Common-Drain Vertical FET Temperature Sensing Without Drain Access
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Solution Overview
Problem
Power delivery and control in USB-enabled devices face challenges in achieving accurate power levels, overvoltage, overcurrent, and overheating protections, particularly with vertical FETs, due to difficulties in temperature sensing and process technology changes required for accessing the common drain node.
Innovation Solution
Implementing temperature sensing techniques for common-drain dual power FET devices with vertical FETs, using a scaled P-N junction diode coupled to the common drain node, and employing replica FETs for voltage measurement, allowing direct access to the drain node without additional process changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature sensing is implemented in vertical FETs by accessing the common drain node, then temperature measurement precision is improved, but device complexity and manufacturing difficulty increase due to required process technology changes
Solution Approach 1:
The patent uses replica FETs that are identical copies of the power FETs but configured for sensing purposes. These replica FETs include P-N junctions at their drains that replicate the temperature characteristics of the power FETs, allowing temperature measurement without directly accessing the common drain node of the power FETs themselves.
Solution Approach 2:
The patent introduces replica FETs as intermediary structures that mediate between the power FETs and the temperature sensing circuitry. The replica FETs transfer temperature information from the power FETs to accessible nodes through voltage measurements, eliminating the need for direct access to the common drain node.
2Adaptability or versatility
If process technology changes are made to access the common drain node for temperature sensing, then temperature sensing capability is improved, but ease of manufacture deteriorates
Solution Approach 1:
The replica FETs serve multiple functions: they act as power FETs during normal operation and as temperature sensors when needed. This multi-functionality eliminates the need for separate temperature sensing structures and avoids additional process technology changes, as the same FET fabrication process creates both power and sensing functionality.
Solution Approach 2:
By creating replica FETs that are copies of the power FETs using the same fabrication process, the patent enables temperature sensing capability without requiring any changes to the existing process technology. The replicas are manufactured using identical processes, ensuring ease of manufacture while providing the needed sensing capability.
3Measurement precision
If replica FETs are used for voltage measurement at the common drain node, then temperature sensing accuracy is improved, but device complexity increases due to additional FET structures
Solution Approach 1:
The patent merges the power FET and temperature sensing FET into a single integrated structure where the replica FET is formed in the same device. The common drain node serves both as the connection point for the power FET and as the sensing point for the replica FET, combining power delivery and temperature sensing functions in one unified structure.
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
Enhances power efficiency and current handling capabilities while providing accurate temperature sensing and protection against overheating, compatible with USB-PD specifications and suitable for integration in electronic devices.
Implementation Method 1
a scaled P-N junction diode coupled to the common drain node
Implementation Method 2
employing replica FETs for voltage measurement
Data Source
AI summary
Techniques for temperature sensing in power FET switches are described. An example power field effect transistor (FET) device includes back-to-back power FETs coupled in series between a first power terminal and a second power terminal and connected to a common drain node. The power FET device also includes a temperature sense diode comprising a cathode coupled to the common drain node. A temperature sense circuit coupled to the power FET device is configured to determine a temperature of the first power FET and the second power FET based on a voltage drop across the temperature sense diode. The temperature sense circuit can include a voltage averaging circuit configured to sense a first voltage at the first power terminal, sense a second voltage at the second power terminal, and average the first voltage and the second voltage to generate a drain voltage representative of a voltage of the common drain node.