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DRV8711EVM not running stepper motor

John Baker97919
Intellectual 460 points
Other Parts Discussed in Thread: DRV8711EVM, DRV8711

GUI loads and seems to run but motor doesn't run. I followed the steps in the DRV8711EVM users manual but have only 20.4VDC connected. The STATUS LED blinks but the FAULTn LED does not light up. I checked and I do have 20.4V at J1.

Connecting and clicking the various WRITE buttons seem to behave as expected.

The motor appears to be powered up as the shaft is locked.

Is 20.4V sufficient?

Any help please.

Thanks, John

  • 0
    TI__Mastermind 26065 points

    Hi John

    20.4V VM will not be a problem.

    I believe the SLEEPn, RESET, and soft ENABLE had been set since the shaft was locked. So, could you check whether there are correct STEP signals on the STEP input.

    If the STEP signals are not presented. You can try a different USB port, connect the COMx (Should be responsed connected immediately after you clicked), and test again.

    Thanks.

  • 0 in reply to Wilson Zuo
    Intellectual 460 points

    My mistake Wilson. The motor was not locked. I had the wrong COM port selected, I should have selected COM9 instead of COM4.

    Thanks very much for  your very helpful reply.

    Now the DRV8711EVM board seems to be working fine but I don't see the FAULTn LED lighting up. Is that a problem?

    John

  • 0 in reply to John Baker97919
    TI__Guru** 114905 points

    Hi John,

    We are glad to hear that the EVM is working. The FAULTn LED should only light when a fault is detected. Under normal conditions, the LED should not be lit.

    Depending on your settings, you may see the STALLn LED light as the motor is coming to a stop. (03/31/14 -- Corrected the LED which may light during operation).

  • 0 in reply to Rick Duncan
    TI__Guru** 114905 points

    Hi John,

    I realized I was thinking about the STALLn LED that might light up as the motor stopped. I have corrected the previous post to reflect this. Sorry for the mistake.

  • 0 in reply to Rick Duncan
    Intellectual 460 points

    Rick:


    The reason for my question about the FAULTn LED is on the Users Manual for the EVM, page 5 section 3.5 it says that the FAULTn LED will light: "The D2, FAULTn LED remains on until Step 11 when the part is taken out of sleep." So that threw me off a bit. Did I misread or misunderstand that statement?

    John

  • 0 in reply to John Baker97919
    TI__Guru** 114905 points

    Hi John,

    You did not misread or misunderstand that statement. It has been some time since I used the EVM.

    Let me double check, and get back with you.

  • 0 in reply to Rick Duncan
    TI__Intellectual 1145 points

    Hi John,

    I'm working close with Rick and checked the FAULTn LED behaviour you mentioned.

    The FAULTn LED is expected to turn off after STEP 9, when the DRV8711 is taken out of reset. We will update the User's Guide and correct this!

    Many thanks for mentioning this.

    -Matthias

     

  • 0 in reply to 5t34m
    Intellectual 460 points

    Thanks Matthias, I don't want to beat a dead horse but I didn't see the FAULTn LED lit at any time, before STEP 9 or anytime. Wilson or Rick had said that it would only be lit when there was a fault of some sort.

    John

  • 0 in reply to John Baker97919
    TI__Guru** 114905 points

    Hi John,

    We are puzzled why the FAULTn LED does not light on your board. We have tried two boards here. The FAULTn LED is lit from the time VM is powered until the device is taken out of sleep.

    We can only suspect that the LED or some other part of the circuit is not operating properly.  I am ruling out the regulator appears to be running properly since you can control the motor.

    When you have time, would you mind trying the following steps and report your findings?

    1) Plug in the USB cable and connect GND to the FAULTn test point (TP16). The FAULTn LED should light. I tried this on our boards and it does. If it does not, please measure the voltage on both sides of R2 and D2 when connected to GND. Also disconnect the GND connection and measure the resistance of R2.

    2) Repeat this for STALLn (TP17). It may also show similar behavior.

    Thanks.

  • 0 in reply to Rick Duncan
    Intellectual 460 points

    Yes Rick, the FAULTn LED lights when the FAULTn test point is grounded. Similar for the STALLn LED.

    The STALLn LED lights as expected during operation of the GUI but the FAULTn LED never lights.


    John

  • 0 in reply to John Baker97919
    TI__Guru** 114905 points

    Thanks John.

