LDO Current Sampling Loop for Precise Over-Current Protection
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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 manage power amplifier currents.
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 control loop, using negative feedback to control the LDO main circuit and prevent over-current by adjusting the gate voltage of the power transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an over-current protection circuit is added to the LDO, then the reliability of power supply is improved, but the device complexity increases
Solution Approach 1:
The patent combines the over-current protection function with the existing LDO circuit structure by integrating a control transistor whose gate is connected to the LDO output and whose drain connects to the power transistor gate. This merging approach adds protection functionality while minimizing additional circuit complexity.
Solution Approach 2:
The patent implements a feedback mechanism where the control transistor monitors the LDO output current and automatically adjusts the power transistor gate voltage when over-current is detected. This feedback-based protection improves reliability without requiring complex external control circuits.
2Measurement precision
If a current sampling circuit is used for over-current protection, then the precision of over-current protection is improved, but the device complexity increases
Solution Approach 1:
The patent employs a current sampling circuit that selectively samples only the relevant current portion through a dedicated sampling transistor connected in parallel with the power transistor. This local sampling approach achieves precise over-current detection without requiring complex system-wide current measurement circuits.
Solution Approach 2:
The patent creates a simplified copy of the power transistor's current path through a sampling transistor with proportional dimensions. This current copy allows precise measurement of the power transistor current without interfering with the main current path, achieving accurate protection with minimal complexity.
3Object-generated harmful factors
If the LDO limits the output current during over-current condition, then the harmful effects are reduced, but the productivity decreases
Solution Approach 1:
The patent implements dynamic current limiting where the control transistor gradually adjusts the power transistor gate voltage based on the severity of over-current condition. This dynamic response reduces excessive heat dissipation while maintaining optimal output current during normal operation, balancing protection with productivity.
Data Source
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.