A Novel Ripple-Coupling Constant on-Time Controlled Buck Converter IC with Highly Digital Charge-Pump Based Error Amplifier

In this paper, a novel ripple-coupling constant on-time (RCCOT) control scheme is presented with a ripplecoupling ac-inner loop and a highly digital dc-outer loop. The ac loop formed by an RC filter couples a ripple to determine the ontime edge without the instability issue due to the ceramic capacitors used. This novel ripple-coupling modulation scheme solves the above issue without using any other analog circuitry. Fast transient response can be also obtained from the implicit capacitor current information. Moreover, a charge-pump based error amplifier (CPEA) just activates in slewing state with only a nano-ampere level current consumption. A digital on-time generator with adjustable interface has been also developed for the same reason. Consequently, both fast response and low quiescent current design can be achieved without facing stability issue.RCCOT is realized with a 300KHz switching frequency buck converter IC in TSMC 0.18um CMOS process. Full transistor simulation result shows that only 345nA and 36uA power consumption under 1uA and 1.25A loading current. Transient response is only 10us settling time and 120mV undershoot with a 0.25A to 1.25A load step.