Level Shifter Slew Detection for False Tripping Prevention
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Solution Overview
Problem
Motor driver level shifters with high slew rates are prone to false tripping due to parasitic capacitances, leading to increased power dissipation and potential damage, as they falsely turn on large power FETs, especially when dealing with high voltage components and noise on the voltage rail.
Innovation Solution
The system includes a level shifter coupled to a voltage source with a slew detector and additional current sources that temporarily increase current to the level shifters during high slew rates or noise events, preventing false tripping by providing additional current when power FETs switch or when noise is detected, thus stabilizing the level shifters without permanent power consumption increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the level shifter operates with high slew rate to meet fast switching requirements, then the switching speed is improved, but false tripping occurs due to parasitic capacitances
Solution Approach 1:
The circuit proactively increases the bias current to the level shifter before high slew rate transitions occur, based on detection of voltage rail activity. This preliminary current increase prepares the level shifter to reject noise and parasitic effects before they can cause false tripping, thus maintaining reliability while enabling fast switching.
Solution Approach 2:
The circuit uses a detector to monitor the voltage rail and provides feedback control of the bias current. When the detector senses high slew rate conditions or noise on the voltage rail, it triggers an increase in bias current through a current source, creating a closed-loop system that dynamically adjusts the level shifter's noise immunity based on real-time conditions.
2Reliability
If additional current is provided to the level shifter during high slew rate events to prevent false tripping, then reliability is improved, but power consumption increases
Solution Approach 1:
Instead of maintaining continuously high bias current, the circuit applies increased current periodically or transiently only when high slew rate events are detected. The bias current is dynamically adjusted based on the presence of noise or fast transitions, consuming extra power only when necessary to prevent false tripping, thus resolving the contradiction between reliability and power consumption.
Solution Approach 2:
The bias current is made dynamic rather than static, allowing the level shifter to operate at low current during normal conditions and switch to high current mode during noisy or fast-transition periods. This dynamic adaptation enables the system to maintain reliability during critical events while minimizing average power consumption during steady-state operation.
Data Source
AI summary
A system includes a level shifter coupled to a voltage source, a first transistor, and a second transistor. The system also includes a first current source coupled to the first transistor and the second transistor and configured to bias the first transistor and the second transistor. The system includes a slew detector coupled to the voltage source and to the first current source, where the slew detector is configured to detect a change in voltage of the voltage source, and further configured to provide current to the first current source responsive to detecting the change. The system also includes a second current source coupled in parallel to the first current source, where the second current source is configured to provide current to the first current source responsive to a control signal.