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DRV8811 always die on EVMbord,why?

Other Parts Discussed in Thread: DRV8811, DRV8412, DRV8829

hello TI: 
     i found a problem  of the DRV8811,i use a FPGA to control DRV8811,i use S-curve accelerate,the max speed is 28khz (Eight microsteps),then the motor's speed from 0,accelerate to 28khz, then run at 28khz ,when motor  reach the Optocoupler ,i get the stop signal,then i immediately turn off the speed,the speed from 28khz become 0hz,then DRV8811 die,it is probability ,not every time ,i must reset the IC or turn off then then on.at first i think the problem is my hardware design,so i use the DRV8811 EVMbord,take the MPS430 out,use my FPGA to control,same phenomenon.
my VM=26V, the other is the same,like the DRV8811 EVMbord,my current is set 2A,decay =3.3V,SRn=0,my board don't have 8 diodes,but your  DRV8811 EVMbord have ,It doesn't matter.


can you tell me why? i found some guys have Had the same problem,in other forum
i konw, this is because of the ocp (Overcurrent Protection.),but i don't know how it happen?,and how to do

this is from your datasheet

If the current through any FET exceeds the preset overcurrent threshold, all FETs in the H-bridge will be disabled
until the ENABLEn pin has been brought inactive high and then back low, or power is removed and re-applied.
Overcurrent conditions are sensed in both directions; i.e., a short to ground, supply, or across the motor winding
will all result in an overcurrent shutdown.
Note that overcurrent protection does not use the current sense circuitry used for PWM current control and is
independent of the Isense resistor value or VREF voltage.

  • Hi Jie,

    When you say the DRV8811 "dies", do you mean it enters protective shutdown, or it actually dies such that it can never recover?

    By your description of the problem, it seems to me we are dealing with an OCP (Over Current Protection) event which kind of makes sense because of the following. You are pushing up to 2A into an inductive load which is moving at quite a fast speed, and then stopping it all of a sudden without a proper deceleration profile. There are two things we can deduce from this piece of information and none of them will help to run without an OCP:

    1. The speed the motor is moving at will tell me the BACK EMF must be substantial.

    and

    2. I imagine when the motor is moving at the 3500 Hz full step, the current may not be 2A since the BACK EMF could be opposing the current charge rate into the inductor. However, if the load is high enough, this could aid in the inertial loading opposing motion, in which case the current will once again have the opportunity to go up to 2A.

    Whether we have just one or both of high Back EMF and high current at the winding, you are dealing with a lot of energy present at the load which must be wanting to go back into the source when the motor is stopped abruptly, the killing factor on this game.

    If the motor driver is not being adversely affected (what I deduce from your explanation), then we are lucky. Chances are you are getting nFAULT asserted in which case you can toggle nRESET and recover without having to power up the system. I do believe this is what you describe has happened.

    Now, I am imagining this is like one of those CNC equipments in which you want to move the motor and then quickly stop if a home sensor is reached, so the concept of slowly decelerating from 28KHz to 0 Hz is not very viable in this scenario. If this is the case, then you may have to buy into the idea of recycling nFAULT when this occurs. In essence a fault has occurred and the system must be reset.

    If your goal is to run such a load without incurring in an over current protection occurrence, then you will need a driver with higher current capability. The DRV8811 is rated at a maximum of 2.5A and this is under the best set of conditions. I would try a 5A system, such as a dual DRV8829 with a microcontroller. It is a more complex and expensive system, but it will definitely be able to take stronger hits. Another option, with even more current capability, would be the DRV8412 or the DRV8432, which can take you up to 12A or even 25A per phase if two devices are used. I think this would be overkill, though. 

    Hope the info helps. Best regards,

    Jose Quinones