Asynchronous Dropout Transition for Buck Converters

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Solution Overview

Problem

Conventional buck converters experience significant perturbations in output voltage and inductor current during transitions from asynchronous to synchronous operation, necessitating improved transition methods to maintain regulation during low dropout conditions.

Innovation Solution

A buck converter design incorporating a first ramp signal generator, cycle timer, and switch controller that generates a first ramp signal responsive to a clock signal during synchronous mode and an asynchronous triggering signal during asynchronous mode, allowing seamless transitions by determining if the control signal is asserted before a cycle timer period plus minimum off-time, and transitioning to synchronous mode when the cycle timer period is sufficiently synchronous with the clock signal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the buck converter operates in synchronous mode with a system clock signal, then the switching operation is synchronized and stable, but the duty cycle cannot approach 100% due to minimum off-time constraints

Engineering Contradiction:

Improveswitching synchronization stabilityVSAvoidachievable duty cycle

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system dynamically switches between synchronous and asynchronous modes based on operating conditions. During low dropout operation when high duty cycle is needed, the controller transitions to asynchronous mode, allowing the switching frequency to vary and the duty cycle to approach 100% without being constrained by the fixed system clock period minus minimum off-time.

Inventive Principle:

Principle #15Dynamics

2Adaptability or versatility

If the buck converter transitions from asynchronous to synchronous operation using conventional methods, then the mode switching is achieved, but large perturbations occur in output voltage and inductor current

Engineering Contradiction:

Improvemode transition capabilityVSAvoidoutput voltage and inductor current stability

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The controller predicts when a transition from asynchronous to synchronous mode should occur based on duty cycle thresholds, and prepares for the transition in advance. By anticipating the transition point and pre-adjusting control parameters, the system minimizes sudden changes in switching behavior that would otherwise cause large perturbations in output voltage and inductor current.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system continuously monitors output voltage and inductor current during mode transitions and uses this feedback to adjust switching control in real-time. This closed-loop control ensures that any deviations caused by mode switching are quickly corrected, maintaining stability during the transition from asynchronous to synchronous operation.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS10998818B2Asynchronous dropout transition for multi-level and single-level buck converters

Publication Date: 2021.05.04 DIALOG SEMICONDUCTOR (UK) LTD

AI summary

A multi-level buck converter is provided with seamless transitions back and forth from synchronous to asynchronous low dropout modes of operation.