Bootstrap Capacitor Refresh for High-Side Switch Shutdown Readiness
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Solution Overview
Problem
Bootstrap capacitors in switching converters often require refreshing to maintain sufficient voltage for reliable operation, especially when the high-side switch needs to be switched ON, and existing methods may not effectively recharge the capacitor if the voltage at the junction of the high-side and low-side switches is not at a suitable level.
Innovation Solution
A refresh block is designed to refresh the bootstrap capacitor by drawing power from the input voltage (Vin) and recharging it only if the voltage at the junction of the high-side and low-side switches is greater than a second threshold, ensuring the cross-terminal voltage across the bootstrap capacitor remains above a first threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bootstrap capacitor is refreshed continuously to maintain sufficient voltage, then the reliability of high-side switch operation is improved, but the energy consumption increases
Solution Approach 1:
The refresh block proactively refreshes the bootstrap capacitor when the power stage is shut down and the junction voltage is favorable, before the capacitor voltage drops below the threshold. This preliminary action ensures the capacitor is ready for the next high-side switch activation without needing continuous monitoring or refreshing during operation.
Solution Approach 2:
The refresh block continuously monitors the voltage at the junction of the high-side and low-side switches and the state of the power stage. Based on this feedback, it intelligently decides when to activate the refresh operation - only when the power stage is shut down and the junction voltage exceeds the second threshold, thereby avoiding unnecessary energy consumption while maintaining reliability.
2Use of energy by moving object
If the bootstrap capacitor is refreshed only when junction voltage is above threshold, then the energy consumption is reduced, but the responsiveness to voltage drops may be delayed
Solution Approach 1:
The system performs the refresh operation in advance during the shut-down period when the junction voltage is naturally high. This ensures that when the power stage needs to activate the high-side switch, the bootstrap capacitor is already charged to the required level, eliminating any delay in responsiveness during actual operation.
Solution Approach 2:
The shut-down period itself provides the opportunity for refreshing - the natural high voltage state during shut-down is utilized to recharge the capacitor without requiring additional external energy input. The system uses its own operational states (shut-down periods) to service the capacitor, turning a non-operational period into a beneficial refresh opportunity.
3Reliability
If the refresh block operates during normal operation, then the capacitor voltage is maintained, but false fault triggering may occur
Solution Approach 1:
The refresh operation is extracted from the normal operational context and restricted to occur only during the shut-down period. By separating the refresh function from the operational context, the system avoids the harmful effect of false fault triggering that would occur if refresh operations attempted to modify capacitor voltage during active switching.
Solution Approach 2:
The system prevents potential false fault conditions by proactively refreshing the capacitor during shut-down before any potential voltage drop issues could manifest during operation. This preliminary anti-action eliminates the need for corrective actions during operation that could trigger false faults.
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
The solution effectively maintains the cross-terminal voltage across the bootstrap capacitor above the required threshold, ensuring reliable operation of the high-side switch and preventing false fault triggering or operational compromise during shut-down and normal operation.
Implementation Method 1
a bootstrap capacitor is often employed to assist in generating the voltages needed for switching ON the high-side switch
Implementation Method 2
A refresh block is designed to refresh the bootstrap capacitor by drawing power from the input voltage (Vin) and recharging it
Data Source
AI summary
A power stage of a voltage regulator includes a high-side switch, a low-side switch, a gate-driver, a power management block, a bootstrap capacitor and a refresh block. The power management block is designed to receive a power-control signal, and to cause both of the high-side switch and low-side switch to be switched OFF when said power-control signal is in a first state. The bootstrap capacitor is provided to enable said high-side switch to be switched ON. The cross-terminal voltage across the bootstrap capacitor is required to be above a first threshold voltage for reliable operation of the high-side switch. The refresh block is designed to refresh the bootstrap capacitor to maintain the cross-terminal voltage above the first threshold voltage while both the high-side switch and low-side switch continue to be in the OFF state when the power-control signal is in the first state.