DRV8711: disruption on PCB, current regulation

Dear Mr. Hernandez,

It's no difference. All Parameters are the same.

I use the Evaluation board of your Company DRV8711EVM Rev E1.

Picture one shwos A1HS, AOUT1, A1LS and the current trough winding A.

The second picture shwos A2HS, AOUT2, A2LS and again the current trough winding A.

The decay mode was mixed.

First problem (first picture) during switching on Q1 and switching off Q3. Second and bigger problem (second Picture) during switching off Q5 and switching on Q7. The disruption is bigger in fast decay phase than in slow decay phase. Seems to me that there is short circuit behaviour.

Best regards,

Marco Larcher

I understand why you would go down the should circuit route. To verify if it is or isnt, can you zoom in on the first waveform disruption on your Q5/Q7 scope capture? There is no change in the half bridge signals except the current. If we can verify which signal is the first to trigger the disruption, we can see from part of the circuit the disruption propagates from.

I think this picture shows the problem better.

With increasing TDRIVEN, TDRIVEP, IDRIVEN, IDRIVEP you get worse results.

I think the problem is that...

... Q5 is switched off (A2HS = AOUT2), but still at 24V. After DTIME (dead time) the signal A2LS, Q7 is switching on. During the ramp of A2LS the voltage at AOUT2 drops. A2HS drops as well but a Little bit slower. Because of that, the Q5 is conducting. Means short circuit.

I see what you are saying. Let me show to team and see if issue has been reproduced before.

What is the lowest magnitude on the TDRIVE/IDRIVE parameters that the short circuit was noticeable from your end?

Dear Hector Hernandez Luque

TDRIVEN = 250ns

TDRIVEP = 250ns

IDRIVEN = 100mA

IDRIVEP = 50mA

With current magnitude it is possible to influence the effect.

Hi Marco,

I need to try this test in the lab and see what I get.

Did you get a FAULT generated?

Hi Hector,

If there is a disroption according short circuit, I think it is possible that all Signal has also a disroption.

Best regards

Marco

Hi Hector

Do you have some interesting News for me?

Best regards

Marco

Hi Marco,

Please note, I am looking into your issue. I apologize for the delay from my end.

To duplicate your setup as much as possible:

Can you send me a screen capture of the GUI home page with config open, then another with Current Reg and another with PWM Mode?

Also, what motor are you using?

PWM Control disable

Stepper Motor 23HS8430 1.8° 3A

Hi Marco,

Apologies for the delay from my end. I have tested with a different stepper motor that is as close to your specs as I could find (https://www. automationdirect.com/adc/Shopping/Catalog/Motion_Control/Stepper_Systems/Stepper_Motors_-z-_Cables/STP-MTR-23055)

In the scope captures I got,  I see disruption and I am interpreting it before I present it to you.

Question: on the evaluation of the competitor part, did you set the same settings as you set for the DRV8711EVM on the GUI? 

Hi Hector,

I'm also using a Evaluation board of Trinamic.

Trinamic has diffrent paremeters as TI. I think a comparison is difficult.

Hoping to hear from you soon. I'm very exciting about your results.

Best regrds

Marco

Dear Hector,

Do you have some informations?

Our project is at a point where we have to decide which stepper driver we will chose.

I like your driver, but I need information what the problem is with and if it will be fixed or is it only a problem for a small series?

Best regards

Marco

Dear Hector,

Are there News about the reasons of disruptions?

Best regards

Marco

Dear Hector,

Reducing the PWM frequency means reducing TOFF. More noise is the result. That isn't an option.

Is it possible to see your results? How is the effect of increasing gate source capacitance on disruption.

If the gate charge is to big. With more driving current it should be possible to load the capacitor faster. But with more current the disruption is higher..

Hi Marco,

I see disruption in my scope captures, one is shown below. The noise propagates from the switching across the driving of the different coils of the motor. This issue can be mitigated with a series resistor, as indicated in the datasheet and in the image above. Now, if you do not want to add a series resistor to your application, you can provide to us your application specifications and I can recommend to you a device that does not have this noise propagation.

Hi Marco,

Did you also increase the dead time? What size of resistor did you use?

Hi Hector,

Yes I increased the dead time, 850ns. Resistor was 120Ohm.