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RE: Motor Driver for 3 phase motor

March 20, 2017, 5:55 am
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Hi Diederik,

The BG3612 EC motor needs the phases to be changed based on the hall inputs. A brushed dc driver with a full bridge or a BLDC driver with three half bridges can perform this function.

Please see www.ti.com/.../TIDA-00875 as an example.
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RE: drv8840: ROHS 2 compliance

March 20, 2017, 6:06 am
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Hi Mahendra,

We will investigate and reply soon.
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drv8840: ROHS 2 compliance

March 20, 2017, 12:03 am
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Part Number: drv8840

Hello Team,

Are DRV8840PWPR and DRV8842PWPR ROHS-2 compliant?

Regards,

Mahendra

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RE: DRV8701: Vref Adjustment based on motor size

March 20, 2017, 9:18 am
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Hi,

I just disassembled my motor and found out there is a PCB that contains a RLC circuit that goes to the brushes.  This seems to be some type of EMI suppression.  I suppose I will need to figure out some way around this.  

Any suggestions other than a different motor? 

Thank you,

Mat

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DRV8701: Vref Adjustment based on motor size

March 16, 2017, 6:52 am
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Part Number: DRV8701

Hi,

I have a product that is to use the DRV8701E for many different applications and different motor ratings.  I have a fixed sense resistor of 0.005 Ohms that I calculated for the maximum Ichop of 50 A. 

 

Ichop = (Vref-Voff) / (Av x Rsense) assuming I want a 50A max, 5V microcontroller, Av is 20 and Voff is about 10mV, I find that Rsense is 0.005 Ω (@ 5 Watts).

 

I have 3 different motors I’m using this design on @ 31 Volts (Bridge rectified AC), with a software adjustable Vref.

 

  1. 24 V, 4.8 A  about 115 watt motor
  2. 24V, 6.7 A about 160 Watt Motor
  3. 24V, 24.5 A about 588 Watt Motor

 

So I was under the assumption I could use the Vref to limit the maximum current of the motor and prevent damage to the MOSFETs.

I made a table and graph of all the different software to voltage values that I’ve included with this data.

If I use the 588W Motor @ 31V I should expect a max current of 18.9A.  This gives me a Vref of 1.91 & a PWM setting of 96/255.  This motor runs fine and has a slight increase as it should.  The 115 watt motor runs fine as well when set to the correct Vref.

 

The problem is the 160 Watt Motor I’m using should have a Vref of 0.54 V.  This gives me a PWM setting of 26/255.  The motor is in a screw drive reducer but fails to run, being limited at this value of Vref.  Even if I set Vref to 96/255 like the large motor it still fails to run.  If I set it around 150/255 ~ 3 volts I can just get it to run!

 

So what I’m gathering is that Vref doesn’t seem to be an Average current cutoff but it’s only an instantaneous value, is this correct?  This makes me afraid of the 588 W motor under load as well (but it will draw 10A with the correct Vref Setting)

Any additional information you would like I will happily provide.

 

Thank you,

Mat

 

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RE: DRV8432: Microstepping Mode, Externally Setting OC CBC Protection Threshold

March 20, 2017, 10:23 am
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Rick,

Thank you for your response. Yes, I've looked at DRV8711. In fact, this IC is my second choice and it's not the first one only because of the need for external bridges. We will have to provide of up to 5+ amps of motor current and it's my concern that 8711's output capabilities might be somewhat dicey to directly drive gates of higher power FETs with Ciss of 1500pF and above. For that reason DRV8432 seems to be a better choice. Please correct me if I'm wrong on that.


And thank you for your explanations of 8432 functionality. Will I have to limit PWM duty cycle in software to chop the motor current based on external current sensing or is it possible to use OC_ADJ pin functionality for that purpose?

Also, since we have some additional application(s) in mind for 8432, I'd still like to ask you to answer my original questions 1, 2, and 3 in the opening post above.

