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UCC28950: Request simulation dithering circuit UCC28950

prarinya Maneechompoo
Intellectual 540 points
Part Number: UCC28950

Dear ALL

Pls help , customer need to know  simulation dithering circuit UCC28950  by LT spice  .

Thank you so much & Bestregard

Prarinya

  • 0
    TI__Mastermind 25570 points

    Hello Prarinya

    Unfortunately I cannot support a LTspice application but I can give a generic design that could be translated into LTspice by the user. 

    First - i need some more details

    Will the UCC28950 device be operated as a Slave or Master device. The reason I need this information is that a Slave device uses an external clock and a Master device uses an internal clock running at a frequency set by a resistor at the RT pin.

    What dither specifications does the designer want to meet

    What is the centre frequency ?

    What is the dither magnitude (+/- x kHz) ?

    What is the dither rate, how many ms should it take for the system to sweep from f_min to f_max ?

    What is the dither pattern - sawtooth (ramp from f_min to f_max with return to fmax), triangular (ramp from f_min to f_max and ramp back to f_min), discrete steps or smoothly varying frequency.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    Intellectual 540 points

    Hi Colin

    Thank you , The UCC28950 is used in Master device . The dithering circuit customer is used in feature jittering of switching frequency to improved EMI function .

    The dither specifications i not have then i request fom customer and send to you .

    Do you have tool to design dither circuit ? 

    Thank you so much & Bestrgrad

    Prarinya

  • 0 in reply to prarinya Maneechompoo
    TI__Mastermind 25570 points

    Hello Prarina

    If the controller is used as a Master then we will have to use a circuit to inject current into the RT pin - approximately 0 to 4.5uA for a 10% dither magnitude at 100kHz. At a minimum this would involve a low frequency oscillator to provide the dither profile (triangular, sawtooth etc) and an accurate, low noise current source to give a stable dithering profile.

    After some thought I think a better solution would be to configure the UCC28950 as a Slave device and use a microcontroller to generate a dithered clock signal. I suspect that this would also be a lower cost, solution - for example the MSP430 device shown at http://www.ti.com/product/MSP430FR2000/samplebuy has a 1k cost of 0.29c. You would also have the flexibility to easily modify the dither profile and rate. The system would also be much less susceptible to noise pickup from outside influences.

    I am interested to know what the customer dithering specs are - if they are confidential then you may send them to me via email, I'm at  colingillmor@ti.com

    Regards
    Colin

  • 0 in reply to Colin Gillmor
    Intellectual 540 points

    Hi Colin

    Thank you so much for your help . I send infomation to you by e mail later .  

    Thank you so much & Bestrgrad

    Prarinya