Parallel Power Transistor Current Sensing With Kelvin Averaging
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Solution Overview
Problem
Accurately measuring current through multiple power transistors connected in parallel is challenging due to parasitic resistances and temperature changes, which deteriorate the accuracy of current measurement in semiconductor devices used in battery packs and automotive systems.
Innovation Solution
A semiconductor device design that includes multiple power transistors in parallel, each with a sense source terminal, a Kelvin terminal, and a source terminal, along with a first and second average circuit that generates average voltages from these terminals, and an arithmetic circuit to measure current values, effectively compensating for parasitic resistances and temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single power transistor is used with sense transistors and shunt resistors for current measurement, then current measurement accuracy is improved, but power loss increases due to parasitic resistances
Solution Approach 1:
The invention divides the current measurement function across multiple power transistors connected in parallel, each with its own sense transistor and shunt resistor. By segmenting the total current into multiple parallel paths, the system reduces the current burden on each individual transistor, thereby reducing power loss while maintaining measurement capability through the sense transistors.
Solution Approach 2:
The sense transistors serve dual functions: they enable accurate current measurement through their current-voltage characteristics while also providing a parallel current path that reduces overall power loss. The same sense transistor structure is used both for measurement and for reducing power dissipation in the main power transistor.
2Loss of energy
If multiple power transistors are connected in parallel to reduce power loss, then power loss is reduced, but current measurement accuracy deteriorates due to parasitic resistances and temperature changes
Solution Approach 1:
The invention uses sense transistors connected in parallel with each power transistor to continuously monitor the current-voltage characteristics. By measuring the voltages at sense source terminals and Kelvin terminals and calculating current values from these measurements, the system provides feedback that compensates for variations in parasitic resistances and temperature effects, maintaining measurement accuracy across multiple parallel transistors.
Solution Approach 2:
Sense transistors act as intermediary elements between the main power transistors and the measurement circuitry. These sense transistors have matched current-voltage characteristics that allow them to accurately represent the current flow through the main power transistors while being easier to measure, thus mediating the measurement process and improving accuracy.
3Loss of energy
If multiple power transistors are used in parallel, then power loss is reduced, but device complexity increases due to multiple sense transistors and shunt resistors
Solution Approach 1:
The invention combines multiple power transistors, sense transistors, and shunt resistors into an integrated semiconductor device structure. By merging these components into a single chip or module, the physical complexity is reduced despite the increased number of electrical components, as the integrated structure allows for compact layout and shared fabrication processes.
Data Source
AI summary
A semiconductor device includes m power transistors (m is an integer of 2 or more) coupled in parallel each of which has a sense source terminal, a Kelvin terminal and a source terminal, a first average circuit that connects the first resistor and the second resistor in order between the sense source terminal and the Kelvin terminal and generates first to fourth average voltages and an arithmetic circuit that measures a first current value flowing through the sense source terminal from the first and second average voltages, measures a second current value flowing through the sense source terminal from the third and fourth average voltages and measures a current value flowing through the source terminal from the first to fourth average voltages and the first and second current values.