Fast adaptive on time control for transient performance improvement

In this paper, a simple but effective method to improve the load transient performance in constant on time (COT) control is proposed along with its circuit implementation. In COT control, if on time (Ton) is too small because of high frequency or conventional adaptive on time control, it might become comparable to minimum off time of the system and hence can create undershoot at load step up. On the other hand, if Ton is too large and load step down is occurred at the beginning of Ton, large overshoot can be created at the output. To solve this issue, this paper presents a new method to increase the Ton at load step up or/and decrease at load step down very quickly to reduce undershoot or/and overshoot at output. The main feature of this proposed method is that it can reduce output undershoot and overshoot both by using one simple circuit and as the change of Ton is proportional to the output change, chance of ringing back problem is very small compared to methods presented in prior arts. Another advantage is that as Ton change occurs only in transient period when duty cycle is saturated, it does not affect the small signal property of COT control. Moreover, the proposed methods are very much compatible with state of art single phase and multiphase COT control structures. Simulation and test results in both single and multiphase operation are also presented in the paper to verify the proposed concept.