Charge Pump Surge Current Reduction via Variable Resistance Switches
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Solution Overview
Problem
Charge pumps draw unacceptably large surge currents from the voltage supply due to large voltage differentials across switches during gain mode switching, exceeding power supply limits and causing voltage ripple.
Innovation Solution
Dynamic adjustment of switch on-resistance over time by using parallel sub-switches and a bypass switch to reduce surge current while maintaining low resistance during steady-state operation, allowing for efficient charge pump operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a charge pump switches gain modes with large voltage differentials across switches, then voltage conversion efficiency is improved, but surge current drawn from the voltage supply increases unacceptably
Solution Approach 1:
The charge pump circuit is segmented into multiple gain modes (first gain mode and second gain mode) with different switching configurations. During the first gain mode, switches are configured to provide higher voltage conversion efficiency, while during the second gain mode, switches are configured to limit surge current. This segmentation allows the system to operate in different configurations depending on the required performance characteristic.
Solution Approach 2:
The charge pump dynamically switches between different gain modes based on operating conditions. The controller adjusts the switching configuration in real-time, transitioning between a first set of switches (providing efficient voltage conversion) and a second set of switches (limiting surge current). This dynamic adaptation allows the system to optimize performance for different operational requirements.
2Productivity
If switch resistance is kept low for efficient operation, then charging efficiency is improved, but surge current during mode switching increases
Solution Approach 1:
Different switches are assigned different resistance characteristics based on their functional requirements. Some switches are designed with lower resistance to maintain charging efficiency during steady-state operation, while other switches are designed with higher resistance to limit surge current during mode transitions. This local differentiation of switch properties allows the system to achieve both efficient operation and surge current limitation.
Solution Approach 2:
The system changes the effective resistance parameter of switches by selecting different switching configurations. During efficient charging phases, the circuit uses switch paths with lower resistance. During mode transitions, the circuit switches to configurations that present higher resistance to surge currents. This dynamic parameter change allows optimization of both charging efficiency and surge current protection.
Data Source
Figure 1~2
Figure 3A
Figure 3B
AI summary
Techniques for reducing surge current in charge pumps. In an exemplary embodiment, one or more switches coupling a terminal of a flying capacitor to a voltage supply are configured to have variable on-resistance. When the charge pump is configured to switch a gain mode from a lower gain to a higher gain, the one or more variable resistance switches are configured to have a decreasing resistance profile over time. In this manner, surge current drawn from the voltage supply at the outset of the gain switch may be limited, while the on-resistance during steady-state charging and discharging may be kept low. Similar techniques are provided to decrease the surge current from a bypass switch coupling the supply voltage to a positive output voltage of the charge pump.