High-Voltage Load Switch Isolation Ring for MOSFET Latch-Up Prevention
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Solution Overview
Problem
MOSFET devices in load switches are prone to latch-up due to parasitic transistors forming a thyristor, leading to excessive power dissipation and potential damage when one of the parasitic transistors is inadvertently turned on.
Innovation Solution
A load switch design incorporating a pair of back-to-back connected transistors with a floating isolation ring and Schottky diodes to prevent latch-up, using a first Schottky diode to interrupt positive feedback and a second Schottky diode to clamp voltage fluctuations, thereby preventing excessive current and heat generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If back-to-back connected transistors are used to achieve bidirectional current blocking, then the load switch can disconnect the load from the power supply in both directions, but parasitic transistors form a thyristor that can inadvertently turn 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 disrupts the parasitic thyristor feedback path, preventing latch-up while maintaining the bidirectional current blocking capability of the load switch
Solution Approach 2:
The load switch structure is segmented into distinct regions including the floating isolation ring that separates the parasitic NPN and PNP transistors. This segmentation breaks the continuous feedback path of the parasitic thyristor, eliminating latch-up conditions while preserving the functional integrity of the bidirectional switch
2Device complexity
If parasitic transistors are present in the load switch structure, then the device can be simplified, but excessive power dissipation occurs when latch-up happens
Solution Approach 1:
The parasitic transistors that would normally create harmful latch-up conditions are reconfigured through the floating isolation ring structure. The isolation ring converts the potentially harmful parasitic feedback path into a benign configuration where the parasitic transistors cannot sustain latch-up, effectively turning the harmful effect into a non-threatening presence
Solution Approach 2:
The floating isolation ring provides beforehand protection by preemptively disrupting the parasitic thyristor feedback path before latch-up can occur. This preventive structure cushions against the potential energy dissipation damage by eliminating the latch-up condition in advance
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 design effectively prevents latch-up by bypassing current through the parasitic diodes, maintaining stable operation and protecting the circuit from damage even under extreme voltage conditions.
Implementation Method 1
a first Schottky diode connected between the substrate and the isolation ring
Implementation Method 2
an isolation ring formed over a substrate, the isolation ring being configured to be floating
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.