Abstract
Fast load transient response and high light-load efficiency are two key features of the constant on-time (COT) control technique that has been widely used in numerous applications, such as for voltage regulators and point-of-load converters. However, when load step-down occurs during an on-time interval, the COT controller cannot respond until the COT interval expires. This delay causes an additional output voltage overshoot, resulting in unloading transient performance limitation. To eliminate the delay and improve the unloading transient response of the COT controller, a load step-down detection circuit is proposed based on capacitor current COT (CC-COT) control. In the detection circuit, the load step-down is monitored by comparing the measured capacitor current with the preset threshold voltage. Once the load step-down is monitored, the on-time is promptly truncated and the switch is turned off. With the proposed detection circuit, the CC-COT-controlled buck converter can monitor the load step-down without any delay and obtain less output voltage overshoot when the load step-down occurs during the on-time interval. PSIM circuit simulations are employed to demonstrate the feasibility of the detection circuit.
Highlights
The constant on-time (COT) control is a kind of variable-frequency control techniques [1,2]
To eliminate the delay when the load step-down occurs during the on-time interval, a load step-down detection circuit is proposed based on the capacitor current COT (CC-COT) control, i.e., the Electronics 2021, 10, 2333 improved CC-COT control, to obtain less output voltage overshoot
An improved CC-COT control is proposed by introducing a detection circuit for monitoring the load step-down
Summary
The constant on-time (COT) control is a kind of variable-frequency control techniques [1,2]. Using capacitor current as the compensation ramp can stabilize the V2-COT-controlled buck converter with small output capacitor ESR but can improve its load transient performance [9]. In [23], the difference of the sensed inductor current and the output voltage of the error amplifier was compared with predefined thresholds to truncate the on-time when load step-down occurred. To eliminate the delay when the load step-down occurs during the on-time interval, a load step-down detection circuit is proposed based on the CC-COT control, i.e., the Electronics 2021, 10, 2333 improved CC-COT control, to obtain less output voltage overshoot. 2. Review of Stability and Transient Performance of Two Control Techniques In Figure 2, a schematic diagram of the CC-COT-controlled buck converter is given, in which the output capacitor current is sensed for output voltage regulation. In the both simulation circuit models, the error amplifier is implemented by the proportional-integral (PI) compensator with the same feedback gain g and time constant τ
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