Capacitive Level Shifter for High-Side Gate Driver Control
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Solution Overview
Problem
High-side gate drivers face challenges in voltage translation and startup conditions due to high voltage requirements, leading to potential damage and undesirable behavior, especially when using NMOS transistors that require large area and high breakdown voltage, and may not turn on properly if the drain voltage is not higher than the source voltage.
Innovation Solution
A stateless level shifting circuit that uses capacitive isolation and AC signals encoded with ON-OFF keying to detect the presence or absence of control signals, allowing the gate driver to be controlled without storing the drive state in a memory, thereby avoiding issues with induced common mode currents and ensuring proper startup conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If NMOS transistors are used to set the state of a memory circuit in a high voltage domain, then the gate driver can be controlled to drive the output high or low, but the transistor may not turn on properly if the drain voltage is not higher than the source voltage, and the required operating parameters are prohibitive due to high voltage requirements including large area and high breakdown voltage
Solution Approach 1:
The patent introduces a level shifting circuit as an intermediary between the control logic in the first voltage domain and the NMOS transistor in the second voltage domain. This level shifter translates control signals from the lower voltage domain to the higher voltage domain, ensuring the gate receives appropriate voltage levels to properly turn on the transistor without requiring the transistor to operate directly with incompatible voltage levels.
Solution Approach 2:
The level shifting circuit changes the voltage parameter of the control signal to match the requirements of the NMOS transistor in the high voltage domain. By transforming the control signal parameters (voltage levels) before they reach the transistor, the system enables reliable transistor operation without requiring the transistor to tolerate incompatible voltage parameters from the control logic.
2Duration of action of stationary object
If a memory circuit is used to store the state of the gate driver, then the drive state can be maintained, but the state may be unknown at power up which can damage the circuit by performing in undesirable manners at startup
Solution Approach 1:
The patent implements preliminary initialization logic that sets the gate driver state to a known safe condition (typically off-state) before normal operation begins. This preliminary action ensures that even if the memory circuit state is unknown at power-up, the circuit starts in a safe state and only transitions to operational states after proper initialization sequences are completed.
Solution Approach 2:
The system uses feedback mechanisms to monitor the actual state of the gate driver and memory circuit, particularly during startup sequences. This feedback allows the control logic to detect when the system is in an uninitialized state and prevent operation until proper initialization is complete, thereby avoiding damage from unknown startup conditions.
3Strength
If high voltage transistors are used in the gate driver, then the output can be driven in the high voltage domain, but rapid voltage swings occur which require relatively high drive current to meet switching demands
Solution Approach 1:
The patent segments the gate driver into multiple transistor stages working in sequence. Rather than using a single high-voltage transistor that must handle the entire switching transition, the driver uses a first transistor to perform initial switching and a second transistor to complete the voltage transition. This segmentation allows each transistor to operate more efficiently with lower individual current requirements while achieving the same overall drive capability.
Solution Approach 2:
The gate driver uses periodic or sequential activation of different transistor stages during the switching process. The first transistor activates during one phase of the switching sequence, then the second transistor activates to complete the transition. This periodic action distributes the current demand over time, reducing peak current requirements compared to a single-transistor approach that would need to handle the entire switching event simultaneously.
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
The solution enables reliable control of high-side gate drivers by maintaining the desired drive state across capacitive isolation, preventing damage from unknown startup conditions and reducing the need for high current control signals, thus ensuring stable operation during rapid voltage swings.
Implementation Method 1
A control signal provided in a first voltage domain is capacitively coupled to a control circuit in a second voltage domain through a capacitor
Data Source
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AI summary
Systems and methods of use relate to a circuit that is designed to detect the state of two control signals, wherein one control signal indicates an ON state for the gate driver and the other control signal indicates an OFF state for the gate driver. The circuit responds to each of the control signals by controlling the gate driver so that it drives an output either high or low. The circuit can also be configured to control the gate driver so that it to drives the output (either high or low) when neither control signal is present.