Frequently Asked Questions

eGaN Devices in Circuits

What is the best place to find general information on applying EPC’s enhancement mode GaN transistors?

EPC’s eGaN® FETs will displace the aging power MOSFET over the next few years due to superior performance and affordable costs. EPC has published several application notes and white papers on using these high-performance power devices which can be found in the GaN Library at http://epc-co.com/epc/GaNLibrary.aspx. EPC has also authored a book titled, “GaN Transistors for Efficient Power Conversion” that can be purchased at Amazon.com or through EPC’s web site at: http://epc-co.com/epc/Products/Publications.aspx We also have a series of video presentations at http://epc-co.com/epc/DesignSupport/TrainingVideos.aspx.

The high frequency capability of the devices could be an issue with the layout of my circuit board. What must I be mindful of when laying out my circuit?

Generally, the eGaN FET should be treated as any other MOSFET, keeping in mind that it does have the capability of higher performance operation because of its relatively low total gate charge (Qg) and small CRSS. Some general guidelines:

  • Drive the gate with 5 V, keep max gate voltage below 5.5 V. There are several ICs available to make this task easy.
  • Minimize gate source circuit impedance. It is advisable keep the gate source loop as small as possible, even at the cost of longer paths in drain circuit.
  • Use a low impedance driver
  • There are driver IC’s developed to optimize the performance of eGaN FETs in circuit. For a list of current available eGaN FET optimized IC’s please see http://epc-co.com/epc/Products/eGaNDrivers.aspx

The “Using GaN on Silicon Power Transistors” application note, has further information. In addition, land pad layouts that minimize inductance can be found on all EPC data sheets at http://epc-co.com/epc/Products/eGaNFETs.aspx . Chapter 3 of the book titled, “GaN Transistors for Efficient Power Conversion” covers this topic in detail. Layout techniques to minimize switching time and voltage overshoot can be found in the white paper Impact of Parasitics on Performance and the white paper Optimizing PCB Layout. There is also a video that you can review at “How to GaN 06: Design Basics – Layout”.

Your threshold voltage is low compared with silicon MOSFETs. How does this impact turn off speed?

eGaN devices have a very low temperature coefficient for their threshold voltage. This gives the user added safety margin despite the lower threshold voltages at room temperature. The Miller Capacitance, CGD of EPC eGaN® FETs is also very low, hence the switching speed is quite high; it can be turned off in a few nano seconds. In order to avoid dv/dt turn-on, it is critical to have very low impedance in the gate-source circuit as well as a low impedance pull down for the gate circuit. Gate drivers like LM5113, LM5114 and UCC27611, from Texas Instruments are designed specifically for eGaN devices and will take care of many of these requirements. For more tips on driving eGaN FETs, see eGaN FET Drivers and Layout Considerations.

Your threshold voltage is low compared with silicon MOSFETs. How do I handle dV/dt immunity?

It should also be noted that eGaN devices have a very low temperature coefficient for their threshold voltage. This gives the user added safety margin despite the lower threshold voltages at room temperature. The ratios of CGD to CGS are quite good in holding the device off under a dV/dt condition. This is a capacitive divider, so care must be taken in the gate drive to have a low resistance turn off and good layout such that inductance is minimized in the turn off loop to keep the effective impedance low. The magnitude will depend on dV/dt and voltage. Gate drivers like LM5113, LM5114 and UCC27611 from Texas Instruments are designed specifically for eGaN FETs; http://epc-co.com/epc/Products/eGaNDrivers.aspx

Can eGaN FETs be paralleled? If so what are the key elements for a good design?

eGaN Devices are positive temperature coefficient devices and are good candidates for parallel operation. However, since these devices can switch up to 10x faster than standard silicon FETs, special care must be taken in the layout and driving aspects of this configuration. EPC has written a white paper comparing different layout schemes and identifying the best paralleling configuration. Please refer to White Paper: Paralleling eGaN FETs at http://epc-co.com/epc/documents/papers/Paralleling eGaN FETs.pdf

How can I provide enhanced cooling to the eGaN FETs?

