Analog Devices Confidential Information—not for external distribution PWRSOC Madrid 2016 BAOXING CHEN Air Core and Magnetic Core Transformers for Isolated Power Conversion 10/03/2016
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
Analog Devices Confidential InformationAnalog Devices Confidential Information
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
Analog Devices Confidential InformationAnalog Devices Confidential Information
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