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Spread spectrum 400kHz

Alexander Kondrov41
Prodigy 20 points

Hi,

I got a 6-phase DC-DC converter. Fsw=400 kHz, synchronization by external clock(CPLD). I need a spread spectrum 400 kHz. What' the best way? All chips what I've seen before worked on MHz and above. Is there solution, based on FPGA?

Maybe someone has faced with that problem .

  • 0
    TI__Genius 10320 points

    Hi Alexander,

    When you say you need a 400 kHz SSC, what spread frequency do you require? What spread amount/direction do you need?

    Gabe

  • 0 in reply to Gabe Ayala
    Prodigy 20 points

    From 375 KHz to 425 KHz. Not more

  • 0 in reply to Alexander Kondrov41
    TI__Genius 10320 points

    Hi Alexander,

    Is the 375-425 kHz the carrier frequency or the SSC modulation frequency?

    Gabe

  • 0
    Intellectual 420 points
    You could certainly do this in an FPGA or even CPLD using counters on a higher frequency clock. The question I'd have is why do you "need" spread-spectrum? If this is for regulatory compliance, I'd be careful to check if it will help. Note that if your modulation frequency is much lower than the 400 KHz of the signal, spreading the spectrum may not happen fast enough to reduce the peak emissions as measured using the standard equipment.
    Another consideration is system start-up. A CPLD comes up running very soon after it gets power. If it is used to synchronize its own power source, there will be some delay during which the source needs to run on its internal timing. The FPGA typically needs more time to start up and thus will extend this period before synchronization starts. You could also look at some "CPLD" parts like MachXL from Lattice, which are really little FPGAs. They come up fairly quickly, but would give you more registers to do the timing.