Vicor Corporation · NASDAQ:VICR
Vicor — Technical Presentation (2019)
42 slides from Vicor's technical presentation, 2019
Slide 1: Basic EMI Pre-Compliance and Troubleshooting Techniques
Basic EMI Pre-Compliance and Troubleshooting Techniques C. R. Swartz, Senior Principal Engineer/Manager ©2019 Vicor 1
Slide 2: Overview
Overview Basic EMI Measurements and the LISN Common and Differential Noise Sources EMI Pre-Compliance Analysis Using Simulation Models Layout Considerations Field Probes, Signal Splitters and Simple Current Probes An Extensive Troubleshooting Example Case History ©2019 Vicor 2
Slide 3: Foreword
Foreword If you work with Power Electronics, sooner or later you will need to know something about EMI. It is better to learn about it sooner and prepare for the day when you may have to solve a difficult problem. Often the problems will not happen at the most convenient time nor will you have the l
Slide 4: What Is EMI?
What Is EMI? EMI stands for “Electromagnetic Interference” and it has been used to describe many different types of noise phenomena observed in modern power electronic systems in use today. The term “interference” is used somewhat loosely today. Interference means that one piece of equipment’s a
Slide 5: How is EMI coupled?
How is EMI coupled? There are four basic noise-coupling mechanisms in electrical systems Conductive Capacitive Inductive Radiated caused by direct caused by fast- caused by fast- caused by far-field contact with metal changing voltages changing currents electromagnetic conductors (ripple or applied
Slide 6: How is conducted EMI measured in commercial equipment?
How is conducted EMI measured in commercial equipment? LISN – Line Impedance Stabilization Network Copper Ground Plane Tied to Earth Ground ©2019 Vicor 6
Slide 7: The Line Impedance Stabilization Network (commercial products)
The Line Impedance Stabilization Network (commercial products) 50u UUT_L L1 250n R1 8u C2 39k C6 Power Source L_M R7 5 R3 R4 1K 50 V1 Unit under test power EARTH supplied here R5 R6 High-frequency chokes L1 and 1K 50 L2 block high-frequency noise R8 5 from the power source. LISN – N_M C6 and R7 alon
Slide 8: The LISN impedance plot (simulated)
The LISN impedance plot (simulated) 100 Impedance approximates 50 Ohms from 150kHz to Impedance 30MHz, the measurement standard for conducted EMI. (Ohms) 10 The LISN will vary depending on the measurement standard but the goal is a flat impedance in the area of interest 1 I :U2_UUT_L/:U2#UUT_L / Ohm
Slide 9: Measurement Filters
Measurement Filters There are several measuring-filter techniques that you should know about: Peak Detection Quasi-Peak Detection Average This method is the fastest of all This detection method is a form of This method is peak detection EMI scans. It also generates the weighted averaging that has a
Slide 10: Measurement Flow
Measurement Flow Start Peak Detector Quasi-Peak I s Peak <AVG limit? No I s Peak <QP limit? No Detector Yes Yes Average I s QP <QP limit? Detector Yes No Yes I s AVG <AVG Limit? I s QP <AVG limit? No Yes Pass!! Fail ©2019 Vicor 10
Slide 11: Differential-mode noise (A.K.A. normal mode)
Differential-mode noise (A.K.A. normal mode) Differential-mode noise is sometimes referred to as Normal-Mode noise. There is a good reason for this. It results from an applied voltage differential (of opposite polarity) between the noise source and the noise return. It can be caused by any or al
Slide 12: Differential-mode noise ideal CCM buck converter model SIMPLIS
Differential-mode noise ideal CCM buck converter model SIMPLIS This ripple current is Consider the open-loop responsible for the 12V – 3.3V ideal buck differential-mode EMI that converter shown will be measured at the LISN. We are concerned about these ripple currents, as they are responsible for th
Slide 13: Differential-mode noise ideal buck converter
Differential-mode noise ideal buck converter To generate the noise model, we modify the circuit as shown below: Add our LISN equivalent circuit ©2019 Vicor 13
Slide 14: Common-mode noise
Common-mode noise Common-mode noise always flows in the same direction in both input feeds (L and N) from an applied voltage between those common lines and earth ground (chassis, baseplate, test equipment, etc.) It can be most difficult to determine the path since it can involve virtually any eq
Slide 15: Common-mode noise origin – isolated full-bridge topology
