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TIDA-010015: Resonant network calculation

JGE
Prodigy 60 points
Part Number: TIDA-010015

Hello,

I was checking the LLC design and some doubts araised regarding the resonant network. 

The specification for minimum bulk voltage at the LLC input is 250V. Then, the calculations show that the gain needs to be 1.542 at this operating point. In addition, the design note adds a margin of 1.1 increasing the gain to 1.697.

However, the resonant network selected is Lr=27uH, Cr=94nF, Lm=240uH. This cannot deliver full power when input voltage is at the minimum (250V). Using fisrt harmonic approximation is clear because at minimum switching frequency the gain is only 1.13 (at full power). The converter would enter in the capacitive region with a gain lower than 1.697.

Simulations show higher gain at 70kHz but anyway far of the necessary gain. 

I guess the design considers the LLC cannot deliver full power at 250V input but then, the design guide should be clear to show that the mecessary gain calculated is not used for the resonant network calculations.

Please, could anyone clarify it?

Thanks

Jesús

  • +1
    TI__Genius 9790 points

    Hi, Jesus

    were you talking about the resonant tank of TIDA-010015? TIDA-010015 is working at 250VDC only at turning off input voltage. The turn on threshold is 320VDC at startup because the turn on threshold of LLC controller.

    You are right, the resonant tank of TIDA-010015 cannot support full load at 250VDC, you can calculate resonant tank based on your requirement with below calculator. 

    sluc675c (1).zip

    Yunsheng

  • 0 in reply to Yunsheng Qu
    Prodigy 60 points

    Hi Yunsheng,

    I cannot see any mention in TIDUEC2B regarding 320V as minimum operating input voltage for LLC. In addition, there are calculations for necessary gain using 250V as input voltage. Hence my confusion.

    Thanks for clarifying it.

    Jesús