High-Side Switch Current Sensing for Low-Current Wire Breaks
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Solution Overview
Problem
High-side switches in automotive or industrial applications face challenges in accurately detecting output currents in the range of 300 microamps to a few milliamps for wire break detection, as existing sense circuitry is unable to sense these smaller currents effectively.
Innovation Solution
The system includes a first power stage with a power FET and a sense transistor, and a second smaller power stage with a PMOS power FET and sense transistor, which switches to a diode-connected configuration during wire break mode to accurately measure lower output currents, using a comparator to determine if the sense current falls below a wire break threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing sense circuitry is used to detect output current, then the circuit area is smaller, but the measurement precision for currents in the range of 300 microamps to a few milliamps deteriorates
Solution Approach 1:
The patent divides the current detection function into two segments: a first sense circuit for detecting higher currents (above threshold) and a second sense circuit for detecting lower currents (at or below threshold). Each segment is optimized for its specific range, with the second circuit providing high-precision detection for wire break conditions while the first circuit handles normal operation. This segmentation resolves the contradiction by achieving high measurement precision for small currents without requiring a single large-area circuit to handle all ranges.
Solution Approach 2:
The patent introduces a current threshold detection circuit as an intermediary that monitors the output current and controls the switching between the first and second sense circuits. When the current falls below the threshold (indicating potential wire break), the intermediary circuit activates the second sense circuit which is optimized for high-precision low-current detection. This intermediary mechanism enables accurate measurement of small currents without permanently dedicating large circuit area to low-current sensing.
2Adaptability or versatility
If a single sense circuit is designed for high current detection, then the device complexity is lower, but the adaptability to detect both high and low currents deteriorates
Solution Approach 1:
The patent implements a dynamic circuit configuration where the second sense circuit is selectively activated based on the detected current level. During normal high-current operation, only the first sense circuit is active, keeping the system simple. When the current drops below the threshold (wire break condition), the control circuit dynamically activates the second sense circuit to provide accurate low-current detection. This dynamic adaptation enables the system to handle both high and low current ranges effectively without maintaining both circuits continuously active, thus managing complexity while maximizing adaptability.
Data Source
AI summary
In an example, a system includes a first power stage including a first power field effect transistor (FET) and a first sense transistor coupled to the first power FET. The system also includes a second power stage including a second power FET and a second sense transistor coupled to the second power FET, where the second power stage is smaller than the first power stage. The system includes a first switch coupled to a gate and a drain of the first power FET and a second switch coupled to the first power stage and the second power stage. The system also includes a sense amplifier coupled to the second switch, where the first power stage, the second power stage, and the sense amplifier are coupled to a load terminal.