MOSFET Current Sense Circuit With Voltage Equalization
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Solution Overview
Problem
The current sense MOS method for load drive devices faces accuracy issues due to differences in the degree of deterioration between main MOS and sense MOS, particularly caused by hot carrier injection, leading to variations in on-resistance ratios and compromised current detection accuracy.
Innovation Solution
A load drive device with an equalizer circuit and a switch is implemented, where the equalizer circuit equalizes terminal voltages during current detection and the switch short-circuits the MOSFETs when no current is detected, maintaining the on-resistance ratio and preventing deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an operational amplifier with a wide operating voltage range is used to equalize terminal voltages of main MOS and sense MOS when no current is detected, then current detection accuracy is maintained, but circuit configuration becomes complicated
Solution Approach 1:
The patent applies dynamics by making the equalizer circuit operational only when needed (during current detection) and inactive otherwise. The control signal dynamically switches the equalizer circuit between active and inactive states, allowing voltage equalization during detection while avoiding unnecessary operation and complexity during non-detection periods.
Solution Approach 2:
The control signal automatically manages the equalizer circuit based on detection needs. When current detection is required, the control signal activates the equalizer circuit; when detection is not required, the control signal deactivates it. This self-managing approach eliminates the need for additional control logic or complex circuit configurations.
2Device complexity
If the terminal voltages of main MOS and sense MOS are not equalized when no current is detected, then circuit configuration remains simple, but the degree of deterioration differs between MOSFETs causing accuracy deterioration
Solution Approach 1:
The patent implements periodic action by activating the equalizer circuit only during current detection periods and deactivating it during non-detection periods. This periodic operation ensures voltage equalization is applied when needed to maintain accuracy while keeping the circuit simple and inactive during unnecessary periods.
Solution Approach 2:
The control signal changes the operational parameter of the equalizer circuit based on detection requirements. During current detection, the equalizer circuit is activated with appropriate voltage equalization parameters; during non-detection, the parameters are changed to an inactive state, simplifying the circuit operation while maintaining accuracy when needed.
3Temperature
If main MOS and sense MOS are arranged to be physically adjacent to match temperature conditions, then temperature matching is achieved, but physical properties such as hot carrier injection deterioration still differ
Solution Approach 1:
The patent applies equipotentiality by using the equalizer circuit to maintain equal terminal voltages between main MOS and sense MOS during current detection. This voltage equalization creates equipotential conditions that compensate for differences in physical properties, ensuring uniform stress conditions and deterioration rates even when the MOSFETs are physically adjacent but have different characteristic values.
Data Source
AI summary
To prevent deterioration of current detection accuracy due to a difference in deterioration between a main MOS and a sense MOS. The load drive device includes a main MOS (101) for supplying a load current to a load, a sense MOS (102) to be used for detection of the load current, and an equalizer circuit (110) and a switch (120) which are provided in parallel between the source terminal of the main MOS and the source terminal of the sense MOS. The drain terminal of the main MOS and the drain terminal of the sense MOS have a common connection, and when a current is detected, the terminal voltage of the main MOS and the terminal voltage of the sense MOS are equalized by the equalizer circuit, and the switch is opened. When a current is not detected, the equalizer circuit is stopped and the switch short-circuits the source terminal of the main MOS and the source terminal of the sense MOS.