air core and magnetic core transformers for isolated power...

Analog Devices Confidential Information—not for external distributionPWRSOC Madrid 2016

BAOXING CHEN

Air Core and Magnetic Core

Transformers for Isolated

Power Conversion

10/03/2016

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Micro-Transformers Replace Discrete Transformers, Diodes &

Opto-couplers

Conventional, Discrete Solution

½ W Isolated Power & 4

High Speed Data Channels• High-freq energy conversion

• low-freq energy regulation

High speed, low power and integration

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®

ADuM1100

First

iCoupler

Digital

Isolator

ADuM140x

4 Channels in

One Package

ADM248x

RS-485

ADuM120x

2 Channels

in Narrow

SO-8

AD7400

ƩΔADC

ADuM125x

I2C

ADuM1220

½ Bridge

Gate Driver

ADuM240x

5 kV rms

Isolation

ADuM540x

isoPower®

ADuM5230

½ Bridge

Driver with

isoPower

ADM3251E

RS-232

ADuM7410

1 kV rms

ADuM4160

USB

ADM2582

RS-485 with

isoPower

ADM305x

Cu

mu

lati

ve

Ch

an

nels

of iC

ou

ple

r Is

ola

tio

n [

Bil

lio

ns

]

ADE791x

Isolated Metering

AFE

ADuM347x

Switching

Regulator

ADuM3190

Linear

Isolator

ADuM124x/144x

Ultra Low

Power Isolator

Micro-Transformers Enable Signal and Power Isolation: >1.8

Billion Micro-Transformers Have Been Shipped

3

ADuM4135

IGBT Gate Driver

ADuM14x

Robust

Quad Data

ADN4651

600Mbps

Isolated LVDS

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Power Transformer Radiation Minimized Through Anti-Phase

Center Tape But PCB Radiation Needs Mitigation

Overall Emission

PCB

Chip

PCB Suppression

techniques

180MHz

360MHz

No PCB Suppression

techniques

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Integrated

Air-Core

Integrated Magnetics Bridge The Gap Between Air-Core and

Discrete Transformers

5

10mH

0.1mH

10nH

1nH

100KHz 1MHz 100MHz 1GHz

30~40%

70~80%

Switching Frequency

Ind

ucta

nce (

Siz

e)

10MHz

Integrated

Magnetic Core

1mH Discrete

EMI Challenge

Efficiency

50~60%

fLI

1~

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REF1

Magnetic layers enclosing spirals

Minimum flex leakage (radiation)

Complex core structure

Difficulty in domain alignment control

Significant core loss

Inductor Configurations: Pot-Core vs Solenoid

6

Windings enclosing magnetic core

Via complexity

Flux leakage (radiation concern)

Simple core structure

Higher permeability

Easy domain alignment

Flux parallel to surface

*Tyndall Cian O’Mathuna Group *Stanford S Wang Group

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Transformer Configurations For Achieving Isolation

Top View

Side by Side or Stacked

Interleaved Primary and Secondary

for Best Mutual Coupling

Analog Approach

>5kVrms Isolation

*Tyndall Cian O’Mathuna Group

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Converter Architectures Suitable For Integration

8

Flyback

Simple with fewest components

No output filtering inductor

Load dependent saturation current

Limited power density

LLC converter

High efficiency (ZVS)

Load current provided by resonant current

High power density

Need Lr or use leakage inductance

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Equations for Magnetic Solenoid Inductors

►Large wc Coil Width

►Large tc Coil Thickness

►Short Length l wc!

►Higher Permeability mr

►Large tm

l

wtNL mr

2

0mm

cc

dctw

NwR

2

i

crt

wwNC 02

mm

l

twNt

R

LQ ccmr

2

0

m

m22

2

1

2

1 satm

satsat

Bt

wl

LiE

N

lBI

Thicker tm=>Higher Energy Density

High Q

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Core Lamination Reduces Loss Tangent

Parameter Measured

Result

Thickness ~microns

Saturation 1.1T

Relative

Permeability

~1000

Coercivity Low < 0.1 Oe

Curie Temp 570ºC

Bulk Permalloy (NiFe)

◦ Stable soft magnetic material

◦ 2 um NiFe

Laminated Permalloy (NiFe)

◦ High quality core with multiple layers of NiFe

◦ 20x (NiFe /AlN)

Dedicated magnetic material deposition

system (Oerlikon EVOII)

0

200

400

600

800

1000

1200

1 10 100 1000 10000

Pe

rme

ab

ilit

y (

-)

Frequency (MHz)

ur' bulk

ur'' bulk

ur' laminated

ur'' laminated

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Transformer On-Wafer Characterization

GSG RF probe

[S] [Z]

4 Port Network

Analyzer

Transformer Open Die

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Transformer Modeling with HFSS

tetrahedral

3D; Full wave EM

simulator; Finite element

method

HFSS

Thickness

(µm)Material Conductivity (S/m)

Winding 4 Gold 3.5875e7

Core 2 NiFe NiFe: 1.4e7

z(not in scale)

xy

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2mm Core Transformer Characteristics – Simulation & Measurement

13

580nH

4.5

0.93

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Improved Quality Factor for 4mm Thick Core

4um amorphous magnetic core

Qmax~7.5 – close to target Q=8,

Major core stability improvement.

0

1

2

3

4

5

6

7

8

0.1 1.0 10.0 100.0 1,000.0

Q (

-)Freq (MHz)

Material 1

Material 2

-2000-1750-1500-1250-1000

-750-500-250

0250500750

10001250150017502000

-50-40-30-20-10 0 10 20 30 40 50

nW

b

Oersteds

Material 1

Material 2

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Winding Thickness Improvement

► Device FEM models

Model: Increased thickness of Au metallization by 2 um will deliver Q>8

Model option Q max (-)

2x6 um Au (default) 7.70

2x8 um Au 8.85

2x10 um Au 9.71

0mm

rf

Skin depth for Au @ 20 MHz:

17.5 um

DCR reduction effect:

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Effect of DC Bias and Large AC Signal on RF Performance

Material 1

NiFe

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Summary

►Magnetic Core Has the Potential to Improve Converter Efficiency and

Reduce EMI for Integrated DC/DC Converters

► Intertwined Solenoid Transformers Have Been Modeled & Characterized

and Have Excellent Magnetic Coupling

►2mm Multilayer Core Lead to a Q of 5 at 20MHz For the Intertwined

Transformers

►4mm Multilayer Core With 8mm Thick Winding Achieved Q > 10

►Effect of DC Bias and Large Signal on Transformer Performance Have

Been Characterized

►DC/DC Converter Passed Class B EMI and Achieved 46% Efficiency at

200mW

Acknowledgements: Contributions from iCoupler group & ADLK

FAB ipassive team in ADI