You should be able to use the LPCOMP (low power comparator) for this.
You can set the threshold to VDD*N/8, where N is a whole number between 1 and 7.
You can also use an external reference voltage, which could be provided by a voltage divider to give you an arbitrary threshold.
The ADC uses way more power. The run current for the LPCOMP is 0.5uA, versus 260uA for the ADC ;)
Typically you don't run the ADC all the time, but you would have to run it very seldom to get down towards a 0.5uA average, and then the latency would be much higher.
In other words it doesn't make sense to use the ADC if you only need to detect if you reach a threshold voltage.
The ADC uses way more power. The run current for the LPCOMP is 0.5uA, versus 260uA for the ADC ;)
Typically you don't run the ADC all the time, but you would have to run it very seldom to get down towards a 0.5uA average, and then the latency would be much higher.
In other words it doesn't make sense to use the ADC if you only need to detect if you reach a threshold voltage.
