Inductive Load Current Sensing With Dual MOSFET Path Comparison
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Solution Overview
Problem
Current solutions for measuring current in inductive loads in automotive applications face challenges such as increased impedance due to duplicated measurement resistors, inability to detect faults in power transistors and leakage resistances, and higher likelihood of dispersion losses, while also being costly and complex.
Innovation Solution
The proposed solution involves using two separate current-measuring paths for the high-side and low-side MOSFETs, with sample-and-hold blocks to compare current peaks at specific transition points, and a window comparator to generate a failure signal, reducing the need for redundant resistances and oversizing of power transistors, and allowing detection of faults and leakage resistances without significant performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two separate current-measuring paths are used with duplicated measurement resistors, then functional safety is guaranteed through fault detection, but impedance increases and power losses occur
Solution Approach 1:
The patent merges the two separate current-measuring paths into a single shared measurement resistor Rs. Instead of using duplicated resistors Rs1 and Rs2 in separate paths, the invention combines both measurement functions through one common resistor, thereby reducing total impedance and minimizing power losses while maintaining the ability to detect faults through differential measurement of voltages at different nodes
Solution Approach 2:
The single measurement resistor Rs serves multiple functions simultaneously: it enables current measurement for both high-side and low-side paths, provides fault detection capability through voltage comparison, and reduces overall impedance. The differential voltage measurement technique allows one resistor to fulfill the role previously requiring two separate resistors
2Reliability
If two separate current-measuring paths with duplicated resistors are used, then current measurement redundancy is achieved, but device complexity and cost increase
Solution Approach 1:
The patent reduces circuit complexity by merging duplicated components into a single shared measurement resistor Rs. The simplified circuit topology eliminates redundant resistors and reduces the number of connection nodes, making the device less complex and more cost-effective while preserving measurement redundancy through differential voltage sensing
Solution Approach 2:
Instead of physically duplicating measurement resistors, the invention creates a virtual copy through differential voltage measurement. By measuring voltages at different nodes relative to the same resistor Rs and calculating the difference, the system achieves redundancy without physical duplication of passive components
3Reliability
If measurement resistors are duplicated in separate paths, then fault detection capability is provided, but dispersion losses increase
Solution Approach 1:
The patent combines both fault detection capabilities into a single measurement resistor Rs, eliminating the dispersion losses associated with having two separate resistors Rs1 and Rs2. The differential voltage measurement technique maintains fault detection capability by comparing voltages at different nodes while using only one physical resistor
Data Source
AI summary
A device measures the current in an inductive load using two separate current-measuring paths to detect the current in the inductive load. The inductive load is connected between first and second nodes, and the first node connected to a first voltage. The device includes first and second transistors cascaded together between the first node and a third node that is connected to a second voltage. First and second sense amplifiers measure the current in the inductive load. The first and second sense amplifiers are connected to at least one terminal of the first and second transistors. Two blocks sample and hold signals from the first and second sense amplifiers, which represent, respectively, the currents in the two separate current-measuring paths. The two currents are subtracted in a comparison node for generating an error signal that is compared with a predefined window and if outside the window a failure signal is generated.