• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 105 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.

LM5122: LM5122 TPA3221 clock synchronisation

David Trotter
Intellectual 730 points
Part Number: LM5122
Other Parts Discussed in Thread: TPA3221

Hi TI

I can't find an answer to this question anywhere so I thought I would ask it here. 

I am using 2x LM5122 boost converters to create the 30V PVDD power supply for TPA3221 audio amplifier. 

Should I attempt to synchronise the clocks of the TPA3221 and the LM5122? 

There appears to be a 2.88Mhz clock output from the TPA3221.. I could div 8 to use this to sync the LM5122. 

Is this advisable in terms of EMI/power supply noise? Or is it best to leave both clocks free running?

Also, what is the difference between LM25122 and LM5122? 

Kind regards

David

  • 0
    TI__Guru 68495 points

    Hi David,

    Thank you for considering the LM5122 for your application.  First, the LM25122 is a lower voltage rated version of LM5122.  They are based on the same core design circuit. 

    Regarding your question, you may need to test both to see which performs better for your system.  Basically, if you let the two LM5122 running on their own clocks, you may see the beat effects at the frequency of the difference between the two clocks.  It may help EMI like some kind of dithering, but it may cause large peak emissions.   Synchronizing the two controller would fix the emission spectrums and it may be more easy to design an EMI filter to attenuated against the know harmonics.   In short, synchronizing is more predicable and controllable. 

    Thanks,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Intellectual 730 points

    Thank you for the reply. 

    I am already using the two LM5122 ICs in polyphase sync mode. My question was whether you advise synchronising the TPA3221 amplifier to the LM5122 regulators. 

    I am guessing that the answer is the same. Also, I imagine that if I drive the sync pin on the LM5122, then it won't be able to go into pulse skip mode? 

    Kind regards

    David

  • 0 in reply to David Trotter
    TI__Guru 68495 points

    Hi David,

    Sorry for misunderstood your previous question.  Yes the answer would be the same, though.   Where did you get the impression that the circuit would not go into pulse skipping when sync pin is driven externally?   You will lose pulse skipping if you set the MODE to FPWM. It is irrelevant to the clock synchronization. 

    Thanks,

    Youhao