Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 62
11.2 Internal Voltage Reference
ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P features an internal bandgap reference. This
reference is used for Brown-out Detection, and it can be used as an input to the Analog Comparator or the ADC.
11.2.1 Voltage Reference Enable Signals and Start-up Time
The voltage reference has a start-up time that may influence the way it should be used. The start-up time is
given in ”” on page 333. To save power, the reference is not always turned on. The reference is on during the
following situations:
1. When the BOD is enabled (by programming the BODLEVEL [2:0] Fuse).
2. When the bandgap reference is connected to the Analog Comparator (by setting the ACBG bit in ACSR).
3. When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user must always allow
the reference to start up before the output from the Analog Comparator or ADC is used. To reduce power
consumption in Power-down mode, the user can avoid the three conditions above to ensure that the reference
is turned off before entering Power-down mode.