Adaptive Bootstrap Recharge Bias for DCM DC-DC Converters
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Solution Overview
Problem
DC-DC converters with high-side NMOS transistors face challenges in maintaining proper gate drive voltage during discontinuous conduction mode and pulse-skip mode, leading to inadequate charging of bootstrap capacitors and subsequent output voltage issues due to the reliance on multiple clamp circuits, which increase complexity and area consumption.
Innovation Solution
A DC-DC converter design incorporating a bootstrap circuit with a gate driver, bootstrap capacitor, clamp circuit, current source, voltage drop circuit, and source follower, along with control circuitry to dynamically adjust the bootstrap voltage by selectively opening and closing switches based on conduction modes, ensuring sufficient charging of the bootstrap capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bootstrap circuit with multiple clamp circuits is used to recharge the bootstrap capacitor in discontinuous mode, then the bootstrap capacitor can be charged, but the device complexity and area consumption increase
Solution Approach 1:
The patent combines multiple clamp circuits into a single integrated clamp circuit that performs the functions of both first and second clamp circuits. This unified circuit uses a single clamp transistor and control logic to achieve the same bootstrap capacitor recharging effect, thereby reducing device complexity and area consumption while maintaining charging reliability
Solution Approach 2:
The single clamp circuit is designed to perform multiple functions: it operates in both continuous conduction mode and discontinuous conduction mode, replacing the need for separate clamp circuits for different operating conditions. The circuit dynamically adapts its behavior based on the operating mode, achieving universality across different conduction modes
2Adaptability or versatility
If multiple clamp circuits are used to ensure proper bootstrap capacitor charging, then the converter can operate in both CCM and DCM modes, but the area consumption increases
Solution Approach 1:
The patent merges the functionality of multiple clamp circuits into a single compact clamp circuit structure. By integrating the clamp transistor and control logic into one unit, the circuit achieves both CCM and DCM mode operation while occupying minimal silicon area compared to implementing separate clamp circuits for each mode
Solution Approach 2:
The clamp circuit incorporates dynamic control mechanisms that allow it to adapt its operation based on the conduction mode. The control logic dynamically adjusts the clamp transistor operation to suit either CCM or DCM conditions, enabling mode adaptability within a fixed, compact circuit footprint
3Reliability
If multiple clamp circuits with switching elements are used to charge the bootstrap capacitor, then proper gate drive voltage can be maintained, but switching delays are introduced
Solution Approach 1:
The patent extracts and eliminates the switching elements from the clamp circuit design. By removing the switching transistor and associated control logic that were present in multi-clamp circuit designs, the circuit avoids introducing switching delays while still maintaining proper gate drive voltage through a continuously conductive clamp structure
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
This design allows for efficient recharging of the bootstrap capacitor across various operation modes, maintaining proper gate drive voltage and output voltage without the need for multiple clamp circuits, reducing complexity and area consumption while avoiding switching delays.
Implementation Method 1
a bootstrap capacitor Cboot coupled between a bootstrap output node and a tap node
Implementation Method 2
a clamp circuit configured to set an intermediate voltage at a first intermediate node to be equal to a lesser of a tap voltage at the tap node and an output voltage at an output voltage node
Implementation Method 3
a source follower configured to buffer the control voltage to a second intermediate node
Data Source
AI summary
Disclosed herein is a DC-DC converter including a power section and a bootstrap circuit for driving the gate of the high-side transistor of the power section. The bootstrap circuit includes an adaptive clamp circuit that maintains a proper voltage differential across the bootstrap capacitor within the bootstrap circuit for recharge during off-times regardless of whether the mode of operation of the DC-DC converter continuous conduction mode (CCM), discontinuous conduction mode (DCM), or pulse-skip mode. This voltage differential is established as being between a bootstrap voltage and a voltage at a tap between the high and low side transistors of the power section. The adaptive clamp circuit maintains the bootstrap voltage as following the lesser of the output voltage and the voltage at the tap.