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UCD3138: Hybrid Hysteretic Control and Capacitive Region Avoidance

Part Number: UCD3138
Other Parts Discussed in Thread: UCC256303,

I've recently seen a very nice analog resonant LLC controller, the UCC256303. It has a couple of very attractive features: 

  • Hybrid Hysteretic Control for improved loop bandwidth and response time.
  • Improved Capacitive Region Avoidance Scheme to avoid the high switching losses and feedback slope reversal.

But for future applications I am seriously thinking to turning to digital controllers like the UCD3138. Are there any app note or similar on implementing this functions in the UCD3138?

  • Hi David,

    We do not have Hybrid Hysteretic Control implemented in UCD3138 at this moment, therefore there is no app note for that. For ZCS avoidance, UCD3138 uses a different approach: if you know the switching frequency that your LLC will enter ZCS region, then you can program UCD3138 to operate always higher than this switching frequency, then it won't enter ZCS region.

    Regards,
    Bosheng
  • Hi Bosheng,

    thanks for the feedback.

    may I suggest this would be a great App note topic. Granted the UCD3138 cannot natively support this feature but I suspect a modest amount of support circuitry may make it possible. I though the inclusion of HHC to the UCC2560x was extremity attractive and negated what is probably the single biggest issue with the LCC being its difficult frequency response.

    It's pretty common to be able to limit frequency on a controller to prevent non-ZVS operation. Although it works in concept it has the major limitation of the critical frequency being load dependant. On analog controllers I find it of marginal use due to tolerances. The UCD3138 will be better as the limit frequency should be highly accurate as it will be xtal clock derived. I had an application where having the ability to achieve higher gain factors for lighter loads was needed. Hence a hard frequency limit would somewhat prevent this ability. Of course one could design for a higher maximum gain but at the cost higher circulating energy and efficiency loss.

    David