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Total dead-time of the MOSFETs ???!!

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ThierryGTLTS
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Total dead-time of the MOSFETs ???!!

Hello,

I noticed that the dead-time of the MOSFETs seems to be composed of 3 parts.

1. HW part DRV8302 (or 01), 10K sets 80nS dead-time, 50µS the min possible + 3nS/1K of resistance.
2. In mc_interface.h #define mcpwm_dead_time_cycles 60, but I ignore the lenght of one cycle, help, please :!:
3. In BLDC Tool or VESC Tool, you can find dead-time compensation, preset to 0.08µS.

So is the total dead-time equivalent to the sum of those 3 parts, and how long (in nS) is the lenght of a cycle :?::!:

Have a Nice Day.

Thierry

ThierryGTLTS
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Here is the response !

1. HW part DRV8302 (or 01), 10K sets 80nS dead-time, 50µS the min possible + 3nS/1K of resistance.
2. In BLDC Tool or VESC Tool, you can find dead-time compensation, preset to 0.08µS allow the user to reduce the HW deadtime.
3. In mc_interface.h #define mcpwm_dead_time_cycles 60, and a cycle is about 6nS because of the 168MHz CPU clocking.

Have a Nice Day.

Thierry

antonchromjak
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Isn't dead-time compensation for dead-time distortion elimination?

ThierryGTLTS
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On the DRV8302, you can find:

The DRV8302 uses automatic hand shaking when the high side or low side MOSFET is switching to prevent current shoot-through.

The problem is that the definitions of the "Deadtime" and "Handshaking" are a bit fuzzy, if anyone can explain me the difference, it would be kind.

 

Automatic Handshaking is used by TI in their driver devices, and it's very useful to prevent shoot-through without the need od adding too long deadtime.

But it seems that it doesn't work well in all circumstances.

So adding a deadtime can solve those problems.

But I don't know if the deatime compensation adds or substract to the HW one defined in the DRV.

 

Have a Nice Day.

Thierry

antonchromjak
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I think deadtime compensation don't change deadtime but only eliminate its negative effect at low rpm https://granitedevices.com/wiki/Dead-time_distortion.

ThierryGTLTS
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Someone says me that on original Benjamin Website forum.

1. 50 nS minimum added to the handshaking. There is an internal hand shake between the high side and low side MOSFETs
during switching transitions to prevent current shoot-through.
2. I think the timers are clocked with 168 MHz so one tick is 5.95 nS (when the value is 0 to 127).
3. This is used by SW to compensate for the HW dead-time, not added.

An it's the best answer I've received to my question.

Have a Nice Day.

Thierry

TechAUmNu
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I have been trying to increase the deadtime, but no matter what I set it to on the #define mcpwm_dead_time_cycles it makes no difference.

Am I missing something?

 

Edit: Nevermind it was not actually uploading the firmware.