Fail-Open Isolator Using Clamp-FET EOS Protection
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Solution Overview
Problem
Existing isolators face challenges in preventing electrical overstress (EOS) events from damaging systems by failing to effectively manage over-voltage and over-current conditions across different voltage domains, particularly when the current is not sufficient to blow traditional fuses, leading to potential damage to circuit components.
Innovation Solution
Incorporating self-heating, meandering fuses and a control circuit that turns a clamp-FET transistor on to reduce voltage and current to safe levels, either by operating in saturation to blow the fuse if current is high enough or in linear mode to maintain safety if current is not, while introducing resistance to manage voltage and current during EOS events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional fuses are used in isolators, then they provide basic over-current protection, but they fail to protect against EOS events when the current is not sufficient to blow the fuse
Solution Approach 1:
The patent changes the operational parameters of the fuse by introducing a clamp-FET that actively controls voltage and current levels. The clamp-FET operates in different regions (linear or saturation) to dynamically adjust the electrical parameters, enabling the fuse to respond to EOS events at lower current levels than traditional fuses would require.
Solution Approach 2:
The clamp-FET acts as an intermediary device between the voltage source and the fuse. It mediates the electrical stress by clamping the voltage and limiting current, thereby protecting the fuse and downstream circuitry from damaging EOS events while allowing the fuse to operate effectively at lower current thresholds.
2Reliability
If the clamp-FET operates in saturation region, then it enables the fuse to blow at lower current levels, but it requires sufficient current to be present
Solution Approach 1:
The clamp-FET dynamically switches between linear and saturation operating regions based on the severity of the EOS event and current conditions. This dynamic operation allows the device to adapt its protection strategy: using saturation mode when sufficient current is present to blow the fuse, and linear mode when current is insufficient but voltage clamping is still needed.
Solution Approach 2:
The control circuit monitors electrical parameters and changes the operating state of the clamp-FET accordingly. By adjusting the gate voltage and operating region of the FET, the system changes its electrical characteristics to match the threat level, enabling effective protection across a wide range of current conditions.
3Object-affected harmful factors
If the clamp-FET operates in linear region, then it maintains safety when current is not sufficient to blow the fuse, but it does not enable the fuse to blow
Solution Approach 1:
The system dynamically transitions between linear and saturation modes based on real-time monitoring of current and voltage levels. When current rises above the trip threshold, the clamp-FET switches from linear to saturation region, enabling the fuse to blow. This dynamic switching ensures both safety under normal conditions and effective protection activation when needed.
Solution Approach 2:
The control circuit implements feedback by continuously monitoring the current through the fuse and the voltage across the clamp-FET. Based on this feedback, the control circuit adjusts the gate drive to the clamp-FET, transitioning it between operating regions to achieve the desired protection outcome - either maintaining safety in linear mode or enabling fuse blow in saturation mode.
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
Effectively prevents damage from EOS events by ensuring the self-heating fuse blows at a lower current level than traditional fuses, and the clamp-FET reduces power dissipation and protects components by managing voltage and current within safe limits, even when the current is not sufficient to blow the fuse.
Implementation Method 1
a fuse, the fuse being a self-heating, serpentine fuse
Implementation Method 2
the clamp-FET reduces power dissipation and protects components by managing voltage and current within safe limits
Data Source
AI summary
A device includes first and second device terminals, a fuse, a first circuit, a first transistor, and a control circuit. The fuse terminal couples to the first device terminal. The first circuit couples to the second fuse terminal. The second fuse terminal has a first voltage. The first transistor has a first control input and first and second current terminals. The first current terminal couples to the second fuse terminal, and the second current terminal couples to the second device terminal. The control circuit: turns “on” the first transistor into a saturation region if the first voltage exceeds a threshold and a current through the fuse exceeds a trip threshold current of the fuse; and turns “on” the first transistor into a linear region if the first voltage exceeds a threshold and a current through the fuse is below the trip threshold current of the fuse.