High-Side N-Type Gate Driving Without a Bootstrap Capacitor
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Solution Overview
Problem
Existing gate driving techniques for high-side transistors in switched-mode power supplies face challenges such as large bootstrap capacitors, inefficiency in charging, and design complexities due to rapid voltage domain transitions, particularly in inverting buck-boost converters.
Innovation Solution
A segmented gate driver architecture is employed, utilizing a pulldown gate driver with a two-step approach, where the high-side gate voltage is initially pulled down using the output voltage domain, and an auxiliary switch completes the turn-off, powered by separate voltage rails, eliminating the need for a large bootstrap capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bootstrap capacitor is used to drive the high-side transistor gate, then the gate can be driven to the required voltage level, but the capacitor size becomes large and charging efficiency decreases
Solution Approach 1:
The gate driver is divided into two independent stages: a first gate driver stage that pulls the gate voltage down to a first level, and a second gate driver stage that pulls the gate voltage up to a second level. This segmentation eliminates the need for a large bootstrap capacitor by using separate voltage rails (first voltage rail and second voltage rail) for each stage, thereby improving charging efficiency while maintaining reliable gate driving capability.
2Reliability
If a bootstrap capacitor is used for gate driving, then the high-side transistor can be controlled, but the overall device complexity increases
Solution Approach 1:
The gate driver is segmented into two independent stages with separate voltage rails, eliminating the need for complex bootstrap capacitor charging/discharging control circuitry. Each stage operates independently with its own voltage reference, simplifying the overall control logic and reducing device complexity while maintaining reliable high-side transistor control.
3Speed
If rapid voltage domain transitions are handled using traditional bootstrap techniques, then the transistor can switch quickly, but design complexity increases due to voltage domain management
Solution Approach 1:
The gate driving process is segmented into two distinct voltage transitions: first pulling the gate voltage down to a first level using the first voltage rail, then pulling it up to a second level using the second voltage rail. This segmentation simplifies voltage domain management by using independent voltage references for each transition, enabling rapid transistor switching without increasing design complexity.
Data Source
AI summary
Techniques and apparatus for driving the gate of a high-side transistor in a switched-mode power supply (SMPS) circuit, such as an inverting buck-boost converter or a buck converter. One example technique to pull down the gate voltage of the high-side transistor involves a multi-step approach, in which the gate voltage is initially discharged to a lower voltage level, and once the gate voltage falls below a certain level, an auxiliary switch can take over to completely turn off the high-side transistor. One example SMPS circuit generally includes a high-side transistor, a pulldown gate driver having an output coupled to a gate of the high-side transistor, a pulse generator having an output coupled to an input of the pulldown gate driver, and a first switch coupled between the gate and a source of the high-side transistor.