Bootstrap DC-DC Converter High Duty Cycle UVP Prevention
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Solution Overview
Problem
Bootstrap DC-DC converters often turn off at high duty cycles due to under voltage protection (UVP) because the bootstrap capacitor is not charged enough, leading to insufficient driving voltage for the upper gate switch, and existing solutions either consume more layout area or require high-voltage comparators.
Innovation Solution
A bootstrap DC-DC converter with a bootstrap voltage maintaining circuit that ensures the lower gate switch turns on for a minimum off time, sufficient to charge the bootstrap capacitor, preventing under voltage protection by maintaining the bootstrap voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the lower gate switch is turned on occasionally at high duty cycle, then the converter efficiency is improved, but the bootstrap capacitor is not charged enough causing the upper gate switch to fail to turn on
Solution Approach 1:
The invention applies preliminary action by forcing the lower gate switch to turn on for a minimum off time before the upper gate switch can turn on. This ensures the bootstrap capacitor is pre-charged to sufficient voltage level, guaranteeing that when the upper gate switch needs to turn on, adequate voltage is available on the bootstrap node. The minimum off time requirement is established in advance to prevent UVP conditions.
2Reliability
If a charge pump is added to increase the driving voltage of the upper gate driver, then the upper gate switch can turn on normally, but the layout area increases
Solution Approach 1:
The invention extracts and removes the charge pump component from the circuit architecture. Instead of adding external voltage multiplication circuitry, the solution uses the existing lower gate switch and bootstrap capacitor to generate the necessary voltage through controlled switching. This extraction eliminates the layout area consumption while maintaining the reliability of upper gate switch operation.
3Reliability
If a comparator with high voltage elements is used to monitor bootstrap voltage and force lower gate switch on, then the bootstrap capacitor can be charged, but the device characteristics worsen and layout area increases
Solution Approach 1:
The invention applies self-service by making the lower gate switch serve dual purposes: its normal switching function and the additional function of charging the bootstrap capacitor. By forcing the lower gate switch to remain on for a minimum off time, the system uses its own existing components to maintain bootstrap voltage, eliminating the need for external comparators and high-voltage monitoring circuitry.
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 solution effectively prevents the bootstrap DC-DC converter from turning off at high duty cycles by ensuring the upper gate switch is always turned on, maintaining a stable output voltage without the need for additional layout-consuming components like charge pumps or high-voltage comparators.
Implementation Method 1
a bootstrap capacitor CBOOT, for charging a bootstrap voltage node BOOT when the lower gate switch is turned on
Implementation Method 2
output an inductance current IL by an output inductor LO
Data Source
AI summary
The present invention discloses a bootstrap DC-DC converter. The bootstrap DC-DC converter includes a lower gate driver, for generating a lower gate control signal according to a control signal; a lower gate, for turning on and turning off according to a lower gate control signal; and a bootstrap voltage maintaining circuit, for generating the control signal, such that the lower gate turns on at least a minimum off time each time.