The ADC integrates a precision, low-drift, 2.5-V reference. The internal reference is enabled by setting REFCON[1:0] to 10 (reference is always on) or 01 (reference is on, but powers down in power-down mode) in the reference control register (05h). By default, the internal voltage reference is powered down. To select the internal reference for use with the ADC, set the REFSEL[1:0] bits to 10. The REFOUT pin provides a buffered reference output voltage when the internal reference voltage is enabled. The negative reference output is the REFCOM pin, as shown in Figure 52. Connect a capacitor in the range of 1 μF to 47 μF between REFOUT and REFCOM. Larger capacitor values help filter more noise at the expense of a longer reference start-up time.
The capacitor is not required if the internal reference is not used. However, the internal reference must be powered on if using the IDACs.
The internal reference requires a start-up time that must be accounted for before starting a conversion, as shown in Table 10.
|REFOUT CAPACITOR||SETTLING ERROR||SETTLING TIME (ms)|