• State
  • Locked Locked
  • Replies 9 replies
  • Subscribers 29 subscribers
  • Views 1171 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8811 Decay Setting and heating when Enable active (No Step)

leroybt
Prodigy 60 points
Other Parts Discussed in Thread: DRV8811EVM, DRV8811

*********** Interested in working with a TI FAE to possibly visit site and view DRV8811EVM Board in action and test results ***********

I have two questions for the DRV8811:

1.) Decay Setting - The setting for the decay signal on the DRV8811 is not clear. The setting can be slow, mixed, and fast. These setting affect the RMS current on AOUT1 and control the chopping waveform riding on each step as the signal approaches to 0V. The datasheet does not specify how to choose the decay voltage setting against a motor. Or how to select a setting that best fits a motor. What would be the best setting? Are there any actual waveforms of how AOUT1 should look with the selected settings? How much chopping should be apparent on the steps (other products do not show as much chopping).

 

2. ) Thermal Characteristics - In testing the DRV8811, the component heat up when the part is enables and no steps are set to the device. Can you explain why the part heats up when there are not step signals set to the device. When steps are applied the part cools down. (Interesting picture below of DRV8811EVM with removed DRV8811) 

 The DRV8811EVM board settings were as follows : Motor attached NEMA23,  PS AMP=.33A,  VREF(V)=1.33V, Motor AMP=1.6635A, Decay (V)=2.46V, DECAY=SLOW, STEP SIZE=HALF (USMO=0V,USM1=3.3V), DIR=0V, STEP=0V, Enablen=0V, Resetn=3.3V, SRn=0V, Sleepn=3.3V, Date=10/18/2011 .

  • 0
    TI__Guru 55615 points

    Leroy,

     

    We are investigating this and will get back to you soon.

     

     

  • 0
    TI__Intellectual 2520 points

    Leroy,

    1. How to select the decay setting? The Decay setting varies per motor. It is difficult to suggest one setting that would work with any motor. Generally, Slow decay when the current is increasing and Fast/ mixed decay when the current is reducing would help any motor. The idea is to make the current waveform as sinusoidal as possible. This will also help in noise reduction of the motor.

    2. Why does the part heat up when the IC doesnt get any steps? Even when the IC doesnt get any step command, it still pumps out current to "hold" its position. This current will cause the IC to heat up. When the IC gets continuous step commands, the current is sinusoidal and the RMS current could be lesser than the DC hold current. Generally, if the motor needs to held at a constant position, it is a good idea to reduce Vref to lowest acceptable level that can hold the motor.

    3. Foot print does n't match? I have to check this. We suggest an acceptabel landpattern on the datasheet and I would strongly recommend following it.

    Sorry for the delay in responding.

    Thanks

    Vivek

     

  • 0 in reply to Vivek Shankar
    Prodigy 60 points

    Vivek,

    3. The snapshot of the landpattern is from the DRV8811EVM Demo Board from Texas Instrument. If you have a new board design for DRV8811EVM with the recommended landpattern is it possible that you could swap my board?  I would like to see the performance of the board with via farms under the DRV8811.

     

    Thanks

    LeRoy

  • 0 in reply to leroybt
    TI__Intellectual 2520 points

    Leroy, At this time we don't have a new board design in works.

    Thanks

    vivek

     

  • 0 in reply to Vivek Shankar
    Prodigy 60 points

    Vivek

     

    I'm comparing the DRV8811 to the Ericsson PBL3770 (old part). I notice when I disable the 3770 (drive high on I1 and I0) the part does not go hot. Does this mean that the 3770 is not holding it postition when disabled?

    In regards to the "hold" position, when enable is not active the output is not driven. Is the temperature a derivative of the charge pump to drive the mosfet gate at the Vref current setting? Would it be ok place the device in sleep mode when enable is not active (Requres 1ms to capture first step)?

    Ericsson 3770 current rating 1.8A (Output Driver are Transistors)

    TI    DRV8811 current Rating 2.5A (Output Driver are MOSFET)

  • 0 in reply to leroybt
    TI__Intellectual 2520 points

    Leroy,

    DRV8811 gets heated only due to the current through the output FETs. the current required to run the Charge pump is not significant in comparison. If the ENABLEn = High (3.3V for eg.) then DRV8811 will not get heated up. Alternatively, if SLEEPn = 0V, the IC is in SLEEP Mode and will not heat up. However, as you mention, it could take upto 1 ms for the IC to "wake up".

    Quick question, with ENABLEn = High are you seeing DRV8811 heating up?

    Thanks

    Vivek

     

  • 0 in reply to Vivek Shankar
    Prodigy 60 points

    Vivek

    OK , just checked my board it's all good. Thanks for your help. Heating occurs when ENABLEn=LOW which is what is expected.

    Thanks

  • 0 in reply to leroybt
    Prodigy 60 points

    Vivek

    Can you send me your phone number so that we can talk over the phone?

    Best Regards,

     

  • 0 in reply to leroybt
    TI__Intellectual 2520 points

    Leroy, You can contact me at 214-793-3039

    or at vivek-s@ti.com if you want to schedule a conference call.