
192
42073A-MCU Wireless-02/13
ATmega2564/1284/644RFR2
Configurable to use an external voltage regulator;
The
internal
voltage
regulators
supply
a
stabilized
voltage
to
the
ATmega2564/1284/644RFR2. The AVREG provides the regulated 1.8V supply voltage
for the analog section and the DVREG supplies the 1.8V supply voltage for the digital
section. The DVREG is enabled during startup and is switched off if the power-chain is
disabled. The AVREG is enabled only on request by either the A/D converter or the
radio transceiver.
Figure 12-4. Simplified Schematic of AVREG/DVREG
B andgap
voltage
reference
1.25V
A V D D ,
D V D D
(D )E V D D
The voltage regulators require bypass capacitors for stable operation. The value of the
bypass capacitors determines their settling time. The bypass capacitors shall be placed
as close as possible to the pins and shall be connected to ground with the shortest
possible traces.
The voltage regulators can be configured with the register VREG_CTRL. It is
recommended to use the internal regulators but it is also possible to supply the low
voltage domains by an external voltage supply. For this configuration the internal
analog voltage regulator needs to be switched off by setting the register bit
on page 127). The internal digital voltage regulator may not be switched off, an external
voltage has to overdrive the internal voltage. A regulated external supply voltage of
1.8V must then be connected to the pins 13, 14 (DVDD) and pin 29 (AVDD). When
turning on the external supply ensure a sufficiently long stabilization time before
interacting with the ATmega2564/1284/644RFR2.
The status bits AVDD_OK = 1 and DVDD_OK = 1 of register VREG_CTRL indicate an
enabled and stable internal supply voltage. Reading value 0 indicates that the internal
supply voltage is disabled or not yet settled to the final value.
In case the ATmega2564/1284/644RFR2 is not supplied with a sufficient (D)EVDD and
the digital voltage regulator output voltage is too low, a power on reset (POR) is
12.5.4 Low Leakage Voltage Regulator (LLVREG)
The main digital voltage regulator (DVREG) will be switched off during the
DEEP_SLEEP modes “power-down” and “power-save”. The Low Leakage Voltage
Regulator will then keep the digital supply voltage to provide data retention. No
application software control is required.
During the active power states, when the main voltage regulator supplies the chip, the
Low Leakage Voltage Regulator is digitally calibrated. Its output voltage is adjusted to