AN4406
Application note
MDmesh™ M2:
the new ST super-junction technology ideal for resonant topologies
Antonino Gaito, Giovanni Ardita, Cristiano Gianluca Stella
Introduction
Today, power supply designers are facing a new and exciting challenge: the necessity to
increase power density and efficient thermal management. A response to this challenge has
been found in resonant topologies that typically employ the LLC resonant converter.
In this topology, the parasitic capacitances of the MOSFETs can impact system behavior by
increasing switching losses and decreasing efficiency.
This application note provides the results of experimental performance analysis of the two
latest and most advanced ST MOSFET super-junction technologies, MDmesh™ M2 and
MDmesh™ M5, and compares them with well-known competitor devices in relation to
MOSFET parasitic capacitance.
March 2015
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Contents
AN4406
Contents
1
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1
1.2
Resonant converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Half-bridge and full-bridge switch networks . . . . . . . . . . . . . . . . . . . . . . . . 4
2
MDmesh™ M2: the new ST super-junction technology ideal for
resonant topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1
Key features and differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3
4
Impact of the MOSFET parasitic capacitances . . . . . . . . . . . . . . . . . . . . 8
Testing and comparing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1
150 W resonant LLC high power adapter based on L6599 and STP9N60M2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1.1
4.1.2
4.1.3
Purpose and description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Main parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2
200 W HB LLC resonant converter for LCD TV and flat panels based on
L6599 and STF13N60M2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2.1
4.2.2
4.2.3
Purpose and description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Main parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.3
400 W HB LLC resonant converter for PDP applications based on L6599
and STP24N60M2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.3.1
4.3.2
4.3.3
Purpose and description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Main parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5
6
7
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
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Description
1
Description
To meet the ever-increasing demand for higher power density in consumer applications like
notebooks, high-power adapters (over 150 W), desktop PCs, FPDTV, gaming SMPS,
lighting, power supplies used for telecommunication equipment, mainframe computers and
high-power systems in general (over 500 W), component counts, power loss, heat-sinks
and reactive component sizes must be reduced.
The LLC resonant half bridge [1] represents a new alternative to the typical hard-switched
half (full) bridge topology, whereby the load enables commutation of the bridge switches
with near-zero voltage or current switch conditions, resulting in low switching losses and
thus eliminating power loss due to overlapping switch current and voltage at each transition.
With this technique, the switching losses associated with the main power switching remain
low even when the system operates at high frequencies, allowing for reduced component
reactive sizes and simplified thermal management.
According to the resonance principle, each reactive component in the circuit contributes to
the overall working frequency. As the frequency of the load range in the LLC topology is
influenced by the magnetic transformer, two main working frequency values can be
distinguished.
When the system operates under a light load, the effects of the intrinsic parasitic
capacitances of the power MOSFET can impact both operation and switching power loss,
resulting in decreased efficiency.
Resonant conversion has attracted concerted academic and industry research efforts over
the last few decades because of the associated waveform, efficiency and power density
improvements. However, the use of this technique in off-line powered equipment has long
been confined to niche applications, such as high-voltage power supplies and audio
systems.
Recent applications like flat panel TVs and the introduction of new voluntary and mandatory
regulations concerning efficient energy use are pushing power designers to find increasingly
efficient AC-DC conversion systems, promoting renewed interest in resonant conversion.
1.1
Resonant converters
Resonant converters form an extremely vast family of devices that are not easily gathered
under one comprehensive definition. Generally speaking, they are switching converters with
a tank circuit which influences the input-to-output power flow.
Most resonant converters are based on "resonant inverters", which are systems that convert
DC into sinusoidal voltages (or AC voltages with low harmonic content) and provide AC
power to a load [2]. To do so, a switch network typically produces a square-wave voltage
applied to a resonant tank tuned to the fundamental component of the square wave. In this
way, the tank responds primarily to this component and negligibly to the higher order
harmonics, so that its voltage and/or current, as well as those of the load, are essentially
sinusoidal or piecewise sinusoidal.
Figure 1
shows a resonant DC-DC converter providing DC power to a load by rectifying and
filtering the AC output of a resonant inverter.
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Description
AN4406
Figure 1. Simplified block diagram of a resonant inverter, the core of resonant
converters
Various types of DC-AC inverters can be built with differing switch networks and resonant
tank characteristics by altering the quantity and configuration of reactive elements.
1.2
Half-bridge and full-bridge switch networks
Switch networks that drive the resonant tank symmetrically with respect to both voltage and
time, and act as a voltage source are known as half-bridge and full-bridge switch networks.
Borrowing from power amplifier terminology, switching inverters driven by this kind of switch
network are categorized "class D resonant inverters".
Figure 2. Resonant tank and load in half-bridge schematic
For resonant tanks with two reactive elements (one L and one C), there are a total of eight
possible configurations, of which four are usable with a voltage source input. Two of these
form part of the popular series-resonant and parallel-resonant converters for which an
abundance of literature is available.
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Description
With three reactive elements, there are 36 possible tank circuit configurations, of which 15
are usable with a voltage source input and two popular resonant inverter topologies can be
formed:
•
•
an LCC (one L and two Cs) resonant inverter – the load is connected in parallel with
one of the capacitors; commonly used in electronic, gas-discharge lamp ballasts;
an LLC (two Ls and one C) resonant inverter – the load is connected in parallel with
one inductor.
As previously stated, for any resonant inverter there is a corresponding DC-DC resonant
converter obtained by rectification and filtering of the inverter output. The above mentioned
inverters of course belong to the "class D resonant converters" category.
In off-line applications, the rectifier block is usually coupled to the resonant inverter through
a transformer to provide the isolation required by safety regulations. To maximize the
efficiency of the inverter, the rectifier block can be configured as:
•
•
a full-wave rectifier (for low voltage / high current output) with a center tap arrangement
of the transformer's secondary winding
a bridge rectifier (for high voltage /low current output) without tapping.
The low-pass filter can be configured with capacitors only or with an L-C type smoothing
filter, depending on the configuration of the tank circuit. The so-called "series-parallel"
converter used in typical in high-voltage power supplies is derived from the LCC resonant
inverter described above. Its mirror configuration, the LLC inverter, generates the converter
with the same name.
We will consider the half-bridge implementation illustrated in
Figure 3,
but it can be easily
extended to the full-bridge version.
Figure 3. LCC resonant half-bridge schematic
GIPG211120131509SR
In resonant inverters and converters, power flow is controlled via the switch network by:
•
•
changing the frequency of the square wave voltage, or its duty cycle, or both
by special control schemes such as phase-shift control.
We shall control power flow through frequency modulation by adjusting the frequency of the
square wave closer to or further from the tank circuit's resonant frequency, while keeping its
duty cycle fixed.
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