void si5351aSetFrequency(uint32_t frequency)
{
   uint32_t pllFreq;
   uint32_t xtalFreq = XTAL_FREQ;
   uint32_t l;
   float f;
   uint8_t mult;
   uint32_t num;
   uint32_t denom;
   uint32_t divider;
   divider = 900000000 / frequency;// Calculate the division ratio. 900,000,000 is the maximum internal 
                           // PLL frequency: 900MHz
   if (divider % 2) divider--;      // Ensure an even integer division ratio
   pllFreq = divider * frequency;   // Calculate the pllFrequency: the divider * desired output frequency
   mult = pllFreq / xtalFreq;      // Determine the multiplier to get to the required pllFrequency
   l = pllFreq % xtalFreq;         // It has three parts:
   f = l;                     // mult is an integer that must be in the range 15..90
   f *= 1048575;               // num and denom are the fractional parts, the numerator and denominator
   f /= xtalFreq;               // each is 20 bits (range 0..1048575)
   num = f;                  // the actual multiplier is  mult + num / denom
   denom = 1048575;            // For simplicity we set the denominator to the maximum 1048575
                           // Set up PLL A with the calculated multiplication ratio
   setupPLL(SI_SYNTH_PLL_A, mult, num, denom);
Веселин, там  
 
 
 
тот же код что и у меня