From your requirement, it means that you need conversions to be done at specific instants of time. Are you using the ADC in free-running mode? In that case you can change it into hardware trigger mode. Now you can call ADC_StartConvert() API each time when you want to start a conversion. In continuous trigger mode the API starts the continuous conversion which makes it necessary to stop the conversion using the StopConvert() API. But in hardware trigger mode each StartConvert() call will act as a single trigger to the ADC to initiate a single conversion, so calling the StopConvert API will not be necessary.