MOSFET for the DRV 8711

Hello Alex,

What is your target stepper motor current?

There are several TI NexFETs available in the TO-220 package with a 60V VDS rating that are compatible with DRV8711: www.ti.com/.../n-channel-mosfet-transistor-products.page

Thanks,
Matt

Hello Matt,

6-7 Amps per Coil.
Currently I have tried the IRF 1018 but got triangle wave like output instead of sinus on the stepper side.
In this configuration my 8711 got over 74C pretty fast (~5A@48V per Coil).
The board layout was made not as well.
I have to made new one anyway.

Beside of this I have got CSD88537NDT (for less then 4,5A), NTTFS5820NLTAG and the CSD18531Q5A.

I would like to get better Solution for the MOSFET before I made another board which generates triangle waves on the output.

Regards,
Alex

Hello Alex,

Do you have a scope capture of the triangle waveform? What is your stepper motor characteristics (R, L, BEMF constant)?

This waveform may not be FET dependant and potentially can be fixed by configuring the DRV8711.

Thanks,
Matt

Hello Matt,

I don't have got exact data about the motor specification as we tried different motors with different settings of the 8711.

Mostly with 24V-2A per Coil and more. Last stepper have got Phase Res = 1,8 ohms, Inductance = 5 mH and 2 Amps per Coil.

Tried at 24 and 48V with 60 RPM and more (200, 400, 600 and 1000).

I don't have got any information about the BEMF constant right now.

It should be around 20V (~3,5V) at slow speed.

Regards,

Alex

Hello Alex,

What were the DRV8711 settings for the registers MODE, TOFF, TBLANK, TDECAY, & DECAYMOD when you generated the above waveforms?

Thanks,
Matt

Hello Matt,

MODE from 1/8, 1/16 to 1/32 (but mostly the 1/8 and 1/16)
TBLANK 200 ns
TDECAY 10,5 µs
DECAYMODE MIX_ALL and AUTO

TOFF was set from 500ns to 80µs in little steps and till 128µs in bigger steps.

I have got more than 60 scope images.
They are more or less the same looking.
No sine wave at any speed or setting.

Basically it's allmost imposible to provocate error on the 8711 with all this settings.

EDIT: This stepper is hooked up right now: http://www.omc-stepperonline.com/nema-23-bipolar-stepper-motor-20a-09nm1275ozin-23hs202004s-p-271.html

Regards,
Alex

Hi Alex,

What is the time per division and Amps per division of the images sent?
Also what is the VM voltage of the image, and the microstep setting?

Have you looked at
• DRV8711 Decay Mode Setting Optimization, SLVA637
• DRV8711 Quick Spin and Tuning Guide, SLVA632

for guidance?

Hello Rick,

VM voltage on this image is 24V (1/16 Microsteps).

2 Div = 1Amps. Actually its set up for 1,75 Amps.

H Div should be 10 ms on the previous images too.

Yes, I have studied several documents you linked here.

Regards,

Alex

Hi Alex,

Thanks for the information. Let's start with some basic settings and move on from there. If 0.5A works as expected, then the current and speed and microstep rate can be increased.

Please try:
VM = 24V
Decay Mode = 101 Automixed decay at all times.
1/4 ustep
200 steps/second (15 RPM)
Gain/Torque set for .5A full scale current
Default Toff
Default Tblank
Enable Adaptive blanking time (does not have an effect at 1/4 step but will at higher step rates)
Default IDRIVE and TDRIVE

Please report if you are seeing proper current regulation running with these settings.
If you are then change the current to determine if you can achieve the desired full scale current at the lower speed.
Once the desired current is achieved, the next step is to change to the desired microstep rate at the same speed and observe the results.
Increasing the motor speed to the desired speed while observing the results is the last step.

If you see a problem at any step, we can assist further.