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UCC2813-3: Oscillator and switching frequency

Part Number: UCC2813-3
Other Parts Discussed in Thread: UCC2813-2, , UCC2813-0, UCC2813-1, UCC2813-4, UCC2813-5

Hi Team,

UC2813-x can work with switching frequency up to 1MHz. But in datasheet 7.5 Electrical Characteristics: Oscillator session. The oscillator is 46KHz for UCx813-0,1,2,4 and 31KHz for UCx813-3,5.

What is the difference between this oscillator spec and switching frequency spec?

Thanks.

Zhou

  • Zhou,

    For the UCC2813-0, UCC2813-2 & UCC2813-3, Dmax = 100%, for these versions OUT pin Fsw= Fosc.

    For the UCC2813-1, UCC2813-4 & UCC2813-5, Dmax = 50%, implemented using an internal toggle flip-flop. So for these versions, Fsw = 0.5 * Fosc.


    The other difference is that UCC2813-0, UCC2813-1, UCC2813-2 & UCC2813-4 use VREF = 5 V, but UCC2813-3 & UCC2813-5 use VREF = 4 V, so this sets a different Fosc eqn, or gives a different Fosc for the same RC values.


    I hope this explains the differences and answers your question. If so, please click the "verify answer" button.

    Thanks,
    Bernard
  • Hi Bernard,

    Thanks for your reply.
    For the UCC2813-0, UCC2813-2 & UCC2813-3, Dmax = 100%, for these versions OUT pin Fsw= Fosc.

    For the UCC2813-1, UCC2813-4 & UCC2813-5, Dmax = 50%, implemented using an internal toggle flip-flop. So for these versions, Fsw = 0.5 * Fosc.


    In datasheet, the oscillator frequency is 46kHz and 31KHz, then why the switching frequency can work up to 1MHz?(Fsw= Fosc or Fsw = 0.5 * Fosc)

    Thanks.

    Zhou
  • Zhou,

    The datasheet shows the expected frequency and tolerance/variation for a specific frequency setting, i.e. Rt = 100 k-ohm & Ct = 330 pF (noted at the top of the Electrical Tables).

    To get 1-MHz, you need to use a different set of RC values, using eqn 1 or 2 on page 11, or else use the curves in Figs. 3 & 4.

    Thanks,
    Bernard