Dynamic Start-Up Circuit for LDO Voltage Divider Ratio Stability
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Solution Overview
Problem
Existing electronic circuit start-up processes, such as those for low-dropout (LDO) voltage regulators, face challenges in maintaining a stable voltage divider ratio during the start-up phase due to the impact of feed-forward capacitors, leading to potential output voltage drops and violations of start-up specifications.
Innovation Solution
A dynamic start-up circuit is employed, which includes a feed-forward capacitor across a feedback resistor of a resistive voltage divider, with a start-up comparator monitoring the output voltage and activating switching mechanisms to maintain the voltage divider ratio by disconnecting the feed-forward capacitor during the start-up phase, ensuring a clean and correct output voltage determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a feed-forward capacitor is connected across the feedback resistor during start-up, then the circuit can achieve stable operation under light load conditions, but the voltage divider ratio is impacted and clean start-up specification cannot be met
Solution Approach 1:
The patent applies preliminary action by pre-charging the feed-forward capacitor to the output voltage before the start-up comparator becomes active. This is achieved through a dedicated charge pump circuit that operates during the start-up phase, ensuring the capacitor is ready to prevent output voltage drops without affecting the voltage divider ratio when the comparator begins monitoring.
Solution Approach 2:
The patent segments the capacitor's function by using two separate capacitors: a feed-forward capacitor for preventing output voltage drops and a compensation capacitor for frequency compensation. This segmentation allows each capacitor to perform its specific function without interfering with the voltage divider ratio, resolving the contradiction between stability and precision.
2Reliability
If a feed-forward capacitor is used in parallel to the feedback resistor, then the circuit can prevent output voltage drops, but the start-up specification may be violated due to impacted voltage divider ratio
Solution Approach 1:
The charge pump circuit performs preliminary action by charging the feed-forward capacitor to the correct voltage level before the start-up comparator becomes active. This ensures the capacitor is ready to prevent output voltage drops without causing start-up specification violations.
Solution Approach 2:
The patent introduces a charge pump circuit as an intermediary mechanism that manages the feed-forward capacitor's charging process. This intermediary ensures the capacitor is charged to the correct voltage without affecting the voltage divider ratio, thereby maintaining both output voltage stability and start-up specification compliance.
3Stability of the object's composition
If the feed-forward capacitor remains connected during the entire operation, then the circuit maintains stability, but the voltage divider ratio cannot be maintained constant during start-up
Solution Approach 1:
The patent applies dynamics by making the feed-forward capacitor's connection dynamic rather than static. The capacitor is connected during normal operation to maintain stability but is isolated during start-up when the charge pump charges it, allowing the voltage divider ratio to remain constant when required.
Solution Approach 2:
The charge pump performs preliminary charging of the feed-forward capacitor before it is connected to the feedback network. This preliminary action ensures the capacitor is charged to the correct voltage, allowing it to be connected without affecting the voltage divider ratio while still providing stability during normal operation.
Data Source
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AI summary
Circuits and methods to maintain a resistive voltage divider ratio during start-up of an electronic circuit comprising a feed-forward capacitor across a feedback resistor using a dynamic start-up circuit are disclosed as e.g. a LDO or an amplifier. In a preferred embodiment of the disclosure is applied to an LDO. Modification of the resistive voltage divider ratio caused by the feed-forward capacitor during start-up is prevented while the voltage level of a voltage access point of the voltage divider on the feed-forward capacitor is maintained. Embodiments of the disclosure presented comprise using a start-up buffer or a start-up capacitor during the start-up phase.