Ferrites in EMC applicationsPaweł WęgrzyniakJohan KenisField Application Engineers - Laird

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• Source of electromagnetic noise can be any circuit which operates with time-changing current

• Path where the noise energy propagates between the source and receiver (victim)

• Receiver (victim) where the noise is measured, or where a disturbance (interference) can affect proper operation of circuit itself of other devices in neiberhood.

Source Victimpath

EMC Basic Model

EMC Basic Model - Sources

• Switching Mode Power converters DC/DC converters (buck, boost, flyback)

DC/AC converters

BLDC motor controllers

D-class amplifiers

• Digital IC’s Clock drivers

SRAM interfaces

Peripherial interfaces (SPI, I2C)

IC’s itselves (power supply lines, silicon structure)

• Analog IC’s Charge pumps

VCO’s

• Brushed motors

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Source

EMC Basic Model - Paths5

Source Victim

radiation

Inductive coupling

capacitive coupling

Source Victim

Source Victim

galvanic coupling

Source Victim

paths

EMC Basic Model - Victims

• Project budget Redesign cost

Additional suppresion components

Remeasurement cost

• Device itself High impedance inputs

Sensitive analog IC’s (RF receivers)

Voltage regulators feedback pins

• Devices in neiberhood or connected by interfaces• Human safety

Car electronics malfunction

Extensive radiation

Cardiac pacemakers

Medical equipment

6

Victim

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Three Main EMI Design Techniques• EMI Filtering

Cable level:

• Ferrite cores for common mode noise Board level:

• Low pass filter with ferrite beads for differential noise

• Common mode chokes for common mode noise

• Ferrite pates for IC shieding

• Shielding Mechanical design on board and chassis level

• Grounding Board level layout grounding design

Chassis grounding including cabling, connectors, etc

Three Main EMI Design Techniques

• EMI/EMC issues can be generally solved by identifying at least two of these three elements and eliminating one of them.

• Filtering, Shielding and Grounding are the three main EMI design technologies.

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Source Victimpathfilter

shielding

grounding

grounding

FILTERING

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Source Victimpathfilter

shielding

Interesting & Unique Properties of Ferrite Exactly what are ferrites?

– First naturally occuring ferrite is magnetite (Fe3O4) part of spinels group

– Ferrite is a homogeneous ceramic material composed of various oxides. The main constituent is iron oxide (Fe2O4), which is blended with small quantities of other metal oxides then fired in temperature up to 1300C then milled and sintered again with specific temperature profile to create magnetic domains. Depending of size of magnetic domains and oxides additives specific L, R, and Z versus frequency is archieved.

Examples of ferrites applicable in electronics

– Manganese Zinc (Mn Zn) with the formula MnaZn(1-a)Fe2O4 is higher permeability material and due to low resistivity is used in low frequency applications

– Nickel Zinc (Ni Zn with the formula NiaZn(1-a)Fe2O4) material is lower perm material and has higher resistivity than Mn Zn material and can be used for high frequency applications

Ferrite material basics

1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+090.00E+00

2.00E+01

4.00E+01

6.00E+01

8.00E+01

1.00E+02

1.20E+02

1.40E+02

1.60E+02

1.80E+02 Ferrite core impedance

RXLZ

Frequency [Hz]

R, X

l, Z

[Ohm

]

1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+090.00E+00

5.00E+02

1.00E+03

1.50E+03

2.00E+03

2.50E+03

Ferrite core inductance

frequency [Hz]

Indu

ctan

ce [n

H]

0.1 1 10 100 1000-200

0

200

400

600

800

1000Complex permeability chart

mu'

mu''

Frequency [MHz]

com

plex

rela

tive

perm

eabi

lity

• From material to ferrite core– μ’ represents imaginary part of impedance

(inductance) – μ’’ represents real part of impedance (losses)

Z

Z

Lossy

Inductive

Inductive ferrite components

Chip Inductors (RF)

Power Inductors

Toroids

𝑗 𝜔𝜇❑′ 𝐿𝑜

Wireless Power Charging Coils

Ferrite components - inductiveDrum core

Multilayer

Molded

EMI ferrite components

Common mode

Differential mode

𝜔𝜇′ ′𝐿𝑜

Special Ferrite plates

Multihole ferrite plates for connectors

Cable cores

Board Level

ML ferrite beads

Wire assembly ferrite beads

ML Common Mode Chokes

Wire assembly ferrite Common Mode

Chokes

Wire wound Common Mode Chokes

Suppresion of noisy IC’s

Ferrite Rods

Ferrite components - EMI

Cable Core Ferrite Materials

Round Solid Cores Round Solid CoresRound Split CoresFlat Cable Solid CoresFlat Cable Split Cores

Round Solid CoresRound Split Cores

Ferrite materials for custom designs

Typical Application Material Initial Permeability Saturation Flux [mT] Relative loss factor [ * 10-6] at 100kHz

Curie temp [oC]

