Topic 2 Understanding Noise-Spreading Techniques And Their Effects In .

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Topic 2Understanding Noise-SpreadingTechniques and their Effects inSwitch-Mode Power ApplicationsJohn Rice, Dirk Gehrke, and Mike Segal

Agenda1.2.3.4.Quantifying the SMPS noise problem Problem Definition Measurement Techniques and EMC StandardsClarifying the principles of SSFD* Implementing Modulation Using simulation to predict harmonic peak reductionApplication of SSFD* Conducted: Power Factor Correction Radiated: AutomotiveConclusion*SSFD Spread-Spectrum Frequency Dithering2-2

A Definition of ElectromagneticCompatibility: (EMC)"You can watch football with your TV set-top box sitting on a working PC"RERECE Set-top BoxCEREREREConducted Emissions REDifferential (Normal) ModeCommon ModeTVCECERERadiated Emissions RE Working Computer CEElectric Field VoltageMagnetic Field CurrentRERECESEM1500, Topic 1: Understanding & Optimizing EMC in SMPS2-3

Disturbances Generated by SMPS Electromagnetic Emission:Sources of H-Field radiation Winding leakage fields Primary loop area Secondary loop areaSource of E-Field radiation High dv/dt on conductive surfacesHigh frequency on ripple cablesICM2E-FieldInput IDME-FieldH- FieldD1VDMN1ICMZCIN2N2VDMZCOUTIDM OutputCphsVCMQ1E-FieldNOutput-to-ChassisCommon ModeChassis2-4

Graphical Prediction ofHarmonic Spectrum Trapezoidal Waveform Fourier Envelope, Nomogram20 log (2A τ /T ) f1 1/πτAmplitude (dB)tftrAτ–20 dB/dec20 log (2At r /T)f 2 1/π t r– 40 dB/decLog Frequency (Hz)TSimulated Response Æ1 MHz, 50% duty cycleτ 480 ns and tr tf 20 nsAmplitude (V)T the period of the repetitive waveformτ pulse width at the 50% pointsTA pulse amplitudetr t f pulse rise and fall times2-5

Limits and Units ofEMI Power MeasurementConverting dBm to dBµVAmplitude (dBµV)9070Class A Quasi-Peak Value79733010 kP V2 / R, R 50 Ω impedancedB(P) 10log10 (V2 / R) 20log10 (V) 10log10 R66605650dB 10log10 (P / Pref ) 20log10 (V / Vref )Class A Mean Value log(an ) nlog log(a / b) loga logbClass B Quasi-Peak Value46dBW (ref 1 W) 10log10 PdBm (ref 1 mW) dBW 30Class B Mean Value150 k 500 k100 k1MFrequency (Hz)dBV 20log10 V30 M5M10 M100 MdBμV (ref 1 μV) dBV 120(dBmW 30) (dBμV 120) 10log10 50 dBμV dBm 107CISPR 22 and FCC Part 15 Conducted Emission Limits2-6

The Swept Spectrum Analyzer (SA) Basic SA block diagramLow-PassFiterLocalOscillatorDisplay response(Relative to IF filter RBW)MixerInputSignal pectrumIF Bandwidth(RBW)DisplayTNarrowband – Signal containedwithin the receiver bandwidthReceiverBandwidthBroadband Signal(e.g. SSFD)Broadband – Signal not fullycontained within the receiver IFbandwidth0.11Frequency (MHz)10Narrow Band Signal0.11Frequency (MHz)102-7

Understanding Detector Operation(simplification)Peak Detector VIN–Quasi-Peak Detector VOUT–Average Detector VOUT– VIN– VOUT– VIN–VideoFilterVPeak DetectionQuasi-Peak DetectionVPeak DetectionAverage DetectionShort Repetition PeriodtLong Repetition PeriodQuasi-Peak DetectionAverage Detectiont2-8

Agenda1.2.3.4.Quantifying the SMPS noise problem Problem Definition Measurement Techniques and EMC StandardsClarifying the principles of SSFD* Implementing Modulation Using simulation to predict harmonic peak reductionApplication of SSFD* Conducted: Power Factor Correction Radiated: AutomotiveConclusion*SSFD Spread-Spectrum Frequency Dithering2-9

First Conceptualization of“Spread Spectrum” (SSFD)Eva Maria Kiesler aka “HedyLamarr”2-10

