Power-Supply Controller Feedback Loop Stability
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Solution Overview
Problem
Traditional constant-on-time buck converters become unstable when using low-ESR filter capacitors, leading to voltage tolerance issues and oscillation, especially at high steady-state switching frequencies, and require additional compensation components or pins on the power-supply controller chip.
Innovation Solution
A power-supply controller with a signal combiner and control circuit that generates a combined feedback signal, allowing the use of low-ESR filter capacitors without additional compensation components or pins, by enhancing the feedback loop stability through an inverse sense signal that replaces the in-phase component of the ripple, maintaining tight and stable output voltage regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a low-ESR filter capacitor is used in a traditional constant-on-time buck converter, then the size and cost of the converter are reduced, but the feedback loop becomes unstable leading to voltage tolerance issues and oscillation
Solution Approach 1:
The patent introduces a modified feedback mechanism that combines the output voltage feedback with a sense signal proportional to the inductor current. This combined feedback signal replaces the traditional reliance on capacitor ESR for stability, allowing low-ESR capacitors to be used while maintaining feedback loop stability through active compensation of the ripple signal.
Solution Approach 2:
The patent changes the parameters of the feedback signal by adding a sense component that is proportional to the inductor current. This modifies the feedback signal characteristics to compensate for the reduced ESR, thereby maintaining the phase margin and stability of the feedback loop even with low-ESR capacitors.
2Reliability
If additional compensation components or pins are added to stabilize the feedback loop with low-ESR capacitors, then the feedback loop stability is improved, but the device complexity increases
Solution Approach 1:
The power-supply controller integrates multiple functions into a single device, including the sense signal generation, signal combination, and control logic. This multi-functionality eliminates the need for separate compensation components and additional pins, as the controller itself provides the necessary compensation through its integrated circuitry.
Solution Approach 2:
The controller generates its own sense signal internally and combines it with the feedback signal without requiring external compensation components. The system serves itself by using internal resources (the sense circuit and signal combiner) to achieve stability, eliminating the need for external aids.
3Reliability
If the in-phase component of the ripple is dominated by large ESR, then the feedback loop is stable, but the filter capacitor size and cost increase
Solution Approach 1:
The patent replaces the passive mechanical/electrical property of high ESR (which naturally provides stability) with an active electronic solution. The sense signal and signal combiner electronically generate the necessary stability compensation, substituting the need for high ESR with an active control mechanism that works effectively with low-ESR capacitors.
Data Source
AI summary
An embodiment of a power-supply controller includes a signal combiner and a control circuit. The signal combiner is operable to generate a combined feedback signal from sense and output feedback signals that are respectively derived from a sense signal and a regulated output signal, and the signal combiner is operable to receive the sense signal from a sense circuit that is operable to generate the sense signal while a current is flowing through an inductor and while a switch that is disposed between the inductor and an input voltage has a first state. The sense signal generated by the sense circuit is related to the current, and the switch and the inductor are operable to generate the regulated output signal. The control circuit is coupled to the signal combiner and is operable to cause the switch to have a second state for a predetermined time in response to the combined feedback signal having a predetermined relationship to a reference signal.