I've been working on both a model and an implementation of the LTC3642-5. It regulates well but I have this supply ripple that is always around 3-6kHz. According to the datasheet, varying the inductor size and the ISET resistance, should affect the frequency. However, it does not in either scenario. It seems as though none of the variables that dictate the switching frequency affect the ripple. I should in theory be able to push to a higher frequency but it seems to not be possible. Is this something that is always going to be present?