Direct-Feedback Buck Converter 100% Mode Without VREF Dropout

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Solution Overview

Problem

In nano-Iq switching regulators with direct feedback, the system reference voltage amplifier enters dropout when the input voltage equals or is below the output voltage target, preventing the converter from entering 100% mode and resulting in continuous switching and regulation towards a lower reference voltage.

Innovation Solution

A new buck converter topology with 100% mode circuitry that applies an offset to the output voltage to anticipate 100% mode entry, avoiding amplifier dropout by injecting a negative offset voltage in the feedback path, ensuring a stable reference voltage and smooth transition into 100% mode.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If direct feedback is used to reduce quiescent current, then quiescent current is reduced, but the reference voltage amplifier enters dropout when VIN equals or is below VOUT target, preventing 100% mode entry

Engineering Contradiction:

Improvequiescent currentVSAvoidreference voltage stability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent applies preliminary action by detecting when VIN approaches VOUT target and proactively adjusting the reference voltage VREF before the amplifier enters dropout. The control circuit monitors the input voltage and preemptively modifies VREF to maintain stability, preventing the dropout condition from occurring in the first place. This allows the converter to smoothly transition into 100% mode without the reference voltage instability that would otherwise occur.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If VREF tracks VIN in dropout mode, then the system keeps switching and regulating, but the output voltage is regulated to VIN−VDROP instead of VOUT, preventing true 100% mode

Engineering Contradiction:

Improvevoltage regulation adaptabilityVSAvoidmode transition smoothness

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The patent uses feedback by continuously monitoring the input voltage VIN and comparing it to the output voltage VOUT target. When VIN approaches VOUT, the control circuit receives feedback and automatically adjusts the reference voltage VREF accordingly. This feedback mechanism ensures that the converter transitions smoothly into 100% mode when appropriate, rather than continuously switching due to reference voltage tracking in dropout mode.

Inventive Principle:

Principle #23Feedback

3Device complexity

If the converter operates without feedback divider, then component count is reduced, but system voltage headroom is compromised when VIN equals VOUT target

Engineering Contradiction:

Improvefeedback circuit complexityVSAvoidvoltage operating range

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent applies dynamics by making the reference voltage VREF adjustable and dynamic rather than fixed. The control circuit dynamically modifies VREF based on the operating conditions, specifically when VIN approaches VOUT target. This dynamic adjustment allows the converter to maintain proper voltage headroom and transition to 100% mode, expanding the voltage operating range without adding a feedback divider and thus maintaining low device complexity.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS11784568B2Low quiescent current buck converter with direct feedback

Publication Date: 2023.10.10 TEXAS INSTRUMENTS INC

AI summary

A switching converter circuit includes a voltage regulation loop configured to provide an output voltage (VOUT) based on an input voltage (VIN). The switching converter circuit also includes a 100% mode circuitry coupled to the voltage regulation loop, wherein the 100% mode circuitry is configured to apply an offset to VOUT in response to detecting that VIN is approaching VOUT.