Capacitor Practical EMI Filter Design Workshop IEEE 2008 Detroit Alexander Gerfer & Michael Eckert FR-PM-3 FR-PM-3 Capacitor : Equivalent Circuit Impedance vs. Frequency of Capacitors Inductance of connection: ESR: SMD-types 1 nH ... 5 nH SMD-types 20 mΩ ... 300 mΩ wired 10 nH ... 50 nH ! up to 1 Ω (see Datasheet ) FR-PM-3 FR-PM-3 978-1-4244-1699-8/08/$25.00 ©2008 IEEE Simulation Datas for Caps from Î KEMET Spice Simulation Datas for Caps from Î KEMET Spice FR-PM-3 FR-PM-3 Capacitance: DC-Bias and Temperature Capacitor : KEMET Spice Simulation Model Capacitance decrease temperature increase (@ = 0VDC Î 18 µF !!) Capacitance decrease by DC-bias !!! Effective only Î 8.6 µF !! C0805C104K3RAC @ 25°C, 0VDC, 41,687 kHz Î LTspice www.kemet.com www.linear.com FR-PM-3 FR-PM-3 Pratice-Tip: SRF of SMD-Capacitors What is an Inductor ? Example 1: Filter with maximum attentuation at f = 500 MHz in a system ZA = ZB = 100 Ω = konst.; T-Filter Step 1: choose C with SRF @ 500 MHz => Nomogramm: size 1206 ; C = 68 pF Step 2: SRF [MHz] SRF calculation of Ls „Headache-Parts“ ?! A mystery......... SRF = 500 MHz : = 1 = L S ⋅ 2 1,49 nH C S ω res 68 pF Capacitance [pF] FR-PM-3 FR-PM-3 What is an Inductor ? What is an EMC-Ferrite ? technical view: technical view: a piece of wire wounded on something Absorber for RF a filter frequency dependent filter an energy-storage-part (short-time) examples: examples: EMC Snap-Ferrites EMC-Ferrites for SMD-Ferrite Flatwire WE-CBF FR-PM-3 FR-PM-3 The basics of Inductive Components The basics of Inductive Components Magnetic Field; example: long, straight wire Magnetic Field; toroidal & rod core Current Magnetic field H wire FR-PM-3 FR-PM-3 Magnetic field strength H of some configurations Magnetic field H in the air and in a ferrite core I H = long, straight wire 2⋅π ⋅R N⋅I Toroidal Coil H = 2⋅π ⋅R Air Ferrite core N⋅I Long solenoid H = l I H =H =H= But : B1=B2 1 2 π 2x xRaverage FR-PM-3 FR-PM-3 Permeability ? Permeability µr Permeability (µr): describes the ability to concentrate the magnetic flux in the core material = µ ⋅µ ⋅ B 0 r H Induction in air: Induction in Ferrite: Typical Permeability µr : = µ ⋅ = µ ⋅µ ⋅ B 0 H B 0 r H Iron Powder Cores / Superflux : 50 ~ 150 Nickel-Zink : 40 ~ 1500 Linear Function ! Non-Linear Function ( µr !) Mangan-Zink : 300 ~ 20000 The relative Permeability is dependent on Field Strength H; Temperature and a frequency-dependent parameter.... FR-PM-3 FR-PM-3 Saturation effect Permeability vs. temperature B~ Permeabilität vs. Temperatur saturated 1400 1200 1000 + 40% 800 H~I Curie-Temperature µr 620 600 (µr = 1 ) - 40% 400 I 200 not saturated 0 -50 23 50 85 125 150 160 250 Temp. (°C) FR-PM-3 FR-PM-3 How to find the best part for my application ? Core Material Properties Measurement XL(NiZn) core material Impedance Analyser core material parameter = 2 + 2 Z R X L The key to success is understanding of : X L Core Material Comparison R (f) FR-PM-3 FR-PM-3 Core Material Parameters of Ferrites Complex Permeability µ = µ| − jµ|| = ω ()µ| − µ|| = + Z j L0 j R jX L inductance without core Impedance of Impedance of 0 same coil but w/o Coil with core core material || core material ! = ω µ material R L 0 frequency dependent = ω ()µ | − µ || = core losses Z j L 0 j = ω µ | X L j L 0 R (f) ω frequency dependent L0 inductive portion ω L FR-PM-3 FR-PM-3 Comparison of core materials: Inductive behaviour Comparison of core materials: Losses => It depends on application frequency for EACH Core-Material ! FR-PM-3 FR-PM-3 When to use an Inductor ? Equivalent circuit : Inductor /Ferrite When to use an EMC-Ferrite ? - Application: Storage Choke Losses: Inductors (at SRF ! ) up to 30 kΩ Request: lowest possible core losses SMD-EMC-Ferrite (broadband !) 10 Ω ... 3 kΩ at application frequency - Application: signal-filter in RF-stages: Request: low losses => high Q in frequency band - Application: EMI absorber-filter Request: high core losses Parasitic Capacitance: at noise frequency range SMD-EMC-Ferrite 5 fF ... 5 pF winded Inductors 10 pF ... 