36.5.5 Selecting the Voltage Reference Source

The user application can select the voltage reference for the ADC module, which can be internal or external. The Voltage Reference Input Selection bits, VREFSEL[2:0] (ADCCON3[15:13]), select the voltage reference for the ADC. The upper voltage reference (VREFH) and the lower voltage reference (VREFL) are the internal AVDD and AVSS voltage rails. When the voltage reference and band gap reference are ready, the BGVRRDY (ADCCON2[31]) bit is set. If a fault occurs in the voltage reference (such as a brown-out), the REFFLT bit (ADCCON2[30]) is set. The BGVRRDY and REFFLT bits can also generate interrupts if the BGVRIEN bit (ADCCON2[15]) and REFFLTIEN bit (ADCCON2[14]), respectively, are set.

The voltages applied to the external reference pins must comply with certain specifications. See Electrical Characteristics from Related Links.