A Hybrid Constant On-Time Mode for Buck Circuits

Abstract

To achieve a designed and fixed operating frequency for a controller with high dynamic performance and a high load capacity, a hybrid constant on-time (COT) voltage mode for a Buck circuit is proposed and discussed in this paper. The proposed hybrid strategy is a combination of the classical COT method, a dynamic reference voltage technology and a proportional–differential (PD) module. The workflow is demonstrated in brief, simulations of a Buck circuit with the proposed hybrid COT mode are conducted and comparisons with developed pulse-width modulation (PWM) technology and the hysteresis mode are made. The results show that, with the help of the proposed control scheme, impressive performance from the Buck circuit can be expected. The operating frequency can be fixed well by the hybrid technology without losses of performance and robustness in steady state and will not jump much even with the sudden change of the inputs and the load. The proposed control strategy contributes to the foundation of circuit design and optimization.

A Detection Circuit for Improving the Unloading Transient Performance of the COT Controller

“…Another comparison can be made to further prove the validity of the proposed method in this paper. In [5], a hybrid constant on-time mode is proposed by introducing the dynamic reference voltage method and a proportional differential (PD) module into the voltage-mode COT control, which can achieve fast load transient performance. With the circuit parameter configurations in [5], the comparison can be made and the results are listed in Table 5.…”

“…In [5], a hybrid constant on-time mode is proposed by introducing the dynamic reference voltage method and a proportional differential (PD) module into the voltage-mode COT control, which can achieve fast load transient performance. With the circuit parameter configurations in [5], the comparison can be made and the results are listed in Table 5. From Table 5, the load transient performance of the work in this paper shows to be better than that of [5] in terms of the loading/unloading recovery time and undershoot/overshoot voltage.…”

“…With the circuit parameter configurations in [5], the comparison can be made and the results are listed in Table 5. From Table 5, the load transient performance of the work in this paper shows to be better than that of [5] in terms of the loading/unloading recovery time and undershoot/overshoot voltage. In addition, the ripple voltage of this work is much smaller than that in [5].…”

“…The on-time of the converter with COT control is fixed and the off-time is modulated to achieve the regulation of output voltage. Compared to the constantfrequency control, such as voltage-mode control [3] and peak-current-mode control [4], the COT control shows higher light-load efficiency [5,6]. Thus, it is ideal for voltage regulators powering the microprocessor, as microprocessors are in standby mode (i.e., light load) most of time [7].…”

“…Specially, the case will be worse when the load step-down occurs at the beginning of the on-time. In [5], a hybrid COT mode was proposed, which could improve the load transient performance of the conventional COT control. However, it did not consider the above delay problem.…”