Radiation of Synchronous Buck Converter
Modelled by Three Magnetic Moments and
Combined
with
SPICE
Simulations
12
3
2
1
Raul Blečić , Renaud Gillon , Bart Nauwelaers and Adrijan Barić
1
University of Zagreb Faculty of Electrical Engineering and Computing, Unska 3, 10000 Zagreb, Croatia
Tel: +385 (0)1 6129547, fax: +385 (0)1 6129653, e-mail: raul.blecic@fer.hr
2
KU Leuven, ESAT-TELEMIC, Kasteelpark Arenberg 10, 3001 Leuven, Belgium
3
ON Semiconductor Belgium BVBA, Westerring 15, 9700 Oudenaarde, Belgium
Abstract
Operation of a Synchronous Buck Converter
Radiation characteristics of a system-in-package (SiP)
synchronous buck converter are analyzed by a set of
3D electromagnetic (EM) simulations. The simulated
radiation characteristics are modelled by three orthogonal magnetic moments. Each magnetic moment is
related to a geometrical loop present in the modelled
structure. The proposed model describes accurately
both the maximum radiated fields and the shape of
the radiation pattern. The application of the proposed
model is demonstrated by combining it with the results
of SPICE simulations of the analyzed converter in order to predict its radiated emissions.
? The first resonance is formed by the capacitance of the low-side FET in the off-state Coss,LS , while the second one by
the capacitance of the high-side FET in the off-state Coss,HS and the total inductance of the input decoupling network.
? The resonance in the input decoupling network is the
main source of EM interference.
? A synchronous buck converter is shown to be a magnetically driven source of radiation in [4].
? Considering the wavelengths in free space at the frequency range of interest (30 cm at 1000 MHz to 10 m
at 30 MHz), DC-DC converters can be treated as electrically small.
? Radiation characteristics of electrically small, magnetically driven sources can be described by three orthogonal
magnetic moments (Mx, My , Mz ) [8].
? In this paper, a System-in-Package (SiP) synchronous
buck converter mounted on a 2-layer PCB is simulated
by a 3D FEM EM solver.
? The simulated structure is excited by an ideal 1-A current source to extract its radiation characteristics.
? The radiation characteristics are modelled by three orthogonal magnetic moments and each magnetic moment is related to a geometrical loop present in the
modelled structure.
? Finally, the proposed model is combined with the SPICE
simulation to predict the radiated emissions of the analyzed converter.
Current, I [A]
40
20
iD,HS
−iD,LS
iB,LS
iOUT
38.36 A
32.33 A
0
−20
0
50
100
Time, t [ns]
150
Lpackage
VCT RL
PWM+
FET
feed- drivers
back
HSFET
LOU T
+
LSFET
VOU T
COU T
GND
−
EM Simulations
? Three characteristic structures are simulated by a 3D EM solver for four substrate thicknesses (h = 0.1, 0.2, 0.5, 1 mm).
? The radiation model consisting of three orthogonal magnetic moments is extracted numerically for each simulated
structure at the frequency of 200 MHz.
1st Characteristic Structure - Input Decoupling Network:
Extracted moments (@ 200 MHz):
FR4 substrate
50 mm
VIN-
h [mm] Mx [A mm2] My [A mm2] Mz [A mm2]
0.1
0.01
-0.01
-0.11
0.2
0.03
-0.01
-0.19
0.5
0.01
-0.03
-0.38
1.0
0.02
-0.02
-0.61
Mx
Decaps
h
My
Excitation VIN+
Mz
50 mm
GND
2nd Characteristic Structure - QFN package Mounted on the Input Decoupling Network:
LSFET
Extracted moments (@ 200 MHz):
VINMz
VIN+
QFN
Mx
h [mm] Mx [A mm2] My [A mm2] Mz [A mm2]
0.1
0.50
0.16
-0.21
0.2
0.53
0.15
-0.30
0.5
0.56
0.17
-0.49
1.0
0.58
0.15
-0.74
My
HSFET
3rd Characteristic Structure - QFN package Mounted on the Input Decoupling Network with Ground
Vias:
VIN+
FR4 substrate
Extracted moments (@ 200 MHz):
Mx
h [mm] Mx [A mm2] My [A mm2] Mz [A mm2]
0.1
0.50
0.73
-0.20
0.2
0.55
1.15
-0.24
0.5
0.59
2.08
-0.45
1.0
0.66
3.00
-0.66
My
Decaps
QFN
Mz
VIN-
R. Erickson and D. Maksimovic, Fundamentals of Power Electronics, ser.
Power electronics. Springer, 2001.