Common Mode Filtering

24 105 >12025 125 360 740 >22528 800 325 91 >17533 2300 450 600 >20035 5000 450 20 >15038 1700 300 53 >120LF 5000 450 20 >150HF 120 360 740 >225

DC Bias Ethernet Transformers

36 4500 450 10 >15046 4000 450 10 >15056 5500 450 15 >13066 3200 480 >200

High Perm for Telecom

42 7500 410 6 >13040 10000 380 5 >120

Special 29 700

Ferrite materials for PoE and PoE+Laird

Material Application General DC bias requirement Temperature range Status

36 Low power PoE (15W) 8mA or up to 18mA 0.1 to 0.4 Oe (DC field strength) 0 to 70C Ready

46 Low Power PoE (15W) 8mA or up to 18mA 0.1 to 0.4 Oe (DC field strength) -40C to 85C Ready

66 High power PoE (>30W) PoE+, PoE++ or Ultra PoE

18mA to 35mA, or even higher 0.4 to 0.6 Oe (DC field strength) 0 to 100C Ready

68 Low or Medium power PoE or PoE+ (30W)

18mA to 24mA (0.6 to 0.9 Oe (DC field strength) -40C to 85C To be Launched

Differential mode current filtering

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dT

overshoot & ringing

Logic 0

Logic 1

dT

Overshoot & ringing less

Logic 0

Logic 1

Ferrite can absorb the high frequency EMI energy, dissipating it as tiny amounts of heat.

0

100

200

300

400

500

600

700

800

1 10 100 1000

Frequency (MHz)

|Impe

danc

e| (W

) 0A

0.1 A A0.2 A A0.3 A A0.4 A A0.5 A A

After

Before

Differential mode current filtering by ferrite beads

Filtering of Power Distribution Networks

Filtering solutions Characteristics

Design considerations – inductance in LF band

XL @ 10MHz =80Ohm

L = 1.26uH

C= 100nF

Fres=1/2pi sqrt(L*C) = 445kHz

Risk of resonance in LF band with wrong selected capacitors

Design consideration – DC bias

Design consideration - PI filter

Year Supply [V] Supply [W] Supply [A]Supply

Impedance target [mOhm]

Supply impedance frequency

range [MHz]

1990 5 5 1 5000 161993 3,3 10 3 1100 661996 2,5 30 12 210 2001999 1,8 90 50 36 6002002 1,2 180 150 8 1200

•Single decoupling capacitor does not provide good broadband, low impedance filtering•Serial ferrite bead makes high impedance barrier for HF currents

Power Distribution network – impedance amalysis

PN Description package impedance at 100MHz

DCR MAX (Ohm)

RATED I Max [mA]

LI0201 Low Current 0201 120 0,8 200-500HZ0201 High Impedance 0201 600 1,5 100HZ0402 High Impedance 0402 1500 2 50-200LI0402 Low Current 0402 30-300 0,500 200-500HI0603 High Current 0603 60 0,030 4000HZ0603 High Impedance 0603 2500 1,500 50-300LI0603 Low Current 0603 47-300 0,400 200-700MI0603 Mid Current 0603 30-600 0,100 1000-2500HI0805 High Current 0805 31-120 0,020 3500 - 5000HZ0805 High Impedance 0805 470-2700 0,800 200-500LI0805 Low Current 0805 75-300 0,300 700-800MI0805 Mid Current 0805 11-1000 0,150 1000-2500HI1206 High Current 1206 50-160 0,035 3000-6000HZ1206 High Impedance 1206 600-1000 0,500 300-500LI1206 Low Current 1206 150 0,150 800MI1206 Mid Current 1206 26-600 0,060 1500-2000MI1210 Mid Current 1210 60 0,035 1500HI1612 High Current 1612 56 0,004 10000HI1806 High Current 1806 60-91 0,030 3000-6000HZ1806 High Impedance 1806 1000 0,150 1500LI1806 Low Current 1806 80-150 0,500 300-500MI1806 Mid Current 1806 78 0,030 1000HI1812 High Current 1806 100 0,010 8000HI2220 High Current 2220 150-800 0,030 4000-5000HR2220 High Retention 2220 800 0,010 8000HI3312 High Current 3312 100 0,004 10000LF0805 Low Frequency 0805 2553 1,250 100LF1206 Low Frequency 1206 2743 1,050 100-500DA1206 Array 3216 1000 0,800 200

Laird ferrite chip beads

Common Mode current filtering

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Common Mode Noise Filtering Via CMC

Clock Driver Receiver

100Ω

C

L

Common Mode Noise

Differential Signal

Low Pass Filter

Common Mode Noise Rejection

Types of Common Mode Chokes

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• Low frequency wire wound power CMC’s – high inductance, – high current (28A and above)

• Low frequency wire wound signal CMC’s – size from 0504 to 2828, – USB 3.0, HDMI, CAN

