Monolithic Power Systems, Inc. · NASDAQ:MPWR
Monolithic Power Systems — Technical Presentation (October 2018)
47 slides from Monolithic Power Systems's technical presentation, Oct 2, 2018
Slide 1: Automotive EMI Demystified
Automotive EMI Demystified Black Magic Busted Speaker: Christian Kueck Oct 2nd, 2018
Slide 2: Speaker Intro: Christian Kueck
Speaker Intro: Christian Kueck • Senior FAE supporting automotive Tier-1 customers throughout Germany • Over two decades of experience managing EMI challenges • Deeply involved in the definition and compliance testing of our leading AEC-Q100 power management solutions. • 22 years at Linear Technolog
Slide 3: Automotive EMI Demystified – Agenda
Automotive EMI Demystified – Agenda Analyzing the Typical Power Stage Magnetic Coupling & Demo Video Key Loops Layout Hints Audience Q&A
Slide 4: Analyzing the Typical Power Stage
Analyzing the Typical Power Stage Automotive EMI Webinar
Slide 5: Typical Power Supply Schematic
Typical Power Supply Schematic Schematic with ideal components
Slide 6: Component Parasitics
Component Parasitics Parasitic elements – still concentrated components
Slide 7: PCB Resistance
PCB Resistance With PCB resistance added
Slide 8: Additional PCB Parasitics
Additional PCB Parasitics Additional inductive, capacitive and resistive PCB parasitics Subcircuit added for all nodes
Slide 9: Why is EMI considered Black Magic? Electric Fields Coupling
Why is EMI Fields Electric considered & “Black Magic”?Coupling Near-Field E-Field, capacitive near-field coupling of components and PCB added. All traces and components couple like capacitor plates. More as higher elevated above PCB, larger area, higher AC amplitude and as higher their AC resistance
Slide 10: Magnetic Fields
Magnetic Fields H-Field/magnetic near-field coupling and shielding of components and PCB added. Traces and components couple like transformer windings. More as higher their median conduction path is elevated above a conducting plane and as longer it is. Induced voltage goes linear up with frequency.
Slide 11: Far-Field Electromagnetic Radiation & Reception
Electromagnetic Why is EMI called BlackFar-Field magic 7 Radiation & Reception Traces and components act as dipole radio antennas. Length has to be a decent fraction of the wavelength to be effective. Keep in mind that 1 𝑐~ ϵ𝑟 µ𝑟 In high ϵ𝑟 material effective dipole antennas can become quite…
Slide 12: How Do I Balance All These Influences?
How Do I Balance All These Influences? • There is hope. • Not all effects are relevant in all components. • We will concentrate on the dominant effects first for non-isolated DC-DC converters
Slide 13: Capacitor Impedance
Capacitor Impedance All 0402 capacitors wind up with similar inductance Even if they are inductive, the impedance is still low and they work as bypass elements With TDK SEAT 2013
Slide 14: Capacitor Magnetic Coupling
Capacitor Magnetic Coupling From an EMI view, the bigger problem of capacitors is that they couple near-field magnetics like two transformer windings. That’s a wide band (GHz) coupling path and defeats their filter function.
Slide 15: Sources of E-Fields and H-Fields
Sources E-Fields are created by (AC) voltages. H-Fields or magnetic fields are created by currents. Current always flows in circles / closed loops. They never end in ground planes or a nail in the flower pot…. So hunt for the full circle.
Slide 16: Magnetic Coupling & Demo Video
Magnetic Coupling & Demo Video Automotive EMI Webinar
Slide 17: Example – MPQ4430 Buck Converter EVB Modified to Show Capacitor Coupling
Example – MPQ4430 Buck Converter EVB Modified to Show Capacitor Coupling Standard EVB Modified EVB C1A removed Only one large input bypass capacitor C1B Inductor L2 placed on the back side to eliminate its field
Slide 18: MPQ4430 Buck Converter EVB 4-Layer PCB
MPQ4430 Buck Converter EVB 4-Layer PCB Layout of this 4-layer board – Top, Inner1, Inner2, bottom
Slide 19: MPQ4430 Buck Converter Schematic
MPQ4430 Buck Converter Schematic
Slide 20: 0805 MLCC Capacitor Probe
0805 MLCC Capacitor Probe Pick-up formed like what a capacitor will see on the board.
Slide 21: Buck Converter Capacitor Magnetic Coupling to 30MHz
Buck Converter Capacitor Magnetic Coupling to 30MHz Probe Switcher VIN bypass Cap Two output caps
Slide 22: Buck Converter Capacitor Magnetic Coupling to 30MHz
Buck Converter Capacitor Magnetic Coupling to 30MHz
Slide 23: Buck Converter Capacitor Magnetic Coupling to 300MHz
Buck Converter Capacitor Magnetic Coupling to 300MHz
Slide 24: Why is the magnetic field amplitude and bandwidth so much higher on input bypass caps?
Buck Converter Capacitor Magnetic Coupling Why is the magnetic field amplitude and bandwidth so much higher on the input bypass caps?