[2] F. L. Luo and H. Ye, “Investigation of EMI, EMS and EMC in power
DC/DC converters,” in Proc. IEEE Int. Conf. on Power Electron. and Drive
Systems (PEDS), vol. 1, Nov. 2003, pp. 572–577.
[3] K. Kam, D. Pommerenke, C.-W. Lam, and R. Steinfeld, “EMI analysis
methods for synchronous buck converter EMI root cause analysis,” in Proc.
IEEE Int. Symp. Electromagn. Compat., Aug. 2008, pp. 1–7.
[4] A. Bhargava, D. Pommerenke, K. Kam, F. Centola, and C. W. Lam, “DCDC Buck Converter EMI Reduction Using PCB Layout Modification,” IEEE
Trans. Electromagn. Compat., vol. 53, no. 3, pp. 806–813, Aug. 2011.
[5] K. Kam, D. Pommerenke, F. Centola, C. wei Lam, and R. Steinfeld, “EMC
guideline for synchronous buck converter design,” in Proc. IEEE Int. Symp.
Electromagn. Compat., Aug. 2009, pp. 47–52.
[6] R. Blecic, R. Gillon, B. Nauwelaers, and A. Baric, “Radiation of Input
Decoupling Network for Switching DC-DC Converters,” in Proc. IEEE Int.
Symp. Electromagn. Compat. Eur. (EMC Europe), Aug. 2015.
[7] A. Bhargava et al., “EMI prediction in switched power supplies by full-wave
and non-linear circuit co-simulation,” in Proc. IEEE Int. Symp. Electromagn.
Compat., Aug. 2009, pp. 41–46.
[8] P. Wilson, “On correlating TEM cell and OATS emission measurements,”
IEEE Trans. Electromagn. Compat., vol. 37, no. 1, pp. 1–16, Feb. 1995.
[9] R. Blecic, R. Gillon, B. Nauwelaers, and A. Baric, “SPICE Analysis of RL
and RC Snubber Circuits for Synchronous Buck DC-DC Converters,” in Proc.
IEEE Int. Conv. MIPRO, Mar. 2015.
[10] J. Rodgers and W. Nicewander, “Thirteen ways to look at the correlation
coefficient,” The Amer. Statistician, no. 42, pp. 59–65, 1988.
[11] J. Roig et al., “Body-diode related losses in Shield-Plate FETs for SiP
12V-input DC/DC buck converters operating at high-frequency (4MHz),” in
24th Int. Symp. on Power Semiconductor Devices and ICs (ISPSD), June
2012, pp. 291–294.
[12] J. Bacmaga, R. Blecic, R. Gillon, and A. Baric, “3D EM Simulation
and Analysis of Metal Interconnect used in Integrated Voltage Regulators,” in
Proc. Int. IEEE Conf. on Electron., Circuits and Syst., Dec. 2015.
[13] T. Mandic, R. Blecic, R. Gillon, and A. Baric, “Dc/dc converter deadtime variation analysis and far-field radiation estimation,” in Int. Workshop
on Electromagn. Compat. of Integrated Circuits (EMC Compo), Nov. 2015,
pp. 7–12.
Cdecap
LP CB
200
References
[1]
VIN
Vias
Combining EM and SPICE Simulations
? The proposed radiation model can be used to predict the radiated emissions of the converter as follows:
1) the proposed radiation model is extracted from the EM simulations of the analyzed structure excited by a 1-A current
excitation,
2) the spectrum of the resonant current is calculated from the time-domain SPICE simulations,
3) the radiated emissions are calculated by multiplying the results from the first two steps.
? Prediction of the radiated emissions of the second simulated structure (h = 0.1 mm) and using
the spectrum of the current through the high-side
FET iD,HS which is used as an approximation of
the resonant current:
max(E) [dB V/m]
? Switching DC-DC converters are sources of increased
EM interference which is a result of the switching operation and high di/dt and dv/dt [2].
Simulated characteristic currents
−
+
Introduction
Lsource
−85
Nominal
Tolerance
−95
−105
−115
0.03
0.1
Frequency, f [GHz]
1
Conclusion
X Radiation characteristics of a synchronous buck converter are analyzed by a 3D electromagnetic solver and a model
consisting of three orthogonal magnetic moments is extracted from the simulation results.
X The magnetic moment normal to the plane of the printed circuit board Mz is dominantly related to the radiation of
the input decoupling network. The magnetic moment perpendicular to the decoupling capacitors Mx is dominantly
related to the radiation of the package as a consequence of the current flowing through the FETs. The magnetic
moment parallel to the decoupling capacitors My is dominantly related to the radiation of the ground vias.
X When combined with the results of the SPICE simulations, the proposed radiation model can be used to predict the
radiated emissions of the converter.