Dual-Stage LDO Regulator With Shared Compensation for Low Power
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Solution Overview
Problem
Low dropout voltage regulators require large output compensation capacitors to ensure stable operation over a wide range of loads, leading to increased cost and quiescent current consumption, making it challenging to maintain operation in low power modes.
Innovation Solution
The implementation of a low output capacitance LDO voltage regulator with a shared internal compensation capacitor across multiple stages, coupled selectively between the operational amplifier and either the first or second LDO stage, reduces area requirements and quiescent current consumption by ensuring stability through a compensation strategy that adds a pole and a zero.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large output compensation capacitor is used to ensure stable operation over a wide load range, then stability is improved, but quiescent current consumption increases and cost increases
Solution Approach 1:
The patent implements dynamic compensation by selectively coupling the compensation capacitor to different LDO stages based on operating conditions. The capacitor is coupled to the first LDO stage during light load conditions and to the second LDO stage during heavy load conditions, allowing the compensation network to adapt dynamically to load variations. This dynamic approach maintains stability across the full load range while avoiding the need for excessive capacitance that would increase quiescent current consumption.
Solution Approach 2:
The patent changes the compensation capacitor coupling configuration based on load current parameters. By monitoring load conditions and selectively connecting the compensation capacitor to appropriate stages, the system optimizes the compensation effect for different operating points. This parameter-based control allows stable operation with reduced capacitance values, thereby lowering quiescent current consumption.
2Reliability
If a large output compensation capacitor is used to ensure stable operation over a wide load range, then stability is improved, but device area increases
Solution Approach 1:
The dynamic selective coupling of the compensation capacitor to different stages allows the system to achieve adequate phase margin and stability with a smaller capacitor value. By optimizing the compensation network's connection based on operating conditions, the patent reduces the required capacitance from what would be needed if a single large capacitor served all conditions, thereby reducing the area occupied by the compensation capacitor.
Solution Approach 2:
The patent merges the compensation function across multiple LDO stages by using a shared compensation capacitor that is selectively coupled to different stages. This consolidation allows a single capacitor to provide compensation for multiple operating modes, reducing the total capacitance required compared to having separate compensation capacitors for each stage, thus reducing overall device area.
3Adaptability or versatility
If multiple LDO stages are used to cover different voltage ranges, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent implements multi-functionality by using a single compensation capacitor that serves multiple LDO stages through selective coupling. The same capacitor provides compensation for both the first LDO stage during light load conditions and the second LDO stage during heavy load conditions. This universal compensation approach reduces device complexity compared to implementing separate compensation networks for each stage, while maintaining the ability to cover a wide voltage and load range.
Solution Approach 2:
The dynamic switching between different LDO stages and their associated compensation connections allows the system to adapt to different voltage and load conditions without requiring permanently active complex circuitry for all stages. The selective coupling mechanism enables simple, condition-based stage activation, reducing overall circuit complexity while maintaining high adaptability.
Data Source
AI summary
A low dropout (LDO) voltage regulator includes a first LDO stage that receives a first supply voltage and is active during a first time interval and a second LDO stage that receives a second supply voltage and is active during a second time interval. An operational amplifier receives a feedback voltage based on the LDO output voltage and provides an amplified feedback signal to the first and second LDO stages. A compensation capacitor is selectively coupled between the operational amplifier and either the first or the second LDO stage. A current limit circuit includes a sense FET coupled to the LDO pass FET, a drain voltage replication circuit coupled between the pass FET and sense FET to provide a sense current is indicative of load current when the pass FET is in a linear region, and a current comparator to compare the sense current to a predetermined current level.