Constant On-Time Regulator Reference Voltage Ramp
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Solution Overview
Problem
Conventional fixed on-time voltage regulators require a minimum equivalent series resistance (ESR) in output capacitors for effective ripple-mode control, limiting their application to cases where output ripple can be tolerated, and preventing the use of low ESR capacitors like ceramic ones, which are cheaper but lack sufficient ESR.
Innovation Solution
A switching regulator implementing a fixed frequency constant on-time control scheme with a reference voltage ramp, allowing the use of output capacitors with any ESR value, including low or zero ESR, by generating a reference voltage ramp that varies over the switching period, ensuring stable feedback control without voltage offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional fixed on-time voltage regulators are used, then ripple-mode control is effective, but output ripple is high and low ESR capacitors cannot be used
Solution Approach 1:
The patent changes the control parameter from relying on output capacitor ESR to using a reference voltage ramp that is varied over the switching period. This parameter change enables the use of low ESR capacitors while maintaining stable feedback control, resolving the contradiction between capacitor selection flexibility and output ripple control.
2Reliability
If minimum ESR capacitors are used for ripple-mode control, then feedback control stability is maintained, but output ripple and noise increase
Solution Approach 1:
The patent introduces a reference voltage ramp as an intermediary element that mediates between the control circuit and the output capacitor. This ramp provides the necessary feedback signal for stable control without depending on the capacitor's ESR, thereby maintaining control stability while enabling the use of low ESR capacitors that reduce output ripple and noise.
3Object-generated harmful factors
If low ESR capacitors are used, then output ripple and noise are minimized, but ripple-mode control becomes ineffective
Solution Approach 1:
Instead of relying on the capacitor's ESR to generate the ripple signal needed for control, the patent inverts the approach by generating a reference voltage ramp that actively provides the control signal. This inversion enables effective control with low ESR capacitors, resolving the contradiction between minimizing output ripple and maintaining control effectiveness.
4Productivity
If conventional constant on-time control is used, then light load efficiency and transient response are improved, but voltage offset occurs with zero ESR capacitors
Solution Approach 1:
The patent makes the reference voltage dynamic by varying it over the switching period rather than using a fixed reference. This dynamic reference voltage adapts to the switching cycle, enabling accurate output voltage control with zero ESR capacitors while preserving the fast transient response and light load efficiency benefits of constant on-time control.
Data Source
AI summary
A control circuit for a switching regulator implementing a fixed frequency constant on-time control scheme incorporates a reference voltage generator to generate a reference voltage ramp that varies over substantially the entire switching period. In one embodiment, the reference voltage increases from an initial voltage value at the start of each switching period towards the end of the switching period and is reset to the initial voltage value at the end of each switching period. The reference voltage ramp ensures stable feedback control operation in the switching regulator without introducing voltage offset for all output voltage values. The control circuit enables the switching regulator to apply constant on-time control scheme while using an output capacitor having any ESR value, including an output capacitor with low or zero ESR.