VESC from Enertion: DRV8302 spectacularly blown, what went wrong?

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cyril.leroux
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Re: VESC from Enertion: DRV8302 spectacularly blown, what went wrong?

Postby cyril.leroux » 07 Sep 2016, 13:17


pf26
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Re: VESC from Enertion: DRV8302 spectacularly blown, what went wrong?

Postby pf26 » 08 Sep 2016, 07:18

I think you first need to make sure your power switch does not open or create too much voltage rise upon hard regen. You could try using a power supply with voltage/current control and your battery to check this.

rew
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Re: VESC from Enertion: DRV8302 spectacularly blown, what went wrong?

Postby rew » 14 Sep 2016, 10:23


robt
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Re: VESC from Enertion: DRV8302 spectacularly blown, what went wrong?

Postby robt » 21 Nov 2016, 14:09

Does adding a 56V zener to the input of the DRV make any sense in trying to protect it from voltage spikes?

rew
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Re: VESC from Enertion: DRV8302 spectacularly blown, what went wrong?

Postby rew » 23 Nov 2016, 12:09

The DRV has several pins connected to voltages related to the battery voltage.

It has a switching regulator chip inside. This has two power pins.

It has a linear regulator inside (on the main chip), it has one power pin.

Then there are three "phase" lines. These are connected to the motor phases. These are quite "strong" signals. Putting a zener across them will just blow up the zener when the zener voltage is exceeded.

Then there are the three "gate drive high side" signals. These are driven from the boost cap by the DRV chip. Oh and the three boost caps themselves.

So... because there is REAL power available when things go wrong, putting in zeners is not much use. You can protect against a 100V 10mA spike (1W) for say a microsecond (only 1 micro Joule!). Maybe you can even handle 1000 times more. Maybe even a million times more. But around 1J is where things become difficult to defend against. When I'm biking at 5m/s there is 1200 J going around.... There is a thousand times more engergy going around than what is "problematic to handle".....

pf26
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Re: VESC from Enertion: DRV8302 spectacularly blown, what went wrong?

Postby pf26 » 23 Nov 2016, 19:20

I have been using Vescs since the first batch from Vedder, mostly on 12s with regen. I always add a 56V zener in parallel with the high voltage DRV power supply (directly soldered at the nearest capacitor, shortest possible wiring). I never had a DRV8032 damaged.
Obviously, this proofs nothing.
But a P6KE56A or 1.5KE56A costs little. If several people try and add these, we will see if blown DRVs still occur. If it does, then ok, we know it is not enough.
I still believe temperature plays a role as explained above in an earlier post I wrote in this thread.

rew
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Re: VESC from Enertion: DRV8302 spectacularly blown, what went wrong?

Postby rew » 24 Nov 2016, 08:18

Yeah, it depends on what the actual failure mechanism is.

If there is somehow just a very short spike that damages the DRV, then adding a zener close to the DRV will use the impedance of the trace towards that point to limit current through the zener and may allow the DRV to survive. But if the "event" has real energy then all hope is lost. But you're right. Maybe it is a low-energy event that can be solved with a zener. Some form of controlled impedance other than the trace impedance might be good too: Otherwise a layout change (layout improvement) may influence the robustness of the device....

Dimitri
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Re: VESC from Enertion: DRV8302 spectacularly blown, what went wrong?

Postby Dimitri » 07 Dec 2016, 04:56

I'm designing also a VESC and am worried about this too, so i might try to isolate potential spikes from the main power (of the MOSFETs) and PVDD1, using series ferrite and small resistor (like 1R) and then it's own capacitors (ceramic and electrolytic) with TVS or Zener in parallel.
The series resistor and ferrite can really help to impede the spike if using a zener or TVS in parallel with PVDD1.

The high current impulses for the Gate drive comes from the capacitors (as is always the case with all high speed circuits), so we don't care about the small voltage drop on the 1R ;)
That small voltage drop would be the [RMS current x series resistor], so that's about: 30mA x 1R = 30mV, so if the main voltage is 50V, you will get 49.97 on PVDD1, which can cause problems for the MOSFET current measurement unit of the DRV8302 (see datasheet page 13), since it measures the voltage drop between the PVDD1 and HS_X pins, so you would end up with approx 30mV less voltage drop than it really should be, but i'd rather have inaccurate FET current fault detection than the DRV8302 blow up.

What i am REALLY worried about though, is the maximum PWM frequency allowed to use, since the IRFS7530 have MASSIVE Qg.. You can see my other post about that here:
viewtopic.php?f=7&t=507

I'm open to scrutiny and advice.


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