Charge Pump Class D Audio Amplifier Current Limit Control
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Solution Overview
Problem
Class D audio amplifiers in portable battery-powered systems face challenges in effectively limiting current draw, which affects operational time, as existing methods like inductor-based boost converters require significant board space and thermal power loss in capacitor-based solutions.
Innovation Solution
An audio amplifier circuit with a multiplexer that selects between different input signals based on current limit values, using a signal generator and driver circuit to control the duty cycle of the pulse-width modulator, thereby regulating the battery current through a current sense terminal and current limit terminal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If inductor-based boost converters are used for current limiting, then current draw is limited, but board space increases significantly
Solution Approach 1:
The patent extracts the inductor component from the current limiting circuit and replaces it with a capacitor-based charge pump mechanism. This removal of the inductor eliminates the need for large magnetic components while maintaining current limiting functionality through capacitive energy storage and transfer.
Solution Approach 2:
The patent substitutes the magnetic field-based inductor system with an electric field-based capacitor system. The charge pump uses capacitors to store and transfer energy, replacing the inductive mechanism with a capacitive one that achieves similar current limiting effects without requiring large board space for magnetic components.
2Area of stationary object
If capacitor-based solutions are used for current limiting, then board space is reduced, but thermal power loss increases
Solution Approach 1:
The patent implements periodic charging and discharging cycles of the capacitors in the charge pump. By operating in discrete switching phases (charging phase and discharging phase), the system minimizes continuous power dissipation and reduces thermal losses compared to linear regulation methods, while maintaining effective current limiting.
Solution Approach 2:
The patent optimizes capacitor values, switching frequencies, and duty cycles to minimize power loss. By carefully selecting capacitance values and controlling the switching parameters of the charge pump, the system achieves efficient operation with reduced thermal dissipation while maintaining compact board layout.
3Loss of energy
If duty cycle control is used to regulate battery current, then current limiting is achieved, but control circuit complexity increases
Solution Approach 1:
The patent employs feedback mechanisms where the output current is sensed and compared with a reference, and the duty cycle of the charge pump is adjusted accordingly. This closed-loop control automatically regulates battery current without requiring complex external control circuits, as the regulation is inherent in the feedback-controlled switching mechanism.
Solution Approach 2:
The patent integrates multiple functions into the charge pump control circuit, including current sensing, duty cycle modulation, and protection logic within a single unified control mechanism. This multi-functional approach reduces overall system complexity by combining what could be separate circuits into one integrated control structure.
Data Source
AI summary
Described embodiments include an audio amplifier circuit that includes a first amplifier having a differential first amplifier input adapted to be coupled to an audio input source, a multiplexer having first and second mux inputs, a control input and a mux output. The first mux input is coupled to the differential amplifier output. There is a signal generator having a generator input coupled to the mux output. There is also a driver circuit having a driver circuit input and a driver circuit output, the driver circuit input coupled to the generator output, and a second amplifier having a first error input coupled to a current sense terminal that is configured to provide a voltage proportional to a current supplied from a power supply terminal, and a second error input coupled to a current limit terminal configured to provide a reference voltage proportional to a current limit value.