• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Subscribers 84 subscribers
  • Views 964 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMS320F28075: HRPWM MEP size electrical data

Lisa Ding
Expert 6525 points
Part Number: TMS320F28075

Hi Champs,

I checked F28377S datasheet and Table 5-65 showed MEP size typical is 150ps and max is 310ps. Could you please tell me how we can calibrate the MEP size ?

 As i know, temperature and voltage will impact MEP size. Could you please tell me why temp&volt will impact MEP size? Is there other condition will impact MEP size ? Thank you for your reply in advance. 

  • 0
    TI__Genius 17370 points
    Hello,
    I am writing to let you know that a C2000 team member has been assigned to this post and should be answering shortly.

    Regards
    Baskaran
  • 0 in reply to Baskaran Chidambaram
    TI__Guru 60865 points
    Hi Lisa,

    There is an SFO library that you can run to populate the scale factors.

    The micro-step timing changes with voltage, temperature, and manufacturing process variation much like anything else speed related in a semiconductor device. Running the SFO library adjusts for these effects by determining how many micro-steps are needed to evenly divide an ePWM cycle. Based on how many steps are needed, the resolution will change a little bit.
  • 0 in reply to Devin Cottier
    TI__Expert 6525 points
    Hi Devin,
    thanks for your reply. Do you mean 150ps can be changed to other number ? thank you
  • 0 in reply to Lisa Ding
    TI__Guru 60865 points
    Hi Lisa,

    The number will change depending on the number of micro-steps needed to subdivide a single ePWM cycle. This will vary with manufacturing process, temperature, and supply voltage. If more steps are needed to divide the period, the resolution will be slightly higher and if less steps are needed the resolution will be slightly lower. e.g. if it takes 100 micro-steps to divide the period each step will be slightly smaller than if it takes say 97 micro-steps.
  • 0 in reply to Devin Cottier
    TI__Expert 6525 points

    Hi Devin,

    thanks for your reply. However, I still a little confused about MEP step size. I checked user guide which show MEP_size which typical is 150ps. It will be changed by  process-parameter/operating temp/voltage. It looks like it can't be changed. Could you please help to clarify this part ? thanks.

  • 0 in reply to Lisa Ding
    TI__Guru 60865 points
    Hi Lisa,

    The micro-step size changes due to voltage, temperature, and process variation. Voltage and temperature can change while the application is running. The SFO library attempts to compensate for this.

    The SFO calibration procedure attempts to measure the actual micro-step size, so an appropriate number of micro-steps can be selected for a given desired edge placement.

    For example, if you command that the edge should change 1.25ns after the regular ePWM edge, then if the step size is 150ps then the edge should be placed 1250ps / 150ps = about 8 steps. However, due to the aforementioned factors, the step size may not actually be 150ps. If the SFO library measures the step size and gets 220ps as the real step size, then we should instead select 1250ps / 220ps = 7 steps. If the temperature changes drastically and now the step size is 135ps, then we should select 9 steps to get as close as possible to the target of 1.25ns.
  • 0 in reply to Devin Cottier
    TI__Expert 6525 points
    Hi Devin,
    thanks for your reply. Please allow me to describe what i understand.
    Base on datasheet, micro-step size is 150ps. However, due to voltage/temp change, micro-step size will be changed. In this case, SFO will measure actual micro-step size then re-calculated scalefactor which mean steps in your post. If i misunderstand your meaning, please point it out. thank you!
  • 0 in reply to Lisa Ding
    TI__Guru 60865 points

    Hi Lisa,

    Yeah, that is correct.  The SFO library effectively measures the current average micro-step size and then populates the scale factor.  The scale factor is then used to select which micro-step count should gives the desired edge placement.