Sides from David Bourner's EMI webinar. The consequences of poor design may not show up until compliance testing, which makes this a particularly stressful time as failure may require expensive and time-consuming redesign work to be carried out. Fortunately, the things engineers need to do if they want to reduce the chance of EMI issues causing problems during compliance testing are simple and straightforward.

1. 1
Simple Ideas to Make EMI Issues
a Thing of the Past
David Bourner
Senior Applications Engineer
December 2016

2. 2
Orientation
› The system you are designing is complex – the many different parts have to
work as one
– Power connectors, cables
– Modules
– Circuit boards
– Components: Analog , digital, electromechanical
– Backplane, chassis, enclosure
› Design time, components and resources are always limited
› Control of CE - conducted emissions - easy to overlook
› Maximum permitted energy levels extremely small
› RE - radiated emissions - are measured across many more decades of
frequency compared with CE – RE suppression applies to the complete
system application

3. 3
Aspects of EMI Control in Switched Mode Power Systems
› Elements of a SMPS
› Causes of “noise” in power trees
› Noise energy management principles
› Some noise control practices at work

4. 4
Let’s look at a SMPS (Switched Mode Power System)
Output filtering,
Hold-up cap bank
External OCL
Load switch
Load
Surge and
transient
protection
Holdup
Cap bank
Conducted
Emissions
Filtering
DC-DC Converter
Output / remote
sensing
Redundant
switching circuitry
Input sensing
OVP/ OCP
circuits
Source(s) and
Redundant
switching
circuits
CM and DM
noise current
control area Bold arrows show DC
power flow
noise energy flows
are different

5. 5
DCM - DC Module: From Module to Application
DCM (DC Module)
Evaluation board
New Vicor Packages
VIA: Vicor Adaptor
ChiP: Converter housed in Package
Double-clamped ZVS power cell
+OUT
-OUT
Proprietary
Buck-boost control
+IN
-IN

6. 6
Voltage Across and Current In DCM Primary Winding
› ZVS eliminates
the discontinuities
seen in hard-switched
converters
› Resulting frequency spectra
show this
No need for external clamps
or snubbers – but other parts
will need to be added, external
to converters

7. 7
EMI Noise Spectrum: Classifying Noise in a SMPS
Control loop
bandwidth not visible
Switching fundamental
term + harmonics
RE 30 MHz – 1GHz
UNFILTERED EMI PEAK SCANS - CISPR 22 - 270 VDC, 10% of Full Load, Red Lead
MODEL #MDCM270P280M500A40
CE 150 kHz – 30 MHz

8. 8
EMI Coupling Mechanisms
› Inductive coupling 𝑽𝒊𝒏𝒅 = −𝑳.
𝒅𝒊
𝒅𝒕
– Voltages induced with inductive coupling
increase with frequency,
permeability and proximity
› Capacitive coupling 𝑰𝒄𝒂𝒑 = 𝑪.
𝒅𝒗
𝒅𝒕
– Currents induced in adjacent conductors
increase with frequency,
permittivity and proximity

9. 9
Keys to Control of EMI
› Switching causes noise - couples in two modes:
– Common mode and differential mode
› Confine noise currents within smallest possible loop areas
Use:
– Y caps for common mode control
› X caps for differential mode control
› These are selected and connected in such a way as to preserve safety
in accordance with various classifications e.g. Y1, Y2
Note the central area of the block diagram (slide #4)
Apply noise control at the converter itself

10. 10
Simplified Model of the Converter Input Power Port
› Common-mode AC
voltages Vcm1, Vcm2
and a differential mode
AC voltage source Vdm
› Cs1 and Cs2: parasitics
› Small loop area current
pathways required
for both the common and
differential mode currents
Cx
Cy1
Cy2
shield plane
Cs1
Vcm1
~
Vdm
~
Vcm2
~
Front-end of
DC-DC converter
Cs2
Suppression of pervasive noise must be effective

11. 11
EMI Control Concepts
› There is a critical order to EMI control component placement. As
much of the CE noise is to be conducted back to its origin. Block and
bypass noise from the converter input port toward the input
power source
– X and Y capacitors are HF energy suppressors – place them close to
converter
– Surge and transient protection may affect X and Y cap action
› The negative impedance of the converter - if unchecked - will
produce input power bus instability
› Input filter damping helps dissipate EMI noise energy and assures
stable operation
On the input side of the system we note that:
The input holdup caps provide bus stability due to ESR

