LDO Regulator Output Transistor Control for Fast Low-Capacitance Transients
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Solution Overview
Problem
Existing low-dropout (LDO) voltage regulators face challenges in reducing current consumption, overshoot, and undershoot during output transients while maintaining efficient performance, particularly in portable systems where battery life is a concern and large output capacitors are not feasible due to area constraints.
Innovation Solution
The proposed voltage regulator circuit incorporates a mode selection circuit that controls the output transistor's conductivity through a mode selection signal, allowing for low-power and high-power modes, utilizing a combination of current sources, transistors, and capacitors to manage current flow and reduce overshoot and undershoot, with an integrated output capacitor to minimize area occupation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the output capacitor size is increased to reduce overshoot and undershoot, then the transient response performance is improved, but the area occupation increases which is not feasible in portable systems
Solution Approach 1:
The patent changes the operational parameters of the output transistor by introducing a mode selection circuit that controls the transistor's conductivity. By adjusting the transistor's operating state rather than increasing capacitor size, the system achieves better transient response within the same area constraints.
Solution Approach 2:
The patent introduces dynamic control of the output transistor through the mode selection circuit, which adjusts the transistor's conductivity based on operational modes. This dynamic adjustment allows the system to optimize transient response performance without requiring a larger output capacitor.
2Use of energy by moving object
If the current consumption is reduced to extend battery life, then the energy efficiency is improved, but the ability to maintain stable output voltage during transients deteriorates
Solution Approach 1:
The patent implements dynamic current management through the mode selection circuit that controls the output transistor's conductivity. The system can switch between low-power mode (reducing current consumption) and high-performance mode (maintaining output voltage stability during transients), thus resolving the contradiction between energy efficiency and voltage stability.
Solution Approach 2:
The patent changes the conductivity parameter of the output transistor dynamically based on operational requirements. By adjusting this parameter through the mode selection circuit, the system achieves low quiescent current consumption while maintaining the capability to respond to transient load changes effectively.
3Speed
If the output transistor conductivity is increased to improve transient response, then the settling speed is improved, but the overshoot and undershoot increase
Solution Approach 1:
The patent introduces dynamic control of the output transistor's conductivity through the mode selection circuit. Instead of using a fixed high conductivity that causes overshoot, the system dynamically adjusts the transistor's state, enabling fast settling when needed while controlling overshoot and undershoot through proper mode selection.
Data Source
AI summary
A low-drop out voltage regulator includes a pass element arranged between an input terminal and an output terminal, a feedback network configured to produce a feedback voltage derived from an output voltage, and an error amplifier configured to drive the pass element as a function of a difference between the feedback voltage and a reference voltage. An output transistor coupled in series with the pass element is controlled by a mode selection circuit. In response to assertion of a mode selection signal, the mode selection circuit turns on the output transistor to sink a current with a controlled magnitude from the output node. In response to de-assertion of the mode selection signal, the mode selection circuit sinks a current with a controlled magnitude from a control terminal of the output transistor to turn off the output transistor at a controlled rate.