Slide 25: Key Loops
Key Loops Automotive EMI Webinar
Slide 26: Synchronous Buck Converter – Inductor Loop
Synchronous Buck Converter – Inductor Loop The triangular inductor current will flow here Harmonics of triangular waveforms decay for higher frequency with 𝑁 2 𝑁 =harmonic number
Slide 27: Synchronous Buck Converter – High Side
Synchronous Buck Converter – High Side In S1 we have a full switched current which moves to and from zero very fast
Slide 28: Synchronous Buck Converter – Low Side
Synchronous Buck Converter – Low Side S2 is fully switched too Harmonics of rectangular waveforms decay for higher frequency only with N
Slide 29: Buck Converter – High + Low Side
Buck Converter – High + Low Side So we have a high dI/dt loop here We call it the “Hot Loop”
Slide 30: Magnetic Antennas
Magnetic Antennas Every trace on your PCB transports AC current Dipole If you create AC current, it forms a magnetic dipole antenna That radiates in the same way that an electric dipole does Radiation goes up proportional to area and current
Slide 31: Skin and Proximity Effect
Skin and Proximity Effect Current density of a rectangular conductor on a single layer PCB Copper conductor Pictured: PCB cross-section, side-view
Slide 32: Skin and Proximity Effect – Shielding Effect of Conductive Planes
Skin and Proximity Effect – Shielding Effect of Conductive Planes Copper conductor Copper conductor Return current flow concentrates here Pictured: PCB cross- section, side-view
Slide 33: Skin and Proximity Effect
Skin and Proximity Effect Multi-layer will separate even their Copper conductor return flows in the plane Copper conductor Pictured: PCB cross-section, Copper conductor side-view
Slide 34: Eddy Currents – Canceling Dipoles
Eddy Currents – Canceling Dipoles Copper conductor Copper conductor Copper conductor Pictured: PCB Here we have our canceling dipoles cross-section, side-view
Slide 35: Magnetic Antennas
Magnetic Antennas For any given aspect ratio, cutting [d] in half reduces the radiated field by 6dB Copper conductor Copper conductor d Copper conductor Pictured: PCB cross-section, side-view
Slide 36: Eddy Current Demonstration (Video)
Eddy Current Demonstration (Video)
Slide 37: Eddy Currents – Cancellation Effect
Eddy Currents – Cancellation Effect Eddy currents can cancel the original magnetic excitation field They do it better when the eddy current conducting plane and the original magnetic excitation field are closer Cancellation works better with: Low profile components (flat, short and wide) A solid gro
Slide 38: Layout Hints
Layout Hints Automotive EMI Webinar
Slide 39: Identify the Hot Loop
Identify the Hot Loop Identify the hot loop and make it as small in diameter as possible For example, in a non-synchronous buck place the freewheeling diode and the input capacitor close to each other both pointing in the IC direction and share a common small GND area. VIN GND
Slide 40: Solid Ground Plane
Solid Ground Plane Place a solid plane under the hot loop, filters etc
Slide 41: Input Filter Placement
Input Filter Placement Place your input filter as far away from magnetic and E-field radiators like the hot loop. For this reason we often put the EMI input filter on the backside. If you can’t move it as far away from the input bypass caps and place a “quiet” GND plane under the filter 4th order EM
Slide 42: Radiated vs Conducted EMI
Radiated vs Conducted EMI Radiated EMI measured with antenna Conducted EMI measured through the cable with a LISN* You will see significant energy differences only as long the fields keep close to the wiring harness, which is up to single-digit MHz when harness length is at least in the range of som
Slide 43: Radiated and Conducted EMI
Radiated and Conducted EMI Up to a few MHz circuits behave like their SPICE simulation. If you’re hunting an EMI problem on the fundamental or first few harmonics, you can still think as SPICE with concentrated components. Above a few MHz for all EMI measures, magnetic field and electric field coupl
Slide 44: Switching Frequency Effect on EMI
Switching Frequency Effect on EMI If we double the switching frequency, we double the number of switch transitions, so we double the EMI energy. That is 3dB more (power is 10*Log(2)) But with double the frequency you have now only half the bins to locate this energy. As a result, the spurs have 6dB
Slide 45: Switching Frequency Effect on EMI
Switching Frequency Effect on EMI If all stays the same except the switching frequency With fixed frequency for every doubling only half the bins are available for the energy Result is 6dB/octave = 20db/decade EMI Increase in dB EMI energy is proportional to switching frequency 3db/octave = 10db/dec
Slide 46: Conclusion
Conclusion Make your hot loops as small as possible. Place a solid ground under the hot loop, EMI filters, inductors etc. Use multi-layer boards with thin dielectric between top and the next GND layer For stringent automotive EMI, use 4th order EMI filters (two inductors) with small components Use a
Slide 47: Q&A
Q&A New MPS EMI test center in Hangzhou, China Additional labs to be built in Detroit, Germany & Shanghai
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