I am using a TPA2013D1 in a new design to drive a small speaker, powered directly by a single cell Li-Ion battery. This works well but there is now a requirement to feed the speaker from an external balanced analog amp when the battery is dead. First thought is to switch the speaker over using MOSFETS when the battery fails (I have access to another low current battery source in this scenario) but what about instead just keeping the TPA2013D1 alive in shutdown and back-feeding the external amp into the speaker with the TPA2013D1 still connected? Any info on the architecture of the output drivers on pins 11-15? Are they just the standard H bridge as labelled in the block diagram that connects to the rails when on, and that could safely be back-fed within the limits of the power supply when off? Or is there additional circuitry that could be damaged?
It doesn't sound safe to connect two amp outputs together, but this is a very space limited, battery powered unit. I definitely can't afford to drive a relay or even an SSR, I have only about 30 mA for the whole system when the main battery is dead. This includes a codec and processor. There is no room for a reed relay either.
An alternative would be to configure MOSFET switches to disconnect the external amp only when the PWM drive is on, effectually paralleling the amps together. In this case the TPA2013 is just driving external switches as in the case of a PWM booster configuration. Any thoughts?
