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UCC28781: DC/DC isolated 30W 5V output

Jack
Prodigy 40 points
Part Number: UCC28781
Other Parts Discussed in Thread: UCC28782, , UCC5304

Hi,

I want to design a  with following specifications:

Input voltage: 30V-200V (if too wide, can be made in two options, 30V - 90V, 80V - 200V)

Output voltage: 5V 6A

Currently, I'm following the UCC28781EVM-053 design. In this design from TI, output is designed 15V-4A.

I tried searching model on WEBENCH® Power Designer, but P/N UCC28781 not support.

Please support and send me new design with output 5V-6A.

  • 0
    TI__Mastermind 31130 points

    Hello Jack, 

    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 "happy". 

    I think the UCC28781 can work from 30V to 200V in one design.  This range (200V/30V= 6.7:1) is only a little wider than the usual "universal line" Vbulk range (375V/70V = 5.4:1). 
    I assume that these are DC input voltages, not AC.  You can probably use a 400-V rated primary MOSFET and 50-60-V rated SR FET.  

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    TI__Mastermind 31130 points

    Hi Jack,

    I forgot to mention that the UCC28781 currently is available in only 2 versions: UCC28781-Q1 and UCC28781A.  
    The UCC28781-Q1 device has all of its datasheet features enabled and is qualified to AEC-Q100 standards, suitable for automotive use.   
    The UCC28781A (tailored more for audio applications) is not automotive qualified and so is less expensive, but two features are disabled:

    1.  switching frequency dithering is disabled in UCC28781A.  
    2.  over-power protection (OPP) is disabled in UCC28781A. 

    If your project requires either or both of these features, then the UCC28781-Q1 must be used, OR, a new device version must be developed and qualified by TI.  Enabling these two features is easy, but qualifying a new part for general release will take some time and a compelling business case to drive it.

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 40 points

    Hello Ulrich Georke,

    Thank you for your support !

    Yes, I saw UCC28782 & UCC28781 same Calculation. 

    In the UCC28781EVM-053 design, Transformer is used have P/N: RLTI-1431 has  P:S:A = 6.6:1:1 ~ 6.7:1:1.

    I don't download spec of RLTI-1431.

    We plan to design single side PCB, can you recomand me a part number of transfomer ?. 

    The best part can be purchased online on mouser or wurth. 

    Gate driver is used have P/N:  UCC5304DWV. Unfortunately, VDD has range 6V-18V, i want output 5V. 

    I tried looking for the isolating gate driver on TI but I can't find a suitable part. Can you recomand me a part number of transfomer ?

    Regards,

    Jack

  • 0 in reply to Jack
    TI__Mastermind 31130 points

    Hello Jack, 

    It is very unlikely that there is an off-the-shelf transformer that matches to your application, and I am not in a position to search for one. 
    Usually, a custom design is needed to optimize the parameters obtained from the design calculator. 

    To power the UCC5304 for a 5V output, you can specify another secondary winding with twice the turns of the main 5V output winding.  That will provide about 10V to bias the isolator and provide good gate-drive voltage to the MOSFET.   

    Regards,
    Ulrich