High Current Test

Hi Mohammad

Could you tell the fault type? OCP or PDF ?

If OCP, proper layout and register setting should be applied.

If PDF, resistors for low side gates may be needed. There is comment on the datasheet about this.

Best regards,

Hi Wilson ,

Thanks for your quick reply .

1) I read this comment and I used resistors for low side gates (R = 47 Ohm) , So I think fault type is OCP , What should I do for this ?

2) First test : ISGAIN = 40 , Torque = 0xFF , Faultn LED : OFF , Motor worked
2nd test : ISGAIN = 5 , Torque = 0x3A , Faultn LED : On , Motor didn't work

In read Operation from registers , the Status value is 0x59 in both tests !! :(

Best regards,

Thanks.

Hi Mohammad,

What are the other register settings?
What is your system voltage?
What is the sense resistor value?

Please confirm the DRV8711 VM voltage is above UVLO during operation.
Also if you have a current probe, please provide the current waveform. If not, please provide a scope capture of the sense resistor voltage and the xOUT voltages.

Hi Rick,

1 ) System Voltage = 12v , Sense Resistor Value = 0.1 Ohm 10W

2 ) Other Register Value
0x0C, 0x21, //CTRL // ISGAIN = 5 MicroStep = 1/16
0x11, 0xFF, //Torque // Torque = 255
0x20, 0x32, //OFF
0x31, 0x00, //BLANK
0x45, 0x10, //DECAY
0x50, 0x02, //STALL
0x60, 0x0F, //DRIVE
0x70, 0x00, //Status

3) Status Of Faultn LED and Stall LED in Some test
3 - 1 - first test
Register:

0x0C, 0x21, //CTRL // ISGAIN = 5 MicroStep = 1/16
0x11, 0xFF, //Torque // Torque = 255
0x20, 0x32, //OFF
0x31, 0x00, //BLANK
0x45, 0x10, //DECAY
0x50, 0x02, //STALL
0x60, 0x0F, //DRIVE
0x70, 0x00, //Status

Board ( Left LED is Stall and Right LED is Faultn)

3 - 2 - Second test
Registers:

0x0D, 0x21, //CTRL // ISGAIN = 10 MicroStep = 1/16
0x11, 0xBF, //Torque // Torque = 191
0x20, 0x32, //OFF
0x31, 0x00, //BLANK
0x45, 0x10, //DECAY
0x50, 0x02, //STALL
0x60, 0x0F, //DRIVE
0x70, 0x00, //Status

Current = 1 A

Board

3 - 3 - Third test
Registers:

0x0E, 0x21, //CTRL // ISGAIN = 20 MicroStep = 1/16
0x11, 0xFF, //Torque // Torque = 255
0x20, 0x32, //OFF
0x31, 0x00, //BLANK
0x45, 0x10, //DECAY
0x50, 0x02, //STALL
0x60, 0x0F, //DRIVE
0x70, 0x00, //Status

Current = 0.4 A

Board

4 ) Current Waveform video

www.youtube.com/watch

Hi Mohammad,

Thank you for the information. The current does not look correct when the motor is running. It should be the same amplitude.

Can you try a few more things?

1) What is the full scale current of the stepper motor used? It appears your Ifs calculations may not be correct. Please double check the settings. Also, once the settings have been confirmed please try running at 1/2 full scale current for debug.

2) What is the current limit of the supply? At lower voltages, VM can droop causing faults. Please raise the either current limit or the supply voltage.

Hi Rick,

Thanks for your reply.

1 ) Motor Current is = 4.4 A ,
IFS = ( 2.75* Torque ) / (256 * ISGAIN * Risense ) , Torque = 191 , ISGAIN = 10 , Risense = 0.1 Ohm
==> IFS = ( 2.75 * 191 ) / ( 256 * 10 * 0.1 ) = 2.05 A
but my current is 0.98 A !! Should I check any other settings ?

2 ) current limit of the supply is 5 A and it is greater than 4.4 A , I raised supply voltage to 24v , then current decreased .

3 ) Please tell me , as you know every motor has special features , generally when I changed motor to another motor with different features , which register parameters should I change ?

4 ) another problem , In Initializing registers process , when I initial 7 registers except Status , motor worked But when I initial all registers , stall led is flasher ( on off on off ....) ( Status value = 0x00 ) and motor didn't work properly .

Thanks a lot

Hi Mohammad,

mohammadmehdi golmeshki said:

1 ) Motor Current is = 4.4 A ,
IFS = ( 2.75* Torque ) / (256 * ISGAIN * Risense ) , Torque = 191 , ISGAIN = 10 , Risense = 0.1 Ohm
==> IFS = ( 2.75 * 191 ) / ( 256 * 10 * 0.1 ) = 2.05 A
but my current is 0.98 A !! Should I check any other settings ?

The current reading on the power supply does not indicate the current in the motor windings. A current probe is your best indication of the current in the windings.

mohammadmehdi golmeshki said:

2 ) current limit of the supply is 5 A and it is greater than 4.4 A , I raised supply voltage to 24v , then current decreased

The current decreases because more charge is stored in the local bulk capacitor. The local bulk capacitor supplies the majority of the current to the stepper motor, while the power supply replenishes the charge used.

mohammadmehdi golmeshki said:

3 ) Please tell me , as you know every motor has special features , generally when I changed motor to another motor with different features , which register parameters should I change ?

Have you read the following documents:

• DRV8711 Decay Mode Setting Optimization, SLVA637

• DRV8711 Quick Spin and Tuning Guide, SLVA632

mohammadmehdi golmeshki said:

4 ) another problem , In Initializing registers process , when I initial 7 registers except Status , motor worked But when I initial all registers , stall led is flasher ( on off on off ....) ( Status value = 0x00 ) and motor didn't work properly .

The stall led is an indicator, and has no effect on the performance of the DRV8711.

I suggest you focus on running the motor smoothly at one current (1 or 2A) and low speed. At that point you can begin to modify the settings to determine the effect. Set the decay mode to 101 (Automixed decay at all times). This should allow you to see the motor currents. The sine wave peaks should remain constant as the motor runs.

Hi Rick ,

Thanks for your quick reply

What's the effect of the Mosfets on the performance ?

My Mosfets features : 33 A 200 V rds(on) = 0.085

Thanks

Hi Mohammad,

There should be little effect. The key is to make sure the IDrive and TDrive settings are correct. There are recommendations in the Quick Spin and Tuning Guide.