Electromagnetic Compatibility (EMC) Design and Test Case Analysis

JUNQI ZHENG, National Radio Interference and Standardization Technical Committee; Shanghai Testing and Inspection Institute for Electrical Equipment, China.

Preface xi

Exordium xv

Introduction xix

1 The EMC Basic Knowledge and the Essence of the EMC Test 1

1.1 What Is EMC? 1

1.2 Conduction, Radiation, and Transient 2

1.3 Theoretical Basis 4

1.3.1 Time Domain and Frequency Domain 4

1.3.2 The Concept of the Unit for Electromagnetic Disturbance, dB 5

1.3.3 The True Meaning of Decibel 6

1.3.4 Electric Field, Magnetic Field, and Antennas 9

1.3.5 Resonance of the RLC Circuit 17

1.4 Common Mode and Differential Mode in the EMC Domain 21

1.5 Essence of the EMC Test 23

1.5.1 Essence of the Radiated Emission Test 23

1.5.2 Essence of the Conducted Emission Test 25

1.5.3 Essence of the ESD Immunity Test 29

1.5.4 Essence of the Radiated Immunity Test 30

1.5.5 Essence of the Common‐Mode Conducted Immunity Test 32

1.5.6 Essence of the Differential‐Mode Conducted Immunity Test 34

1.5.7 Differential‐Mode and Common‐Mode Hybrid Conducted Immunity Test 35

2 Architecture, Shielding, and Grounding Versus EMC of the Product 37

2.1 Introduction 37

2.1.1 Architecture Versus EMC of the Product 37

2.1.2 Shielding Versus EMC of the Product 38

2.1.3 Grounding Versus EMC of the Product 40

2.2 Analyses of Related Cases 41

2.2.1 Case 1: The Conducted Disturbance and the Grounding 41

2.2.2 Case 2: The Ground Loop During the Conducted Emission Test 46

2.2.3 Case 3: Where the Radiated Emission Outside the Shield Comes From 49

2.2.4 Case 4: The “Floating” Metal and the Radiation 52

2.2.5 Case 5: Radiated Emission Caused by the Bolt Extended Outside the Shield 55

2.2.6 Case 6: The Compression Amount of the Shield and Its Shielding Effectiveness 59

2.2.7 Case 7: The EMI Suppression Effectiveness of the Shielding Layer Between the Transformer’s Primary Winding and Secondary Winding in the Switching‐Mode Power Supply 62

2.2.8 Case 8: Bad Contact of the Metallic Casing and System Reset 68

2.2.9 Case 9: ESD Discharge and the Screw 70

2.2.10 Case 10: Heatsink Also Affects the ESD Immunity 71

2.2.11 Case 11: How Grounding Benefits EMC Performance 72

2.2.12 Case 12: The Heatsink Shape Affects Conducted Emissions from the Power Ports 76

2.2.13 Case 13: The Metallic Casing Oppositely Causes the EMI Test Failed 82

2.2.14 Case 14: Whether Directly Connecting the PCB Reference Ground to the Metallic Casing Will Lead to ESD 88

2.2.15 Case 15: How to Interconnect the Digital Ground and the Analog Ground in the Digital‐Analog Mixed Devices 94

3 EMC Issues with Cables, Connectors, and Interface Circuits 101

3.1 Introduction 101

3.1.1 Cable Is the Weakest Link in the System 101

3.1.2 The Interface Circuit Provides Solutions to the Cable Radiation Problem 102

3.1.3 Connectors Are the Path Between the Interface Circuit and the Cable 103

3.1.4 The Interconnection between the PCBs Is the Weakest Link of the Product EMC 104

3.2 Analyses of Related Cases 107

3.2.1 Case 16: The Excessive Radiation Caused by the Cabling 107

3.2.2 Case 17: Impact from the Pigtail of the Shielded Cable 110

3.2.3 Case 18: The Radiated Emission from the Grounding Cable 113

3.2.4 Case 19: Is the Shielded Cable Clearly Better than the Unshielded Cable? 117

3.2.5 Case 20: Impacts on ESD Immunity of the Plastic Shell Connectors and the Metallic Shell Connector 124

3.2.6 Case 21: The Selection of the Plastic Shell Connector and the ESD Immunity 126

3.2.7 Case 22: When the Shield Layer of the Shielded Cable Is Not Grounded 128

3.2.8 Case 23: The Radiated Emission Problem Brings Out Two EMC Design Problems of a Digital Camera 131

3.2.9 Case 24: Why PCB Interconnecting Ribbon Is So Important for EMC 138

3.2.10 Case 25: Excessive Radiated Emission Caused by the Loop 144

3.2.11 Case 26: Pay Attention to the Interconnection and Wiring Inside the Product 149

3.2.12 Case 27: Consequences of the Mixed Wiring Between Signal Cable and Power Cable 151

3.2.13 Case 28: What Should Be Noticed When Installing the Power Filters 155

4 Filtering and Suppression for EMC Performance Improvement 161

4.1 Introduction 161

4.1.1 Filtering Components 161

4.1.2 Surge Protection Components 167

4.2 Analyses of Related Cases 173

4.2.1 Case 29: The Radiated Emission Caused by a Hub Exceeds the Standard Limit 173

4.2.2 Case 30: Installation of the Power Supply Filter and the Conducted Emission 178

4.2.3 Case 31: Filtering the Output Port May Impact the Conducted Disturbance of the Input Port 182

4.2.4 Case 32: Properly Using the Common‐Mode Inductor to Solve the Problem in the Radiated and Conducted Immunity Test 187

