Startup Charge Balancing for Switched-Capacitor Power Converters
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Solution Overview
Problem
Switched-capacitor power converters face challenges in startup due to unbalanced voltage conditions, leading to excessive in-rush currents and voltage spikes, which can cause stress on converter circuit switches and gate driver circuits.
Innovation Solution
The implementation of a charge balance circuit that compares the output voltage to a feedback voltage from charge pump capacitors, using a digital controller to enable a constant current source or sink until voltage balance is achieved, independent of leakage currents, allowing for efficient and rapid startup without excessive voltage spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If switched-capacitor power converter starts up with unbalanced voltage conditions, then startup is initiated, but excessive in-rush currents and voltage spikes occur causing stress on switches and gate driver circuits
Solution Approach 1:
The charge balance circuit performs preliminary voltage balancing of the charge pump capacitors before the main power converter startup sequence is initiated. By pre-charging or discharging the capacitors to appropriate voltage levels, the system eliminates unbalanced voltage conditions that would otherwise cause excessive in-rush currents and voltage spikes during startup, thereby protecting the switches and gate driver circuits from stress.
2Reliability
If charge balance circuit uses traditional voltage-dependent current sourcing, then charge balancing is achieved, but the process is slow and dependent on leakage currents
Solution Approach 1:
The invention changes the operating parameters of the charge balance circuit by using constant current sources instead of voltage-dependent current sources. The digital controller dynamically adjusts the magnitude of constant current based on the voltage difference between the output capacitor and charge pump capacitors, enabling fast and accurate charge balancing that is independent of leakage currents and operates rapidly during startup.
Data Source
AI summary
Startup charge balancing circuits and methods for capacitive charge pumps that avoid large in-rush currents and resulting voltage spikes. Embodiments include a charge balance circuit coupled to a corresponding charge pump capacitor of a charge pump. The charge balance circuit includes a comparator that compares the output voltage of the charge pump to a feedback voltage derived from the voltage across the corresponding charge pump capacitor. In response, either a constant current source or a constant current sink is coupled to the charge pump capacitor. Current sourcing or sinking continues until the voltage across the corresponding charge pump capacitor approximates a target voltage, at which point the comparator output toggles, which results in uncoupling of the coupled current source or current sink from the corresponding charge pump capacitor. Embodiments only need one current sink and one current source per charge pump capacitor, and charge balancing is independent of leakage currents.