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UCC28064A: Regarding the maximum operating frequency of the UCC28064A

shibanoki.takashi
Prodigy 50 points
Part Number: UCC28064A

Tool/software:

Hi E2E

When I asked a question before, I was told that the maximum switching frequency was 300kHz, but when I checked the actual device, the maximum frequency was about 370kHz.
What is the maximum frequency of the UCC28064A, including the tolerance?
The URL for the answer is below.
https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1297194/ucc28064a-regarding-the-case-where-we-want-the-pfc-circuit-to-operate-at-a-high-frequency/4924662#4924662

Best regards



  • +1
    TI__Mastermind 31610 points

    Hello Shibanoki-san, 

    The maximum frequency of the UCC28064A is limited by a "minimum period timer" within the device, and this timer is programmed by the TSET resistance.   
    RTSET is selected for other design reasons, but a by-product of that selection is the limitation of the minimum allowable switching period. 

    In the datasheet Electrical Characteristics table (page 8), there is one test point: 

    This indicates that for RTSET = 133kR, the nominal minimum period is 2.7us, which is 1/370kHz, with min and max limits of 1/526kHz and 1/286kHz.
    Maximum frequencies at the min and max extremes are unlikely to occur since these limits include generous guardbands for temperature extremes and several standard deviations from the mean.   

    Those specified timer values are for RTSET = 133kR, but RTSET can be set between 66.5kR and 400kR (from Recommended Operating conditions table, page 5).
    This sentence in Section 8.3.3 (located just above Figure 16, page 16) indicates that the minimum period timing varies as 1/RTSET.

    By extension, the maximum frequency varies proportionally to RTSET. 

    Therefore, the minimum period (maximum frequency) that you can measure depends on the value of RTSET.
    Since a curve or equation for this relationship is not provided, I suggest that if  370kHz (nominal) corresponds to 133kR, then some factor "K" * RTSET = K*370kHz.
    Lower TSET resistance (than 133kR) results in lower maximum frequency and higher R results in higher F. 

    For RTSET = 133kR, the max/min limits for maximum frequency are equivalent to +42.2% and -22.7%of nominal 370kHz.
    I cannot say that the same +/- tolerance range will apply to the nominal calculated maximum frequency at any RTEST (other than 133kR), but I imagine that the % variation ranges are likely to be similar.  

    Regards,
    Ulrich