Dual-Loop LDO Feedback Switching for Fast and Accurate Regulation
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Solution Overview
Problem
Existing voltage regulator systems for microcontrollers and systems-on-a-chip face challenges in providing accurate and responsive voltage supply, especially when dealing with peak currents, as they often compromise between speed and accuracy.
Innovation Solution
A dual loop low dropout (LDO) regulator system is introduced, featuring a fast loop for quick voltage settling and a slow loop with a switch circuit in the feedback path, enabling conditional feedback to optimize speed while ensuring accurate output voltage. The system includes a first amplifier stage, a second amplifier stage, a load circuit, and a logic control circuit to manage feedback paths and provide active indication signals for current sourcing, allowing the fast loop to settle voltage quickly and the slow loop to accurately set it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single loop voltage regulator is used, then the device complexity is low, but the voltage response speed and accuracy deteriorate when supplying peak currents
Solution Approach 1:
The voltage regulator is segmented into two separate feedback loops: a fast loop (second amplifier circuit 104) that responds quickly to transient changes, and a slow loop (first amplifier circuit 102) that provides accurate steady-state regulation. This segmentation allows each loop to be optimized for its specific function, resolving the contradiction between speed and complexity by distributing regulatory functions across multiple specialized circuits rather than attempting to achieve both goals in a single circuit.
Solution Approach 2:
The system dynamically switches between different feedback paths using switch circuit 110. During transient conditions, the fast loop is activated for rapid response; during steady-state conditions, the slow loop provides precise regulation. This dynamic operation allows the system to adapt its complexity based on operational requirements, achieving high speed when needed while maintaining accuracy during normal operation.
2Measurement precision
If feedback path is always active, then voltage accuracy is improved, but response speed to peak currents deteriorates
Solution Approach 1:
The feedback path is made dynamic through switch circuit 110, which selectively connects the output to either the fast loop or slow loop based on operational conditions. When transient current demands are detected, the switch redirects feedback to the fast loop for rapid response; during steady-state operation, it connects to the slow loop for high accuracy. This dynamic switching resolves the contradiction by allowing the system to prioritize speed or accuracy based on real-time requirements.
Solution Approach 2:
Switch circuit 110 acts as an intermediary that mediates between the two feedback paths and the amplifier circuits. It receives control signals from logic control circuit 108 and dynamically routes the feedback signal to the appropriate amplifier, enabling the system to achieve both fast transient response and accurate steady-state regulation without compromising either performance metric.
3Loss of time
If fast loop is optimized for speed, then voltage settling time is reduced, but voltage setting accuracy deteriorates
Solution Approach 1:
The regulatory function is segmented into two specialized circuits: the second amplifier circuit 104 (fast loop) is optimized for rapid voltage settling with minimal phase margin, while the first amplifier circuit 102 (slow loop) is optimized for high accuracy with adequate phase margin. This segmentation allows each circuit to excel at its specific function without compromise, resolving the contradiction between speed and accuracy by assigning different optimization goals to different segments of the overall system.
Solution Approach 2:
The fast loop is designed with excessive speed characteristics (minimal phase margin of approximately 45 degrees) that would normally cause instability, but this is acceptable because the fast loop operates only during transient conditions when speed is critical. The slow loop then takes over for steady-state operation where accuracy is paramount. This partial optimization approach allows the fast loop to be aggressively optimized for speed without sacrificing overall system accuracy.
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AI summary
A low dropout (LDO) regulator system is provided. The LDO regulator system includes a first amplifier circuit, a second amplifier circuit, and a switch circuit. The first amplifier circuit has a first input coupled to receive a reference voltage and an output. The second amplifier circuit has a first input coupled to the output of the first amplifier and is configured to provide a predetermined voltage at a first output. The switch circuit is coupled between the first output of the second amplifier circuit and a second input of the first amplifier circuit and is configured to cause an open circuit in a first feedback path from the first output of the second amplifier circuit to the second input of the first amplifier circuit based on a control signal.