MOSFET Assembly Current Sensing for Accurate Overcurrent Detection
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Solution Overview
Problem
Existing current sensing power MOSFETs face challenges in accurately detecting overcurrent conditions due to high current mirror ratios and sensitivity to noise, leading to delayed detection and complex circuitry requirements.
Innovation Solution
A semiconductor assembly with a current sense unit that measures sense current by resistive shunt or magnetic field sensing, allowing for a higher fraction of load current to be tapped as sense current, thereby improving detection accuracy and reducing noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high current mirror ratio is used in typical current sensing power MOSFETs, then the sense current is reduced to a measurable level, but the detection accuracy deteriorates and noise sensitivity increases
Solution Approach 1:
The invention extracts the current sensing function from the power MOSFET itself by using a separate current sensing element connected in parallel. This separation allows the sensing element to carry a higher fraction of the sense current (reducing the current mirror ratio effect) while the power MOSFET continues its switching function, thereby improving detection accuracy and reducing noise sensitivity.
Solution Approach 2:
The patent introduces an intermediary current sensing element that acts as a mediator between the power MOSFET and the measurement circuit. This sensing element provides a direct measurement path for the load current, bypassing the need for high current mirror ratios and reducing the impact of noise on the measurement.
2Measurement precision
If separate sense pins and additional circuitry are used for current sensing, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The invention merges the current sensing function with the existing parallel structure of power MOSFETs by adding a current sensing element that connects to the same source and drain structures. This integration approach enables current sensing without requiring separate sense pins or additional complex circuitry, as the sensing element utilizes the existing electrical paths.
3Reliability
If the sense current fraction is increased to improve detection accuracy, then overcurrent detection reliability is improved, but the available sense current for measurement decreases due to current mirror ratio constraints
Solution Approach 1:
Instead of using a high current mirror ratio to reduce sense current to measurable levels (conventional approach), the invention inverts the approach by using a low current mirror ratio and allowing the sensing element to carry a higher fraction of the sense current. This inversion improves both detection reliability and measurement precision simultaneously.
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
The solution enables reliable and efficient overcurrent detection with minimal additional circuitry, distinguishing between critical overload conditions and transient events, and maintaining precise dynamic response to load current changes.
Implementation Method 1
measures sense current by resistive shunt or magnetic field sensing
Implementation Method 2
measures sense current by resistive shunt or magnetic field sensing
Data Source
Figure 1A~1B
Figure 2~3
Figure 4~5
AI summary
A semiconductor assembly (400) includes a semiconductor switching device (100), a conductive load base structure (422), and a current sense unit (200). The semiconductor switching device (100) includes a drain structure (121) and one or more array units (AU), wherein each array unit (AU) includes a load pad (122) and a plurality of transistor cells (TC) electrically connected in parallel between the load pad (122) of the array unit (AU) and the drain structure (121). The current sense unit (200) is electrically connected between a first one of the load pads (122-1) and the load base structure (422).