Current Sense Devices with Reference Transistor Aging Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional non-dissipative current sense devices experience degraded accuracy over time due to mismatch between power and sense transistors, caused by stress factors like hot carrier injection and transient voltage spikes, which alter the power transistor's on-resistance, affecting current magnitude sensing accuracy.
Innovation Solution
Incorporating a reference transistor that undergoes similar operating voltage stress as the power transistor, with control circuitry calibrating the sense transistor's current based on the reference transistor's conditions to compensate for aging, ensuring accurate current sensing despite power transistor aging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a discrete current sense resistor is used to sense current magnitude, then current sensing is achieved, but significant power is dissipated causing power loss and heat generation
Solution Approach 1:
The invention extracts the current sensing function from a separate power-dissipating resistor and integrates it into the power transistor itself by utilizing the transistor's on-resistance as the sensing element. This eliminates the need for a discrete sense resistor and removes the associated power loss while maintaining current sensing capability.
Solution Approach 2:
The power transistor is made multi-functional by using its inherent on-resistance for both power switching and current sensing purposes. The same transistor that controls power delivery also provides the sensing function, eliminating the need for separate sensing components and reducing overall power loss.
2Loss of energy
If parasitic resistance of an inductor is used as a current sense element, then power dissipation is reduced, but current magnitude sensing precision deteriorates due to variations in parasitic resistance
Solution Approach 1:
The invention changes the sensing parameter from variable parasitic resistance of an inductor to the controlled on-resistance of a power transistor. The transistor's on-resistance can be precisely controlled and is much more stable than inductor parasitic resistance, enabling accurate current sensing without significant power dissipation.
Solution Approach 2:
The invention uses the inherently present on-resistance of the power transistor as a disposable sensing element that does not require separate calibration or compensation circuits, unlike inductor parasitic resistance sensing which requires complex compensation for accuracy.
3Loss of energy
If a sense transistor is used to measure current through a power transistor, then power dissipation is reduced, but sensing accuracy degrades over time due to mismatch caused by stress factors like hot carrier injection
Solution Approach 1:
The invention creates a copy of the power transistor's electrical characteristics by using the same transistor for both power delivery and sensing. Since the sensing function uses the identical physical transistor that experiences the same stress conditions, any drift in characteristics affects both power delivery and sensing equally, maintaining accuracy over time.
Solution Approach 2:
The invention achieves homogeneity by using the same power transistor for both power switching and current sensing functions. The sensing operation uses the transistor's own on-resistance, ensuring that the sensing path experiences identical environmental conditions and aging effects as the power path, thereby maintaining consistent accuracy throughout the device lifetime.
Data Source
AI summary
A current sense device includes a reference transistor for electrically coupling to a power transistor, a sense transistor for electrically coupling to the power transistor, and control circuitry. The control circuitry is configured to (a) control current through the sense transistor such that a voltage at the sense transistor has a predetermined relationship to a voltage at the power transistor, and (b) control current through the sense transistor according to one or more operating conditions at the reference transistor, to compensate for aging of the power transistor.