Explaining Harmonic Spreadingwith FM TheorySine modulation of a square wavePeriod (t) Modulation profile1fc 1 ( Δf sin 2π fm t ) / fc dfd sin(t) cos(t)dtdtTFrequency 2 ΔffcCenter Frequencyfmdtdf050Time (µs)100β Δf / fm modulation indexSpread -spectrum parameters: Modulation frequency, fm Center frequency , fc Frequency deviation, Δf Other modulation shapes triangular, exponential, complex2-11

Periodic Modulation Waveformsand their Spreading EffectModulation Waveforms1fm 10 kHzTriangularFrequency xponential200kVoltage Controlled Oscillator -VCOGndFMfm 10 kHZVofc 310 kHzΔf 31 kHztr tf 10 ns1MFrequency (Hz) Energy of f0 spread into band:BT 2(Δfc fm) 2(β 1)fm Energy of fn spread into band:BTn 2fm(1 nβ) Fundamental reduction betweenunmodulated (black) waveform andtriangular (green) waveform 7 dB2M2-12

TPS40200EVM-001 Simulation Modelvin68.1 k 104 μAESR10 mΩin C2100 nFU 3 LISNRt68.1 kΩvim m 17.8 μA56 k470 pFR356 kΩR220 mΩ100 kΩ10 pFGDRVGND0Ω1 nHVSWMBR330Rtop100 kΩL1 33 µHDCR 50 mΩESR300 mΩC11C12220 µF 1 µFESR5 mΩESL50 nHESL10 nHRload3.9 ΩModulation waveformfmax fc(1 δ ) 344 kHzδ Δf100 k 0.172fc 2 295 kRate of Modulation (center spreading):Modulation Index: β Rbot26.7 kΩΔf 100 k 7.7fm 13 kCenter SpreadingFrequencyfc (i n im )inV17.1 VFDC654P30.1 kΩ 470 pF1.5 nFfmin 50 ΩESL50 nH10 pF2 kΩVDDCt470 pFfc (i n im )inM2 M120 nFCOMPfmax C1100 µFESR300 mΩfc 295 kHzfmin fc(1 – δ ) 244 kHzfm 13 kHz2-13

Conducted Emission Testing:Line Impedance Stabilization Network (LISN)Purpose:1.Present a constant impedance to the DUT power cord2.Block external conducted emissions from adding to the measurement3.Transfer high-frequency conducted emissions to the measurement equipmentINV17.1 V LoadTerminalOutR25 mΩC2100 nFL150 nHC31 µFL350 nHR11 kΩR350 ΩRFJackM1Impedance (Ω)L243.2 µHDCR 200 mΩC410 pFImpedance withInput/Output Capacitor ESLImpedance withoutCapacitor ESL2-14

Predicted Waveforms in Steady-State3.4Output Ripple3.3Vout (V)3.2LISN Output(V)0.6–0.50.8OSC Ramp(V)0.1Switch Node(V)8–0.51.1Error AmplifierOutput (V)0.93.403.45Time (ms)3.512-15

Predicted Spectral Responseof Line CurrentSimulated LISN output at 50% duty cycle Modulation: fm 13 kHz triangular wave Predicted fundamental reduction 13 dB (higher than measureddue to input-filter parasitics and resonance) Amplitude (dBµV)7419Δ 13 dBNo 0 k368.4 kFrequency (Hz)1.36 M5M2-16

Measured Spectral Content of Line CurrentLISN output at 50% duty cycle FFT RBW 222 Hz Modulation 13-kHz triangular wave Actual fundamental reduction 7.7 dB Frequency Domain70Δ 7.7 dBNo ModulationTime Domainfres 2.2 MHzWith ModulationLISN Output(500 mV/div)Amplitude (dBµV)50Under-damped filterresponse, fres 2.2 MHz30Switch Node(5 V/div)10–10Time (500 ns/div)–30RBW 222 Hz–500.151.773.38Frequency (MHz)52-17

Complex-Wave Modulation: Pseudo-Random Linear-feedback shift register (LFSR)made up of 17 flip flops and XOR gatecreate a (217 – 1) repeating pseudorandom sequence Bitsn4567891011121314151617XOR acts as linear feedback to achievemaximum-length sequence according tothe feedback polynomialSeedOSC INFeedback polynomialx4 x3 1x5 x3 1x6 x5 1x7 x6 1x8 x6 x5 x4 1x9 x5 1x10 x7 1x11 x9 112x x11 x10 x4 1x13 x12 x11 x8 1x14 x13 x12 x2 1x15 x14 116x x14 x13 x11 1x17 x14 1SeedD P QD P QD P QD P QD P QD P QD P QD P QD P Q U1 C QCCSeedCCSeedCCSeedCSeedD P QD P QD P QD P QD P QD P QD P QD P Q U17C17 Bits ( 217–1) states 131071CCU18CLogicHighC C QPeriod2n 071CCCTap 14Tap 17SW –SpreadSpectrumClock toPWMRC pinVoltageControlledSwitch2-18

