Adaptive LDO Load Switch Capacitance Sensing
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Solution Overview
Problem
Capacitor-less LDOs and load switch regulators face limitations in power supply rejection and load transient regulation, unable to support a wide range of load capacitance values and resistances, leading to instability and poor performance compared to external capacitor-based designs.
Innovation Solution
A capacitance sensing circuit determines the estimated output capacitance and adjusts an adaptive RC network to introduce an adaptive zero in the feedback network, placing the dominant pole at the output node without requiring an external capacitor, allowing for improved power supply rejection and load transient regulation across a wide range of load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an external capacitor is used in LDO design, then power supply rejection and load transient regulation are improved, but device complexity and cost increase due to additional external components
Solution Approach 1:
The invention extracts the capacitor function from external components and implements it using on-chip circuitry. The capacitance sensing circuit and adaptive RC network are integrated within the LDO chip, eliminating the need for external capacitors while maintaining the stability and performance benefits they provided.
Solution Approach 2:
The invention introduces a capacitance sensing circuit as an intermediary that detects load capacitance conditions and an adaptive RC network that generates frequency-dependent impedance. This intermediary mechanism enables the LDO to adapt its behavior based on loading conditions without requiring external capacitors, resolving the contradiction between reliability and device complexity.
2Device complexity
If capacitor-less LDO architecture is used, then device complexity is reduced, but power supply rejection and load transient regulation deteriorate
Solution Approach 1:
The invention makes the LDO dynamically adaptive by implementing a capacitance sensing circuit that detects load conditions and an adaptive RC network that adjusts its characteristics based on frequency and loading. This dynamic adaptation enables the capacitor-less LDO to achieve load transient regulation performance comparable to external capacitor designs while maintaining simplified device architecture.
Solution Approach 2:
The invention changes the impedance parameters of the feedback network dynamically through the adaptive RC network. By adjusting the RC time constant based on detected load capacitance, the system optimizes its frequency response and phase margin to maintain stability and performance across varying load conditions without external capacitors.
3Device complexity
If fixed RC network is used in feedback, then device complexity is minimized, but adaptability to different load capacitance values is lost
Solution Approach 1:
The invention implements a feedback mechanism where the capacitance sensing circuit continuously monitors load capacitance conditions and provides information to the adaptive RC network. This feedback loop enables the system to automatically adjust its RC time constant to match the loading conditions, achieving adaptability across different load capacitance values while maintaining relatively simple device architecture.
Solution Approach 2:
The adaptive RC network serves multiple functions: it acts as a frequency-dependent impedance element for stability compensation, a load sensing mechanism for detecting loading conditions, and an adaptive tuning element for optimizing performance across different capacitance values. This multi-functionality achieves adaptability without proportionally increasing device complexity.
Data Source
AI summary
A method to maintain stability of a low drop-out (LDO)/load switch linear voltage regulator (LVR). The method includes determining, during a power-up phase and by a capacitance sensing circuit, an estimated output capacitance value at an output node of the LDO/load switch LVR, and adjusting, based on the estimated output capacitance value, an adaptive RC network in the LDO/load switch LVR, wherein the adaptive RC network produces an adaptive zero in a feedback network transfer function of the LDO/load switch LVR, wherein the adaptive zero reduces an effect of a non-dominant pole in the open loop transfer function of the LDO/load switch LVR, and wherein a frequency of the adaptive zero is inversely proportional to the estimated output capacitance value.