LDO Bias Control Circuit for Fast Transient Response

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Solution Overview

Problem

Low power low dropout voltage regulators (LDOs) exhibit a slow dynamic response to transient changes in load impedance due to their low quiescent current, leading to a slow adjustment in output voltage.

Innovation Solution

Incorporating a comparator with a small offset and a switched current source that dynamically adjusts the bias current based on the output voltage, allowing for a faster transient response by increasing the bias current proportionally with the output current and providing additional current through a pulldown transistor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If low quiescent current is used in low power LDOs, then power consumption is reduced, but dynamic response to transient changes becomes slow

Engineering Contradiction:

Improvepower consumptionVSAvoiddynamic response speed

Core Design Contradiction:

Use of energy by moving objectVSSpeed

Solution Approach 1:

The bias current is made dynamically adjustable rather than fixed. The circuit transitions from a static low bias current state to a dynamic state where the bias current can be increased in response to transient load changes, allowing the system to optimize between low power consumption and fast response based on operating conditions

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The bias current parameter is changed from a constant low value to a variable value that can be increased during transient events. The circuit modifies the bias current parameter in response to detected transient conditions, enabling faster response while maintaining low average power consumption

Inventive Principle:

Principle #35Parameter changes

2Speed

If adaptive bias is implemented to improve dynamic performance, then response to transient changes improves, but quiescent current increases

Engineering Contradiction:

Improvedynamic response speedVSAvoidquiescent current

Core Design Contradiction:

SpeedVSUse of energy by moving object

Solution Approach 1:

The circuit employs periodic or event-driven adjustment of the bias current rather than continuous high bias current. The adaptive bias is activated periodically or in response to specific transient events, allowing fast response when needed while maintaining low quiescent current during steady-state operation

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The circuit automatically detects transient conditions and self-adjusts the bias current without external intervention. The transient detection circuit triggers the bias current increase automatically, eliminating the need for continuous external control while maintaining both low quiescent current and fast transient response

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS8716993B2Low dropout voltage regulator including a bias control circuit

Publication Date: 2014.05.06 SEMICON COMPONENTS IND LLC

AI summary

A low dropout (LDO) regulator includes a voltage regulation loop for providing an output voltage to an output terminal, where the output voltage is proportional to a reference voltage. The voltage regulation loop includes a current bias input for receiving a bias current. The LDO regulator also includes a bias current control circuit for providing the bias current at a first value when the reference voltage is greater than a feedback voltage and at a second value higher than the first value when the reference voltage is less than the feedback voltage.