Negative Bootstrap Signal Transfer Across Low Floating Voltage Domains
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Solution Overview
Problem
High-voltage half-bridge switching circuits face challenges in transferring control signals across different voltage domains, particularly when the floating supply voltage drops below a certain threshold, leading to issues with noise immunity and correct signal transfer, especially when driving GaN transistors.
Innovation Solution
A negative bootstrap circuit using pump capacitors and selection circuits is implemented to shift the ground reference voltage synchronically with the activation of commanded current generators, ensuring reliable signal transfer across voltage domains, even when the floating supply is lower than the system ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional level shifting circuit is used to transfer signals from low voltage domain to floating high voltage domain, then signal transfer is possible, but noise immunity deteriorates when floating supply voltage drops below threshold
Solution Approach 1:
The pump capacitor is pre-charged to the voltage difference between first and second voltage domains before signal transfer occurs. This preliminary charging action ensures that when the capacitor couples the current generator to the first voltage supply, it can immediately provide the necessary voltage shift without delay, maintaining noise immunity even when the floating supply voltage is low.
Solution Approach 2:
The pump capacitor acts as an intermediary energy storage element between the two voltage domains. It temporarily stores the voltage difference and releases it during signal transfer, mediating the voltage level transition. This intermediary approach allows reliable signal transfer without directly depending on the floating supply voltage being above a certain threshold.
2Object-affected harmful factors
If the floating supply voltage is kept above a certain threshold, then noise immunity is maintained, but circuit adaptability deteriorates when voltage drops below threshold
Solution Approach 1:
The circuit dynamically changes its operating parameters by switching the coupling configuration of the pump capacitor. When voltage conditions require it, the selection circuit couples the capacitor to the first voltage supply, changing the voltage reference point and allowing operation with lower floating supply voltages. This parameter change enables the circuit to adapt to varying voltage conditions while maintaining noise immunity.
3Device complexity
If a simple level shifting approach is used, then circuit complexity is reduced, but signal transfer correctness deteriorates across varying voltage conditions
Solution Approach 1:
The pump capacitor is pre-charged to the appropriate voltage difference before signal transfer. This preliminary action ensures that the voltage shift is already prepared, eliminating the need for complex real-time voltage adjustment circuits and maintaining signal transfer correctness with minimal additional complexity.
Solution Approach 2:
The pump capacitor automatically provides the necessary voltage shift based on its pre-charged state, serving itself to correct the voltage level without requiring complex external control circuits. The selection circuit simply needs to switch the coupling, and the capacitor self-adjusts the voltage reference, maintaining correctness with minimal added complexity.
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 enhances noise immunity and ensures correct signal transfer to floating well logic, maintaining operational integrity across varying voltage conditions, including those below the typical threshold, thus supporting applications with GaN transistors and reducing circuit complexity and current consumption.
Implementation Method 1
a negative bootstrap circuit including at least a pump capacitor arranged between the current generators and the first ground reference and configured to shift at a negative voltage said first ground reference synchronically with the activation of the respective commanded current generator
Data Source
AI summary
A circuit includes a current path and a negative bootstrap circuitry coupled to the current path. The current path is coupled between a floating voltage and a reference ground, and includes a current generator coupled through a resistor to the floating voltage at a first node of the current generator. The current generator is controlled by a pulse signal. The negative bootstrap circuitry includes a pump capacitor coupled to a second node of the current generator and to the reference ground. The pump capacitor is configured to provide a negative voltage at the second node of the current generator based on the pulse signal.