Pseudo-Random Modulation Uniform spreading, maximum reduction of fundamental Predicted attenuation of f0 30 dBTime Domain WaveformsFrequency Domain Response3.34Output RippleVout (V)3.150.6LISN Output(V)–0.60.8OSC Ramp(V)0.1Switch Node(V)Error AmpOutput (V)Clock In(V)ModulatedAmplitude d0.8435–116150 k04.904.95866 kFrequency (Hz)5M5.00Time (ms)2-19

Agenda1.2.3.4.Quantifying the SMPS noise problem Problem Definition Measurement Techniques and EMC StandardsClarifying the principles of SSFD* Implementing Modulation Using simulation to predict harmonic peak reductionApplication of SSFD* Conducted: Power Factor Correction Radiated: AutomotiveConclusion*SSFD Spread-Spectrum Frequency Dithering2-20

Why Power-Factor Correction (PFC)? Reduce harmonics of IACMinimize Phase Angle between VAC, IACCHold-UpACLineLineCurrent LoadLineVoltage2-21

2-Phase Interleaved Boost OFFL2I2 IL1IIN/2S2 IL2IIN IL1 IL2Attenuates input ripple current Reduces capacitor RMS current I1I20A(See SEM1700 Topic 5)ICOUT (I1 I2) - IOUT2-22

– UCC28070 Interleaved PFC with SSFDSet Δf, fm2-23

UCC28070: Setting DitherMagnitude and Rate Modulation Waveshape:TriangularDMAX20CLKARDMXRT Dither Magnitude(Δf 30 kHz)R RDM 937.5 31.6 kΩfDM (kHz)Oscillator withFrequency Dither19CLKBOffARRTRDM/SYNCOffB2SYNCLogic1SYNC DitherEnable DisableRRDMDither Rate(fm 10 kHz)CDR 5V– R(kΩ) CCDR 66.7 RDM 220 pF fDR (kHz) 2-24

Peak Conducted EMI: 150 kHz to 30 MHz SSFD reduces peaks at both low and high frequenciesAmplitude (dBµV)130110Without Dither 113 dBµV at 340 kHzWith Dither 109 dBµV at 330 kHzResolution BW 9 kHz9070500.151Frequency (MHz)1030Input 120 VAC, Load 640 W,Input Filter: Corcom 15EJT1LISN: Solar 9509-50-R-24-BNCSA: HP8591EM2-25

Quasi-Peak Conducted EMI at 330 kHz130Amplitude (dBµV)Resolution BW 9 kHz110907050300Without Dither 113 dBµV at 339 kHzWith Dither 108 dBµV at 328 kHzFrequency (kHz)3702-26

Average Conducted EMI at 330 kHz130Amplitude (dBµV)Resolution BW 9 kHz110907050300Without Dither 109 dBµV at 338 kHzWith Dither 104 dBµV at 328 kHzFrequency (kHz)3702-27

PFC Summary (Interleaved, 120 VAC, 640 W) With and Without Dither (30-kHz magnitude, 10-kHz rate) 330 kHz: 4-dB decrease (Peak, Qpk and AVG)20 30 MHz: 5-dB decreaseAmplitude (dBµV)130110Without Dither 113 dBµV at 340 kHzWith Dither 109 dBµV at 330 kHzResolution BW 9 kHz9070500.151Frequency (MHz)10302-28

Agenda1.2.3.4.Quantifying the SMPS noise problem Problem Definition Measurement Techniques and EMC StandardsClarifying the principles of SSFD* Implementing Modulation Using simulation to predict harmonic peak reductionApplication of SSFD* Conducted: Power Factor Correction Radiated: AutomotiveConclusion*SSFD Spread-Spectrum Frequency Dithering2-29

