An application example for the KM family would be a smoke detector. As far as how the low battery detect operates, the ADC is referenced to VDD, and then continually measures the internal band gap. As the internal band gap is a constant, any changes in the ADC value represent a change in VDD. As VDD decreases the ADC will show an increased band gap reading. Once the ADC value represents VDD falling below a designated trip point the low battery detect will go off. The picture also shows how the smoke chamber analysis works with two integrated OpAmps, one on the transmitter side and the other on the receiving side. When smoke is detected, the transmitter reflects the IR light and the receiver will see the light. The transmit OpAmp controls the intensity and the receiving OpAmp enables sensitivity control to measure the intensity. The output of the OpAmp goes to ADC which does the conversion to digital. Finally, an 8-bit DAC drives the horn for the alarm.