A built-in activity detector monitors the PWM activity of the OUT_X pins. TPA3223 is designed to drive unclipped output signals all the way to PVDD and GND rails. In case of audio signal clipping when applying excessive input signal voltage, or in case of CB3C current protection being active, the amplifier feedback loop of the audio channel will respond to this condition with a saturated state, and the output PWM signals will stop unless special circuitry is implemented to handle this situation. To prevent the output PWM signals from stopping in a clipping or CB3C situation, narrow pulses are injected to the gate drive to maintain output activity. The injected narrow pulses are injected at every 4^th PWM frame, and thus the effective switching frequency during this state is reduced to 1/4 of the normal switching frequency.

Signal clipping is signaled on the OTW_CLIP pin and is self clearing when signal level reduces and the device reverts to normal operation. The OTW_CLIP pulses start at the onset to output clipping, typically at a THD level around 0.01%, resulting in narrow OTW_CLIP pulses starting with a pulse width of approximately 500 ns.

Figure 9-15 Signal Clipping PWM and Speaker Output Signals