2

The drone world uses ESCs (Electronic Speed Controllers) to control brushless DC motors. Typically there are six discrete FETs, a driver IC, and a small MCU to sequence things. Typical currents range from 5-100A at 3-25V. For many of the smaller drones weight and PCB area are at a premium.

I'm wondering if GaN Half-Bridge arrays would help out here. With typically lower gate capacitance, Vt, and great Rds(on) at a 5V drive would we really even need to have a driver ? Could the MCU logic outputs (assume to be 5V levels for now) be utilized directly ? If so the package count would drop from eight to four, and with CSP GaNs the area would be dramatically reduced. I've not found any small multi-phase GaN half-bridges specifically in the 5-10A @5-10V range, does anyone know of any ?

Russell Mirov
  • 21
  • 1

3 Answers3

1

Of course much of this depends on the system requirements, switching speed, cost goals, performance requirements.

The main challenge is there are no P-Channel GAN FETs available as far as I know. So you would need some way to drive the high side N-FETs even if you could drive the low side directly and were operating the bridge at 5V.

GAN gate drive requirements are tricky- Exceeding the max specified gate voltage even during transients or ringing can destroy the device.

GAN is also still much more expensive than silicon, and there are no integrated 3 phase GAN bridges like the ones you can find in silicon. There are integrated driver + GAN fet half bridge parts however, like this one from TI.

John D
  • 22,677
  • 1
  • 39
  • 56
  • Yeah, I forgot how hard it is to get that upper FET turned on. That LMG5200 is nice, but is overkill for this app ($$), and is actually pretty large. I'd become interested in GaNs for this usage because they have low Vt & gate capacitance, but perhaps a small half-bridge with conventional FETs and integrated driver would be a better choice. I wonder if there's some middle ground ? – Russell Mirov Mar 13 '21 at 22:28
  • Oh, I just came across this device: https://epc-co.com/epc/Portals/0/epc/documents/datasheets/EPC2152_datasheet.pdf It is similar to the LMG5200, but quite a bit smaller (and a lighter CSP - no metal slugs in the pkg). – Russell Mirov Mar 13 '21 at 22:45
  • Yes epc-co.com I was also going to suggest. Devices are _tiny_ so you can gain a lot of space. They have a large number of evaluations boards with full design details. – Henning Larsen Mar 13 '21 at 23:40
1

in regards to the GaN EPC2152, there is also a motor drive reference board https://epc-co.com/epc/Products/DemoBoards/EPC9146.aspx Here is also an article on this board and some advantages of using GaN in motor drives: https://eepower.com/technical-articles/gan-epower-stage-ic-based-inverter-for-battery-powered-motor-drive-applications/# The main advantage is size and reduced losses, which can be taken advantage of in several ways. Quite interesting is the topic of increased switching frequencies (since the penalty is so small with GaN) to reduce requirements on capacitors and input filters, as well as better sine modulation with less harmonics (mainly thanks to lower dead time) which can help with less torque ripple, increased motor efficiency and reduced motor noise...

user291017
  • 11
  • 2
  • user291017 - Welcome :-) Are you associated with EPC? This answer seems to be promoting their products. Site rules [here](/help/promotion) and [here](/help/behavior) explain that any relevant affiliation needs to be disclosed. So if this applies, please [Edit] your answer to explain your affiliation. Thanks. – SamGibson Jul 15 '21 at 01:43
0

GaN's transistors are not yet a drop-in Mosfet's replacement.

They cost 10/15 times a direct Mosfet competitor.

Vgate thresholds recently went down to 4 Volts.

They are tipically used in 1kW to 4 kW AC/DC power supplies where 99% efficiency is reached using an MCU that optimizes the phase of ON-OFF switching events.

See Transphormusa.com for more details.

To answer your question: I don't think at the moment there is a small multi-phase GaN half-bridges specifically in the 5-10A @5-10V range

Enrico Migliore
  • 4,161
  • 1
  • 9
  • 12
  • The rapid consensus is saying that the cost and difficulty of using GaNs will be an issue. Interestingly, drone ESCs is quite a challenging application - a "smallish" ESC like this one: https://www.readytoflyquads.com/littlebee-30a-s-blheli-s-pro-naked can be controlling several hundred watts. The good news is that they normally get quite a bit of airflow. – Russell Mirov Mar 13 '21 at 22:33
  • we are now seeing them in small power supply to charge phones – julienfr112 Apr 03 '22 at 13:29