[GaN FET] LMG5200 review

Published in

Daily Power Electronics

4 min readFeb 4, 2019

GaN FET, Rising star in the low-power circuit design

As a mobile robot industry such as drone grows, a low-power design that not only increases the amount of battery using time but also reduces the volume and weight of the system is the biggest issue in the motor driver circuit design. Evolved from existing 1st generation switching devices such as IGBT, Si MOSFET, switching devices using new properties such as GaN and SiC are expected to be commercialized out of the research phase. Among them, today’s device is the ‘LMG5200’ half bridge power stage from Texas Instruments.

Gallium Nitride FET, low Rds(on) and low input capacitance

The loss of the switching device can be broadly divided into conduction loss and switching loss. The conduction loss is a heat generated by a current flowing while the switch is on, and it is proportional to the turn on resistance(Rds(on)). Therefore turn on resistance is an important factor in choosing a switch, and the GaN based FET has a low on resistance value due to its structural characteristics.

https://www.transphormusa.com/zh/gan-technology/

The graph above shows that in the same break down voltage, GaN has a relatively low turn on resistance value for other devices.

https://www.digikey.com/en/articles/techzone/2014/aug/a-review-of-zero-voltage-switching-and-its-importance-to-voltage-regulation

Another loss in the semiconductor device is switching loss. This is the loss generated when the switching state changes. As shown in the above waveform, the loss at the switching moment is proportional to the area between blocking voltage(Vdc) and the load current(Id). So, the larget the switching time, the greater the switching loss. Because GaN has low input capacity, it has fast switching time and relatively low switching loss.

Alatawi, K.; Almasoudi, F.; Manandhar, M.; Matin, M. Comparative Analysis of Si- and GaN-Based Single-Phase Transformer-Less PV Grid-Tied Inverter. *Electronics* **2018**, 7, 34.

FET driver design is the key to GaN’s success

Galium nitride is a very proper materials for switching device in motor drive circuit. However, due to fast rising time, it is so vulnerable to stray inductance between the driver and the GaN FET. There is also a way to reduce an oscillatory response by adding the gate resistor. However, this solution deteriorates one of the merits of GaN FET, fast switching time. Therefore, the layout which minimizes the stray inductance is required when using the GaN FET as a main PWM switching device.

Why LMG5200 is recommendable?

Minimize stray inductance between GaN driver and GaN FET

Under this circumstances, LMG5200 from TI can be a great solution. Their package includes GaN driver and the two half bridge GaN FET in a single package. So, PCD layout designer is no longer considering the stray inductance or limits of PCB fabrication.

2. Example user guidelines

Also, TI offers various application of this components, so the critical information to use this component is easily obtainable.