COT Buck Regulator Reference Voltage Ripple for Phase Lag Compensation
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Solution Overview
Problem
Constant On-Time (COT) control buck regulators using low Equivalent Series Resistance (ESR) output capacitors face instability due to phase lag, requiring additional components that increase cost and reduce efficiency, while existing solutions either increase output voltage ripple or degrade transient response.
Innovation Solution
A reference voltage that varies within a PWM cycle is used to stabilize the COT control, compensating for phase lag without sensing the inductor current, allowing for internal phase-lag compensation and maintaining stability with low ESR capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a low ESR ceramic capacitor is used as the output capacitor, then energy density and cost are improved, but system stability deteriorates due to phase lag compensation failure
Solution Approach 1:
The patent changes the parameter of reference voltage from constant to varying (ripple added) to compensate for phase lag. By superimposing a ripple signal on the reference voltage, the system gains phase correction capability that works effectively with low ESR capacitors, resolving the stability issue while maintaining the benefits of low ESR ceramic capacitors.
Solution Approach 2:
The patent introduces an intermediary ripple signal as a mediator between the reference voltage and the feedback voltage comparison. This ripple signal acts as a phase correction mechanism that enables stable operation with low ESR capacitors without requiring additional external components.
2Stability of the object's composition
If an additional resistor is added in series with the output capacitor to stabilize the system, then system stability is improved, but output voltage ripple increases and transient response degrades
Solution Approach 1:
The patent extracts the phase correction function from external components (resistors) and implements it internally by adding a ripple signal to the reference voltage. This eliminates the need for additional series resistors, thereby reducing output voltage ripple and maintaining fast transient response while achieving system stability.
3Stability of the object's composition
If an RC circuit is added to compensate for phase lag, then system stability is improved, but device complexity and component count increase
Solution Approach 1:
The patent merges the phase compensation function with the existing reference voltage generation circuitry. By generating the ripple signal within the controller and combining it with the reference voltage, the system achieves phase lag compensation without requiring separate external RC circuits, thereby reducing component count and device complexity.
4Stability of the object's composition
If a resistor is added in series with the inductor together with an RC circuit filter to stabilize the system, then system stability is improved, but efficiency decreases due to additional power loss
Solution Approach 1:
The patent extracts the stabilization function from power-lossy external resistors and implements it through voltage signal manipulation (adding ripple to reference voltage). This approach achieves system stability without introducing additional series resistors that would cause power loss, thereby maintaining high efficiency.
Data Source
AI summary
The present invention uses a reference voltage that varies within a Pulse Width Modulation (PWM) cycle to generate the PWM signal. This allows for stability in the feedback of Constant On-Time (COT) control for buck controllers when low Equivalent Series Resistance (ESR) capacitors are used as the output capacitor. The reference voltage is adjusted using features of a PWM cycle in a voltage mode without using external inductor current information.