The most basic of all control algorithms for a buck converter is shown on this slide, basic hysteretic control. A hysteretic circuit turns on the high side switch until an upper threshold is reached. At this point the switch turns off. The output voltage then decays to the lower threshold, then the switch turns back on again. This is often referred to as a bang-bang type regulator. The solution this offers is that it is very simple and has very fast transient response. This algorithm does not feature a fixed switching frequency, in fact it could be all over the map in terms of frequency of operation. This makes it difficult for a filter design and for noise susceptibility.