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MCF8329A: OCP_SNS_Fault

Ashwin Coumar
Prodigy 30 points
Part Number: MCF8329A
Other Parts Discussed in Thread: MCT8329A

Tool/software:

Hello,

I am currently working with the MCF8329A gate driver. A few days ago, the system was running in closed loop—although not optimally—mainly because I do not yet have the precise BEMF constant. While MPET does determine a BEMF constant, it is not accurate enough for stable closed-loop operation when running on PWM.

However, for the past two days I have encountered a persistent issue: whenever I connect my hardware (not the EVM) to the PC, the OCP_SNS_Fault occurs immediately—even before running MPET or applying PWM. This happens regardless of which register file I load. For example, even with the default MCF8329A register set, running MPET directly triggers the OCP_SNS_Fault. Writing the default registers to EEPROM does not resolve the problem.

I find this unusual, because the same parameter sets that worked on PWM just two days ago now consistently trigger the fault. I have carefully checked my hardware and found no apparent issues. This raises the question: if the hardware and parameter set were working before, why does the same configuration now fail?

For reference, the two register files I have used are:

  • BLDC_fan_40A_1p8KHz_MCF8329A

  • Default Registers MCF8329A

Motor specifications:

  • Resistance: 0.232 Ω

  • Inductance: 0.19 mH

  • BEMF constant: unknown

  • Peak current: unknown

Additionally, even when using the default registers, I always modify the base current to 0x2731 (100 A).

Could you please help me identify the cause of this persistent OCP_SNS_Fault and suggest a resolution?

  • 0
    TI__Expert 3325 points

    Hi Ashwin,

    Are you using MCF8329A EVM for this testing? if yes, have you changed the shunt resister value?

    Please note that OCP_SNS_Fault will get triggered if the voltage across the shunt resister exceeds 0.5V. can you monitor the voltage across shunt resister during the fault scenario?

    Thanks,

    Dhinesh

  • 0 in reply to Dhinesh
    Prodigy 30 points

    Hi Dhinesh,

    No I am using my own 24V hardware. I am using 3mohm shunt resistor. Today I have checked the voltage acorss the shunt while this fault gets triggerd and it is 0V. I could not understand what is happeneng. I did not run MPET, PWM or anything. The moment I connect the hardware with motor studio the fault gets triggered. 

  • 0 in reply to Ashwin Coumar
    TI__Expert 3325 points

    Hi Ashwin,

    OCP_SNS_Fault should not be triggered if there is no voltage across the shunt resistor. Could you please share the shunt resistor voltage signal scope screen capture taken during device power-up?

    Thanks,

    Dhinesh

  • 0 in reply to Dhinesh
    Prodigy 30 points

    Hi Dhinesh,

    I will do that but please give me some time. In the meantime, I have a question. I have already built a PCB using the MCF8329A1IREER, but now I am planning to use the MCT8329A1IREER on the same board.

    Since the board was designed according to the MCF8329A datasheet, and given that the MCT8329A appears to be quite similar, can I simply desolder the MCF8329A and replace it with the MCT8329A on the same PCB? Will this work as expected, or is there anything specific I should keep in mind before making the replacement?

  • 0 in reply to Ashwin Coumar
    TI__Expert 3325 points

    Hi Ashwin,

    Yes, you can replace the MCF8329A with MCT8329A without any other HW change on the board.

    Thanks,

    Dhinesh