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UCC28950EVM-442: AS A BUS CONVERTER

alon druker
Prodigy 30 points
Part Number: UCC28950EVM-442
Other Parts Discussed in Thread: UCC28950,

Tool/software:

Hi , can i operate the UCC28950 as a bus converter ? what should i change in the application to operate the UCC28950 with no feedback ?

Thank you

  • 0
    TI__Mastermind 40430 points

    Hello Alon, 

    Yes, you can operate the UCC28950 as a bus converter if you wish. 
    You simply have to fix the PWM duty cycle to a constant value that delivers the output voltage based on the input voltage and transformer turns-ratio. 

    Depending on the input and output specifications, the UCC28950EVM-442 may or may not be able to meet your requirements without extensive modification. 

    Fixing the duty cycle means keeping the COMP output at a constant voltage.   
    Since the EVM loop compensation is an integrating one, you can't simply tie the VSENSE input network to VREF.
    I suggest to remove the integrating caps from COMP and give it a resistive load.  Then you can set the VSENSE divider on the EA- input appropriately to achieve the error voltage needed on COMP for the duty cycle needed for your application. 

    Regards,
    Ulrich

  • 0
    Prodigy 30 points

    Hi ,i want to work at maximum duty cycle 95% , what should i do with the COMP , EA+ , EA -  ?

  • 0 in reply to alon druker
    TI__Guru* 86106 points

    Hello,

     

    Max duty cycle for this device is 95% typical with a maximum duty cycle of 97%.  Even though it is not specified the minimum maximum duty cycle is 93%.  That being said if you want to run at maximum duty cycle.  That being said if you want the controller to always run at maximum duty cycle I would tie the EA- pin to the comp pin setting up the voltage amplifier into a voltage follower.  Then set the EA + to 3 V with a resistor divider off of VREF.

     

    Regards,