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UCC28781-Q1: Calculating VBUR target voltage VBUR_tgt

Ashlesh Bhat
Prodigy 10 points
Part Number: UCC28781-Q1
Other Parts Discussed in Thread: UCC28781, UCC28782

Hello,

I am going through the design steps in the datasheet of UCC28781-Q1 to design a AC - DC converter. But I am stuck at VBUR calculations in 8.2.2.4 which says

"The procedure to determine the value of VCST(BUR) is quite complex and is not provided in this datasheet.
Instead, a soon-to-be-released UCC28781 Excel Calculator Tool automatically calculates this value based on
user input and determines the VBUR target voltage VBUR_tgt. Using this target value, it further determines the
appropriate values for RBUR2 and RBUR1 to meet the BUR pin targets based on user selections for the following
set of equations"

I am not able to find this excel calculator, could you please help me with this? I am not sure what value to use for VBUR_tgt.

Thanks in advance,

  • 0
    TI__Genius 10946 points

    Hi Ashlesh,

    Looks like the Excel Calculator Tool is not released yet. I am not sure about the date it will be available. The expert on this device is out of the office today, but he will provide more information and support once is back on Wednesday. Thanks

  • 0 in reply to Manuel Alva Hernandez
    TI__Mastermind 24365 points

    Hi Ashlesh,

    Thank you for your interest in the UCC28781 ZVS-flyback controller. 

    Unfortunately, TI is behind in providing significant design documentation for this device at this time.  Design tools are in progress, but I can't predict the schedule. 
    But for now, I suggest to use the UCC28782 Excel Design Calculator https://www.ti.com/lit/zip/sluraz0 as an alternative tool. 
    Designing with the UCC28781 is similar to that of the UCC28782, except there is no active clamp sub-circuit, no boost-stage option, and no secondary-side resonance.  

    In the -782 tool, I suggest to characterize the High-side FET as 1Megohm on-resistance and 0pF for capacitances.  Vxh value doesn't matter; use 1V. 
    For the Clamp Capacitance value, I suggest to put in the value that is recommended (even though there really is no Cclamp) just to keep the tool satisfied so with this  VBUR taget  can be calculated.

    Regards,

    Harish