• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 82 subscribers
  • Views 548 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

TIDM-1022: Is an external crystal required for valley switching?

Wayne Huang
Genius 17125 points

Other Parts Discussed in Thread: TIDM-1007

Dear Champs,

I am asking this for our customer.

The customer is interested in our valley switching application for PFC.

They have system concern if an external crystal is used on the primary side.

Therefore, they are asking if an external crystal is needed for valley switching?

We know that by only internal osc, the clock accuracy is much worse than an external crystal, so they wonder if this affects valley switching, especially during the full temperature (-40C and 125C)?

Wayne

  • 0
    TI__Genius 16085 points

    Hi Wayne,

    1. In F28004x, there is a slope trim that is performed during factory testing to compensate for the frequency shift across temperature, we do not have a spec across temperature but typically we can attain across temperature drift of about 1% (but note that accuracy is still within +/-3% of 10MHz). 

     

    2. I have not tested it using internal osc in valley switching project. But for PFC, it might be ok because it does not require a absolute reference. We have tested in TIDM-1007, and results show that it does not impact the THD much. This is expected because the osc inaccuracy does not create any jitter. 

     

    Regards,

    Chen

  • 0 in reply to Chen Jiang ti
    TI__Genius 17125 points

    Dear Chen,

    The user has experience to use only internal osc for boost PFC and they only concern if our valley switching application (especially the valley switching submodule) will be impacted/degraded a lot if only internal osc is used.

    So you meant the user can use the internal osc only for this reference design without sacrificing the performance much.

    Is our understanding correct?

    Wayne

  • 0 in reply to Wayne Huang
    TI__Genius 16085 points

    Hi Wayne,

    Yes, it should not be impacted too much.

    Regards,

    Chen