EPC has conducted electro-thermal experiments using our standard development boards, EPC9002 and EPC9006, to evaluate the impact of providing top side die cooling. A small heatsink was mounted on top of the EPC devices using a thermal interface material, that also provided electrical isolation, and tests were conducted to determine the impact on the temperature of the devices when operated under increased power loss conditions. Details of the experimental setup and results can be found in the white paper eGaN FETs for Envelope Tracking and in the video How to GaN 03: Design Example – Hard-Switching Applications.

Wireless charging is getting popular these days, are eGaN FETs a good choice for wireless charging?

EPC’s eGaN FETs are superb for wireless charging applications! There are a couple of popular wireless charging architectures available in the market. eGaN FETs offer the unique opportunity and possibilities of flexibility and distance by enabling operations in the multi-MHz range, EPC’s white paper on this subject Low Power Wireless Energy Converters is available as well as the video How to GaN 04: Design Example – Soft-Switching Applications.

To see a demo of EPC’s eGaN FETs in a wireless power transfer system please view the video http://epc-co.com/epc/DesignSupport/TrainingVideos/WirelessDemo.aspx

Do you see any benefits from using eGaN FETS in power amplifiers in Wireless Base Stations?

EPC’s eGaN FETs are superb for applications in RF power amplifiers – especially in envelope tracking. Today Power Amplifiers (PA) commonly use depletion mode GaN FETs since they are capable of switching at several hundreds of MHz. The typical efficiency of PA is in the the 20 to 30% since the Peak to Average Ratio (PAR) is very low. With the emerging technologies like LTE for wireless, the demand for power is going up and several new techniques like Envelope Tracking (ET) – where the voltage feeding the power amplifier is modulated corresponding the modulating signal – are evolving to improve the efficiency of PAs. eGaN FETs are capable of switching at several tens of MHz at the voltage of interest in PAs, enabling the adoption of efficient Envelope Tracking architectures in these applications for improving the efficiencies. For more information on eGaN FETs in Envelope Tracking applications please see: http://epc-co.com/epc/Applications/EnvelopeTracking.aspx

Does EPC have a development board for evaluation of eGaN® FETs in Class D Amplifiers?

In Class D audio systems, the audio performance is impacted by the FET characteristics. GaN FETs enable higher fidelity Class D Audio Amplifiers.

The low on resistance and low capacitance of the eGaN FET enables high efficiency and lowers open loop impedance for low Transient Intermodulation Distortion (T-IMD). The fast switching capability and zero reverse recovery charge enable higher output linearity and low cross over distortion for lower Total Harmonic Distortion (THD).

For more information on eGaN FETs in Class-D audio amplifier applications at http://epc-co.com/epc/Applications/ClassDAudio.aspx

What are the benefits of eGaN FETs in resonant and soft-switching applications?

eGaN FETs have a distinct advantage over silicon MOSFETS in hard switching applications because of the reduction of two key parameters – QGD and QRR,both of which have little impact in resonant and soft-switching converters. It has been demonstrated that eGaN FETs can also provide significant improvements in resonant and soft-switching applications when compared to Si MOSFETs by offering reduced output charge, QOSS, and gate charge, QG.

For more information, please refer to the white paper “eGaN FETs in High Frequency Resonant Converters

Does EPC have application information on the use of eGaN® FETs in micro inverter applications for solar panels?

The EPC9001 and EPC9002 development boards can be used to create inverters for solar panels as they are designed for buck / half-bridge -type applications and can operate over a wide range of duty cycles. Since these development boards form a complete half-bridge with gate drive, it can easily be connected to an existing inverter circuit by replacing the current half-bridge devices. To get more information about EPC’s growing list of development and demo boards, or to purchase these boards, go to http://epc-co.com/epc/Products/DemoBoards.aspx

Does EPC have application information on the use of eGaN® FETs in LED illumination applications?

