• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 29 subscribers
  • Views 415 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.

DRV8800 over current protection timing

K S
Prodigy 60 points
Other Parts Discussed in Thread: DRV8800

Dear Texas Instruments

 

I have implemented the DRV8800 into my design, while not using it as a motor driver, rather as a current protection and status feedback mechanism. The protection mechanism will protect my output interface if overloaded or shorten. I will by this have the output always on, with an expected current of typ. 100mA and a voltage of about 12V. I am using a switching controller, opening and closing MOSFETs, at the output of the motor driver, turning on and off the output sourced from the motor driver.

When using the current overload protection mechanism in the motor driver, it is stated in the data-sheet a shut-down time of typically 1.2ms. What I am having challenge in finding, is the information of the time from a fault is loaded on the output, to the motor driver actually is shutting down the output. If I have a small pulse (low energy) on the MOSFETs on the outside of the motor driver, will these spikes be enough to enable the over current protection mechanism...(?) I have a simulated average of 30mA, while simulating short spikes of about 6A. The simulation is of course a theoretical value, only giving a guide of the actual performance. I would also expect that the over current mechanism enable-timing will be dependent on the level of the current spikes. But lets say that the simulation is the actual levels in real life;

 

Is there any measurements or theoretical approximation of the time from the current fault is started, to the motor driver is defining it as a over current load situation, enabling the shutdown mechanism?

 

 

Sincerely

yours

K S

  • 0
    TI__Mastermind 26065 points

    Hi Knut

    We have both independent current regulation function and OCP function.

    1.2ms timing is related to OCP function which make sure the current <3A in output short conditions.

    Usually we setting the current limit by the regulation function as I = 0.5v / Rsense, this funciton can make the current limited at the setting value. So if you have a 100mA normal running current, you can just set the limit to a higher value like 0.5A. in this case, the OCP will hardly triggered and no nfault output. Also the output will not stop even there is noise.

    Thanks.

    Wilson

    Motor Application Team

  • 0 in reply to Wilson Zuo
    Prodigy 60 points

    Hi

     

    Thank you for your feedback.

    I will be needing to be able of providing a current of maximum 2A, so I do not want to adjust the current protection mechanism threshold.

    It is always challenging to write down a question, formulating so that the attention are brought on the actual question. When reading your feedback, I get the impression that I have been misunderstood;

    My question relates to the speed of the current mechanism. How long time is there from a short are done, to the current protection mechanism are enabled? After the current protection mechanism have been enabled, a 1.2msec period can bee seen (according to the data-sheet) Will small spikes make my design useless, not having a fault situation when the small spikes are generated(?)

    Is there any measurements or theoretical approximation of the time from the current fault is started, to the motor driver is defining it as a over current load situation, enabling the shutdown mechanism?

     

     

     

    Sincerely yours

    KS

  • 0 in reply to K S
    TI__Mastermind 26065 points

    Hi Knut,

    There is a time that we let the current rising without detect we call Tblank time which is about 3us. After this time, the driver will detect the current, if it is > OCP value, then there will be 1.2ms off, if it is < OCP and > current setting value by Rsense, it will regulate the current to the setting value. 

    In any case we should not let the OCP issued because the avarage current at that condition will be very small (~3us/1ms duty), usually at several mA, it is useless just to protect the device from short condition.

    So, if you need limit output 2A, just set your current at 2A by using a 250m ohm resistor to the sense pin. After you do this, the OCP will not be triggered unless there is a hard short of output.

    You can see this result on bench easily.

    Thanks.

    Wilson