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TIDA-00643: TIDA-00643

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Replies: 5

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Part Number: TIDA-00643

Hello,

I am referring to the reference design TIDA-006643 which specifies a current limit of 15 amps. I am trying to design a version which can handle way more current. The MOSFETS in the design can handle more current. So I was wondering which components limit the current to 15 A. I have two assumptions. The first assumption would be the layout of the board itself or the rating on the current sensing resistors ? 

 I was wondering if there is anything else that will needs to be replaced.

Thanks

  • Hi,

    From looking at the design, You are correct that the sense resistor and the board layout are probably the two things limiting the boards current capability. The sense resistors are .007 Ohms so if 15A are flowing through them then .007*15A =.105V and this means that gain setting has to be either 10 or 20 V/V. If the sense resistor is the limiting factor you can either lower the gain to 10V/V and/or decrease the sense resistors value. I think that the PCB could probably handle more current it was just tested up to the 15A limit to make sure that it could operate there but was not tested up until the point at which the board failed. You could also make it with thicker copper and it would handle more current.

    Regards,

    Michael 

  • In reply to Michael.Walker:

    Hi Michael,

    In my system, the gain is already at 10 V/V. I can't lower it any further. So, I think the only way to go about this would be lowering the shunt resistance in my design or changing the board layout for my PCB. 

    I also had one more question related to this. Is the parameter USER_MOTOR_MAX_CURRENT in header file user.h  limited by the 15 A current limitation or is there some other parameter limiting it ? I am able to increase USER_MOTOR_MAX_CURRENT only upto 23 A but I want to increase it.

    If I manage to increase the current by changing the shunt resistance or the PCB design, will I then be able to increase USER_MOTOR_MAX_CURRENT higher than 23 A  ?

    I will notify as I test and verify the suggested implementations.

    Thanks,

    Anushka 

  • In reply to Anushka Agarwala:

    Hi Anushka,

    I am not very familiar with the software for the TIDA-00643, so I do not know if you can increase that higher. If you do change the shunt resistance on the board, remember to find the equations in the code that use the previous shunt value and change it to your new number.

    Regards,

    Michael W. 

  • In reply to Michael.Walker:

    Hello,

    Thanks for your response. I changed the shunt resistance to a lower value to allow around 38 A and I changed the following parameters to compensate for the change to allow 30 A :

    1. user_motor_max_current

    2. iq_full_scale_current 

    3. adc_full_scale_current

    My board is still not able to pull more than 15 A. Could the gate driver or the microcontroller unit be limiting it? As per your suggestion, I looked at the DRV8305 and TMS320F28027 but I could not find the maximum working current for any of them. Please help me out.

    Thanks,

    Anushka

  • In reply to Anushka Agarwala:

    Hi Anushka,

    I do not see how the DRV8305 would be limiting the amount of current. What speed is your motor running at when the max current is seen? There must be something else in the code limiting the current. What is the max duty cycle on the phases when the current is at max?

    Regards,

    Michael