LDMOS Isolation Structure to Suppress Parasitic SCR Turn-On
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Solution Overview
Problem
In switching regulators, parasitic silicon controlled rectifiers (SCRs) can be inadvertently turned on when the load is in a light load condition, leading to error operations and potential damage to high voltage devices, limiting the safe operation area (SOA) and application scope.
Innovation Solution
A high voltage device with a lateral diffused metal oxide semiconductor (LDMOS) structure and a current limiting device, such as a Schottky barrier diode, is used to suppress the parasitic SCR from being turned on, enhancing the SOA and broadening the application scope by forming specific conductivity regions and isolation structures within the semiconductor layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional high voltage device is used in a switching regulator, then the device can operate under normal load conditions, but the parasitic SCR may be inadvertently turned on under light load conditions, causing error operations and potential device damage
Solution Approach 1:
A current limiting device is introduced as an intermediary component between the high voltage device and the parasitic SCR. This current limiting device actively monitors and restricts the current flowing through the high voltage device, preventing the parasitic SCR from receiving sufficient current to activate. The intermediary device thus mediates between the operational current needs and the SCR activation threshold, ensuring reliable operation across all load conditions.
Solution Approach 2:
The current limiting device implements preliminary anti-action by proactively restricting current flow before the parasitic SCR can be activated. Rather than reacting after SCR activation occurs, the system preemptively limits current to levels below the SCR turn-on threshold, thereby preventing the harmful effect from occurring in the first place. This is achieved through the current limiting device's inherent current restriction capability.
2Adaptability or versatility
If the safe operation area is expanded to include light load conditions, then the application scope is broadened, but the parasitic SCR activation risk increases
Solution Approach 1:
The current limiting device serves as a mediator that enables the system to safely operate in previously unsafe light load conditions. By introducing this intermediary component, the system gains adaptability to handle a broader range of load conditions without incurring the penalty of parasitic SCR activation, thus expanding the application scope while maintaining reliability.
Solution Approach 2:
The current limiting device provides beforehand cushioning by preparing the system in advance for light load conditions that could trigger parasitic SCR activation. The device is pre-configured to limit current flow, creating a protective buffer that cushions the system against the harmful effects of SCR activation during light load operation, thereby enabling broader application scope.
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 prevents parasitic SCR activation, thereby enhancing the safe operation area and expanding the application scope of switching regulators by ensuring reliable operation even under light load conditions.
Implementation Method 1
a current limiting device, which is electrically connected to the second isolation region and which is configured to operably suppress a parasitic silicon controlled rectifier (SCR) from being turned on
Implementation Method 2
part of the body region, which is between the source and a boundary of the body region, and is right below the gate, forms an inversion region which serves as an inversion current channel in an ON operation of the LDMOS device
Implementation Method 3
part of the well between the body region and the drain is a drift region, which serves as adrift current channel in the ON operation of the LDMOS device
Data Source
AI summary
A high voltage device is used as a lower switch in a power stage of a switching regulator. The high voltage device includes at least one lateral diffused metal oxide semiconductor (LDMOS) device, a first isolation region, a second isolation region, a third isolation region, and a current limiting device. The first isolation region is located in a semiconductor layer, and encloses the LDMOS device. The second isolation region has a first conductivity type, and encloses the first isolation region in the semiconductor layer. The third isolation region has a second conductivity type, and encloses the second isolation region in the semiconductor layer. The current limiting device is electrically connected to the second isolation region, and is configured to operably suppress a parasitic silicon controlled rectifier (SCR) from being turned on.