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DRV8350H-EVM: Overcurrent Fault

GAGANDIP SINGH DADHWAL
Prodigy 145 points
Part Number: DRV8350H-EVM
Other Parts Discussed in Thread: MSP430F5529, DRV8350, DRV8350S-EVM

Dear TI Team,

I am trying to control a BLDC Motor using DRV8350H-EVM in sensored operation. But as soon as I increase my Motor Speed over 50%, my motor stops and an Overcurrent Fault is triggered in the DRV8350x EVM GUI Software.

Below are the specifications of motor:

  1. No. of Pole Pairs : 8 Pairs
  2. Max peak current: 10A
  3. Operating Voltage: 24V
  4. Hall Sensors: 3 (120deg)
  5. Nominal Current:25A
  6. Power: 150W

Steps performed:

  1. Flashed the EVM, with Sensored Firmware Provided by TI, installed in the following path: C:\ti\DRV8350x_EVM_BLDC_FW_1.0.0\DRV8350x_EVM_FW\DRV8350x_EVM_BLDC_FW_1.0.0\DRV835X_MSP430F5529_Trapezoidal_Sensored_BLDC.
  1. Connected to DRV8350x EVM GUI Software and tried to control motor speed.

Observations:

  1. Initially, the overcurrent fault was triggered as soon as we tried to increase the motor speed over 20%. Increasing the PWM Switching Frequency from 25kHz to 60kHz (maximum) helped in increasing the Motor Speed upto 50%.
  1. As per the documentation available, MOTOR_PHASE_CURRENT_LIMIT is the parameter that triggers over-current fault. The default value of this parameter in the firmware is 900.


    Considering the above formula,

    MOTOR_PHASE_CURRENT_LIMIT = 900;

    CSA = 5V/V

    We get amperes as 20.71 A.

     My motor has peak current of 10A. So ideally with these settings I should not get an overcurrent fault.

  2. We were unable to verify the value of the current sense amplifier (CSA) from the Hardware. Also, from the documentation below, it was inferred that the DRV8350-H must have 4 pins, GAIN, IDRIVE, MODE & VDS

       

        4. But in the schematic, I am unable to find the GAIN pin

             

        5. As per my understanding this GAIN pin is required to set/read the value of CSA as shown below:

         

        6. Kindly help us identify the actual reason for this overcurrent fault so that we can run the motor at its full RPM.

       Thanks & Regards

       Gagandip Singh Dadhwal

  • 0
    TI__Expert 5035 points

    Hi Gagandip Singh Dadhwal,

    Thank you for the E2E post!

    I'll need sometime to review your issue but I wanted to go ahead and share some initial thoughts. 

    GAGANDIP SINGH DADHWAL said:
    We were unable to verify the value of the current sense amplifier (CSA) from the Hardware. Also, from the documentation below, it was inferred that the DRV8350-H must have 4 pins, GAIN, IDRIVE, MODE & VDS
    GAGANDIP SINGH DADHWAL said:
    4. But in the schematic, I am unable to find the GAIN pin

    The schematic you are looking at shows the SPI variant of DRV8350, DRV8350SRTVR, that is why you are unable to find the gain pin.

    I will give an update to your issue within the week.

    Regards,

    Yara

  • 0 in reply to Yara Al Shami
    Prodigy 145 points

    Hi Yara,
    Thanks for your quick feedback.

    I checked the schematic of 'H' variant and still I am unable to find the correct value of GAIN which is required to calculate the MOTOR_PHASE_CURRENT_LIMIT

    Also, as per my understanding the the overcurrent issue is due to little or no flexibilty over the configuration parameters in DRV8350H-EVM. I would like to know, if this issue can be solved by using "DRV8350S-EVM", as it allows more control using the SPI interface. 


    Thanks & Regards

    Gagandip Singh Dadhwal

  • 0 in reply to GAGANDIP SINGH DADHWAL
    TI__Expert 5035 points

    Hi Gagandip Singh Dadhwal,

    I should've mentioned earlier that the DRV8350 does not have integrated CSAs so there will not be a GAIN pin present however there are other devices in the DRV835x family that do have integrated CSAs.

    So I can get a better understanding of the issue at hand and verify that there are no spikes that could be causing the overcurrent fault can you provide the following:

    Can you use a current clamp on the motor phases to measure current and provide waveforms?

    Can you also measure and provide waveforms for voltage across the shunt resistors?

    Regards,

    Yara

  • 0 in reply to Yara Al Shami
    Prodigy 145 points

    Hi Yara, 

    Yes we agree that DRV8350H doesnot have an integrated CSA so there we will be no gain pin. 

    But as per the formula to calculate the value of MOTOR_PHASE_CURRENT_LIMIT, we require Gain (V/V). 

    We tried bruteforcing to check the correct value of MOTOR_PHASE_CURRENT_LIMIT for our motor, and found that when MOTOR_PHASE_CURRENT_LIMIT =4079 (default = 900) the overcurrent fault is not triggered. 

    Could you please provide information on how to calculate the MOTOR_PHASE_CURRENT_LIMIT  value based upon the ampere rating of the motor (which is 10A in our case) as the same needs to be set in the firmware. 

    Thanks & Regards

    Gagandip Singh Dadhwal

  • 0 in reply to GAGANDIP SINGH DADHWAL
    TI__Expert 5035 points

    Hi Gagandip Singh Dadhwal,

    Please allow some time for a response, I'll have to consult with the Systems team to get you the most accurate answer.

    Thank you,

    Yara

  • 0 in reply to Yara Al Shami
    Prodigy 145 points

    Hi Yara, 

    We are awaiting your kind response.

    Thanks & Regards

    Gagandip Singh Dadhwal

  • 0 in reply to GAGANDIP SINGH DADHWAL
    TI__Expert 5035 points

    Hi Gagandip Singh Dadhwal,

    I believe the best course of action would be to find out the gain of the amplifier used in the EVM for DRV8350.

    https://www.ti.com/lit/ds/symlink/opa374.pdf?ts=1699915207031&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FOPA374%252Fpart-details%252FOPA374AIDBVT

    Then using that as Gain in the MOTOR_PHASE_CURRENT_LIMIT equation.

    Feel free to post your work here so I can double check.

    Regards,

    Yara