500 pF ! FR-PM-3 FR-PM-3 SMD-Ferrite listed in LTspice Normal Type SMD-Ferrites in LTspice You can sort database by : Part.Nr.; DCR; Current ; Impedance @100MHz or Freeware !Download at www.linear.com_ maximum Impedance @ desired frequency FR-PM-3 FR-PM-3 Simulation-Modell for EMC-Ferrites SMD-Ferrites Models in LTspice Model as Parallel-Circuit with constant Parametern for Rp / Lp / Cp can be used in any Z[I] Simulationprogram All High Current Chip Beads (> 1A) (like P-SPICE or Electronics are modeled in their Current Workbench, ...) ! Dependend Impedance behaviour Datas: see Book „Trilogy of Inductors“ Seite 113ff FR-PM-3 FR-PM-3 SMD-Ferrites Models in LTspice SMD-Ferrites Models in LTspice: Impedance vs. DC-bias P/N: 74279252 FR-PM-3 FR-PM-3 Inductors listed in LTspice Structured interference suppression • Recognise the coupling mode: • common mode noise • differential mode noise FR-PM-3 FR-PM-3 Structured interference suppression How can we find out what interference we have on the PCB‘s? 1. Basics 2. Coupling mode 3. Filter topologies • Procedure to find out 4. Measuring Take a Snap Ferrite and fix it on the cable 5. Simulation tools – Use split ferrite (both lines e.g. VCC and GND) 6. Layout recommend. 7. Application • common mode noise ⇒ noise reduction / stable noise immunity if noise is reduced or noise immuntiy increase • differential mode noise => no difference to see you have Common Mode Interference if not you have Differential Mode Interference FR-PM-3 FR-PM-3 Ferrite as Common-Mode Filter Increase impedance with more turns increase Impedance Fres.-decrease FR-PM-3 FR-PM-3 Why current compensation? Filtering with two Inductors Signal before Filter: Signal after Filter: The Filter is effective on both: Differential & Common Mode Currents ! N1 Power line Noise signal rise-time affected ! not usefull for high-speed signals N2 FR-PM-3 FR-PM-3 Filtering with common mode chokes Why bifilar / sectional winding ? Signal before Filter Signal after Filter The Filter is only active for Common Mode Noise ! sectional winding bifilar winding < advantage? > FR-PM-3 FR-PM-3 Sectional winding: Bifilar winding: For example: WE-SL2 744227S For example: WE-SL2 744227 Common Mode suppression Common Mode suppression Differential Mode S-Type Differential Mode suppression Differential Mode suppression is high! is low! ATTENTION: SECTIONELL WINDING MUST BE USED ON MAINS-POWER SUPPLY ! FR-PM-3 FR-PM-3 Common Mode Choke Filtering with Common Mode Choke: USB example: USB 2.0 Datenline Filter Data signal (Differential) noise (Common Mode ) FR-PM-3 FR-PM-3 Common Mode Choke Model in LTspice USB 2.0 Filtering with WE-CNSW CMC Measuring Point TP2 EMI-part EMI-part 90 Ohm @ 100 MHz C.M. 600 Ohm @ 100 MHz C.M. WE-CBF 20 Ohm @ 240 MHz D.M. 40 Ohm @ 240 MHz D.M. 120 Ohm @ 100 MHz FR-PM-3 FR-PM-3 Common Mode Choke Model in LTspice Common Mode Choke Model in LTspice P/N: 744212100 FR-PM-3 FR-PM-3 Find where the noise come from ! EMI-Filter topologies, Simulation and Layout tips Vcc FR-PM-3 FR-PM-3 Which impedance do we need ? Differential noise filter: SMD-Ferrite WE-CBF (Chip Bead Ferrite) Level [dBµV/m] 60 50 40 30 20 SMD-Ferrite Link Aufbau 10 WE - CBF 0 30M 40M 50M 70M 100M 200M 300M 400M 600M 1G Frequency [Hz] FR-PM-3 FR-PM-3 Impedance: SMD-Ferrite (Chip Bead) Insertion Loss Model Z A ZF U0 U1 U2 ZB XL(NiZn) Equivalent circuit of Filter Equivalent circuit Equivalent circuit of of source Advantage of SMD-Ferrites: system impedance wideband, frequency-dependent Absorber for RF-noise in the frequency + + ZA ZF ZB range 10 MHz ... > 2GHz Insertion Loss => A = 20log in (dB) with very low DC-Resistance + Z A ZB (< 0,8 Ohm max. !) FR-PM-3 FR-PM-3 The real world........ ! Practical figures for ZA / ZB Simulation device source Model Fer. Noise * Groundplanes : Impedance range 1 ... 2 Ω source Simulation Ω ? Model Cap ? * VCC-Distribution: Impedance range 10 ... 20 * Video-/ Clock-/ Dataline: Impedance range 50 ... 90 Ω Equivalent Circuit of Equivalent circuit of source Filter-Components * Long Datalines: Impedance range 90 ... >150 Ω Equivalent circuit of load for Inductor and Capacitor one With this we can make a first decision of a Ferrite-Impedance ZF can find Simulation-Models which would suppress noise in our application : FR-PM-3 FR-PM-3 Which Impedance ZF is needed ? case 1: Attentuation reached Example 1: required attentuation The initial = 20dB @ 200 MHz setup that System Impedance is VCC-Distribution around 10 Ohm System impedance ca. 10 Ohm at 200 MHz is true ! => goto Nomogramm: 180 Ω => choise: 220 Ω 180Ω 220Ω FR-PM-3 FR-PM-3 case 2: More Attentuation reached Analyse of the results Measurement of Level [dBµV/m] e.g. 40dB with Ferrit. 60 --- : Perfect 20 dB attenuation 50 The System- impedance ZA and ZB are 40 much lower (at around 1 Ohm)! 30 20 --- : Only 10 dB attenuation ?? 10 0 30M 40M 50M 70M 100M 200M 300M 400M 600M 1G Frequency [Hz] 220Ω FR-PM-3 FR-PM-3 Insertion Loss vs.