I have several piezoelectric crystal speakers connected to a TI MSP430 series MCU.
All speakers share a common PWM driven MCU pin and each one use a distinct MCU pin to select them. If only one of those select pins is driven low or high and the others are in open state, one distinct speaker can output the audio waveform delivered by the PWM pin. The peak-to-peak PWM amplitude is 3V this way, as the select pins can't be driven by the PWM frequency too.
Now I need to raise the volume level of the audio output.
I tried to use an integrated amplifier, however the options are scarce as the circuit should be battery powered for years, and only amplifiers with uA standby consumption are usable. I tried some, but they are meant for analog input and can't cope with the PWM drive, thus producing a massive noise floor.
What else options are there? It is possible to use some IC providing an balanced PWM drive (eg. dual H bridge to provide 6V peak-to-peak) which operate with one-digit uA standby power? Or is there any discrete circuit with equally low static consumption?