Michael

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RE: DRV8825: Irregularities in output waveform

March 20, 2017, 10:30 am
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I missed one of the mods in the list below the schematic: R2 is now 6.8K and R3 is now 2.0K. This gives me 1.5A max current.
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DRV8825: Irregularities in output waveform

March 20, 2017, 10:07 am
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Part Number: DRV8825

I am designing a custom controller board for controlling steppers on a telescope mount.  For my initial prototype (Rev A) I used two Pololu DRV8825 Stepper Motor Driver Carrier boards plugged into a custom board design.  This prototype drives two 1.5A NEMA 17 bipolar steppers and works very well. 

I designed a second board (Rev B) using three DRV8825 devices mounted directly on the board and I am experiencing erratic motion on all three motors and see some serious irregularities on the current waveform as shown below.  This trace was captured while in full step mode with a step rate of 40Hz. to a single NEMA 17 stepper.  The corresponding trace of the Rev A system looks good.

In looking further into the problem I also see serious irregularities in the PWM waveforms for both A and B outputs as shown below.  Again, the corresponding traces from the Rev A system look normal.

Details of the Rev B design are:

  • Three DRV8825 devices controlled by PIC18F46K20 microprocessor
  • Two NEMA 17 2.0A bipolar stepper motors, phase resistance 1.4 Ohms, phase inductance 3.0 mH
  • One Nema 11 670mA bipolar stepper motor
  • 12V power supply (same supply successfully used on Rev A board)
  • Decay is set to Fast Decay.
  • I used a stencil, solder paste, and a hot plate to do the reflow soldering of all components, monitoring the board temperature with an IR thermometer.
  • Schematic and layout shown below

The board as tested differs from this schematic as follows:

  1. Resistors R4 and R5 are tied to the board 3.3V net rather than the DRV8825's local 3.3V.  This was accomplished by cutting a trace and adding a wire.
  2. Resistors R7 and R8 are now 0.1 Ohm 0.5W.  The original resistors did not have an adequate power rating.
  3. A 100mF 35V electrolytic capacitor was added at the device.  The original design had a single bulk capacitor for the entire board.

I realize that much of the layout is not according to recommendations.  After reading most of the DRV8825-releated posts on this forum I realize that much needs to change here.  Previously I had not seen the EVM so I will use it as a model for the next rev.

I have tested all three DRV8825's on the board and they all show this behavior.  Has anyone seen anything like this in the past?  Is there anything in the information here that would point to a possible cause?  I will be redesigning the board in any case but I would like to have an idea of what caused this before I do that.  My only theory at this point is that my solder reflow method resulted in the devices getting too hot and being damaged.  It seems unlikely to me that all three devices would be damaged in the same exact way however.

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RE: DRV8432: Microstepping Mode, Externally Setting OC CBC Protection Threshold

March 20, 2017, 11:01 am
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Hi Michael,


We will have to provide of up to 5+ amps of motor current and it's my concern that 8711's output capabilities might be somewhat dicey to directly drive gates of higher power FETs with Ciss of 1500pF and above. For that reason DRV8432 seems to be a better choice. Please correct me if I'm wrong on that.

The DRV8711 is driving FETs with a typical Ciss of 3200pf. The switching time can be lowered to account for higher Ciss FETs.

And thank you for your explanations of 8432 functionality. Will I have to limit PWM duty cycle in software to chop the motor current based on external current sensing or is it possible to use OC_ADJ pin functionality for that purpose?

It is not possible in microstepping mode. Two OC_ADJ pins would be required to independently control the current in each winding.

Questions 1, 2, and 3 may take some time to answer.
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RE: DRV8432: Microstepping Mode, Externally Setting OC CBC Protection Threshold

March 20, 2017, 11:27 am
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Rick,


Thank you for clarifying that staff for me. I missed it entirely that I would need two independent winding current controls in microstepping mode. And 8711 device's ability to drive a typical Ciss of 3200pF is really encouraging so now I will reconsider and look into DRV8711 device much closer.

Although I'll still wait for you to answer questions 1, 2, and 3 to cover my other 8432 application needs.


