Gate Driver Voltage Sensing for Safe Power FET Switching
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Solution Overview
Problem
Existing gate driver circuits for power transistors in class-D amplifiers face issues with high peak current sourcing and sinking, leading to potential damage due to excessive gate-source voltage, especially in mobile applications where supply voltages exceed the maximum rating of the gate driver FETs.
Innovation Solution
A gate driver circuit architecture that includes a high side and low side portion with a voltage sensor to detect and limit the gate voltage of power transistors to a safe value below the supply voltage, using a sense circuit to switch between a first and second voltage, preventing excessive charging and connecting the gate to a high impedance reference voltage when the maximum allowed value is reached.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the supply voltage is increased to maximize output power in mobile devices, then the output power is improved, but the gate driver FETs may be damaged due to excessive gate-source voltage exceeding their maximum rating
Solution Approach 1:
A voltage sensor circuit acts as an intermediary between the power supply and the gate driver FETs. The sensor detects the gate-source voltage and generates a feedback signal that controls switching elements to limit the voltage applied to the gate driver FETs, preventing damage while allowing higher supply voltages for maximum output power
Solution Approach 2:
The circuit employs feedback by using the voltage sensor to continuously monitor the gate-source voltage of the power transistors. When the voltage approaches the maximum rating, the sensor triggers switching elements to disconnect or clamp the voltage, creating a closed-loop protection mechanism that prevents overvoltage damage to the gate driver FETs
2Power
If external decoupling capacitors are added to supply large peak currents to the gate drivers, then the gate driver performance is improved, but the die area and cost increase
Solution Approach 1:
The voltage sensor circuit and switching elements are integrated directly into the gate driver structure, merging the protection function with the existing circuitry. This eliminates the need for separate external decoupling capacitors while maintaining the ability to supply large peak currents through the integrated switching transistors that can rapidly charge and discharge the gate capacitance
Data Source
AI summary
In High Voltage CMOS technologies the supply voltage is typically higher than the maximum allowed gate voltage. In a switching output stage of amplifiers such class-D amplifiers and DC-DC converters the gates of the power field effect transistors need to be charged quickly. This requires a gate driver that is capable of delivering large currents without exceeding the maximum allowed voltage on the gate of the power field effect transistors.