GaN Current Sense Transistor Layout for High-Voltage Sensing
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Solution Overview
Problem
GaN power electronics face challenges in accurate current sensing at high frequencies due to short ON phases, aging of GaN devices, and sensing voltages up to 600V with low voltage technology, which complicates low voltage protection.
Innovation Solution
A GaN die with current sense terminals, a main GaN power transistor, a GaN current sense transistor, and diode devices connected in series, along with voltage protection devices to safeguard the current sense circuitry from full drain voltage, enabling accurate current sensing and protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high switching frequencies above 200-250kHz are used with low operational duty cycles, then switching speed is improved, but current sensing accuracy deteriorates due to very short ON phases
Solution Approach 1:
A current sense transistor is introduced as an intermediary device that replicates the main GaN power transistor's current characteristics. This sense transistor provides a scaled-down version of the main transistor's drain current that can be accurately measured, enabling precise current sensing even at very high switching frequencies where direct measurement would be too difficult.
2Power
If the main GaN power device operates at high voltages up to 600V, then power handling capability is improved, but protection of low voltage sense circuitry becomes more difficult
Solution Approach 1:
The voltage protection function is segmented into multiple discrete protection devices rather than using a single complex protection circuit. Multiple protection devices are connected in series between the high voltage node and the low voltage sense circuitry, with each device handling a portion of the voltage stress, thereby protecting the sense circuit while maintaining simplicity.
3Measurement precision
If the main GaN power transistor and sense transistor are operated under different voltage stresses, then current sensing is enabled, but aging mismatch increases over time
Solution Approach 1:
The sense transistor is pre-exposed to the same high voltage stress conditions as the main power transistor by connecting it to the high voltage node through protection devices. This ensures both transistors undergo identical aging processes from the outset, preventing mismatch development over time while still enabling accurate current sensing through the sense transistor's scaled current output.
Data Source
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AI summary
A GaN (gallium nitride) die comprises: a first current sense terminal; a second current sense terminal; a main GaN power transistor; a GaN current sense transistor having a source electrically connected to a source of the main GaN power transistor; a diode device electrically connected in series between a drain of the main GaN power transistor and a drain of the GaN current sense transistor; a first voltage protection device electrically connecting the drain of the main GaN power transistor to the first sense terminal; and a second voltage protection device electrically connecting the drain of the GaN current sense transistor to the second sense terminal. A power electronics device that includes the GaN die is also described.