LDO Regulator Over-Current Protection Using Segmented PMOS Transistors
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Solution Overview
Problem
Conventional Low Drop-Out (LDO) regulators experience increased equivalent impedance and power waste due to the series connection of the sensing resistor and transistor, leading to decreased efficiency and increased temperature rise.
Innovation Solution
The LDO regulator design incorporates two PMOS transistors with different channel aspect ratios, where the sensing resistor is connected in series with a transistor having a smaller channel aspect ratio, allowing for independent control of sensing and loading currents, thereby reducing the equivalent resistance and power waste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sensing resistor is connected in series with the transistor to implement over-current protection, then the current limit function is achieved, but the equivalent impedance increases and power waste increases
Solution Approach 1:
The patent divides the single transistor into two parallel transistors: a first transistor for current sensing with a larger channel aspect ratio, and a second transistor for power delivery with a smaller channel aspect ratio. This segmentation allows the sensing function to be separated from the power transmission function, reducing the impact on overall system efficiency while maintaining over-current protection capability.
Solution Approach 2:
The patent applies different channel aspect ratios to different transistors based on their specific functions. The first transistor has a larger channel aspect ratio optimized for sensing accuracy, while the second transistor has a smaller channel aspect ratio optimized for power delivery with minimal voltage drop. This local optimization resolves the contradiction between sensing requirements and power efficiency.
2Measurement precision
If the sensing resistor is connected in series with the transistor, then the current sensing function is achieved, but the minimal voltage difference between input and output increases
Solution Approach 1:
The patent segments the current path into two parallel branches: one through the first transistor dedicated to sensing, and another through the second transistor for power delivery. This segmentation allows the sensing resistor to be placed in series with only the first transistor, isolating its voltage drop from the main power path and thus reducing the minimal voltage difference requirement for the LDO regulator.
Solution Approach 2:
The first transistor acts as an intermediary element that carries the sensing current through the sensing resistor without requiring the full power transmission capability. This intermediary structure allows accurate current sensing while minimizing the impact on the voltage difference between input and output, as the sensing path is electrically separated from the main power path.
3Reliability
If the sensing resistor is connected in series with the transistor, then the over-current protection is achieved, but the efficiency of the LDO regulator decreases
Solution Approach 1:
The patent segments the transistor function into two parallel paths: a sensing path through the first transistor with larger channel aspect ratio, and a power delivery path through the second transistor with smaller channel aspect ratio. This segmentation enables over-current protection through the sensing path while maintaining high efficiency in the power delivery path, thus resolving the contradiction between protection reliability and regulator efficiency.
Solution Approach 2:
The patent optimizes each transistor's channel aspect ratio according to its specific function: the first transistor uses a larger aspect ratio for precise sensing, while the second transistor uses a smaller aspect ratio for efficient power delivery. This local quality optimization ensures that the sensing function does not degrade the overall efficiency of the LDO regulator.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces power waste and temperature rise, enhancing the efficiency of the LDO regulator by minimizing the impact of the sensing resistor on the input to output voltage difference.
Implementation Method 1
The sensing resistor is coupled to an input voltage source. The sensing resistor is serially connected with a second transistor
Implementation Method 2
The comparator comprises a positive input end for receiving a reference voltage, a negative input end coupled to the sensing resistor for receiving a sensing voltage, and an output end for outputting a current limit control signal according to signals received on the positive and negative input ends of the comparator
Implementation Method 3
The error amplifier comprises a positive input end for receiving the feedback voltage, a negative input end for receiving a reference voltage, and an output end for outputting the current control signal according to the signal received on the positive and negative input ends of the error amplifier
Data Source
AI summary
An LDO with over-current protection includes a first and a second P-type transistor, a sensing resistor, a comparator, and an error amplifier. The channel aspect ratio of the first P-type transistor is much higher than that of the second P-type transistor. The first P-type transistor generates output voltage source according to input voltage source and current control signal. The sensing resistor is coupled among the input voltage source, the second P-type transistor, and the comparator, providing a sensing voltage. The comparator generates a current limiting signal according to first reference voltage and the sensing voltage. When the current limiting signal enables the error amplifier, the error amplifier adjusts voltage of the current control signal according to second reference voltage and voltage divided from the output voltage source; when the current limiting signal disables the error amplifier, voltage of the current control signal is not adjusted.