The use of LEDs for illumination (not just backlighting) has proliferated in recent years and there are numerous applications and topologies. The EPC9001 and EPC9002 development boards can be used to create LED backlighting solutions with very high contrast ratio, but are designed for buck / half-bridge type topologies. For anyone experienced in the art it is possible to operate this ‘backwards’ as a synchronous boost – noting that the input PWM will now be complimentary to what is required. Care should be taken in doing so as the output bus voltage can easily be boosted above the rated maximum voltage.

To get more information about EPC’s growing list of development and demo boards, or to purchase these boards, go to http://epc-co.com/epc/Products/DemoBoards.aspx.

Does EPC have application information on the use of eGaN® FETs in backlight applications?

The main question here would be the choice of topology to be employed. The EPC9001 and EPC9002 development boards can be used to create LED backlighting solutions with very high contrast ratio, but are designed for buck / half-bridge type topologies. For anyone experienced in the art it is possible to operate this ‘backwards’ as a synchronous boost – noting that the input PWM will now be complimentary to what is required. Care should be taken in doing so as the output bus voltage can easily be boosted above the rated maximum voltage.

To get more information about EPC’s growing list of development and demo boards, or to purchase these boards, go to http://epc-co.com/epc/Products/DemoBoards.aspx

Where can I learn more about radiation requirements in space?

There is an excellent overview published by NASA at: http://www.nasa.gov/offices/oce/llis/0824.html

How do eGaN FETs behave when exposed to radiation such as would be in a satellite application?

EPC has written papers on the excellent radiation performance of eGaN FETs. You can find two papers on our web site at:

1. This paper describes the basic gamma radiation tolerance and tolerance to single event effects (SEE): http://epc-co.com/epc/EventsandNews/Events/GOMACTechConference2012.aspx
2. This paper shows improved DC-DC converter performance in a satellite power supply: http://epc-co.com/epc/documents/papers/Radiation Tolerant eGaN FETs in DC-DC Converters.pdf

There is little overhead between the recommended drive voltage and the absolute maximum gate drive voltage. How do I handle this?

It is important to keep the max gate voltage below 6V for long term reliability. To make this easy for the designer, we have developed drive level shifters, and discrete gate drivers that not only manage drive voltage, but also manage deadtime. Examples are currently implemented on development boards EPC9003, EPC9004, EPC9005, and EPC9006. For a detailed description of our recommended discrete solution please see the article http://www.how2power.com/newsletters/1006/articles/H2PowerToday1006_design_EPC.pdf

In June of 2011, Texas Instruments announced the industry’s first eGaN FET driver. The LM5113 is a 100V half-bridge driver addressing a wide range of power converter topologies. They have subsequently released the LM5114, a low side gate drive compatible with eGaN FETs as well as the UCC27611 high speed gate driver (http://epc-co.com/epc/Products/eGaNDrivers.aspx).

A list of known partner IC’s is maintained at http://epc-co.com/epc/Products/eGaNDrivers.aspx

Your higher voltage devices have lower thresholds than silicon MOSFETs. Where can I find a driver to work with these?

To make this easy for the designer, in June of 2011, Texas Instruments announced the industry’s first eGaN FET driver. The LM5113 is a 100V half-bridge driver addressing a wide range of power converter topologies. They have subsequently released the LM5114, a low side gate drive compatible with eGaN FETs (http://epc-co.com/epc/EventsandNews/News/ArticleID/477/ArtMID/1627.aspx)and the UCC27611 high speed gate driver

A list of known partner IC’s is maintained at http://epc-co.com/epc/Products/eGaNDrivers.aspx

Additionally, we have developed drive level shifters, and discrete gate drivers that not only manage drive voltage, but also manage deadtime. Examples are implemented on development boards EPC9003, EPC9004, EPC9005, and EPC9006. For a detailed description of our recommended discrete solution please see the article “How2 Get the Most Out of GaN Power Transistors”. It should also be noted that eGaN devices have a very low temperature coefficient for their threshold voltage. This gives the user added safety margin despite the lower threshold voltages at room temperature.