LDO Current Limiting with Precision Sampling and Soft Over-Current Control
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Solution Overview
Problem
Existing low dropout regulators (LDOs) face issues with limited current copy precision and hard shutoff during current limiting, particularly in radio frequency front-end modules where precise over-current protection is required to prevent burnout and ensure gradual power output reduction with increasing load current.
Innovation Solution
A low dropout regulator with over-current protection incorporating a high-precision current sampling circuit and an over-current protection control loop forms a closed feedback system, using a comparator and operational amplifiers to adjust the gate voltage of the power transistor, ensuring precise current limiting without hard shutoff.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional current sampling circuit is used in the LDO, then the device complexity is low, but the current copy precision is limited
Solution Approach 1:
The patent uses a current mirror circuit to copy the reference current and generate a proportional sampling current. The current mirror accurately replicates the reference current through matched transistor pairs, achieving high precision current sampling without complex measurement circuits. This resolves the contradiction by providing precise current copying through the mirror mechanism.
Solution Approach 2:
The patent replaces direct current measurement with a voltage comparison approach. Instead of directly measuring current, the circuit converts current to voltage through resistors and uses operational amplifiers to compare voltages. This substitution of measurement method achieves high precision while maintaining relatively simple circuit structure.
2Reliability
If a conventional over-current protection circuit is used, then the structure is simple, but hard shutoff occurs during current limiting
Solution Approach 1:
The patent implements a feedback mechanism where the operational amplifier continuously monitors the voltage across the current sampling resistor and adjusts the power transistor gate voltage accordingly. When over-current is detected, the feedback loop gradually reduces the gate voltage to limit current, preventing hard shutoff while maintaining reliable over-current protection.
Solution Approach 2:
The protection circuit dynamically adjusts the power transistor gate voltage based on the detected current level. Instead of a fixed threshold that causes abrupt shutoff, the circuit continuously modulates the gate voltage to achieve smooth current limiting. This dynamic control ensures both reliability and operational smoothness.
3Reliability
If over-current protection is added to the LDO, then the reliability of power supply is improved, but the device complexity increases
Solution Approach 1:
The patent integrates multiple functions into existing circuit components. The operational amplifier serves both as an error amplifier for voltage regulation and as a comparator for over-current detection. The current sampling resistor is part of the existing output circuitry. This multi-functionality approach adds over-current protection capability without significantly increasing overall circuit complexity.
Solution Approach 2:
The patent merges the over-current protection function with the existing voltage regulation circuit. The same operational amplifier and feedback network used for voltage control are utilized for current protection. By combining these functions into a unified control mechanism, the patent achieves enhanced reliability while minimizing the increase in device complexity.
Data Source
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AI summary
A low dropout regulator (LDO) with over-current protection, and a chip and an electronic device. The LDO comprises an LDO main circuit (100), a high-precision current sampling circuit (200), and an over-current protection control loop (300), wherein an output end of the LDO main circuit (100) is connected to an input end of the high-precision current sampling circuit (200), an output end of the high-precision current sampling circuit (200) is connected to an input end of the over-current protection control loop (300), and an output end of the over-current protection control loop (300) is connected to both the LDO main circuit (100) and the high-precision current sampling circuit (200), so as to form a closed control loop. When the current of a load exceeds a current-limiting value, the LDO can effectively protect a power transistor (MP0) of the LDO main circuit (100) and the load, and a hard shutoff phenomenon of a system may not occur.