LDO Current Sink Stage for Voltage Overshoot Control
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Solution Overview
Problem
Low drop-out (LDO) regulators face challenges in activating a current sink independently of output voltage overshoot, leading to potential brown-out conditions and requiring large capacitors, especially when sourcing current less than the sink capability, which skews internal nodes and increases power consumption.
Innovation Solution
A Low Drop-Out voltage regulator with a current sink circuitry that activates independently of output voltage overshoot percentage, using a differential amplifier to regulate the pass device gate and a sensing circuit to detect overshoots, allowing current sinking until the voltage is remediated, without additional compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a comparator is used for current sink, then no compensation is required, but chattering occurs and output voltage regulation fails when sourced current is less than sink capability
Solution Approach 1:
The patent uses a differential amplifier instead of a comparator to provide continuous analog feedback control. The differential amplifier compares the output voltage with a reference voltage and continuously adjusts the sink current to maintain regulation, eliminating the chattering problem inherent in comparator-based digital switching control.
Solution Approach 2:
The patent implements a dynamic current sink capability where the sink current magnitude is continuously adjustable based on the load conditions. This allows the LDO to adapt the sink current to match the sourced current magnitude, enabling effective regulation even when sourced current is less than the maximum sink capability.
2Reliability
If output decoupling capacitor is increased to reduce output voltage dip, then brown-out condition is avoided, but PCB footprint increases
Solution Approach 1:
The patent implements a continuous current sink capability that actively compensates for output voltage dips in real-time. By continuously monitoring the output voltage and adjusting the sink current accordingly, the system maintains regulation without requiring large decoupling capacitors to passively store energy.
Solution Approach 2:
The LDO regulates its own output voltage by using the current sink to compensate for voltage dips caused by load transients. The system self-corrects the output voltage deviation without external intervention or large capacitive storage, reducing the burden on external decoupling capacitors.
3Adaptability or versatility
If bi-directional push-pull LDO is used to achieve current sink capability, then current sinking is enabled, but device complexity and quiescent current increase
Solution Approach 1:
The patent separates the current sink function from the main LDO regulation path by implementing it as an independent controlled current sink stage. This modular approach allows the current sink to be added without fundamentally redesigning the core LDO architecture, maintaining simplicity while adding functionality.
Solution Approach 2:
The differential amplifier serves multiple functions: it provides both the main LDO voltage regulation control and the current sink control. By using the same amplifier for both functions, the patent avoids adding separate control circuits, thereby reducing overall device complexity while achieving bi-directional current capability.
Data Source
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AI summary
An LDO circuit with a current sink stage reduces significantly overshooting of the output voltage due to sudden changes of output current. The activation of the current sink stage is independent of the overshoot percentage of the regulated output voltage. The disclosure doesn't require large output capacitors to avoid the possibility of brownouts of chips supplied by the LDO.