Michael

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RE: DRV8880: AutoTune Feature for 5 A Stepper Motor

March 20, 2017, 11:53 am
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Hi Rick,

Thanks for prompt reply.

Once manually tuned during installation, do I need to retune the stepper motor to account for the aging of motor(and other variations in system over a period of time) or is it that it(the aging and time factor) will not make a big difference as far as avoiding the resonance effect of the motor is concerned ?
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RE: DRV8825: Irregularities in output waveform

March 20, 2017, 1:42 pm
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Hello jcarter,

Is your revB layout design very similar to your revA? If it is, then please isolate the 3rd device and see if you can successfully run the two motors from revA.
If you are not successful I would go back to one device and even resolder a new device to see if is a layout issue or device soldering issue. Your Schematic snapshot looks okay.
I see some problems in your layout and I think you are aware of them. Following the EVM layout is a good example to follow in your next revision.
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RE: drv8840: ROHS 2 compliance

March 20, 2017, 2:25 pm
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Hi Mahendra,

Please see the following link:

www.ti.com/ecoinfo

Under this you will find:

TI RoHS and Product Status Designation www.ti.com/.../szzq088

There you will find the answer.
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RE: DRV8825: Irregularities in output waveform

March 20, 2017, 2:32 pm
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Hello Luis,

The Rev B design is similar to the Rev A except that on the Rev A the DRV8825 devices are on the Pololu carrier board rather than on my board as mentioned. For the testing thus far I only use one 2.0A motor. I can connect that motor to the Rev A board (adjusted for 1.5A max output), connect the power, and watch the motor work normally. I then take the same power supply and same motor, connect them to the Rev B board and see the erratic behavior I described. I repeated the Rev B test with each of the three devices on the board and I see the same result for each one.

Have you had any reports of irregularities in the PWM waveform such as the ones I posted? Have there been reports of devices being damaged by overheating during the reflow process? If so what were some of the failure modes?

Thanks for your help,

John
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RE: DRV8825: Irregularities in output waveform

March 20, 2017, 2:42 pm
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Hello Luis,

After looking more closely at your question about similarities in layout between my Rev A and Rev B, I think the answer is that they are not very similar with regards to the DRV8825 since the layout around that device was done by Pololu in Rev A and by me in Rev B.

Thanks,

John
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RE: DRV8860: DRV8860 output channels question

March 20, 2017, 3:27 pm
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Hi Gavin,

We are investigating. This may take a few days.
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RE: DRV8825: Irregularities in output waveform

March 20, 2017, 3:44 pm
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Hello jcarter,

Thank you for the clarification. I see the thermal PAD which connects to the GND is missing, it is recommended to have that thermal Pad to remove heat. One thing we can try is to lower the current so see if that is one of the problems.
Could you please try running your motor around 300mA, that would let us see if the fault is due to an OTS event because of not enough heat dissipation.
Also, Could you please clarify your captures above. I see the red waveform has an offset of 6V, is this correct? if so this could also be a problem.
What pins are you capturing? Could you also monitor the nFault pin please and share your captures?
The other capture (only blue waveform) shows that maybe even the revA could be having a problem. Could you please add a larger capacitor than 4.7uF? Please also share that capture and let me know what pins exactly you are monitoring. I hope this helps, thank you very much.

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RE: DRV8711: Can DRV8711 operate without SPI?

March 20, 2017, 5:10 pm
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Hi Rick,
thanks for your quick answer.
I understood that SPI is required.
So is there any software (code example for SPI communication) at TI?
I couldn't find from DRV8711 webpage.

thanks,
TS
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RE: Universal Stepper Motor Driver Reference Design-TIDA-000716

March 20, 2017, 6:23 pm
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I need the code of TIDA-00736 too, this is not open ? Or I need to find an agent for it?
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Universal Stepper Motor Driver Reference Design-TIDA-000716

March 8, 2017, 11:59 pm
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Hi,

if you have code for TIDA-000716?

Thanks

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