Power Switch Fault Detection Using Parallel FET Segmentation
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Solution Overview
Problem
Advanced driver-assistance systems (ADAS) and automated driving (AD) systems require reliable fault detection in power switch field-effect transistors (FETs to ensure safe operation, as faults like shorted or stuck-open current paths can compromise system functionality.
Innovation Solution
A method and apparatus that determine the drain-source voltage difference between two sets of parallel connected field-effect transistors in a current path, comparing this difference to tolerance and stuck-open thresholds to identify compromised transistors, using differential amplifiers and a processor to deactivate faulty paths and maintain system safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional single FET power switch design is used, then device complexity is low, but reliability is insufficient for ADAS/AD systems
Solution Approach 1:
The power switch is divided into multiple parallel-connected FETs (first set and second set) instead of using a single FET. This segmentation allows the system to tolerate individual FET failures while maintaining overall functionality, thereby improving reliability without requiring complete system failure upon single component failure.
Solution Approach 2:
Different sets of parallel FETs are configured with different body diode orientations (first set with cathodes toward current path, second set with anodes toward current path). This local quality differentiation enables the system to detect and identify specific failure modes in different FET sets, enhancing both reliability and diagnostic capability.
2Reliability
If fault detection capability is added to power switches, then reliability improves, but device complexity increases
Solution Approach 1:
The fault detection mechanism utilizes the existing body diodes of the parallel FETs themselves as sensing elements. By monitoring voltage drops across these inherent diodes during reverse current flow, the system achieves self-diagnosis without requiring external sensing components, thus improving reliability while minimizing added complexity.
Solution Approach 2:
The system continuously monitors voltage drops across the body diodes of parallel FETs and compares them against expected values. This feedback mechanism enables real-time detection of FET failures (stuck-open or stuck-closed conditions), allowing the control system to respond appropriately and maintain reliable operation.
3Reliability
If multiple parallel FETs are used, then reliability improves, but difficulty of detecting and measuring faults increases
Solution Approach 1:
The body diodes of FETs in different parallel sets are oriented in opposite directions relative to the current path. This creates distinct electrical characteristics for each set, enabling the monitoring circuit to differentiate between failures in the first set versus failures in the second set, thereby simplifying fault identification despite the increased number of components.
Data Source
AI summary
A power switch fault detector detects faults in the current paths of power switches. A first operational amplifier detects a drain-source voltage of a first set of parallel connected field-effect transistors in a current path. A second operational amplifier detects a drain-source voltage of a second set of parallel connected field-effect transistors in the current path. A hardware or software processor is configured to compare a difference in magnitude of the drain-source voltages to a threshold voltage to determine whether a field-effect transistor of one of the first set or second set is compromised. The current path is isolated and one of the first set or second set of field-effect transistors is deactivated to determine whether a field-effect transistor of the first set or second set is stuck-open or shorted.