DRV8302 faults with FOC

Discussions regarding the Field Oriented Control (FOC) implementation on the VESC.
benjamin
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DRV8302 faults with FOC

Postby benjamin » 24 Jan 2016, 01:12

I heard that several people get DRV8302 errors when running FOC, but not with BLDC. The same thing happened to me today. I tested a few things, and what solved my problem was adding another 2.2µF capacitor to GVDD on the drv8302 (C18). I just soldered it on top of the other one, as in the attached picture.

vesc_c18_2x.jpg
c18_2x
vesc_c18_2x.jpg (45.8 KiB) Viewed 9329 times


I assume the reported DRV fault is GVDD_UNDERVOLTAGE, and that the extra capacitor makes the GVDD rail more stable. The reason that this only happens in FOC can be that the switching is completely different.

Can anyone who gets DRV8302 faults in FOC mode give this mod a try?

david
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Re: DRV8302 faults with FOC

Postby david » 24 Jan 2016, 11:44

Thanks Benjamin.
I'm testing it at the moment. The only way I can reproduce it is when connecting a 16V/5A power supply to it, the GVDD_UNDERVOLTAGE occurs then while accelerating hard (8V limit). Added the cap on top at C18 and it's performing now without error. Soldering this tiny little thing on top is just a little bit tricky, would there be a fitting cap with 4.4mF or something that could replace the smaller one on C18?

The other FOC versus BLDC error I was able to get was an over_current fault (only random on 12s with 40cm battery cables) and shorten the battery cables to 20-25cm worked there.
VESCs made in Germany

benjamin
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Re: DRV8302 faults with FOC

Postby benjamin » 24 Jan 2016, 15:07

I just confirmed that this solved some issues on my ebike as well.

whitepony
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Re: DRV8302 faults with FOC

Postby whitepony » 24 Jan 2016, 20:55

is this doable with a normal soldering station and practice in soldering 4mm bullet connector or will i potentially screw up everything? :lol: what voltage is the 2.2uF?

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Re: DRV8302 faults with FOC

Postby benjamin » 24 Jan 2016, 21:33


whitepony
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Re: DRV8302 faults with FOC

Postby whitepony » 24 Jan 2016, 22:47


david
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Re: DRV8302 faults with FOC

Postby david » 24 Jan 2016, 23:13

It's this one here (Mouser Part no. 810-C1608X5R1C225M):
http://www2.mouser.com/ProductDetail/TDK/C1608X5R1C225M
VESCs made in Germany

whitepony
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Re: DRV8302 faults with FOC

Postby whitepony » 25 Jan 2016, 06:50

ty! 1.6 x 0.8mm omg :lol: :roll:

whitepony
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Re: DRV8302 faults with FOC

Postby whitepony » 27 Jan 2016, 22:24

operation successful and I can confirm: it solved my braking issue, I can now use FOC like BLCD (tested in the living room, its raining outside so I cannot say more currently). :)

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Re: DRV8302 faults with FOC

Postby arvidb » 27 Jan 2016, 23:16

I've tried to decipher what the DRV8302 datasheet says regarding the GVDD cap. Under "RECOMMENDED OPERATING CONDITIONS" it states that 2.2 µF is a "typical" value for this cap. Further down it lists fgate ("Operating switching frequency of gate driver") as 200 kHz typically, but here it also states conditions: "Qg(TOT) = 25 nC or total 30 mA gate drive average current". Wouldn't it make sense that both Qg and switching frequency also affects the neccessary capacitor size for the gate drive voltage?

The total gate charge for the IRFS7530 is 236 nC (typ), 354 nC (max), for a total of >1400 nC (typical) for all six MOSFETs. If the average gate current is proportional to both gate charge and switching frequency, this corresponds to 177 nC @ 25 kHz. So maybe it's no wonder that GVDD gets too low sometimes with the "typical" 2.2 µF cap?

I must say the datasheet is very unclear on this, and very brief in general!


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