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UCC28700: About T_R and T_ZTO

Ryoma Ohashi
Expert 5045 points
Part Number: UCC28700

Hi team,

In the application note SLUA783, it is said that the customer should care about LC period that it should not exceed T_ZTO to maintain proper valley switching.

In the datasheet for UCC28700, T_ZTO is spec'd at min 1.8us.

In the mathcad file, the TR is assumed at 2us as below.

Isn't this TR same with the LC resonant period? If so, I was confused that the assumed LC tank resonant period is exceeding the T_ZTO, which might make unproper valley switching.

Regards,

Ohashi

  • +1
    TI__Mastermind 24375 points

    Hi Ohashi-San,

    Thank you for the querry.

    I think in one of our previous post, I already mentioned about the need to keep the DCM ringing in the frequency range between 500khz to 1.2Mhz to have effective valley switching and satisfy the tzto requirement. 

    If Tr is designed high (by improper Lpri and Csw), valley switching will be missed.

    Regards,

    Harish