28.6.3 Prescaler

The ADC is clocked by GCLK_ADC. There is also a prescaler in the ADC to enable conversion at lower clock rates.

Refer to CTRLB for details on prescaler settings.

Figure 28-2. ADC Prescaler
The propagation delay of an ADC measurement depends on the selected mode and is given by:
  • Single-shot mode:
    PropagationDelay=1+Resolution2+DelayGainfCLK+ADC
  • Free-running mode:
    PropagationDelay=Resolution2+DelayGainfCLK+ADC
    Table 28-1. Delay Gain
    Delay Gain (in CLK_ADC Period)
    INTPUTCTRL.GAIN[3:0]Free-running modeSingle shot mode
    NameDifferential ModeSingle-Ended ModeDifferential modeSingle-Ended mode
    1X0x00001
    2X0x1010.51.5
    4X0x21112
    8X0x3121.52.5
    16X0x42223
    Reserved0x5 ... 0xEReservedReservedReservedReserved
    DIV20xF010.51.5