Boosted High-Side Gate Drive for Low-Duty Bootstrap Charging
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Solution Overview
Problem
Traditional high-side gate drive circuits in class D amplifiers face challenges with energy starvation due to inadequate charging of bootstrap capacitors, especially under varying duty cycle conditions, leading to inefficiencies and increased complexity and cost.
Innovation Solution
A high-side boosted gate drive circuit that includes a switching device, a charging device, a charge control device, and a discharge control device, which selectively conducts, charges, and discharges current to maintain a charge for at least 50% of the clock cycle, using a logic circuit to delay the falling edge of the clock signal during low duty cycles to ensure proper charging and discharging of the bootstrap capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If bootstrap circuits are used to provide gate voltage for high-side NMOS FET, then switching speed and drain-source resistance are improved, but circuit complexity and cost increase due to extra pins and external components
Solution Approach 1:
The patent merges the bootstrap capacitor and charging transistor directly into the integrated circuit package, combining functions that were previously separated into discrete external components. This integration eliminates the need for extra IC pins and external capacitors, reducing circuit complexity while maintaining the fast switching performance enabled by the bootstrap circuit.
2Reliability
If bootstrap capacitor is used for high-side gate drive, then gate voltage is maintained, but charging time conflicts with gate drive operation under varying duty cycle conditions
Solution Approach 1:
The patent implements dynamic control of the bootstrap capacitor charging process through a charging transistor whose operation is synchronized with the gate drive timing. The charging transistor is enabled during specific phases of the clock cycle, allowing the bootstrap capacitor to charge dynamically rather than statically. This dynamic charging mechanism adapts to varying duty cycles by adjusting the charging window, ensuring reliable gate drive voltage maintenance across different operating conditions.
3Reliability
If bootstrap capacitor charging time is increased, then gate drive energy is sufficient, but layout area and quiescent current increase
Solution Approach 1:
The patent employs periodic charging action by synchronizing the bootstrap capacitor charging to specific time windows within the clock cycle. Rather than continuous charging, the charging transistor is activated periodically during designated phases when the gate drive does not require maximum current. This periodic charging approach ensures sufficient energy replenishment while minimizing the time and area required for charging circuits, and reducing quiescent current consumption during non-charging phases.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces layout area by approximately 40% and lowers overall quiescent current by 30% compared to traditional architectures, while ensuring reliable operation across varying duty cycles without completely draining the bootstrap capacitor.
Implementation Method 1
A charging device is provided to deliver charge to the control terminal. A charge control device is configured to selectively couple the charging device to deliver charge to the control terminal and to selectively decouple the charging device from the control terminal to charge the charging device.
Implementation Method 2
A discharge control device is provided to remove charge from the control terminal.
Data Source
AI summary
A high-side boosted gate drive circuit is disclosed. In a particular example, an output driver is described, comprising a switching device configured to selectively conduct current in response to a charge being present at a control terminal for a duty cycle, a charging device configured to deliver charge to the control terminal based on the first duty cycle, a charge control device configured to selectively couple the charging device to deliver charge to the control terminal and to selectively decouple the charging device from the control terminal to charge the charging device, and a discharge control device configured to remove charge from the control terminal.