Output Driver Slew Rate Circuit With Fast Turn-On Assist
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Solution Overview
Problem
Conventional slew rate control circuits in output drivers face challenges in reducing turn-on time while maintaining controlled slew rates, particularly in applications requiring small latency and minimizing electromagnetic interference (EMI).
Innovation Solution
A control circuit with a turn-on facilitating module that supplies a supplementary voltage to the output driver, in addition to the current injected by the slew rate control circuit, to reduce turn-on time, and a sensing module that switches off the facilitating module once the input voltage reaches a threshold, ensuring the slew rate remains unimpacted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a well-controlled current is injected into the driver to control the output slew rate, then the slew rate is well-controlled, but the turn on time becomes large
Solution Approach 1:
The patent applies preliminary action by pre-charging the gate of the output transistor through a dedicated turn-on path before the main drive signal arrives. This preliminary charging action reduces the turn-on time by ensuring the gate is already partially charged when the drive signal activates the transistor, thereby resolving the contradiction between fast turn-on and controlled slew rate.
Solution Approach 2:
The patent segments the gate charging process into two distinct phases: a preliminary fast charging phase through the turn-on path, and a controlled charging phase through the slew rate control circuit. This segmentation allows the system to achieve both fast turn-on (during the preliminary phase) and controlled slew rate (during the controlled phase), resolving the technical contradiction.
2Loss of time
If the turn on time is reduced by supplying supplementary voltage, then the propagation delay decreases, but the slew rate control may be impacted
Solution Approach 1:
The patent introduces an intermediary sensing circuit that monitors the gate voltage and controls the discharge of the supplementary voltage source. This intermediary mechanism ensures that the supplementary voltage is discharged only after the drive signal has fully charged the gate, thereby maintaining accurate slew rate control while still benefiting from the reduced propagation delay provided by the preliminary charging.
Solution Approach 2:
The patent employs feedback through a sensing circuit that detects the gate voltage level and uses this information to control the discharge timing of the supplementary voltage. This feedback mechanism ensures that the supplementary voltage is discharged at the appropriate moment, preventing interference with the slew rate control while maintaining the propagation delay benefits.
Data Source
AI summary
A control circuit for an output driver with a slew rate control circuit is disclosed. The control circuit includes a turn-on facilitating module having a control input and configured to be connected to the output driver and to supply a supplementary voltage to the output driver in response to a control voltage at the control input; and a sensing module configured to be connected to the turn-on facilitating module and the output driver and to switch off the turn-on facilitating module in response to an input voltage of the output driver sensed by the sensing module.