MCC LDO Regulator Compensation for Stable Load Transients
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Solution Overview
Problem
Miller Cascode Compensation (MCC) LDO regulators face challenges with stability and transient response due to potential oscillations in the regulated voltage during load variations.
Innovation Solution
The proposed solution involves an MCC LDO regulator architecture that includes additional loops, such as a DC-coupled loop and an AC-coupled loop, which inject current into the compensation path to increase the transconductance of the cascode device, thereby improving stability and transient response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If Miller Cascode Compensation (MCC) is used in LDO regulator, then bandwidth and power supply rejection ratio are improved, but stability deteriorates due to potential oscillations during load variations
Solution Approach 1:
The patent implements a stability improvement circuit that includes an additional feedback path from the output node to the control node. This feedback mechanism detects oscillations and provides corrective action by adjusting the control signal to the cascode device, thereby suppressing oscillations while maintaining the high bandwidth benefits of MCC architecture
Solution Approach 2:
The stability improvement circuit proactively counteracts potential oscillations before they fully develop by monitoring the state of the cascode device and preemptively adjusting control parameters. The circuit is designed to detect early signs of instability and apply corrective feedback in advance
2Reliability
If cascode stage is added to LDO regulator, then power supply rejection ratio is improved, but device complexity increases
Solution Approach 1:
The stability improvement circuit is integrated with the existing MCC architecture by sharing common nodes and components. The additional feedback path is merged into the existing control structure, utilizing available nodes such as the control node and output node, thereby minimizing the increase in device complexity while achieving the desired power supply rejection ratio improvement
Data Source
AI summary
An LDO regulator has a pass device arranged between an input node and an output node. The pass device is controlled at a control node by an error amplifier. A first current generator sources compensation current to the control node, a cascode device is arranged between the control node and a compensation node, and a second current generator sinks compensation current from the compensation node. A compensation capacitor is arranged between the output and compensation nodes. Load current through the pass device is sensed to generate a feedback current at a first feedback node. An input branch of a current mirror receives the feedback current. A filtering circuit is coupled between a control terminal of the input branch and a second feedback node. Output branches of the current mirror sink and source additional compensation current from the compensation node and the control node, respectively, proportional to the feedback current.