COVER STORY


flyback to be higher, thus reducing the overall size of the power supply.


Another topology gaining in popularity is the Resonant LLC converters that are characterised as switching converters which include a tank circuit actively participating in determining input-to-output power flow. The Resonant LLC inverter has three reactive elements where the DC input voltage is turned into a square wave by a switch network arranged as either a half- or full-bridge to feed the resonant LLC tank that effectively filters out harmonics providing a sinusoidal like voltage and current waveform. This in turn feeds a transformer that provides voltage scaling and primary-secondary isolation. The converter power flow is controlled by modulating the square wave frequency with respect to the tank circuit’s resonance. In an LLC resonant converter, all semiconductor switches are soft-switching, or zero-voltage switching (ZVS), at turn-on for the primary MOSFETs and zero-current switching (ZCS) at both turn-on and turn-off for the rectifiers in the secondary; resulting in low electro-magnetic emissions levels (EMI). In addition, it can enable a high degree of integration in the magnetic parts, enabling the design of converters with higher efficiency and power density.


Typical application diagram – Resonant LLC converter in half-bridge configuration


switching topologies used in AC/DC and DC/DC converters and DC/AC inverters.


The MasterGaN family is currently available in mass production across three devices with more on the future roadmap. The first device is MasterGaN1 which has been optimised for Resonant LLC converter topologies up to 400W. The MasterGaN2 device is suited to soft-switching and Active Clamp Flyback converter topologies up to 65W whilst the MasterGaN4 device is suitable for Resonant LLC converter topologies up to 200W.


quickly create new topologies without the need for complete PCB design. The boards provide on-board programmable inputs deadtime generator with a single VCC supply and an embedded linear voltage regulator offering 3.3 V rail to supply low voltage logic circuits like microcontrollers or FPGAs. The boards all incorporate spare footprints allowing designers to customise the boards so they can be integrated easily into the customers final application. The boards can be further customised to allow the use of a separate input signal or single PWM signal, use of external bootstrap diode, separate supply for VCC, PVCC or Vbo and also the use of low side shunt resistor for peak current mode topologies. The boards provide full access to all pins of the MasterGaN devices further extending flexibility. The development boards measure just 56 x 70 mm wide and use a standard FR-4 PCB delivering an impressive thermal resistance Rth(J-A) of 35 °C/W, without forced airflow.


The MasterGaN family of advanced power system- in-package devices all integrate a gate driver and two enhancement mode GaN transistors in a compact package. MasterGaN1 and MasterGaN4 devices are configured in a half-bridge and MasterGaN2 employs an asymmetrical half bridge configuration.


Resonant LLC converters are suitable for a wide range of applications and are now commonly found in consumer products such as flat panel TVs, and small form factor PCs, where the regulatory requirements for efficiency and power density of their SMPS are getting tougher and tougher, the resonant LLC half-bridge with its many benefits including smooth waveforms, high efficiency and high-power density and very few drawbacks offers an excellent solution. MasterGaN is extremely well suited to resonant LLC converters and can replace the traditional silicon MOSFETs (Q1 & Q2) and the Half-bridge Driver with one compact, efficient and simple to design in device.


MasterGaN Family


The MasterGaN family of devices span different GaN- transistors and are offered as pin-compatible half-bridge products that let engineers scale successful designs with minimal hardware changes. Leveraging the low turn-on losses and absence of body-diode recovery that characterize GaN transistors, the products offer superior efficiency and overall performance enhancement in high-end, high-efficiency topologies such as flyback or forward with active clamp, resonant, bridgeless totem pole PFC and other soft- and hard-


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The integrated power GaNs have an RDS(ON) of 150 mΩ for MasterGaN1 and RDS(ON) of 225 mΩ for MasterGaN4 devices for both Low side and High side. For the asymmetrical MasterGaN2 devices the integrated power GaNs have an RDS(ON) of 150 mΩ and 225 mΩ for Low side and High side, respectively. The MasterGaN devices all have 650 V drain-source breakdown voltage, while the high side of the embedded gate driver can be easily supplied by the integrated bootstrap diode.


The MasterGaN1 device is capable of maximum continuous drain current IDS(MAX) of 10A and the MasterGaN4 device has an IDS(MAX) of 6.5A for both the High side and Low side. The asymmetrical MasterGaN2 device offers an IDS(MAX) of 6.5A and 10A for the High Side and Low Side, respectively. The MasterGaN devices all feature UVLO protection on both the lower and upper driving sections, preventing the power switches from operating in low efficiency or dangerous conditions, and the interlocking function avoids cross- conduction conditions. The input pins extended range allow for easy interfacing with microcontrollers, DSP units or Hall effect sensors.


The devices are designed to operate over the industrial temperature range -40°C to 125°C and are supplied in a compact 9x9 mm QFN package.


Design Support


To assist designers, STMicroelectronics have also made available development boards which are easy to use and quick to adapt tools to evaluate the characteristics of the MasterGaN family of devices. The boards help designers


Conclusion


To summarise, by integrating GaN devices and gate drivers into the same device package the MasterGaN family offers a wide range of benefits over traditional silicon-based solutions including: Higher power density – Higher switching speeds also enable reduced system size and cost. Higher efficiency – Reduced power losses, reduced power consumption, which exceed the most stringent energy requirements.


Faster go-to-market – Packaged integrated solution simplifies the design and at the same time gives a higher level of performance.


Anglia offer support for customer designs with free evaluation kits, demonstration boards and samples of STMicroelectronics products via the EZYsample service which is available to all registered Anglia Live account customers. Anglia’s engineering team are also on hand to support designers with their extensive experience of working with power system designs and can offer advice and support at component and system level. This expertise is available to assist customers with all aspects of their product design, providing hands on support and access to additional comprehensive STMicroelectronics resources including technical application notes and reference designs.


Visit www.anglia-live.com to see the full range of STMicroelectronics products available from Anglia.


Components in Electronics April 2021 9


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