VDS Short-Circuit Protection With NTC Temperature Compensation
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Solution Overview
Problem
VDS-based current sensing in short circuit protection circuits is inaccurate due to the temperature-dependent variation of the on-resistance (RDSON) of field effect transistors (FETs), leading to inconsistent short circuit current detection across temperature ranges, and resistor-based sensing is costly and power-consuming.
Innovation Solution
Incorporating a negative temperature coefficient (NTC) resistor to compensate for RDSON variations by generating a temperature-dependent offset voltage that adjusts the short circuit protection threshold, using a VDS-sensing overcurrent protection circuit with dual resistor settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If VDS-based current sensing is used, then cost and power consumption are reduced, but measurement precision deteriorates due to temperature-dependent on-resistance variation
Solution Approach 1:
An NTC resistor is introduced as an intermediary component to compensate for the temperature-dependent on-resistance variation of the FET. The NTC resistor's negative temperature coefficient characteristics counterbalance the positive temperature coefficient of the FET's on-resistance, thereby maintaining accurate current sensing across temperature ranges without requiring complex external resistor networks
Solution Approach 2:
The invention changes the electrical parameters of the sensing circuit by incorporating an NTC resistor with negative temperature coefficient to offset the positive temperature coefficient of the FET's on-resistance. This parameter change enables the circuit to maintain stable current sensing accuracy across varying temperatures while keeping the overall device complexity low
2Measurement precision
If resistor-based current sensing is used, then measurement precision is improved, but cost and power consumption increase
Solution Approach 1:
The NTC resistor serves as a mediator that enables the VDS-based sensing method to achieve accuracy comparable to resistor-based sensing. By compensating for temperature effects, the NTC resistor allows the circuit to use the lower-power VDS sensing approach while maintaining high measurement precision
Solution Approach 2:
The invention substitutes the traditional resistor-based current sensing mechanism with a VDS-based sensing mechanism enhanced by NTC temperature compensation. This substitution reduces power consumption while maintaining measurement precision through the temperature-compensated voltage drop across the FET
3Measurement precision
If VDS-based current sensing is used, then device complexity is reduced, but measurement precision deteriorates at extreme temperatures
Solution Approach 1:
The invention converts the harmful effect of temperature-dependent on-resistance variation into a beneficial compensation mechanism. The NTC resistor's negative temperature coefficient, which would normally cause measurement errors, is used to counterbalance the FET's positive temperature coefficient, transforming the temperature sensitivity problem into a self-correcting system
Solution Approach 2:
The sensing circuit employs a composite approach by combining the FET's on-resistance sensing mechanism with an NTC resistor's temperature compensation characteristics. This composite structure enables the circuit to maintain accurate current measurement across extreme temperature ranges by leveraging the complementary temperature coefficients of the two components
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
Achieves accurate short circuit current detection across a wide temperature range without the need for external resistors, reducing costs and power consumption while ensuring reliable protection.
Implementation Method 1
Incorporating a negative temperature coefficient (NTC) resistor to compensate for RDSON variations by generating a temperature-dependent offset voltage
Data Source
AI summary
Described embodiments include a circuit for overcurrent protection includes an amplifier having first and second amplifier inputs and an amplifier output. A reference voltage source has first and second reference voltage terminals and is configured to provide a reference voltage. The first reference voltage terminal is adapted to be coupled to a first transistor current terminal, and the second reference voltage terminal is coupled to the first amplifier input. A negative temperature coefficient (NTC) resistor has first and second NTC terminals. The first NTC terminal is adapted to be coupled to a second transistor current terminal, and the second NTC terminal is coupled to the second amplifier input. A transistor shutoff signal is provided at the amplifier output responsive to a voltage at the second amplifier input being greater than a voltage at the first amplifier input.