AltiumLive 2017: Component selection for EMC

Transcription

1 AltiumLive 2017: Component selection for EMC Martin O Hara Victory Lighting Ltd Munich, October 2017

2 Component Selection Passives resistors, capacitors and inductors Discrete diodes, bipolar transistors, FETs Integrated Circuits logic, microprocessors, i/o interface Others crystals, heatsinks

3 Component Packaging Surface Mount Preference lower parasitic inductance and capacitance Smaller Parts Usually Better same reason as above Be Aware of Mechanical Effects Avoid Sockets in Production add more parasitics

4 Resistors Surface Mount Preference lower parasitic inductance and capacitance Carbon and Film Preferred have more high frequency losses than metal no intrinsic resonances of significance Wirewound Highly Inductive can be reduced by winding style Noise Voltage Not Critical to EMC

5 Impedance (Ω) Chip Resistors 10, R, kHz 1GHz

6 Capacitors Surface Mount Preference parasitic inductance limits frequency response Low Equivalent Series Resistance higher rejection at specific frequencies Low Equivalent Series Inductance limits frequency response Cure many EMC problems at circuit level filtering, decoupling, slew limiting

7 Capacitor Model 4-Element Model Simulates Impedance Characteristics Rs - series resistance (resistance of lead/electrodes) ESL equivalent series inductance (inductance of lead/electrodes) Rp - dissipative resistance (leakage/hysteresis losses) Cp - primary capacitance (design value)

8 Capacitor Dielectric DC 10Hz 100Hz 1kHz 10kHz 100kHz 1MHz 10MHz 100MHz 1GHz Aluminium Electrolytic Tantalum Electrolytic Paper Mylar Ceramic (High-K) Polystyrene Mica, Glass, Low-Loss Ceramic

9 Ceramic Dielectrics Dielectric Self Resonant Frequency (MHz) Y5V 46 X7R 44 COG 40

10 Impedance (Ohms) Capacitor Lead Length 1 10uF Ceramic Disc Capacitor 15mm 10mm 0mm kHz 100kHz Frequency 1MHz 10MHz

11 Impedance (Ohms) ESR Limited Capacitor ESR 1 1kHz 10kHz 100kHz 1MHz 10MHz frequency

12 Impedance (Ohms) Impedance MLCC Capacitors nF 100nF 1uF 10uF Hz 100Hz 1kHz 10kHz 100kHz 1MHz 10MHz frequency

13 Capacitance as a Percentage of Nominal (%) DC Bias of MLCC Capacitors COG X7R Y5V Applied DC Bias (Volts)

14 Change in Nominal Capacitance (%) Temperature Bias of MLCC 10 0 C0G X7R Y5V Temperature (C)

15 Impedance (Ohms) Parallel Capacitors Parallel Resonance of 1uF and 1nF Capacitors Hz 100Hz 1kHz 10kHz 100kHz 1MHz 10MHz 100MHz 1GHz frequency

16 Inductors Surface Mount Not Important! Parasitic Capacitance effected by winding style (unquoted) form factor (closed loop or air cored) Few Useful for Higher Frequency Filtering Self Resonance Potential EMC Problem often within radiated emissions band

17 Inductor Model 4-Element Model Simulates Impedance Characteristics Rs - series resistance (resistance of wire) Cw - winding capacitance (varies with winding style) Rp - dissipative resistance (limits resonance peak) Lp - primary inductance (design value)

18 Impedance (Ohms) Inductor Impedance Curves f o 2 1 LC W 10mH 1mH 100uH 10uH ,000 10, ,000 1,000,000 10,000, ,000,000 1,000,000,000 frequency (Hz)

19 Impenance (Ohms) Inductor Form Factor Q R 2 f p o L δ Bobbin 1 Toroid Rod Ideal ,000 10, ,000 1,000,000 10,000,000 Frequency (Hz)

20 Percentage of Nominal Inductance (%) Current Limited Inductance Rod 70 Toroid Bobbin DC Bias Current (A)

21 Attenuation(dB) Ferrite Bead frequency (MHz)

22 Ferrite Beads: 1T Inductors

23 Discrete Components Surface Mount Preference lower parasitic inductance and capacitance Diodes unusually fast is often good for EMC Transistors opposite of above!

