Split-Die Current Sensing for High-Bandgap Power Converters
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Solution Overview
Problem
Power converters designed using high bandgap compound semiconductors face challenges in current sensing due to incompatibility with CMOS logic circuits, leading to inadequate monitoring of current levels through switches, which can result in reduced device lifetime and increased failures.
Innovation Solution
A current sensor system is implemented, comprising a first portion on a high bandgap semiconductor die and a second portion on a companion silicon die, with a sense transistor and feedback circuit to accurately measure currents through high-side and low-side switching transistors, using averaging or sampling techniques to output representative currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high bandgap compound semiconductor technology is used for power converters, then power conversion performance is improved, but current sensing capability deteriorates due to incompatibility with CMOS logic circuits
Solution Approach 1:
The current sensing function is segmented into two separate portions: a first portion implemented on the high bandgap compound semiconductor die (non-CMOS) and a second portion implemented on a companion silicon die (CMOS). This segmentation allows each portion to operate in its optimal technology environment, resolving the incompatibility between high bandgap semiconductor power conversion and CMOS-based current sensing.
Solution Approach 2:
A sense transistor is introduced as an intermediary element that mirrors the current through the switching transistor. The sense transistor translates the high current through the power switch into a scaled-down, measurable current that can be processed by CMOS circuitry, enabling accurate current sensing without direct exposure to the full power current.
2Device complexity
If current sensing is not implemented in high bandgap power converters, then device complexity is reduced, but device reliability deteriorates due to inadequate monitoring of current levels
Solution Approach 1:
Instead of directly measuring the full current through the switching transistor, a copy of the current is created through the sense transistor. This copied current signal contains the same information about current levels but at a scaled-down magnitude that is safe and accurate for measurement, enabling reliability monitoring without adding excessive complexity.
Solution Approach 2:
The current sensing circuit implements feedback by continuously monitoring the current through the switching transistor via the sense transistor and providing this information to the control circuitry. This feedback enables real-time detection of overcurrent conditions and allows the control system to respond appropriately, improving device reliability.
3Measurement precision
If current sensing is implemented using sense transistor with feedback circuit, then current measurement precision is improved, but device complexity increases due to additional circuit portions on multiple dies
Solution Approach 1:
The current sensing function is segmented into two separate portions: a first portion implemented on the high bandgap compound semiconductor die (non-CMOS) and a second portion implemented on a companion silicon die (CMOS). This segmentation allows each portion to operate in its optimal technology environment, resolving the incompatibility between high bandgap semiconductor power conversion and CMOS-based current sensing.
Solution Approach 2:
The sense transistor serves multiple functions: it acts as a current mirror to replicate the switching transistor current, functions as a sensing element to translate high current into measurable signal, and interfaces between non-CMOS and CMOS domains. This multi-functionality reduces the need for separate dedicated sensing circuits, mitigating the increase in device complexity.
Data Source
AI summary
Embodiments herein relate to a current sensor for a power converter such as a buck converter. The power converter is fabricated on a high bandgap semiconductor die while the current sensor includes a portion on the same die and a portion on a silicon die. The portion on the same die includes a sense transistor, while the portion on the silicon die includes a feedback circuit for controlling a voltage of the sense transistor to ensure it is biased according to the bias of a switching transistor of the power converter. A current of the sense transistor can then be processed such as by an averaging or sampling process.