Hi Sanjeev,

an internal ADC was cheaper, but its more difficult to avoid additional noise from the digital power supply. E.g. analog and digital ground must be connected together close as possible and the pcb should be designed more carefully.
In case, if I can deal with 8 bit resolution an internal ADC can do the job. But for 12 bit or higher or if noise can happen between the analog and the digital ground, then an external ADC was better to use.


Peter