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DRV8412

turg
Prodigy 50 points
Other Parts Discussed in Thread: DRV8412DDWEVM, DRV8412

 

I started using DRV8412DDWEVM for driving a Brush Servo motor (with low current consumption ~0.6A). I’m working with 20KHz PWM, and the DRV8412DDWEVM is working fine when I give duty cycle up to 60%.

Using duty cycle greater than 60% the DRV8412DDWEVM output is 0 (OUTA & OUTB are both following the input and therefore the total output is 0). After the problem occurs, I tried to give duty cycle lower than 60% but the output stays on 0 until I give RESET AB, and then the motor starts running.  

in addition, sometimes when working with up to 60% and changing the motor movement direction, the DRV8412 output is 0 until I give RESET AB.

In the datasheet & in TI forums I found comments that say that when using duty cycle greater than 90% for 10KHz PWM or below there might be a problem due to the bootstrap capacitors, although I’m using higher frequency I tried to increase these capacitors (from 100nF to 330nF) but it didn’t solved the issue. 

Thanks

 

  • 0
    TI__Guru 55595 points

    Tomer,

     

    I am going to need a little more information to troubleshoot this problem.  

     

    First, what is your supply voltage?  Please also verify that your 12V supply for VDD and GVDD is stable when you are conducting your experiment.  

    What MODE are your operating the device in?  Please check the voltage on the M1/M2/M3 pins and let me know.  

    Is the /FAULT pin cycling low at any time?  

    Is the /OTW pin cycling low?

    When you provide 60% duty cycle, are you holding one of the outputs HIGH or LOW?  

     

    Regards,

    Ryan

  • 0 in reply to Ryan Kehr
    Prodigy 50 points

    Ryan,

     

    Supply voltage: GVDD = 12V, PVDD = 24V. both are stable.

    Mode: 2 FB (M1 = M2 = M3 = 0), Verified that voltage is 0 on those pins.. 

    Both /FAULT & /OTW pins are high, and not cycling even when I’m going from 53% duty-cycle (output ok) to 65% duty-cycle (no output).

    In my experiment I provide PWM signal to input PWM_B and 0V to PWM_A. OUT_A & OUTB are connected to the motor and PWM_C, PWM_D, OUT_C & OUT_D are not connected (not to the controller and not to a load). 

     

    Thanks,

    Tomer

  • 0 in reply to turg
    TI__Guru 55595 points

    Tomer,

     

    It sounds like the device is going into a cycle-by-cycle current limiting mode where one of the outputs is going to a HiZ state.  If you have a load connected across the outputs, it will appear like you have the same signal on each output and they are both tracking one of the inputs.  

    Why you are current limiting is confusing to me since the OC_ADJ resistor on the EVM is 47k and that sets the current limit at >5A.  Are you using a current probe on the output to measure current just before the device goes into protection?

    You could verify that the device is going into protection by connecting the MODE1 pin to VREG.  That will put the device in a latched state and the /FAULT pin will cycle to the low state.  

     

    Regards,

    Ryan

  • 0 in reply to turg
    Prodigy 50 points

    Ryan,

     

    In addition my earlier response:

    I replaced the DRV8412 and I returned on the experiment, now I can work with full range duty-cycle when I provide PWM signal to input PWM_D (and 0v to PWM_C) but when I switch between the inputs (PWM signal to input PWM_C and 0v to PWM_D) I see the issue again. 

     

    Tomer

  • 0 in reply to Ryan Kehr
    Prodigy 50 points

    Ryan,

     

    You are right.

    When MODE1 was connected to VREG i saw that the device entered /FAULT, I measured the output current and found out that I have transients of up to 9.8A!!! for the first 5ms (and then the current stabilizes on 0.6A).

    I replaced the OC_ADJ resistor to 22K for 11.6A limit and it is working fine.

    I would like to add the DRV8412 to a custom design, one of the requirements is to have a small form factor design so I need to use small capacitors and inductors, do you have design guidelines in order correctly select these components?

    Thanks a lot for your help!

    Tomer 

  • 0 in reply to turg
    TI__Guru 55595 points

    Tomer,

     

    Glad you are up and running!  As far as component recommendations, please reference the schematic in the datasheet.  You can shrink the case size of the decoupling/and BS capacitors to 0603 with a lower voltage range for your application.  

     

    Also, the bulk decoupling doesn't need to be 1000uF...you could probably drop that down to a 220uF to save a significant amount of area.  For inductors, they are technically not needed for a motor application that is already an inductive load.  You could remove those all together in your application.  

     

    Regards,

     

    Ryan