Load Switch Isolation Ring Layout to Prevent Latch-Up
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Solution Overview
Problem
Existing load switches are prone to latch-up, a highly undesirable operating condition caused by parasitic transistors turning on inadvertently, leading to excessive power dissipation and potential damage due to large leakage currents.
Innovation Solution
A latch-up free load switch design incorporating a pair of back-to-back connected transistors with a floating isolation ring and Schottky diodes to prevent positive feedback and current buildup, using a Schottky diode between the substrate and isolation ring to interrupt current flow and a second Schottky diode to clamp voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If back-to-back connected transistors are used to achieve bidirectional current blocking, then the load switch can connect or disconnect the load to the power supply, but parasitic transistors can be inadvertently turned on causing latch-up
Solution Approach 1:
A floating isolation ring is introduced as an intermediary structure between the back-to-back connected transistors. This isolation ring acts as a mediator that physically separates and electrically isolates the parasitic PNP and NPN transistors, preventing the formation of a low-impedance latch-up path while maintaining the bidirectional current blocking function of the load switch.
Solution Approach 2:
The device structure is segmented into distinct regions: the floating isolation ring divides the substrate into isolated zones, separating the parasitic transistor paths. This segmentation interrupts the positive feedback loop between parasitic transistors, allowing the load switch to maintain bidirectional blocking capability without suffering from latch-up conditions.
2Device complexity
If parasitic transistors are present in the load switch structure, then the back-to-back transistor configuration can be implemented, but excessive power dissipation occurs due to large leakage current
Solution Approach 1:
The floating isolation ring serves as an intermediary that blocks leakage current paths between parasitic transistors. By introducing this isolated conductive region, the patent prevents direct current flow between opposite polarity regions, thereby reducing power dissipation while preserving the necessary transistor configuration for load switching operation.
3Reliability
If a floating isolation ring is introduced to prevent latch-up, then parasitic transistor activation is reduced, but the device structure becomes more complex
Solution Approach 1:
The floating isolation ring performs multiple functions simultaneously: it provides electrical isolation between parasitic transistors, maintains proper biasing conditions, reduces leakage current paths, and preserves the bidirectional blocking capability. This multi-functionality reduces the need for additional separate structures, thereby limiting the increase in device complexity while achieving comprehensive latch-up prevention.
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
Prevents latch-up by interrupting positive feedback in the thyristor structure, thereby protecting the load switch from excessive current and heat generation, ensuring reliable operation even under negative voltage conditions.
Implementation Method 1
a first Schottky diode connected between the substrate and the isolation ring
Data Source
AI summary
An apparatus includes a first drain/source region and a second drain/source region surrounded by an isolation ring formed over a substrate, the isolation ring formed being configured to be floating, and a first diode connected between the substrate and the isolation ring, wherein the first diode is a Schottky diode.