Digital Boost Feedback Voltage Controller for Switch-Mode Power Supplies
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
DC-to-DC converters, particularly those using Pulse-Frequency Modulation (PFM) mode, face challenges in maintaining a stable boost feedback voltage, which can become arbitrarily low, making it difficult to guarantee the charge pump output voltage remains above the required minimum value, especially in light load conditions.
Innovation Solution
The solution involves generating additional switching pulses with a high-side on-time/low-side on-time ratio less than that of PFM pulses, ensuring minimal impact on the main switch-mode power supply voltage, and using boost feedback (BFB) pulses to maintain the boost feedback voltage without affecting the net charge at the output capacitor, allowing PFM mode to be used even when efficiency is desired at light loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PFM mode is used to improve efficiency at light load conditions, then efficiency is improved, but the switching signal frequency can become arbitrarily low making it impossible to guarantee the charge pump output voltage remains above the required minimum value
Solution Approach 1:
The patent segments the switching signal into two distinct components: standard PFM pulses for main power conversion and additional BFB pulses specifically for charge pump voltage regulation. This segmentation allows independent optimization of each function - PFM for efficiency and BFB for voltage reliability.
Solution Approach 2:
The switching signal is designed to serve multiple functions simultaneously: the standard PFM pulses handle main power conversion while additional BFB pulses provide charge pump voltage regulation. This multi-functionality resolves the contradiction by making the single switching signal capable of both improving efficiency and maintaining voltage reliability.
2Reliability
If additional BFB pulses are applied to maintain the boost feedback voltage, then the charge pump output voltage is maintained, but there is a risk of affecting the main switch-mode power supply voltage
Solution Approach 1:
The BFB pulses are designed with specific local characteristics - a high-side on-time/low-side on-time ratio less than the PFM pulses (theoretically half) - that creates a localized effect on the charge pump circuit while minimizing impact on the main power stage output voltage.
Solution Approach 2:
The patent applies preliminary anti-action by designing the BFB pulses with a charge balance characteristic where the net charge delivered to the output capacitor is zero or slightly negative. This pre-compensates for potential voltage disturbances, ensuring the main power stage output voltage remains stable despite the additional pulses.
3Loss of energy
If the switching signal frequency is reduced in PFM mode, then efficiency at light load conditions is improved, but it becomes impossible to guarantee adequate charge pump operation
Solution Approach 1:
The patent applies preliminary action by proactively injecting additional BFB pulses into the switching signal before the charge pump voltage can drop below the minimum required value. This preventive measure ensures adequate charge pump operation is maintained even when PFM frequency is reduced for efficiency.
Solution Approach 2:
The system uses feedback from the charge pump output voltage to determine when additional BFB pulses are needed. This feedback mechanism allows the switching signal to adapt dynamically, maintaining charge pump operation while preserving PFM efficiency benefits.
Data Source
AI summary
A controller produces high-side and low-side control signals. The high and low-side signals are used to switch high-side and low-side transistors in the power stage to control the voltage across the power stage output capacitor of the power stage. A boost feedback charge pump receives the low or high-side signal to increase the charge on a charge pump output capacitor. The controller is configured to send Pulse Frequency Modulation (PFM) high and low-side signals that control the voltage on the power stage output capacitor and charge the charge pump output capacitor. The controller is also configured to send boost feedback (BFB) high and low-side signals that charge the boost feedback capacitor, but are designed to not significantly change the charge on the power stage output capacitor.