Common-mode noise origin – isolated full-bridge topology 10p 10p 50m C7 C1 Si9956DY L_IN UUT_L U2 R6 Si9956DY 100p 1 1m L_M 1m C17 10p 100p B+ 48 C18 Q4 R20 A+ V3 C3 V1 R14 Q1 C8 B- LISN EARTH 100u IC=46.8 E2 N_M P1 A- 10m N_IN UUT_N R13 10p 10p 10p B+ V2 Si9956DY C4 C5 S2 S1 L1 L3 C6 200p TX1 200p
Slide 16: Common-mode noise origin – isolated full-bridge topology
Common-mode noise origin – isolated full-bridge topology 10p 10p 50m C7 C1 Si9956DY L_IN UUT_L U2 R6 Si9956DY 100p 1 1m L_M 1m C17 10p 100p B+ 48 C18 Q4 R20 A+ V3 C3 V1 R14 Q1 C8 B- LISN EARTH 100u IC=46.8 E2 N_M P1 A- 10m N_IN UUT_N R13 10p 10p 10p B+ V2 Si9956DY C4 C5 S2 S1 L1 L3 C6 200p TX1 200p
Slide 17: Common-mode noise origin – isolated full-bridge topology
Common-mode noise origin – isolated full-bridge topology 20p 20p 50m C7 C1 Si9956DY L_IN UUT_L U2 R6 Si9956DY 100p 1 1 L_M 1 C17 20p 100p B+ 48 C18 Q4 R20 A+ V3 C3 V1 R14 Q1 C8 B- LISN EARTH 100u IC=46.8 E2 N_M P1 A- 10m N_IN UUT_N R13 10p 20p B+ V2 Si9956DY C4 S2 S1 L1 C6 100p TX1 Si9956DY 1 100p 1
Slide 18: Common-mode noise origin – isolated full-bridge topology
Common-mode noise origin – isolated full-bridge topology 20p 20p 50m C7 C1 Si9956DY L_IN UUT_L U2 R6 Si9956DY 100p 1 1 L_M 1 C17 20p 100p B+ 48 C18 Q4 R20 A+ V3 C3 V1 R14 Q1 C8 B- LISN EARTH 100u IC=46.8 E2 N_M P1 A- 10m N_IN UUT_N R13 10p 20p B+ V2 Si9956DY C4 S2 S1 L1 C6 100p TX1 Si9956DY 1 100p 1
Slide 19: When does a buck regulator generate common-mode noise?
When does a buck regulator generate common-mode noise? Consider the simplified Buck regulator circuit shown below connected to an electronic load It is powered from a LISN and set up to measure EMI. Can anyone find a common-mode EMI source? ©2019 Vicor 19
Slide 20: When there is parasitic capacitance to earth ground
When there is parasitic capacitance to earth ground Voltages at LISN that are in phase with respect to earth are common mode, out of phase are differential-mode EMI Noise source is output ripple! Current through parasitic capacitance shows up at LISN as in phase voltages when measured across each 50
Slide 21: Layout Matters!
Layout Matters! Up to now, we have been simulating and discussing ideal layout filters. No layout is ideal. Most layouts are a compromise as there are many resources requiring the PCB area. Parasitic inductance will limit the high-frequency performance of capacitors when it appears as ESL! The
Slide 22: From Schematic…
From Schematic… ©2019 Vicor 22
Slide 23: To PCB Layout…
To PCB Layout… Copper strap link for PGND PGND HS MOSFET Drain PGND L1 The parasitic paths around the loops must be considered in your Q1 final simulations and analysis or you will find the filter attenuation will not be as accurate. Use the ideal filter schematic to generate a first pass VIN result
Slide 24: Extracted layout from L1 to HS MOSFET-drain and PGND
Extracted layout from L1 to HS MOSFET-drain and PGND ©2019 Vicor 24
Slide 25: Tools – Beehive
Tools – Beehive 100 Includes wideband RF amplifier and cables Three H-field probes and one E-field probe 100D is the E-field probe to the far right Buy as a kit, a must have! Use the amplifier for the small field probes as they are less sensitive. The bigger probes allow you to find the appr
Slide 26: Tools – power splitters
Tools – power splitters ZSCJ-2-2+ Mini-Circuits Blocks Common-Mode ZSC-2-2+ Mini-Circuits Blocks Differential-Mode LISN-L LISN-N LISN-L LISN-N Both require dual or two single LISN(S) Analyzer Analyzer Must use matched equal- Signals in Signals out of phase are length coax cables. Length
Slide 27: Tools – Swartzomatic-1
Tools – Swartzomatic-1 Hand-wound HF current probe Measures CM and DM current High-permeability core 50 Ohm cable Wide BW, high sensitivity Much better for high-frequency current with very low Pass wires through core in same direction to amplitudes than traditional measure common-mode cu
Slide 28: Tools – Swartzomatic-2
Tools – Swartzomatic-2 Hand-wound near-field probe Helps find high H-fields on PCB Hand-made using RG-58U 50 Ohm cable Common-mode beads can be Connect to 50 Ohm termination on scope. Start with higher added to cable as an option volts/div while moving around PCB. Then reduce volts/div to
Slide 29: Troubleshooting – design challenges
Troubleshooting – design challenges 250W+ Critical Conduction Buck Regulator – Efficiency had to be 96% or higher, high switching frequency 700kHz – PCB area was small, isolated metal box enclosure, potted. – High ambient environment up to 65°C Thermal Management – Power SiP and PCB needed therm
