The Hershey Kiss chocolate shape is doing wonders with EMI reduction. This profile is known to provide more dB EMI reduction than any other modulation profile like Linear or Triangular. More spread should reduce the EMI, although normally there is diminished return as the spread increases. In other words, doubling the spread amount should translate to less than double the improvement in EMI reduction. A maximum of 5% total spread that Cypress devices provide is proved to be more than enough with the Hershey Kiss or the Lexmark Profile.
The waveform of this profile is important in producing the maximum amount of dB reduction. The modulation rate of this profile is also very important. If the modulation rate is below 20 kHz, it is possible to generate audible noise in the system. If the modulation rate is too high, in excess of 200 kHz, the effect of modulation might be defeated by the loop bandwidth of the filters used in downstream PLL’s. We have the classic that can be selected during configuration which is 31.5KHz.
Finding this more interesting, check details provided in Chapter 9 on EMI of Perfect Timing II book. Also check the Lexmark Profile and Spread Spectrum Technology web pages.