A ripple-based constant on-time control (RB-COT) buck converter with switched current integrator is proposed. The direct feedback loop was compensated by inductor current ripple, and the sample-hold circuit was introduced to improve output accuracy. Furthermore, the switched current integrator circuit replaced the fixed RC filter in the original architecture, effectively improved the transient response of the system at high switching frequency, and achieved both stability and fast transient response for full switching frequency range. Taking the loop stability in the full switching frequency range as the basic design criterion, the buck converter designed in this paper effectively improved the transient response, especially for high-switching frequency. For 1.0MHz switching frequency, the step up/down transient recovery time is reduced by 20 μs compared with fixed RC filter.