Slide 30: Tools – at my disposal
Tools – at my disposal An excellent simulation model of powertrain and filter design – Performed AC and transient analysis of power system with filter, no issues – Performed parasitic extraction of layout after it was done. Test Equipment – All tools shown previously plus Spectrum Analyzer and O
Slide 31: Troubleshooting EMI – the filter used
Troubleshooting EMI – the filter used The EMI filter is shown below (idealized) for purposes of illustration EMI DM noise source EMI is measured across each 50 Ohm resistor to earth ground High-amplitude, high-frequency AC current “sloshes” around in this loop. The voltage developed across it is the
Slide 32: Troubleshooting EMI – the initial measurements
Troubleshooting EMI – the initial measurements High-frequency EMI was totally The initial measurement spurred my work on a new book entitled unexpected. The only thing that matched expectations was the fundamental. “What You Thought You Knew About EMI” !! EMI is measured across each 50 Ohm resisto
Slide 33: Troubleshooting EMI – the initial measurements
Troubleshooting EMI – the initial measurements DM signal measured at SiP input on customer board: high frequency (6 – 10MHz) is higher by DM Signal measured on evaluation 8 – 12dB, a noticeable ringing observed board with better ground plane ©2019 Vicor 33
Slide 34: Troubleshooting EMI – the ground plane differences
Troubleshooting EMI – the ground plane differences Customer layout MID-1 PGND Input capacitors Input capacitors VIN is major heat source. Needed to be carried through all 4 layers in customer design to form robust pad to thermally bond to plate. Notice the large amount of via’s needed to carry the h
Slide 35: Troubleshooting EMI – what I know and don't know – what next?
Troubleshooting EMI – what I know and don’t know – what next? The measured EMI at input to SiP shows significant high-frequency ringing in the area where EMI is failing. I believe this ringing to be caused by layout – result of higher parasitic inductance and higher Q noise loop How does this
Slide 36: Troubleshooting EMI – next steps
Troubleshooting EMI – next steps Determine if noise is CM or DM… EMI is measured across each 50 Ohm resistor to earth ground Added power splitters between LISN and spectrum analyzer. Blocking CM noise showed no change to high-frequency measurement. Blocking DM noise knock all high-frequency emission
Slide 37: Troubleshooting EMI – next steps
Troubleshooting EMI – next steps Determine which parts of EMI filter Use diff-amp to measure this voltage. Take FFT and are working properly... measure attenuation of first stage filter. - Does it match simulated expected results? Yes! First stage appears to work as designed. Use diffamp to measure
Slide 38: Troubleshooting EMI – next steps
Troubleshooting EMI – next steps Open circuit and use network analyzer to sweep both filters. Check simulation model of second-stage filter. - Does attenuation appear as shown in simulation Was anything missed like self resonance of inductor core? to be close? Yes! First and second stage filters app
Slide 39: Troubleshooting EMI – next steps
Troubleshooting EMI – next steps 1. Highest H-field is inductor. Good starting point. 4. Probe C17-C19. 8MHz and other frequencies - Any evidence of 8MHz Use field probes to isolate where detected! Next, vary the line voltage. ringing here? No! - Does the EMI amplitude go up with line No evidence he
Slide 40: Troubleshooting EMI – fix layout
Troubleshooting EMI – fix layout Problem area isolated and fix implemented Fix implementation Area of suspected coupling 8MHz detected here with near field probe ©2019 Vicor 40
Slide 41: Acknowledgements
Acknowledgements The following material was used as references in the presentation : – Controlling Conducted Emissions By Design by John C. Fluke (an excellent book, highly recommended) – Predict Differential Conducted EMI with a SPICE Simulator Christophe Basso; April 12, 1996 – Making EMI Compli
Slide 42: Thank you
Thank you Questions? The information contained herein and presented by Vicor is for general informational purposes only. Vicor assumes no responsibility for inaccuracies, errors or omissions in this presentation. Users of power supply products remain responsible for the design, testing and operation