High-Side Switch Current Sensing for Wire Break Detection
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Solution Overview
Problem
Existing high-side switches struggle to accurately sense both high load currents and small currents in the range of 300 microamps to a few milliamps for wire break detection, as conventional sense circuitry is inadequate for this range.
Innovation Solution
Incorporating a PMOS power stage with smaller transistors that operate in parallel with the main power FET during a wire break detection mode, allowing the high-side switch to accurately sense smaller currents by connecting the power FET in a diode-configured mode, which also maintains output voltage during sudden load changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sense circuitry is used in high-side switches, then the circuit can handle high load currents, but it cannot accurately sense small currents in the range of 300 microamps to a few milliamps for wire break detection
Solution Approach 1:
The patent divides the current sensing function into two separate power stages: a first power stage for sensing high load currents and a second power stage for sensing small currents in the wire break detection range. Each stage has its own sense transistor optimized for its specific current range, allowing the system to accurately measure currents across a wide spectrum from 300 microamps to 40 amps without compromise in precision for either range
Solution Approach 2:
The patent implements dynamic switching between the first and second power stages based on the operating conditions. A switch selectively connects either the first sense transistor or the second sense transistor to the sense amplifier depending on whether the system is operating in normal high-current mode or wire break detection mode. This dynamic reconfiguration allows the circuit to adapt its sensing capability to match the required measurement range
2Measurement precision
If a single power stage is used, then the device complexity is low, but the sensing accuracy for both high and low currents cannot be achieved
Solution Approach 1:
The patent designs the second power stage and its associated switch to serve dual functions: acting as an active sensing element during wire break detection mode, and serving as a protective element during normal operation. The second power stage can provide voltage clamping and protection against voltage spikes or transients, thereby reducing the need for separate protection circuitry and offsetting the added complexity of having an additional power stage
Solution Approach 2:
The patent merges the wire break detection functionality with the existing power stage architecture by integrating the second sense transistor and switch into the same circuit block as the first power stage. The sense amplifier serves as a shared resource for both power stages, and the control logic for switching between stages is integrated into the overall power management system, thereby minimizing the increase in overall device complexity
3Stability of the object's composition
If the high-side switch uses a diode-connected power FET configuration, then output voltage is maintained during sudden load changes, but the current sensing capability for wire break detection must be separated from the main power function
Solution Approach 1:
The patent segments the power delivery function into two distinct paths: the first power FET handles the main high-current power delivery to the load, while the second power FET in diode-connected configuration handles voltage stabilization during sudden load changes. This segmentation allows each FET to be optimized for its specific function without compromise
Solution Approach 2:
The patent introduces a switch as an intermediary element that mediates between the two power stages and the sense amplifier. This switch selectively connects either the first sense transistor or the second sense transistor to the sense amplifier based on the operating mode, thereby enabling the system to achieve both voltage stability and accurate current sensing without permanent circuit conflicts
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
In an example, a system (100) includes a first power stage (102) including a first power field effect transistor (FET) (104) and a first sense transistor (106) coupled to the first power FET (104). The system (100) also includes a second power stage (162) including a second power FET (172) and a second sense transistor (174) coupled to the second power FET (172), where the second power stage (162) is smaller than the first power stage (102). The system (100) includes a first switch (160) coupled to a gate (108) and a drain (112) of the first power FET (104) and a second switch (130) coupled to the first power stage (102) and the second power stage (162). The system (100) also includes a sense amplifier (132) coupled to the second switch (130), where the first power stage (102), the second power stage (162), and the sense amplifier (132) are coupled to a load terminal (140).