eFuse Current Limiting for Digital Isolator Overheat Protection
Solution Overview
Problem
Existing protection devices for temperature-sensitive electrical components, such as digital isolators, face challenges in accurately and quickly measuring junction temperature, leading to potential device failure when maximum thresholds are exceeded, compromising isolation integrity.
Innovation Solution
The implementation of an electronic fuse (eFuse) arranged in series with the digital isolator, which interrupts current based on temperature dependency characteristics, using an internal sense resistor and an electronic switch to limit or remove current, with an optional external current setting resistor and auto-retry functionality to prevent overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct temperature measurement of the component is used, then temperature monitoring is achieved, but accurate and quick temperature reading is difficult to obtain
Solution Approach 1:
The patent introduces an intermediary thermal sensor that is thermally coupled to the power dissipating component. This intermediary sensor indirectly measures the component's temperature through thermal conduction, allowing accurate temperature monitoring without direct contact with the component, thus resolving the contradiction between measurement accuracy and response time.
Solution Approach 2:
The patent replaces direct mechanical/physical temperature measurement of the component with an electrical measurement system. The thermal sensor converts temperature information into an electrical signal that can be quickly processed by the control circuit, substituting difficult direct temperature reading with easier electrical parameter measurement.
2Power
If a current limiting resistor is used, then current limiting is achieved, but voltage drop causes additional power dissipation
Solution Approach 1:
The patent uses a dynamic control system with a control circuit that actively adjusts the current limiting resistance based on real-time temperature feedback from the thermal sensor. Unlike a fixed resistor, this dynamic system only applies current limiting when temperature thresholds are exceeded, minimizing unnecessary power dissipation while maintaining current limiting capability when needed.
Solution Approach 2:
The patent implements a feedback control loop where the thermal sensor continuously monitors temperature and feeds this information to the control circuit. The control circuit then adjusts the current limiting resistance accordingly, creating a closed-loop system that optimizes power dissipation by applying current limiting only when thermally necessary.
3Reliability
If an external low-dropout regulator is used, then overcurrent limiting is achieved for a period of time, but current limit cannot be controlled accurately and internal voltage drop is significantly larger
Solution Approach 1:
The patent employs feedback control where the control circuit receives temperature information from the thermal sensor and uses this feedback to precisely control the current limiting resistance. This feedback mechanism enables accurate control of the current limit threshold, unlike external regulators that operate open-loop with fixed characteristics.
Solution Approach 2:
The patent dynamically changes the resistance parameter of the current limiting element based on temperature conditions. The control circuit adjusts the resistance value to achieve precise current limiting at specific temperature thresholds, allowing accurate control of the current limit parameter rather than relying on fixed regulator characteristics.
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 eFuse provides fast, reliable, and accurate current interruption with minimal voltage drop, ensuring the digital isolator's integrity by preventing overheating and maintaining isolation integrity during fault conditions, thus extending the component's lifespan and ensuring system safety.
Implementation Method 1
the eFuse is configured to interrupt a current on a power supply rail of the digital isolator based upon temperature dependency characteristics of the digital isolator
Implementation Method 2
A sense resistor may be used to measure the current in the system
Implementation Method 3
In the eFuse, an integrated electronic switch such as a field effect transistor (FET) or a bipolar junction transistor is provided to limit or remove current applied to the electrical component
Data Source
AI summary
Digital isolator devices, and many other devices, have a maximum device junction temperature, which, if exceeded, may cause device failure and the integrity of the isolation is no longer guaranteed. The use of an electronic fuse, eFuse, arranged in series with the digital isolator, provides a protection scheme for the digital isolator in which current is limited by the eFuse when it is determined that the supply current of the digital isolator exceeds a predetermined threshold that would the cause junction temperature to increase above an absolute maximum rating. As such, the integrity of the digital isolator is preserved in the event of a system fault.