Q: Can the audio section ADC be used as a general purpose converter? Is there anything special about the audio ADC that could hamper general purpose conversion?
A: You can use the audio ADC for general purpose conversion. The potential problem comes from the microphone amplifier. The input impedance is not infinity. It is equal 40K to 60K.
Q: Can PMIC DAC be used for converting ECG data to analog representation for output (this is a standard feature of defibrillators)? Signal would be in 0Hz - 400Hz range? What's the DC performance near DC?
A: The Audio DAC can be used to convert DC value. In the digital section, the high pass filter can be bypassed by using register configuration. The DC performance should be equivalent to the performance @ 1KHz.