    So there appears to be a possible problem with either the connection between the FAULTn pin and R2 or the DRV8711 is not behaving properly.

    One last check if you don't mind. Please measure continuity between pin 18 (FAULTn) and R2. If it is 0, then the DRV8711 is suspect. If open, there could be a solder problem.

    You can then return the board for a new one.  Thanks again for your help in debugging this, and sorry for the inconvenience.

  • 0 in reply to Rick Duncan
    Intellectual 460 points

    Rick, the connection looks good, 000.0 using the diode connection on my Fluke 87. Surprising if there's a problem with the DRV8711 chip, since otherwise it's working fine as far as I can tell. Very strange.

  • 0 in reply to John Baker97919
    TI__Guru** 114905 points

    John,

    It is indeed strange. FAULTn should light when VM is initially powered. This is due to an undervoltage condition as VM is ramping. When the device is taken out of SLEEP, the fault is removed by writing a 0 to the UVLO bit in the STATUS register.

    Since the connection is correct, the remaining suspects are the DRV8711 itself and bulk capacitor. You can try to induce a fault by lowering VM to around 5V; it should set somewhere between 6.5V and 5V, typically 6.3V.

    If the LED lights between 6.5V and 5V, it could be that the bulk capacitor is suspect and the VM ramp is faster than expected.

    In any event, your board does not appear to act as any of the others.

     

  • 0 in reply to Rick Duncan
    Intellectual 460 points

    Ok, I'm completely confused now. Connecting the board to a BK PRECISION POWER SUPPLY model 1610, the board operates as per the Users Manual. The FAULTn LED lights when the PS is turned on and doesn't turn off until STEP 9, clicking the nSleep button.

    However, when connecting to a 20.4V Lithium ion 6.5Ah battery, the FAULTn LED never lights.


    So the DRV8711EVM board shouldn't be used with a battery or doesn't operate properly with a battery?

  • 0 in reply to John Baker97919
    TI__Guru** 114905 points

    Hi John,

    The DRV8711EVM board can be used with a battery, but appears to have at least one difference between battery and power supply operation. When testing, we have used a power supply.

    In my last response, I mentioned that the VM ramp could be faster than expected (due to a possible bad bulk capacitor). I was assuming that a power supply was used.

    The VM ramp using a battery is faster than the power supply. This should be observable on the scope. During VM power up, there is a period of time when the circuitry is fully functional but the VM voltage is below the UVLO threshold. This will cause the UVLO fault seen when using the power supply. If the battery ramps passes through this range (for example 5V to 8V) very quickly, the circuitry may not have seen an undervoltage condition.

    The users guide will now be updated for two items. One is correcting the step at which the FAULTn LED turns off when using a power supply. The second is adding a note stating that it is possible to power up the EVM without seeing the FAULTn LED light.

    Thank you again for working through this with us.

     

  • 0 in reply to Rick Duncan
    Intellectual 460 points

    Rick, Winston and All:

    Thanks for your help.

    John

  • 0 in reply to Rick Duncan
    Intellectual 310 points

    Hi,


    any news regarding the update of the DRV8711 manual?

    I have the same problems with the fault LEDs. I also found JP1 not being installed, while the manual says it shoudl be?!

    With kind regards,

    Thorsten Ostermann

  • 0 in reply to Thorsten Ostermann
    Intellectual 460 points

    Thorsten:

    JP1 is also not installed on my board and it looks like it's needed only for the JTAG, for loading a new program into the MSP430 chip. So you shouldn't need it.


    The problem that I was having with the FAULT LED is that I was powering the motor with a battery and apparently the voltage from the battery was rising too quickly for the DRV8711 chip to recognize that it was below the limit. When a power supply is used to power the motor, the DRV8711 sees that the voltage is initially low, and then turns on the FAULT LED. So if you're using a battery, try a power supply to see if the FAULT LED turns on as expected.

    Other than the FAULT LED not being turned on when using the battery, I had no problem with the DRV8711EVM board and it otherwise operated just fine to control the stepper motor.

    John

  • 0 in reply to John Baker97919
    TI__Intellectual 1145 points

    Thorsten,

    an updated User Guide for DRV8711 EVM will be released tomorrow to http://www.ti.com/tool/drv8711evm.

    Regards,

    Matthias