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Coupled inductors on silicon for PwrSoC in the frame of
PowerSwipe project
Santosh Kulkarni*, Bruno Allard**
*Microsystems Centre, Tyndall National Institute, University College Cork, Ireland**Ampere lab, INSA Lyon, France
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PowerSwipe Concept
2
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PowerSwipe Consortium Partners
3
First EU Funded programme on PwrSoC/PwrSiP
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Powerswipe-Demonstrators
Demo 1- Low Frequency dc-dc for Automotive
Demo 2- High Frequency dc-dc for multi-phase IVR applications
Passive LC
PCB Motherboard
SOC + LV-PMICPassive Interposer
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Summary of presentation
● Powerswipe’ integrated coupled inductors
● Design, Fabrication & Small Signal testing of ‘Loosely’ coupled inductor device
● Large Signal characterization of integrated coupled inductors
● Large signal Inductance, resistance, BH loop
● Impact of dc bias on magnetic material under test
● Summary
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HF DC-DC converter-Specs
●Achieve miniaturisation of power passives: ● Increased switching frequency of switched-mode DC-DC converter
(10-200 MHz)● Power passives footprint comparable to DC-DC converter IC (1 to 2 mm2)
PowerSwipe Motivation/Objectives
Design 1: Coupled inductor
Inductordesign
Freq. (MHz)
L (nH)
Coupling factor
Efficiency (magnetics)
Efficiency(IC)
Total efficiency
Coupled 100 45 ~0.4 90% 90,4% 81%
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L (nH) Core Length
Core Thickness
Copper width
Copper Thickness
DCR(Ohm)
Device Footprint
45 Coupled 0.95 mm 2 μm 40 μm 15 μm 0.282 1.25 mm2
45nH Coupled
PowerSwipe coupled inductor – Design & Fabrication
Device Cross-section
Coupled inductor prototype
Device Schematic
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Powerswipe coupled inductor – Small signal Characterization
Small signal testing: LCR meter & 4-probe Kelvin setup- INSA Lyon
ü Good frequency & current response
20% drop
Isat=650mA
Small signal testing: L vs DC bias-Tyndall
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Powerswipe coupled inductor – Coupling Measurement
• Two port VNA test for coupling
kmeasured= 0.38; kdesign= 0.4
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Large Signal Characterization Set-up
• Signal generator- Agilent E8257D• Power amplifier- Applied Research 25A250A• Current probe- Pearson current 2877• Voltage probe- Tap 1500
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Test circuit for coupled inductor measurement
Key issues with large signal testing set-up- Noise
- Use 4 wire measurement for the DUT- Error in amplitude & phase measurement
- Attenuation & time delay from current & voltage probes- Accurate compensation system to correct this skew
- Compensation is done through a measurement on a capacitor of known impedance
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Voltage & Current waveforms for Capacitor-Compensation
• Time lag @ 40MHz- 0.671 ns• Current attenuation- 0.895
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Inductance & DC resistance measurements
• Inductance (Self/Mutual) stays constant upto 60MHz• Resistance measurement shows a dramatic increase after 60MHz• This behaviour not consistent with small signal test data• Possible explanation- Voltage probes damaged
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DC bias measurements
• Voltage & Current waveforms including compensated current loops• Iac- 20mA; Ferquency- 60MHz• DC saturation current- 700 mA (consistent with small signal measurement)
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Large signal testing to plot BH loops @ different bias currents
- B value estimated using Faraday’s law- H value estimated using Ampere’s law
10 Hz
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Final circuit testing of Powerswipe coupled inductors
Inductor Passive Interposer
Switch
• Initial test on single phase discrete inductor with Interposer completed• Circuit testing of coupled inductor with VR ongoing at INSA, Lyon- Result
will be presented at future conferences
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Benchmarking Powerswipe VR performance
50
55
60
65
70
75
80
85
90
0 0.1 0.2 0.3 0.4
Effic
ienc
y (V
)
Load current (A)
110MHz, board
0 0.1 0.2 0.3 0.4Load current (A)
110MHz, interposer
1.2V 1.8V 2.4V
55
60
65
70
75
80
85
90
95
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Effic
ienc
y (%
)
VOUT/VIN
State of the art100 MHz cascode
100 MHz standard 10
20
40
100
200
500
Freq
uenc
y (M
Hz)
Active dieInterposer
16 nF
60 nH
11 nF11 nF
33 nF
11 nF
Ä Efficiency– Globally better on interposer– Slightly increased on-board for
low load current
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Summary• First EU funded project on PwrSoC/PwrSiP
• Target applications- Automotive & IVR
• Developed multiphase coupled inductors for IVR
• Racetrack coupled inductors designed using CAD tool• Fabricated using Tyndall’s Double Metal Layer process
• Small signal measurement in good agreement with design data• Developed large signal characterization system for measuring coupled
inductor performance
• Circuit level testing of VR’s ongoing
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Acknowledgements
Tyndall National Institute- Prof. Cian O’Mathuna, Dr. Paul McCloskey, Dr. Ningning Wang, Dr. Zoran Pavolvic, Ricky Anthony, Nicolas Cordero, Margaret Hegarty, Joe O’Brien, Declan Casey, James Rohan, Anne-Marie Kelleher, Graeme Maxwell
Lab Ampere, INSA, Lyon- Florian Neveu, Dr. Christian Martin
Funding- European Union for funding the work through FP7 (Project: PowerSwipe) under Grant 318529.
Universidad Carlos III de Madrid- Dr. Cristina Fernandez Herrero
