9.3.4 Speaker Load Limitation

Speakers are nonlinear loads with varying impedance (magnitude and phase) over the audio frequency. A portion of speaker load current can flow back into the boost converter output through the Class-D output H-bridge high-side device. This is dependent on the phase change over frequency on the speaker, and the audio signal amplitude and frequency content. Most portable speakers have limited phase change at the resonant frequency, typically no more than 40 or 50 degrees. To avoid excess flow-back current, use speakers with limited phase change. Otherwise, flow-back current could drive the PVDD voltage above the absolute maximum recommended operational voltage.

Confirm proper operation by connecting the speaker to the TPA2080D1 and driving it at maximum output swing. Observe the PVDD voltage with an oscilloscope. In the unlikely event the PVDD voltage exceeds 6.5 V, add a 6.8-V Zener diode between PVDD and ground to ensure the TPA2080D1 operates properly. The amplifier has thermal overload protection and deactivates if the die temperature exceeds 150°C. It automatically reactivates once die temperature returns below 150°C. Built-in output overcurrent protection deactivates the amplifier if the speaker load becomes short-circuited. The amplifier automatically restarts 1.6 seconds after the overcurrent event. Although the TPA2080D1 Class-D output can withstand a short between OUT+ and OUT–, do not connect either output directly to GND, VDD, or VBAT as this could damage the device.