Constant On-Time Buck Regulator Controller Noise Immunity
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Solution Overview
Problem
Constant on-time controllers in buck regulator devices face stability and noise susceptibility issues due to small equivalent series resistance (ESR) in multilayer ceramic capacitors, leading to increased jitter and reduced noise margin.
Innovation Solution
A constant on-time controller comprising a voltage divider, current ripple extractor, one-shot on-timer, comparator, and flip-flop, along with a modulation circuit and ramp generator, is used to generate feedback and modulation signals that determine the on-time and off-time of the buck regulator, eliminating DC components from sensed currents and incorporating a ramp voltage to reduce noise susceptibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If multilayer ceramic capacitor with small ESR is used in buck regulator, then voltage ripple from energy storage inductor is small, but noise margin of constant on-time controller is reduced
Solution Approach 1:
The patent introduces an artificial ramp signal as an intermediary element added to the comparator input. This ramp signal serves as a mediator that provides a dominant, controlled slope to the comparison operation, preventing the comparator from being overly sensitive to small voltage ripple variations caused by low ESR capacitors. The ramp signal effectively decouples the comparator's sensitivity from the actual output voltage ripple, thereby improving noise margin while maintaining low ripple performance.
2Object-generated harmful factors
If multilayer ceramic capacitor with small ESR is used in buck regulator, then voltage ripple from energy storage inductor is small, but susceptibility to noise is increased
Solution Approach 1:
The artificial ramp signal acts as an intermediary that dominates the comparator's decision-making process. By providing a large, predictable slope that overwhelms noise-induced variations in the feedback voltage, the ramp signal reduces the comparator's susceptibility to noise. This allows the system to maintain low voltage ripple with small ESR capacitors while simultaneously reducing noise susceptibility through the ramp's stabilizing influence on the switching decision.
3Object-generated harmful factors
If multilayer ceramic capacitor with small ESR is used in buck regulator, then voltage ripple from energy storage inductor is small, but jitter is increased
Solution Approach 1:
The artificial ramp signal serves as a mediator that provides a dominant timing reference for the comparator. By ensuring that the ramp signal's slope is much larger than the slope caused by output voltage ripple, the ramp signal becomes the primary determinant of the switching transition timing. This effectively filters out jitter caused by small voltage variations, allowing the system to achieve both low voltage ripple and low jitter performance simultaneously.
Data Source
AI summary
A constant on-time controller has a voltage divider, a current ripple extractor, a one-shot on-timer, a comparator and a flip flop. The voltage divider generates a feedback voltage according to a regulator output voltage. The current ripple extractor senses a current in an energy storage inductor of a buck regulator flowing through flowing through an output capacitor's ESR, and generates an extracted ripple current having no DC component accordingly. The one-shot on-timer outputs a constant-on time control signal according to a buck regulator input voltage and the regulator output voltage. The modulation circuit outputs a modulation signal according to a reference voltage signal, the feedback voltage and the extracted ripple current. The flip flop generates a control signal to the buck regulator according to the modulation signal and the constant-on time control signal. An off-time of the buck regulator is determined according to the modulation signal.