TPIC74100 Buck-Boost ConverterControl Modulation waveshape:TriangularVΔf 110 kHz,330 550 kHzBoostVdriverINCVregIntegrates power FETsInput: 1.5 to 40 VDCOutput: 5 V @ 1 AFs 440 kHz (nom)Adjustable:- Dither Rate- Slew Rate of Q1OscCboot2Q4AINV OUT 5VSyncBoost22 to470 µF-5Vg ENABLE22 to100 deController WithDead TimeVlogicRmod ChargePumpQ2ENABLE Cboot1Q1VrefChargePumpInrushCurrent LimitPGND5 Vg SCR0SCR1CLPSlew ndgapRefTempMonitorPOR WithDelay TimerAOUTRESETGNDREST2-30

TPIC74100 EVM2 Schematic12-V VbattSlew-RateAdjustDitherRateAdjust5-V VOUT625 mA Fs 440 kHz (nom)Input 12-V Battery, Output 5 V at 625 mANo input-filter inductor (JP1 shunts L2)CISPR25 Setup, 1-m monopole (NB) antenna2-31

Peak—No Dither (0.15 30-MHz Band)Slowing slew rate reduces 20 30-MHz peaks 70Amplitude (dBµV/m)42dBµV/mRBW 9 kHzFastest Slew Rate(Slew Rate 18.8 A/µs)Slowest Slew Rate(Slew Rate 2.8 A/µs)60504042 dBµV/m3026 dBµV/m26dBµV/m20100–10150 k500 k1MFrequency (Hz)5M10 M20 M 30 M2-32

Peak—28-kHz Dither Rate(0.15 30-MHz Band) Highlighted peaks were 42 and 26 without dither35 dBµV/mAmplitude (dBµV/m)(7 dB less)70RBW 9 kHzFastest Slew Rate60Slowest Slew Rate504020 dBµV/m35 dBµV/m(6 dB less)3020 dBµV/m20100–10150 k500 k1MFrequency (Hz)5M10 M20 M 30 M2-33

Peak—56-kHz Dither Rate(0.15 30-MHz Band) Highlighted peaks were 35 and 20 with 28-kHz dither7033 dBµV/mRBW 9 kHzFastest Slew Rate60Amplitude (dBµV/m)(2 dB less)Slowest Slew Rate504017 dBµV/m33 dBµV/m30(3 dB less)2017 dBµV/m100–10150 k500 k1MFrequency (Hz)5M10 M20 M 30 M2-34

Peak—No Dither (30 200-MHz Band) Slower Slew reduces peaks, especially above 108 MHz60Amplitude (dBµV/m)50Fastest Slew RateSlowest Slew Rate403020 RBW(FM Band)100–10–20304050607080 90 100Frequency (MHz)200NOTE: In FM band (76-108 MHz) noise floor increase due to wider RBW, not switcher.2-35

Peak—Slowest Slew (30 200-MHz Band) 56-kHz dither reduces peaks, especially below 60 MHz60Amplitude (dBµV/m)50SlowestSlewFastestSlewRateRatewith No ModulationSlowest Slew Ratewith 56-kHz Modulation403020 RBW(FM Band)100–10–20304050607080 90 100Frequency (MHz)200NOTE: In FM band (76-108 MHz) noise floor increase due to wider RBW, not switcher.2-36

Automotive DC/DC Summary Tested TPIC74100 EVM2 Radiated Emissions (RE) Without input filter chokePCB layout NOT optimized for EMCSlew Rate Control Little impact on RE from 150 kHz to 30 MHzReduces RE from 30 MHz to 200 MHz Dither reduces RE at both low and high frequencies As dithering rate increases, peaks are reduced2-37

Additional Considerations of SSFD Tends to raise the noise floor Potential audible noise ( if fm in audible range ) May increase ripple Magnetics – design for Δf2-38

ConclusionsSpread-Spectrum Frequency Dithering (SSFD): CAN facilitate EMC: Total-noise energy is unchangedHowever , Narrowband becomes broadband Spectral peaks are reduced May reduce input filter size and cost Is NOT a substitute forcareful attention to: LayoutComponent selectionShieldingetc TReceiverBandwidthBroadband Signal(e.g. SSFD)0.11Frequency (MHz)10Narrow Band Signal0.11Frequency (MHz)102-39

3. Transfer high-frequency conducted emissions to the measurement equipment Conducted Emission Testing: Line Impedance Stabilization Network (LISN) Impedance ()Ω IN C4 10 pF L1 50 nH L3 50 nH L2 43.2 µH DCR 200 mΩ Load Terminal Out RF Jack M1 R2 V1 5 mΩ 7.1 V C2 100 nF R1 1 kΩ R3 50 Ω C3 1 µF Impedance without Capacitor ESL Impedance .

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