12. 12
Noise current pathways change with frequency
AC source
VIAs going through
substrate, to solid
ground plane
trace on topside of board
lower end of each via makes good electrical
contact to the ground plane, the brown solid layer
At LF --- circuit completed through straight segment of ground plane between the
via contacts there, through minimum resistance path
At HF --- circuit completed in image traces in the ground plane, through
minimum inductance path
resistive load
~

13. 13
Glimpse of CE for a standalone PRM/VTM power tree
PRM switches at ~1.3 MHz
VTM switches at ~ 1.6 – 1.9 MHz Common mode input noise spectrum at PRM black power terminal
Note that the oscilloscope traces are measured in limited (20 MHz) bandwidth

14. 14
28V PWR
SOURCE
+
_
M-FIAM7B
+
_
EMI
GND
FIAM BASEPLATE
+
_
+
_
PRM
L2
R
VTM
+
_
+12 VDC
DC_RTN
MP028F036M12AL / MV036F120T100 TEST FIXTURE CE CONTROL ARRANGEMENT
28V
RTN
lL1a
lL1b
28V lL3
SHIELD PLANE (COPPER BENCH TOP)
CY1(a,b) CY2(a,b)
CY3(a,b)
CX1
CY4(a,b)
CX2
CX3
Notes ---------------------------------------------------------------------------------------------------
Y and bypass caps
CY1(a,b), CY2(a,b), CY4(a,b): 4.7 nF HV safety caps Vishay
VY1472M63Y5UQ63V0 or equivalent
CY3(a,b): 4.7 nF 250v a.c. rated part Vicor part number #01000
X-caps
CX1: 1000uF 63V rated ALEL paralleled with two 2.2 uF 50V rated ceramic caps
CX2: two paralleled 10uF 25V rated ceramic caps, parallel 4.7nF HV cap added
CX3: four paralleled 10 uF 25V rated ceramic caps
-----------------------------------------------------------------------------------------------------------------
Inductors (all based on the Coilcraft SLC7530D-101ML power inductor)
L1a, L1b one winding each for common-mode choke implementation
L2, L3 series connection of each winding in the part
Detuning resistor
R 1206 sized 10 W resistor for detuning
An example of a line-up for controlling CE

15. 15
Simple lab-based CE check outcome
Test setup – prototype built up with
FIAM, PRM (Pre-regulator) and
VTM (isolated Voltage
Transformation Module)
Zero input test FFT CM FFT spectrum PRM black power terminal

16. 16
Implementing RE Control
Detecting noise
sources in
the system
in the near
H field
Cable harness design
and placement;
Use twisted wire,
ribbons or coaxial cable.
Apply CM filtering
to harnesses
to minimize RE.
Grounding of
heatsink
turns it into
a shield

17. 17
Checklist for Addressing EMI Concerns
› Design for EMI from the beginning; know what performance you require
› Select components, circuits with EMI in mind
› Plan your PCB layout
– Board stack-up: ground planes to be located close to matched power and
signal trace layers
– Assign placements for filters, SMPS modules, analog/digital circuits and returns
› Determine cable harness design – select connectors – consider their placement
› Plan Grounding Strategy at component, circuit, module, circuit card and system level
› Filters: verify ratings, use correct components, keep input & output routes separate
› Shielding: select materials appropriate to noise spectrum, target usage: look for gaps, openings
and deploy conductive gaskets (critical gaps < λ/20 guide)
› Use the schematic as tool to document EMI control design
– Apply a flow check to ensure assignment of appropriate in-circuit control measures
– Ensure that the input filtering design is conducive to input power bus stability
› Carry out EMI pre-assessments continuously as the design progresses

18. 18
Acknowledgments - Question Session
Special thanks to the very patient Vicor folks
who helped me out with this project
Scott Lee
Hannes Schachenmayr
Bob Pauplis
Chris Swartz
Arthur Russell
Harry Vig
Joe Aguilar
Ankur Patel
Peter Makrum
Mike DeGaetano
Vamshi Domudala

19. 19
IEEE PDH Information
› Code: 1206SOL
› Link for form: http://fs25.formsite.com/ieeevcep/form36/index.html