4.2.5 Case 33: The Design of Differential‐Mode Filter for Switching‐Mode Power Supply 190

4.2.6 Case 34: Design of the Common‐Mode Filter for Switching‐Mode Power Supply 196

4.2.7 Case 35: Whether More Filtering Components Mean Better Filtering Effectiveness 203

4.2.8 Case 36: The Events Should Be Noticed When Positioning the Filters 208

4.2.9 Case 37: How to Solve Excessive Harmonic Currents of Switching‐Mode Power Supply 211

4.2.10 Case 38: Protections from Resistors and TVSs on the Interface Circuit 213

4.2.11 Case 39: Can the Surge Protection Components Be in Parallel Arbitrarily? 218

4.2.12 Case 40: Components in Surge Protection Design Must Be Coordinated 224

4.2.13 Case 41: The Lightning Protection Circuit Design and the Component Selections Must Be Careful 226

4.2.14 Case 42: Strict Rule for Installing the Lightening Protections 227

4.2.15 Case 43: How to Choose the Clamping Voltage and the Peak Power of TVS 230

4.2.16 Case 44: Choose the Diode for Clamping or the TVS for Protection 232

4.2.17 Case 45: Ferrite Ring Core and EFT/B Immunity 235

4.2.18 Case 46: How Ferrite Bead Reduces the Radiated Emission of Switching‐Mode Power Supply 238

5 Bypassing and Decoupling 243

5.1 Introduction 243

5.1.1 The Concept of Decoupling, Bypassing, and Energy Storage 243

5.1.2 Resonance 244

5.1.3 Impedance 248

5.1.4 The Selection of Decoupling Capacitor and Bypass Capacitor 249

5.1.5 Capacitor Paralleling 251

5.2 Analyses of Related Cases 253

5.2.1 Case 47: The Decoupling Effectiveness for the Power Supply and the Capacitance of Capacitor 253

5.2.2 Case 48: Locations of the Ferrite Bead and Decoupling Capacitor Connected to the Chip’s Power Supply Pin 258

5.2.3 Case 49: Producing Interference of the ESD Discharge 263

5.2.4 Case 50: Using Small Capacitance Can Help Solve a Longstanding Problem 266

5.2.5 Case 51: How to Deal with the ESD Air Discharge Point for the Product with Metallic Casing 268

5.2.6 Case 52: ESD and Bypass Capacitor for Sensitive Signals 270

5.2.7 Case 53: Problems Caused by the Inappropriate Positioning of the Magnetic Bead During Surge Test 273

5.2.8 Case 54: The Role of the Bypass Capacitor 275

5.2.9 Case 55: How to Connect the Digital Ground and the Analog Ground at Both Sides of the Opto‐Coupler 278

5.2.10 Case 56: Diode and Energy Storage, the Immunity of Voltage Dip, and Voltage Interruption 282

6 PCB Design and EMC 289

6.1 Introduction 289

6.1.1 PCB Is a Microcosm of a Complete Product 289

6.1.2 Loops Are Everywhere in PCB 289

6.1.3 Crosstalk Must Be Prevented 290

6.1.4 There Are Many Antennas in the PCB 291

6.1.5 The Impedance of the Ground Plane in PCB Directly Influences the Transient Immunity 291

6.2 Analyses of Related Cases 293

6.2.1 Case 57: The Role of “Quiet” Ground 293

6.2.2 Case 58: The Loop Formed by PCB Routing Causes Product Reset During ESD Test 298

6.2.3 Case 59: Unreasonable PCB Wiring Causes the Interface Damaged by Lightning Surge 303

6.2.4 Case 60: How to Dispose the Grounds at Both Sides of Common‐Mode Inductor 305

6.2.5 Case 61: Avoid Coupling When the Ground Plane and the Power Plane Are Poured on PCB 309

6.2.6 Case 62: The Relationship Between the Width of PCB Trace and the Magnitude of the Surge Current 314

6.2.7 Case 63: How to Avoid the Noise of the Oscillator Being Transmitted to the Cable Port 317

6.2.8 Case 64: The Radiated Emission Caused by the Noise from the Address Lines 319

6.2.9 Case 65: The Disturbance Produced by the Loop 324

6.2.10 Case 66: The Spacing Between PCB Layers and EMI 329

6.2.11 Case 67: Why the Sensitive Trace Routed at the Edge of the PCB Is Susceptible to the ESD Disturbance 334

6.2.12 Case 68: EMC Test Can Be Passed by Reducing the Series Resistance on the Signal Line 338

6.2.13 Case 69: Detailed Analysis Case for the PCB Design of Analog‐Digital Mixed Circuit 339

6.2.14 Case 70: Why the Oscillator Cannot Be Placed on the Edge of the PCB 357

6.2.15 Case 71: Why the Local Ground Plane Needs to Be Placed Under the Strong Radiator 360

6.2.16 Case 72: The Routing of the Interface Circuit and the ESD Immunity 363

7 Components, Software, and Frequency Jitter Technique 367

7.1 Components, Software, and EMC 367

7.2 Frequency Jitter Technique and EMC 368

7.3 Analyses of Related Cases 368

7.3.1 Case 73: Effect on the System EMC Performance from the EMC Characteristics of the Component and Software Versus Cannot Be Ignored 368

7.3.2 Case 74: Software and ESD Immunity 371

7.3.3 Case 75: The Conducted Emission Problem Caused by Frequency Jitter Technique 373

7.3.4 Case 76: The Problems of Circuit and Software Detected by Voltage Dip and Voltage Interruption Tests 379

Appendix A EMC Terms 381

Appendix B EMC Tests in Relevant Standard for Residential Product, Industrial, Scientific, and Medical Product, Railway Product, and Others 385

Appendix C EMC Test for Automotive Electronic and Electrical Components 405

Appendix D Military Standard Commonly Used for EMC Test 429

Appendix E EMC Standards and Certification 455

Further Reading 467

Index 469