Isolation Architecture with Floating Substrates for ESD Protection
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Solution Overview
Problem
Existing isolated circuits with large isolation voltage ratings are vulnerable to damage from electrostatic discharge (ESD) transients, especially when subjected to repeated discharges, as the isolating communication element often has a lower ESD rating than the interface pins and accumulates charge with each strike.
Innovation Solution
A two-die isolation architecture with high-voltage isolation tubs and floating substrates, where each die has an isolation tub rated for 150V, providing robust ESD protection by using a voltage clamp set by the breakdown voltage of the tub-substrate junction, eliminating snapback and allowing significant voltage offset between interfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If an isolating communication element is used to provide electrical isolation between interfaces, then voltage offset tolerance is improved, but ESD protection capability deteriorates
Solution Approach 1:
A dedicated ESD protection circuit is introduced as an intermediary component between the isolating communication element and the interfaces. This mediator captures and dissipates ESD transient energy through controlled breakdown and clamping mechanisms, preventing the isolating communication element from being directly exposed to high-voltage ESD strikes while maintaining its voltage offset tolerance capability.
Solution Approach 2:
The ESD protection circuit is configured to activate before the isolating communication element can be damaged by ESD transients. The protection circuit includes components designed to break down at predetermined voltage thresholds, creating a cushioning effect that absorbs ESD energy in advance and prevents it from reaching the more vulnerable isolating communication element.
2Stress or pressure
If the isolating communication element is designed to tolerate high voltage, then isolation voltage rating is improved, but ESD robustness deteriorates
Solution Approach 1:
Different parts of the circuit are assigned different voltage handling characteristics. The isolating communication element is optimized for voltage offset tolerance with a moderate voltage rating, while the ESD protection circuit is specifically designed with components rated for high-voltage ESD transients. This local differentiation allows each component to operate in its optimal performance range without compromising overall system robustness.
Solution Approach 2:
The ESD protection circuit employs a breakdown diode that creates a controlled copy or model of the ESD transient path, allowing the transient energy to be safely redirected through a dedicated protection pathway rather than forcing the isolating communication element to handle the full ESD stress.
3Reliability
If the isolating communication element handles repeated ESD discharges, then ESD rating is improved, but cumulative damage risk increases
Solution Approach 1:
The ESD protection circuit is designed to discard harmful ESD energy through controlled breakdown and clamping actions. Each ESD event is handled independently, with the protection circuit resetting to its original state after dissipating the transient energy. This prevents cumulative damage by ensuring that each ESD strike is contained and neutralized without leaving residual stress or degradation in the isolating communication element.
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 effectively protects against ESD transients larger than the isolating communication element's rating, enabling a large offset voltage and handling significant energy during EOS events without damaging the circuit, while being compatible with standard IC process technologies and allowing bidirectional buffering.
Implementation Method 1
a voltage rating of the signaling and electrical isolation is defined by a voltage clamp set by a breakdown voltage
Data Source
AI summary
The subject technology provides for an architecture that isolates two interfaces of a circuit with an isolating communication element while also protecting against overstress transients such as electro-static discharge (ESD) and other electrical overstress (EOS) transients across the isolating communication element that can be significantly larger than the ESD rating of the isolating communication element, and/or that may be repeated in succession. The subject technology provides isolation using a two die implementation with an isolation interface including an isolation tub in each die, or a single die containing both isolation tubs in the die. The two dice include respective substrates that are connected together and float with respect to any signal or ground. The isolation enables a large offset voltage on the order of hundreds of volts to exist between the sides. Being relatively large, each isolation tub can handle a significant amount of energy.