DC-DC Converter Filter Capacitance for Voltage Overshoot
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Solution Overview
Problem
Capacitive DC-DC converters experience voltage overshoot due to external parasitic inductances, leading to increased noise and design constraints, which affect the converter's operational stability and reliability.
Innovation Solution
Incorporating a filter capacitance coupled with the switching capacitor arrangement, which is calibrated to reduce voltage overshoot and maintain high current capability, using a variable capacitor that can be set through a calibration operation to account for parasitic elements in the customer application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitive DC-DC converter is used, then charge transfer and constant output voltage are provided, but voltage overshoot occurs due to external parasitic inductances
Solution Approach 1:
The patent introduces a filter capacitor as an intermediary element connected in parallel with the output capacitor. This filter capacitor acts as a mediator that decouples the harmful effect of parasitic inductances from the output voltage, absorbing voltage overshoots and reducing switching noise without affecting the core charge transfer function of the DC-DC converter.
Solution Approach 2:
The patent converts the harmful voltage overshoot caused by parasitic inductances into a beneficial filtering opportunity. By adding the filter capacitor, the previously harmful high-frequency voltage spikes are transformed into charge transfer opportunities for the capacitor, which then releases this energy smoothly to stabilize the output voltage, effectively turning the harmful overshoot into a stabilizing mechanism.
2Object-generated harmful factors
If filter capacitance is added to reduce voltage overshoot, then switching noise is reduced, but device complexity increases
Solution Approach 1:
The patent modifies the electrical parameters of the existing output capacitor by adding a parallel filter capacitor with specific capacitance value. This parameter change increases the total output capacitance and alters the frequency response of the output filter, thereby reducing switching noise and voltage overshoot while maintaining the existing circuit topology and avoiding significant complexity increase.
3Power
If the converter operates with high current capability, then power delivery is improved, but voltage overshoot and noise increase
Solution Approach 1:
The filter capacitor is pre-configured in parallel with the output capacitor before the converter operates at high current. This preliminary arrangement ensures that the filtering mechanism is already in place to handle high-current operation, preventing voltage overshoot and noise generation at the source rather than attempting to correct them after they occur during high-power delivery.
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 reduces switching noise, increases the lifespan of IC components, and enhances the accuracy of current protection in DC-DC converters, making them less sensitive to external parasitic influences and improving operational stability.
Implementation Method 1
a filter capacitance coupled to the switching capacitor arrangement, which is added to reduce the voltage overshoot of the circuit
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A DC-DC converter uses a switched capacitor arrangement. A filter capacitor is connected between one terminal of the capacitor arrangement and a fixed voltage line and a calibration arrangement is used for setting or enabling selection of the capacitance of the filter capacitor. In this way, a capacitance is added to a terminal of the switched capacitor arrangement. The capacitance value can be chosen or adjusted to keep the DC-DC converter current capability within specification limits.