The increasing demand for high-definition audio in mobile platforms is creating the necessity of adequate operation limits for smart amplifiers to safely maximize the power delivered to micro-speakers. The maximum voice-coil temperature (Tmax) is an important parameter for protection algorithms that prevent damage. Standard tests used by micro-speaker suppliers to specify Tmax provide a conservative estimate that depends on the voice-coil materials. Other tests consider the rated noise power, a specification obtained by rigorous lifetime tests. This paper investigates the thermal limits when micro-speakers operate at their specified rated power. These power-based thermal limits are contrasted with values of Tmax specified in datasheets. The evidence found is used to recommend procedures to measure power-based thermal limits that avoid over-protection.
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