350 V GaN transistor: 20 times smaller than comparable silicon and at a lower cost
Wide Band Gap (WBG) power electronic devices reduce component size, increase efficiency and improve performance of hybrid and all-electric vehicles. In particular, the exceptionally high electron mobility of gallium nitride (GaN) and its low temperature coefficient allow a very low on-state resistance (RDS (enabled)), while its lateral device structure and majority carrier diode provide low total gate charge (Qg) and zero reverse collection charges (QRR).
The end result is a device that can handle tasks where very high switching frequency (which results in lower switching losses and drive power) and low on-time are beneficial. It also improves results where losses to the state might otherwise dominate.
As an example, Efficient Power Conversion (EPC) announced the production release of the EPC2050, a 350 V GaN transistor with maximum RDS (enabled) of 80 mΩ and a pulsed output current of 26 A. The EPC2050 measures only 1.95 × 1.95 mm. According to the company, the small size enables power solutions that take up 10 times less space than comparable silicon solutions. Automotive applications benefiting from the EPC2050’s fast switching speed and tiny size include fast chargers, battery management systems, LiDAR and LED lighting.
“With the EPC2050, designers no longer have to choose between size and performance – they can have both for less!” says Alex Lidow, CEO of EPC.
EPC’s GaN FETs behave similarly to silicon power MOSFETs. A positive bias on the gate with respect to the source causes a field effect. This attracts electrons which complete a bi-directional channel between drain and source. When the bias is removed from the gate, electrons below it are dispersed into the GaN, recreating the depletion region and giving it back the ability to block voltage.
The relatively high frequency response of GaN FETs is an improvement over earlier silicon devices and an additional consideration for the user when configuring circuits. Still, EPC says users can leverage their past design experience and achieve new levels of performance in their products.
EPC also notes that its GaN transistor structure is a purely lateral device, lacking the parasitic bipolar transistor common to silicon-based MOSFETs. As such, reverse bias or “diode” operation has a different mechanism but a similar function. With a zero-bias gate towards the source, there is an absence of electrons below the gate region.
As the drain voltage decreases, a positive bias on the gate is created relative to the drift region, injecting electrons below the gate. Once the gate threshold is reached, there will be enough electrons under the gate to form a conductive channel. The advantage of this mechanism is that there are no minority carriers involved in the conduction, and therefore no QRR.
Development Board Details
EPC’s EPC90121 development board is a 350V maximum device voltage, 4A maximum output current half-bridge including onsemi’s EPC2050 and NCP51820 gate driver. The board measures 2 × 2 in and contains all the critical components; the layout supports optimal switching performance. In addition, various probe points facilitate simple waveform measurement and efficiency calculation.
The purpose of this development board is to simplify the evaluation process of the EPC2050. It includes all critical components on a single board that can be easily connected to many existing converter topologies.
EPC has undertaken extensive reliability testing to continue to better understand the behavior of GaN devices under a wide range of stress conditions. At EPC, GaN devices have been in volume production since March 2010, and the company claims to have demonstrated high reliability in both lab testing and high-volume customer applications.
Additionally, EPC claims that the results of these reliability studies show that GaN is an extremely robust technology and continues to improve at a rapid rate. The company is committed to holding GaN devices to rigid reliability standards and sharing the results with the power conversion industry.
EPC2050 GaN FETs are supplied only as a passivated die with solder bumps. They are priced at $3.05 each in 1,000 units. The EPC90121 development board costs $156.25.