MOSFET Rdson Compensation for Temperature and VGS Variations
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Solution Overview
Problem
Current sensing in MOSFETs using Rdson is affected by temperature and gate driving voltage (VGS) variations, leading to accuracy issues, and existing compensation methods require complex digital circuitry and memory for look-up tables that are not adaptable to all MOSFET types.
Innovation Solution
An analog circuitry-based compensation device that utilizes the linear resistance characteristic of MOSFETs in the deep triode region to compensate for Rdson variations due to temperature and VGS changes, eliminating the need for digital processing and look-up tables by using trans-conductance amplifiers and carefully selected MOSFET configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital processing based on Look-up table is used for temperature compensation, then temperature compensation accuracy is improved, but device complexity and memory requirements increase
Solution Approach 1:
The patent replaces the digital processing system (microcontroller with Look-up table) with an analog circuit system that performs temperature compensation through continuous voltage generation and comparison. The analog circuit uses transistors, resistors, and operational amplifiers to generate compensation voltages that directly counteract temperature drift effects, eliminating the need for digital computation and memory storage.
Solution Approach 2:
The compensation circuit automatically adjusts the compensation voltage based on the actual temperature conditions without external intervention. The circuit continuously monitors the sensor output and dynamically generates the appropriate compensation signal through its internal analog components, making the system self-regulating and adaptive to temperature changes.
2Measurement precision
If Look-up table method is used for compensation, then temperature compensation is achieved, but adaptability to different MOSFET types is limited
Solution Approach 1:
The patent designs a universal compensation circuit that can accommodate multiple MOSFET types without requiring type-specific configuration. The analog circuit uses generic components and topology that work across different MOSFET technologies (DMOS, VMOS, LDMOS, etc.) by relying on fundamental electrical characteristics common to all MOSFETs, such as temperature-dependent resistance changes and voltage-current relationships.
Solution Approach 2:
The compensation circuit dynamically adjusts its operating parameters (voltages, currents, resistance values) based on real-time temperature conditions rather than relying on pre-stored fixed values. This continuous parameter adjustment allows the circuit to adapt to different MOSFET types by automatically finding the appropriate compensation levels for each device.
3Measurement precision
If discrete resistor is used for current sensing, then current sensing accuracy is improved, but power loss and cost increase
Solution Approach 1:
The patent extracts the current sensing function from a separate discrete resistor and integrates it into the MOSFET's inherent on-resistance (Rds(on)). By utilizing the MOSFET's own resistance when in the on-state, the system eliminates the need for an additional sensing resistor, thereby removing the associated power loss and cost while maintaining sensing capability through voltage measurement across the MOSFET terminals.
Data Source
AI summary
A power MOSFET Rdson compensation device comprising analog circuitry receives an input signal proportional to a voltage drop across a power MOSFET, one or more base reference voltages, a voltage-dependent reference voltage, and a temperature-dependent reference voltage. The analog circuitry is configured to produce an output current corresponding to the input signal with compensation for voltage and temperature variation of a drain-source on resistance of the power MOSFET.