LDO Regulator Transient Loop for Fast Load Step Response
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Solution Overview
Problem
Existing low-dropout regulator (LDO) circuits face challenges in achieving a fast step response to abrupt load current changes without requiring large decoupling capacitors, as conventional methods like increasing bandwidth or using high-slew rate error amplifiers often consume high current and interfere with the voltage control loop stability.
Innovation Solution
A voltage regulator circuit with a supplemental control loop that detects transients in the output voltage and adjusts the voltage applied to the transistor's control electrode, using a transient detector coupled to the gate of the transistor via capacitors, allowing for independent operation from the main control loop and reducing overshoot/undershoot without interfering with the main voltage control loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large decoupling capacitors are used at the VREG output, then transient response to load changes is improved, but device complexity and cost increase
Solution Approach 1:
The control system is segmented into two independent loops: a main control loop for steady-state voltage regulation and a supplemental control loop for transient response. The supplemental loop includes a transient detector that specifically monitors load current changes and generates compensating signals, while the main loop continues to regulate the output voltage. This segmentation allows each loop to be optimized for its specific function without interfering with the other, achieving fast transient response without requiring large capacitors.
Solution Approach 2:
A transient detector is introduced as an intermediary component between the load and the control electrode of the pass transistor. This detector monitors load current changes and generates transient compensation signals that are superimposed on the main control signal. The intermediary transient detector enables the system to respond to load changes before they manifest as output voltage deviations, eliminating the need for large decoupling capacitors while maintaining stability.
2Reliability
If bandwidth of the voltage control loop is increased to improve step response, then transient response is improved, but current consumption increases and stability may be compromised
Solution Approach 1:
The control functionality is segmented into two independent loops with different bandwidths and current consumption characteristics. The main control loop operates at a lower bandwidth with moderate current consumption for steady-state regulation, while the supplemental transient compensation loop operates only during transient events with high bandwidth but minimal average current consumption. This segmentation allows the system to achieve fast step response without continuously consuming high current.
Solution Approach 2:
The supplemental control loop is activated periodically only when transients are detected by the transient detector, rather than operating continuously. The transient detector monitors load current changes and enables the supplemental loop only during transient events. This periodic activation significantly reduces average current consumption while maintaining fast response capability when needed.
3Reliability
If high-slew rate error amplifiers are employed to improve transient response, then step response is improved, but current consumption increases and interference with voltage control loop stability occurs
Solution Approach 1:
The control system is divided into two independent loops: the main voltage control loop that ensures stability through proper compensation, and a supplemental transient compensation loop that provides fast response without affecting main loop stability. The supplemental loop uses a transient detector to generate compensation signals that are added to the main control signal, allowing fast transient response while the main loop continues to maintain stability through its designed compensation network.
Solution Approach 2:
A transient detector serves as an intermediary that generates transient compensation signals without directly interfering with the main voltage control loop. The detector monitors load current changes and produces compensation signals that are superimposed on the control electrode voltage. This intermediary approach allows the supplemental loop to improve transient response while the main loop continues to regulate voltage and maintain stability independently.
Data Source
AI summary
In accordance with one embodiment, a voltage regulator includes a transistor having a load current path connecting an input node with an output node, wherein the input node is configured to receive an input voltage and the output node is configured to provide an output voltage. The voltage regulator further includes a main control loop coupled between the output node and a control electrode of the transistor and configured to control a voltage applied to the control electrode so that the output voltage matches a set-point. Furthermore, the voltage regulator includes a supplemental control loop that is coupled between the output node and the control electrode of the transistor and configured to detect a transient in the output voltage and to adjust the voltage applied to the control electrode in response to the detection of a transient. A corresponding method is described.