24 Discrete Component Packaging Package Type Lead and Bond Wire Inductance (nh) Inter-Lead Capacitance (pf) E-Line SOT

25 Transistors: Generalisations Terminate Base/Gate Drive from Logic high R for BJT, low R for FET Bipolar Higher ESD Tolerance back-to-back diode structure beneficial Slew Limit Drive with Capacitor BJT can switch very quickly BJT/FET can demodulate RF as EXP/SQ law

26 Reverse Recovery Time Soft recovery best for lower ripple

27 Integrated Circuits Surface Mount Preference lower parasitic inductance and capacitance Digital Components use lowest speed you can functionally Analogue Components look for bandwidth limited parts slew rate limiting now popular (for good reason) Avoid Using Sockets in Production

28 IC Packages Lead Count Dual-in-Line (DIL) Small Outline (SOIC) Plastic Leaded Chip Carrier (PLCC) L (nh) C (pf) L (nh) C (pf) L (nh) C (pf) / /

29 Newer Packages R (mohms) C (pf) L (nh) Cm (pf) Lm (nh) MQFP PQFP TSOP BGA ubga CWLP Compliant Wafer Level Packaging Lead inductance inc at 0.8nH/mm Lead capacitance inc at pF/mm Bond wire inductance inc. at 1nH/mm

30 Ultra-Low Parasitics

31 Pin Pitch Fine Pitch Packages increases mutual inductance/capacitance (increases cross talk) reduced parasitic pin inductance/capacitance (due to shorter leads) Pitch mm Lm nh Cm pf

32 Special Package Configuration

33 Logic Family Parameters Logic Family Rise/Fall Time (ns) Bandwidth (MHz) Noise Margin (V) Decoupling Capacitor (nf) CMOS LTTTL 20/ TTL HC CMOS LS 10/ ALS S 3/ F ECL-10K ECL-100K

34 Power Disipation (W) Loaded CMOS Drivers pF pF pF 0pF Clock Frequency (MHz)

35 Power Dissipation per Port (Pd) High Data Rate Drive PECL 60MHz-70MHz CMOS Frequency (MHz)

36 Decoupling Capacitors Decouple Every IC can share for low speed, slew limited circuits Calculate C If Possible can use Rule of Thumb Multiple Decoupling for Microprocessors every supply pin parallel capacitors of 1:100 Lower Cost than Large Bypass Capacitor

37 Amplitude (dbuv) Spread Spectrum Clocks Spread Spectrum Clock Standard Clock Modulation (%)

38 Low Operating Voltage Trend for Low Operating Voltage Reduces Current Surges hence decoupling requirement reduced Reduced Emissions for same rise/time and frequency 3.3V has 3.6dB lower emissions than 5V part Increased Susceptibility Avoid or buffer at interfaces differential signalling improves susceptibility

39 Buyer Beware IC Manufacturer May Change Process improve their yield, increases rise/fall time won t advise if no parametric change Not All IC s Made The Same different manufacturers, different EMI performance EMC is not a usual datasheet parameter Emission Problem with Digital ICs datasheets specify maximum time parameters only Susceptibility Usually with Analogue ICs

40 Other Components Transformers similar to inductors for EMC parameters Thyristors, TRIACs, SCR s etc DC-DC Converters and SMPS often bought as component Electromechanical relays, switches, heatsinks, cabling use snubber circuits on relays and switches

41 Ideal Square Wave tp tw tr

42 Frequency Domain f f o 1 t t 1 p 1 w 1 f 2 t r f o f 1 f 2

43 Conducted Emission (dbuv) Switched Mode Power Supply dB/decade 40dB/decade Frequency (Hz)

44 Summary Component Selection for EMC is Secondary to Functional Selection Preference for SMD over PTH Generally Slower is Better fit for purpose, no need for 100MHz controller on a washing machine except diodes Use Where Other Criteria are Exhausted note: slower is usually lower cost!

45 Thanks for your Attention! Questions?