一种适用于低ESR应用的高精度RBCOT环路

提出了一种适用于低ESR电容、具有快速瞬态响应和高输出精度的纹波控制COT(RBCOT)实现电路,并利用改进的等效三端开关模型,对包含分压网络的控制环路进行了精确的小信号建模。该环路在保持快速瞬态响应能力的同时,利用SW点的1阶滤波信号来产生虚拟电感电流纹波,避免了次谐波振荡现象。通过谷值采样电路,对滤波信号的谷值进行采样。采样电路在每个开关周期执行刷新操作,并在上电和瞬态变化阶段进行加速充电。纹波叠加电路将增强纹波和谷值采样信号精确地叠加到反馈电压端,保证电路输出精度较高。采用0.35μm 18 V BCD工艺,对纹波控制COT控制环路进行仿真。结果表明,在4.5~18 V输入电压范围内,输出电压的失调在1 mV范围以内,控制环路可以对瞬态变化进行快速调整。

A High Precision RBCOT Loop for Low ESR Applications

A ripple-based COT implementation circuit for low ESR capacitors with fast transient response and high output accuracy was proposed. Accurate small-signal modeling of control loops with voltage divider networks was performed by an improved equivalent three-terminal switch model. While maintaining the fast transient response capability, the first-order filtered signal of SW was used to generate the virtual inductor current ripple, thereby the subharmonic oscillation could be avoided. The valley of the filtered signal was sampled through the valley sampling circuit. The sampling circuit performed a refresh operation in every switching cycle, so accelerated charging could be performed during power-on and transient phases. The enhanced ripple and valley sampling signals were accurately superimposed on the feedback voltage terminal by the ripple superposition circuit, which ensured the high output accuracy of the circuit. The RBCOT control loop was designed in a 0.35 μm 18 V BCD process to verify this method. Simulation results showed that the output voltage offset was within 1 mV in the input voltage range of 4.5~18 V. The control loop could quickly adjust for transient changes.