MOSFET Rdson Compensation Circuit for Accurate Current Sensing
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Solution Overview
Problem
Current methods for current sensing in MOSFETs using Rdson are affected by temperature and gate driving voltage variations, leading to inaccuracies, especially at extreme conditions, and do not adequately compensate for nonlinear changes, resulting in unreliable operation and inaccuracy in power converter systems.
Innovation Solution
A compensation device utilizing a linear discrete voltage divider with cascaded switches, employing first and second-order temperature and gate-source voltage coefficients to accurately model and compensate for Rdson variations, providing a stable compensated current and voltage output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If Rdson sensing is used for current sensing, then energy efficiency and cost are improved, but measurement precision deteriorates due to temperature and Vgs variations
Solution Approach 1:
The patent changes the parameters of the compensation circuit by using multiple MOSFETs with different threshold voltages and transconductance parameters. These MOSFETs are configured in parallel with different on-resistances to compensate for the temperature and Vgs variations in the main sensing MOSFET, thereby maintaining measurement precision while preserving energy efficiency.
Solution Approach 2:
The patent introduces compensation MOSFETs as intermediary elements that mediate between the temperature/Vgs variations and the current sensing accuracy. These compensation MOSFETs generate compensating voltages that offset the effects of temperature and gate voltage variations on the main sensing MOSFET, thus improving measurement precision without sacrificing the energy efficiency of Rdson sensing.
2Reliability
If deep triode region MOSFETs are used for compensation, then temperature and Vgs compensation is achieved, but reliability deteriorates at extreme temperatures and voltages
Solution Approach 1:
The patent applies local quality by assigning different roles to different MOSFETs in the circuit. The main MOSFET operates in the linear region for current sensing, while compensation MOSFETs are specifically designed to operate in the deep triode region only under normal conditions. This localized functional assignment allows the system to maintain reliability across extreme conditions while achieving accurate compensation when needed.
Solution Approach 2:
The patent implements dynamic operation by allowing MOSFETs to transition between different operating regions based on temperature and voltage conditions. The compensation circuit dynamically adjusts which MOSFETs are active and in what region they operate, ensuring reliable performance across the full range of operating conditions while maintaining compensation accuracy when required.
3Measurement precision
If previous compensation methods are used, then some temperature compensation is achieved, but measurement precision deteriorates due to unaccounted nonlinear variations
Solution Approach 1:
The patent segments the compensation function into multiple independent MOSFETs, each handling specific aspects of temperature and Vgs compensation. By dividing the compensation task among several devices with different parameters, the circuit achieves accurate nonlinear compensation without requiring a single complex compensation mechanism, thus improving measurement precision while managing device complexity.
Solution Approach 2:
The patent creates a composite compensation structure by combining multiple MOSFETs with different electrical characteristics in parallel. This composite approach allows the compensation circuit to capture nonlinear variations in Rdson across different operating conditions, achieving high measurement precision through the synergistic effect of multiple devices rather than a single complex element.
Data Source
AI summary
A power MOSFET drain-source on resistance (Rdson) compensation device comprises circuitry configured to receive an input signal proportional to a voltage drop across a power MOSFET, a temperature dependent information and a gate-source voltage dependent information. The circuitry includes control logic and a first linear discrete voltage divider, wherein the first linear discrete voltage divider is configured to output a compensated voltage based on an at least one compensating control signal from the control logic that is based on at least one of the temperature dependent information or gate-source voltage dependent information.