• Cable cores– LF, BB, HF – solid and split– impedance up to 500Ohm at 100MHz

• Multilayer CMC’s– low profile 2.1mm to 2.85mm– high currents up to 10A

• High frequency ferrite assembly arrays CMC’s – multipath or multiturn configuration possible– scalable impedance (multiturn)

Common Mode Choke Arrays – more freedom in a design

PN TypeZ @

100MHz [Ohm]

Z @ 500MHz [Ohm]

Z @ 1GHz [Ohm]

DCR MAX [Ohm]

RATED I Max [mA]

CM2722R201R-10 SMD 1 pass 200 202 187 0.0200 5000

CM2722R201R-10 SMD 2 pass 433 362 187 0.0400 5000

CM3822R201R-10 SMD 1 pass 200 207 187 0.0200 5000

CM3822R201R-10 SMD 2 pass 433 362 187 0.0400 5000

CM3822R201R-10 SMD 3 passs 670 470 208 0.0600 5000

CM6032V201R-10 SMD 1 pass 200 219 213 0.0100 8000

CM6032V201R-10 SMD 2 pass 472 313 179 0.0200 8000

CM6032V201R-10 SMD 3 pass 737 315 193 0.0300 8000

CM6032V201R-10 SMD 4 pass 995 358 250 0.0400 8000

•High frequency ferrite assembly array CMCs – multipath or multiturn configuration possible– scalable impedance (multiturn)– low parasitic capacitance (comparison to wire-wound)– cheap (comparison to wire-wound)– various current ratings and sizes– easy customizable (various materials -> different bands)– low differential mode impedance– AEC-Q200 compliant

DC brushed motor filtering example

• Main switch is usualy intergrated with speed controll and forward – rewerse switch

• In modern designs baterry is equipped with charging / discharging controller

M+

M-

+ -motor

+ -battery

speedcontroll

mainswitch

forward - rewerseswitch

Main source of EMC disturbance are brushes In some cases PWM switch at speed controll circuit

can be also source of EMC disturbance

LAIRD’s solution for DC brushed motors – case 1

• EMC disturbances given by brushes can be a common mode behavior and differential mode

• To reduce common mode emmision ferrite core is cheap and effective solution

• Example presents efect of usage of 300Ohm ferrite as a common mode choke

+

-m

otor

To speed controller

• EMC disturbances given by brushes can be a common mode behavior and differential mode

• ferrite core is cheap and effective solution to reduce common mode and differential mode emmision

• Example presents efect of usage of 300Ohm ferrite as a common mode choke and 240Ohm ferrite as differential mode choke

+

-m

otor

To speed controller

LAIRD’s solution for DC brushed motors – case 2

LAIRD’s solution for DC brushed motors – case 3

+

-m

otor

To speed controller

• EMC disturbances given by brushes can be a common mode behavior and differential mode

• ferrite common mode choke is a single part solution for EMC disturbances

• Example presents efect of usage of CM5441Z161R-10 part

Ferrites is wireless charging applications

Ferrite Disk and Plates for wireless charging and NFC applications

• Ferrite disks and plates– two different materias with different permeability– reduce EMI of noisy IC package – Wireless power charging – Near Field Communication devices

Digital Control Section

Sensitive Analog Section

Noisy heat-sink problem

Materials for ferrite plates

Qi compliant Wireless Power Charging coils• Laird is a Wireless Power

Consortium member

• 28T material is listed on the WPC specification

• Several standard coils according to WPC specification

• Incomming „Medium Power” – 15Watts coils

• AEC-Q200 compliant components.

• Customer design coils

Product Definition – TX & RX Module

• TX Module : An assembly of magnetic plate / sheet and coil, used to transmit wireless power out to receiver. Magnetic shielding can be ferrite, iron powder or Polymeric material in solid or flexible state. Coil can be wire wound, embedded copper trace in PCB, or any metallized printed circuit. TX module can be open construction, molded or potted in plastic case / housing / header, and additional overheat protection (NTC) or heat dissipation (heat sink) components may be required.

• RX Module : Construction similar to TX module but the function is to receive (couple) wireless power transmitted from TX.

Flexible ferrite material

• NFC, RFID application & wireless charging application

• Cavity noise suppresors• Made by thin, high permeability sintered

ferrite with PET film and adhesive tape • Standard ferrite layer thickness

0.05mm,0.1mm and 0.2mm • Custom size or thickness available upon

request • Operating temperature -40 to 85 ℃ ℃

(possibility to extend in custom applications)

• WS series – highest permeability on the market

Property MHLL series MSLL series MULL series WS series

Real Permeability, @13.56MHz, 0.1V 130 +/-20% 100+/-20% 150+/-20% 250 +/-20%

Imaginary Permeability, @13.56MHz, 0.1V 5 max 5 max 5 max ~110

Common Mode Generation Example

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DC/DC converter example- ideal circuit

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DC/DC converter example- components parasitics

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DC/DC converter example- components parasitics and PCB layout

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