Capacitor-Less LDO Dual Feedback Loops for Load-Adaptive Stability
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Solution Overview
Problem
Capacitor-less low dropout regulators face challenges in maintaining stability and transient response performance across varying load currents due to the movement of high-frequency poles and the absence of an external capacitor, leading to reduced bandwidth and operational limitations.
Innovation Solution
A dual feedback loop structure with a dynamic compensation unit that applies the Miller effect to adjust pole frequencies based on load current conditions, using small capacitors and a differential amplifier to maintain loop stability and widen bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a capacitor-less LDO regulator structure is used to reduce cost and simplify the circuit, then the device complexity and cost are reduced, but the transient response performance deteriorates due to the absence of an external output capacitor
Solution Approach 1:
The patent implements a dynamic compensation mechanism where the compensation capacitor is controlled to vary its capacitance value based on load current conditions. During transient states, the capacitor is connected to provide immediate current support, while during steady-state operation, it is disconnected to prevent stability issues. This dynamic behavior resolves the contradiction by providing transient response enhancement only when needed, rather than requiring a permanently large capacitor.
Solution Approach 2:
The compensation capacitor is periodically connected and disconnected based on the operational state of the LDO regulator. The control circuit monitors load current changes and activates the capacitor during transient periods, then deactivates it during steady-state periods. This periodic action allows the system to achieve good transient response without the continuous presence of a large capacitor that would compromise stability.
2Reliability
If a large external output capacitor is added to improve transient response performance, then the transient response performance is improved, but the device complexity and cost increase
Solution Approach 1:
Instead of using a permanently connected large capacitor, the patent employs a dynamically controlled compensation capacitor that changes its effective capacitance based on operational needs. The control circuit activates the capacitor during transient load changes to provide necessary current support, then disconnects it during steady-state operation to maintain stability and minimize component requirements.
Solution Approach 2:
The LDO regulator incorporates an integrated compensation mechanism that automatically activates the compensation capacitor when transient conditions are detected. The control circuit monitors load current changes and autonomously connects the capacitor to provide the necessary transient response enhancement without external intervention or permanently requiring a large capacitor.
3Use of energy by stationary object
If the load current decreases to reduce power consumption, then the power consumption is reduced, but the stability of the feedback loop deteriorates as high-frequency poles move closer to low-frequency poles
Solution Approach 1:
The patent implements a dynamic compensation mechanism that adjusts the compensation capacitor's effective capacitance based on load current levels. When load current decreases and poles approach each other, the control circuit activates the compensation capacitor to restore adequate phase margin and maintain stability. When load current is high and poles are well-separated, the capacitor remains inactive to minimize power consumption and component stress.
Solution Approach 2:
The control circuit continuously monitors the operational state of the LDO regulator, including load current levels and pole positions, and dynamically adjusts the compensation capacitor's connection state accordingly. This feedback mechanism ensures that the compensation capacitor is activated only when stability is at risk due to low load current, thereby maintaining stability while minimizing the impact on power consumption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables stable operation across a wide range of load currents, improving transient response performance and reducing production costs by minimizing capacitor usage while maintaining accurate output voltage with minimal ripple.
Implementation Method 1
A capacitor-less low dropout regulator using a dual feedback loop structure includes: ... a dynamic compensation unit connected to a first main pole located at an output of the error amplifier and a second main pole located at an output of the gm cell to provide dynamic frequency compensation using a Miller effect to the first main pole and the second main pole according to a load current of the capacitor-less dual feedback loop unit
Data Source
AI summary
A capacitor-less low dropout regulator includes: a capacitor-less dual feedback loop unit including a plurality of feedback resistors, an error amplifier, and a transconductance cell to form a main loop passing through the error amplifier and a sub-loop passing through the gm cell without passing through the error amplifier; a dynamic compensation unit connected to a first main pole located at an output of the error amplifier and a second main pole located at an output of the gm cell to provide dynamic frequency compensation using a Miller effect to the first main pole and the second main pole according to a load current of the capacitor-less dual feedback loop unit; and a load current measurement unit configured to measure a load current of a third main pole formed at a load of the dual feedback loop unit to provide the load current to the dynamic compensation unit.