-mode noise reduction?
• Does the multi-layer LINE/RTN structure help in controlling common-mode noise?
• Are the isolation clearances sufficient for 6 kV surge immunity?
• Is the via stitching near DC-DC input help for EMI ?
• Is this approach suitable for meeting CISPR 32 Class A requirements?
• Could you suggest the standard routing procedure for the earth connection and the primary isolated power supply input?
• Could you suggest the standard routing procedure for the earth connection and the primary isolated power supply input?
Your guidance on the above points would be very helpful.

QDrives , 01-22-2026, 11:48 PM

Do note that both your picture and text are not very clear to me, but here goes...
1) "*Is this routing approach effective for differential-mode noise reduction?*"
Hardly
2) "*Does the multi-layer LINE/RTN structure help in controlling common-mode noise?*"
No
3) "*Are the isolation clearances sufficient for 6 kV surge immunity?*"
No, check IEC 60950 or IEC 60664
4) "*Is the via stitching near DC-DC input help for EMI ?*"
I do not see how compared to needing it for current sharing.
5) "*Is this approach suitable for meeting CISPR 32 Class A requirements?*"
That depends on many other things as well.
6) "*Could you suggest the standard routing procedure for the earth connection and the primary isolated power supply input?*"
No. Much more information is required. And that would turn it into consultancy...