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CCS/TMS320F28075: Issue with CMPSS6

Dimitar Penev
Intellectual 600 points

Part Number: TMS320F28075

Tool/software: Code Composer Studio

Hello,

I need to implement tripping logic for the invertor system we are developing. (PWM stops if some analog signals become bigger than certain threshold from internal DAC)
I want to trip on 4 analog signals so I use CMPSS1, CMPSS2, CMPSS6 and CMPSS8. All is working as expected except  CMPSS6  which is triggering
even if I have the analog signal below the treshold. I initialize all CMPSS the same way.
I don't see difference between CMPSS1/2/6/8 in the datasheet so I am puzzled.
The only (I think irrelevant) difference I see is that CMPSS6 does not share the input pin CMPIN6P with an ADC. 

 Anyone having an idea what can be wrong at my side?

Thanks
Dimitar

  • 0
    Intellectual 600 points

    Hello,

    To answer my own question.

    There is a short transient CTRIPH pulse just after initializing the CMPSS6 which was tripping the ePWM.
    This does not happen with  my other CMPSS1, CMPSS2 and CMPSS8
    I have put  200us delay after initialization of the CMPSS and  before initialization of ePWM and the behavior become logical.
    Probably there is a special order in the CMPSS initialization which can help. 

    Best Regards
    Dimitar 

  • 0 in reply to Dimitar Penev
    TI__Mastermind 28275 points

    Hi Dimitar,

    Glad the issue is resolved. To explain why you were seeing what you were seeing, the CMPSS has a power up time specification of 500us which must be exercised every time a CMPSS is turned on. You might want to increase that 200us to 500us to be on the safer side. Let us know if you have anymore questions.