Soft-Start Switch Circuit With Output Slope Fault Cutoff
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Solution Overview
Problem
Existing switch circuits for hot-swap applications face challenges in achieving high accuracy current balance during soft start while being capable of disabling the path switch with a short response time, and they have stringent Safe Operating Area (SOA) requirements due to prolonged power dissipation and temperature rise under fault conditions.
Innovation Solution
A switch control circuit that includes an amplifier to control the gate voltage based on the voltage drop across a current sensing resistor, a slope detection circuit to monitor the output voltage slope, and a pull-down switch to turn off the path switch when the slope is below a threshold, with optional deglitch and re-attempt functions to enhance fault tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gate voltage slope control method is used for soft start, then the MOSFET stress is reduced and SOA demands are minimized, but current sharing accuracy deteriorates due to variations in MOSFET threshold voltage among parallel devices
Solution Approach 1:
The patent implements a feedback mechanism by sensing the current through each parallel MOSFET and adjusting the gate voltage dynamically. The control circuit monitors the actual current flow and modifies the gate drive signal to compensate for threshold voltage variations, ensuring equal current distribution while maintaining soft-start functionality and reducing MOSFET stress.
2Measurement precision
If current limit method with extended soft-start duration is used, then current sharing accuracy improves and SOA requirements are reduced, but response time to fault conditions deteriorates and power dissipation increases
Solution Approach 1:
The patent employs dynamic control of the soft-start parameters, allowing the system to adapt the soft-start duration and current limit based on real-time conditions. The control circuit can accelerate or decelerate the ramp-up rate dynamically, providing both accurate current sharing during normal operation and rapid response to fault conditions, thereby resolving the contradiction between extended soft-start duration and fast fault response.
3Measurement precision
If current limit method is used during both normal and fault conditions, then current sharing accuracy is maintained, but the system cannot distinguish between normal operation and fault conditions, preventing soft-start time reduction
Solution Approach 1:
The patent segments the control function by implementing separate control paths or modes for normal operation and fault conditions. The system divides the operational states and applies different control strategies accordingly, enabling accurate current sharing during normal operation while simultaneously providing rapid fault detection and response, thus resolving the inability to distinguish between normal and fault conditions.
Data Source
AI summary
A switch control circuit, for controlling a path switch and a current sense resistor connected in series between an input voltage and an output voltage, includes: an amplifier, which controls the gate voltage of the path switch based on a voltage drop across the current sense resistor to perform current-limited soft start; a slope detection circuit, coupled to the output voltage, for monitoring the rising slope of the output voltage; and a pull-down switch, coupled between the gate of the path switch and a disabling potential. When the slope detection circuit detects that a rising slope of the output voltage is below a preset slope threshold, the pull-down switch is triggered to conduct, thereby turning off the path switch.