Soft-Start Reference Delay Circuit for Regulator Overshoot Control
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Solution Overview
Problem
Existing soft-start circuits for voltage regulators in System-on-Chips (SoCs) are large and costly due to their complex components, leading to overshoot issues that can damage functional circuits during power-up, necessitating a more efficient solution.
Innovation Solution
A soft-start circuit comprising a comparator, delay circuit, logic gate, latch, buffer, and minimal additional components that delays the reference voltage during start-up, preventing overshoot by gradually ramping up the output voltage to match the reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional soft-start circuit includes various current sources, switches, an unbalanced differential pair of transistors, and a differential amplifier, then the overshoot of the output voltage can be mitigated, but the size and manufacturing cost of the soft-start circuit and SoC increase
Solution Approach 1:
The soft-start circuit is segmented into distinct functional modules: a delay circuit that generates a delayed enable signal, a latch that stores this signal, and a buffer that provides the final controlled enable output. This segmentation allows each component to perform a specific function with minimal complexity, replacing the need for complex current sources and differential pairs while achieving the same overshoot mitigation effect.
Solution Approach 2:
The invention extracts and isolates the essential function of soft-start (delayed enabling) from the complex conventional circuitry. By taking out only the necessary delay and control logic elements (delay circuit, latch, buffer) and removing unnecessary components (current sources, differential amplifiers), the circuit achieves the same protective function with significantly reduced size and complexity.
2Reliability
If a conventional soft-start circuit includes various current sources, switches, an unbalanced differential pair of transistors, and a differential amplifier, then the overshoot of the output voltage can be mitigated, but the manufacturing cost of the soft-start circuit and SoC increases
Solution Approach 1:
The circuit is divided into simple, manufacturable segments (delay circuit, latch, buffer) that use standard, low-cost components. This segmentation reduces manufacturing complexity and cost while maintaining the reliability function of overshoot mitigation.
Solution Approach 2:
By extracting only the essential delay and control functions and removing expensive components like differential amplifiers and unbalanced transistor pairs, the invention reduces manufacturing cost while preserving the core protective function against voltage overshoot.
3Speed
If the reference voltage increases at a significant rate during power-up, then the voltage regulator can quickly reach its operating voltage, but the output voltage experiences overshoot that can damage functional circuits
Solution Approach 1:
The delay circuit generates an enabled signal in advance that is delayed by a predetermined time period. This preliminary delayed signal is stored in the latch and buffered to control the voltage regulator's enabling, ensuring that the regulator starts up gradually rather than immediately, thus preventing overshoot while maintaining quick operation.
Solution Approach 2:
The circuit uses a feedback mechanism where the delayed enable signal controls the voltage regulator's operation. The buffer provides a controlled enable signal that feedback-regulates the startup process, ensuring the voltage increases at a controlled rate that prevents overshoot while maintaining speed.
Data Source
AI summary
A soft-start circuit for a voltage regulator includes a comparator and a delay circuit. The comparator compares an output voltage, that is generated by the voltage regulator, and a reference voltage to generate a comparison signal. Further, the delay circuit receives the reference voltage and a control signal that is outputted based on the comparison signal, and outputs and provides another reference voltage to the voltage regulator. During a start-up of the voltage regulator, the reference voltage outputted by the delay circuit is a delayed version of the reference voltage received by the delay circuit. Thus, the soft-start circuit mitigates an overshoot of the output voltage during the start-up. Further, on completion of the start-up, the reference voltage outputted by the delay circuit is equal to the reference voltage received by the delay circuit.