在本次网络研讨会中，我们将回顾采用 GaN 的实用系统设计，展示 EMI、浪涌、热和驱动电路性能。 一些示例将说明适当的系统设计满足所需的系统要求。
- EMI 和高频兼容； 提供解决方案设计和应用示例
Questions & Answers
Which controllers do you recommend for applications with PWM generation and don’t require external Gate Drivers?
There are many controllers with a driver integrated, e.g. NCP1618 (PFC), TEA2016 (PFC+LLC), HR1210(PFC+LLC), etc. They all can drive GaN Systems GaN directly with the EZdrive circuit. Refer to our application notes.
What is the recommended dead-time for 650 V devices with 10 ohms turn-on? 100 ns?
Deadtime setup is related to the load current. 100nS is a very good starting point.
How do I calculate turn-off impedance of the EZdrive solution?
The turn-off impedance calculation is the same as a conventional driving circuit for the EZdrive solution: RG(OFF) + circuit parasitic resistance (driver and GaN). RG(OFF) is dominant.
Do you have examples of IMS?
Yes, you can find our IMS Eva kits with the link below: 1. https://gansystems.com/evaluation-boards/gsp65rxxhb-evb/ 2. https://gansystems.com/evaluation-boards/gsp665x-evbims2/
Is the Renesas Eval board pin-to-pin compatible to your previous daughter card?
Yes, they are pin-to-pin compatible. You can just unplug your previous daughter card from your system and plug the new Renesas board and enjoy the new features from Renesas.
What’s the recommended turn-on/turn-off gate resistors for EMI?
Typically, we recommend to start the Rgon/Rgoff with 10/2 ohm for 650V parts and 5/1 ohm for 100V parts. Then it depends on your system and EMI performance. You can fine tune the resistance values according to your EMI test results.
What is the simplest and, meanwhile, accurate simulation tool for EMI tests? Is LTspice accurate enough?
LTspice is a good simulate tool for EMI. Or try the impedance matrix association. The advantage of simulation is determining the impedance matrices before construction, so the designer needs to build fewer prototypes. Moreover, the only frequency band limitation is the modeling details, which means the model validity. Otherwise, the band can be chosen by the user.
How much does shielding help with radiated EMI?
The shielding case is critical for radiated EMI, in all of its shapes and types, is fundamental to EMI
In motor control application .. there is no need for anti parallel diode with GaN devices, correct?
Correct, there are no body diodes in GaN HEMTs, GaN HEMTs freewheel current during deadtime. In reverse conduction mode with Vgs < Vth, the drain of the GaN will behave as a source, while the source will behave as a drain. When Vgs>Vth, the GaN will be fully turned on like a Si MOSFET. Refer to the page 5 of GN001 Application Note for more information.
Please explain "enabling OCP" in Gate Driver
The driver IC includes over-current protection detection function. OCP is realized by a differential voltage measurement on the shunt resistor. The OCP trigger point can be adjusted by the IDSET pin setup and/or the shunt resistance.
Please explain, what is "Adjustable slew rate for EMC In the Gate Driver on slide 47"
The switching speed of a GaN transistor is controllable, with the adjustment of The external resistor, Rg, which helps optimize EMC performance. Furthermore, the higher switching frequency of GaN makes it possible to reduce the EMC Filter size.
How does Driver slew rate affect EMI?
The greater the slew rate, the faster the rate of change of voltage (or current) that can occur. Another way of looking at this is to observe that the faster the voltage can change, the higher the frequency that can pass or be generated. It is important because this is what leads to EMI.
For the EMI data shown, what is the converter switching frequency?
The adapter Fsw is around 150kHz to 180kHz from full load to light load.
I am considering a class D amp @100 w 60V. Any full bridge drive recommendations??
Please refer to our EVB (part number GS-EVB-AUD-AMP1-GS) Audio Class D 250W 2-channel amplifier which is a 250W class D amplifier solution.
Can rdson be used to estimate junction temperature?
Yes, you can use Rdson to indirectly estimate device junction temperature.
How accurate is the junction temperature when measured by the junction resistance?
We heated up the device and did the comparison between Tj measured by thermal camera and Rdson (V/I) measured by digital multimeter. The values are quite similar.
What is the software simulation used to show Rth vs Case value?
For system-level thermal simulation, we use ANSYS icepak.
GaN can switch at high frequency. For a grid tie inverter. How does the high frequency ripple affect the inductor losses (skin effect at 1MHz is very much pronouced)
“1. The design of coupled inductors needs to consider the polarity of the coupling and the direction of the magnetic flux. A good coupled inductor design can increase the inductance and reduce the size of the magnetic core.
2. The loss of magnetic components can be divided into two parts, core loss and copper loss. The high-frequency design will increase the core loss (caused by the material), but ΔI will decrease, and ΔB will also decrease, reducing the core loss. The solution is very system specific.
3. As stated, the high-frequency design will increase the skin effect of the wire; it is recommended to use Litz wire to reduce this effect.”
Are IMS boards good for single layer only? Can I use GaN with two layer IMS board? What will be the difference in both cases.
It’s possible, but with the compromise on thermal performance. Single layer IMS offers the best thermal solution, and multi-layer IMS eases the PCB boards assembly with a better parastics.
What is the thermal conduction feature of the topside of your bottom cooling device?
For our PQFN package, it is molding compound. There is no problem to use its topside for thermal conduction, but the thermal dissipation effect is not as good as the copper pad on the bottom side.
Why is OCP adjustibilty important?
A well-adjusted OCP can effectively prevent damage without affecting the regular operation.
Can you comment on dv/dt induced turn on during 720v VDC?
A scenario might be dv/dt dip due to loop inductance: deltaV=Lp*di/dt. The breakdown voltage of GaN is >750V. As shown in our datasheet, the drain-source of GaN can withstand <1uS 750V pulse. So under surge conditions, GaN can operate through the surge without avalanching. [/av_toggle] [av_toggle title='What are reasonable design margins for GaN part selection in terms of voltage current ratings' tags='' custom_id='' av_uid='av-1ya430z'] The derating ratio is usually designed according to the product category. It is recommended that consumer products have 5~10% voltage and current margin, and industrial products have 20% voltage and current margin. [/av_toggle] [av_toggle title='Can we use the thermal PAD of GS66516T to conduct Ids current' tags='' custom_id='' av_uid='av-1rxo27n'] No. Although the thermal pad is connected to source, it is for thermal connection only, not for electrical connection. [/av_toggle] [av_toggle title='In your top cooled devices, is the thermal pad internally connected to source or should we connect it manually?' tags='' custom_id='' av_uid='av-fse7n'] Except for our GS66508P and GS61008P, for all other devices, you don’t need to manually connect source to the thermal pad. They are internally connected. Only for the GS66508P and GS61008P part numbers is manual connection required.
Moderator: Paul Wiener
VP Strategic Marketing at GaN Systems
Paul Wiener is GaN Systems’ Vice President of Strategic Marketing. Prior to joining GaN Systems, Paul led the power magnetics business unit at Eaton. Paul brings more than 25 years’ experience in operations, sales and marketing, and business development. His experience includes vice president of sales at Fultec Semiconductor Inc. and several management roles at Genoa, BroadLogic, and Raychem.