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32145C–06/2013
AT32UC3L0128/256
6.
Supply and Startup Considerations
6.1
Supply Considerations
6.1.1
Power Supplies
The AT32UC3L0128/256 has several types of power supply pins:
VDDIO: Powers I/O lines. Voltage is 1.8 to 3.3V nominal.
VDDIN: Powers I/O lines and the internal regulator. Voltage is 1.8 to 3.3V nominal.
VDDANA: Powers the ADC. Voltage is 1.8V nominal.
VDDCORE: Powers the core, memories, and peripherals. Voltage is 1.8V nominal.
The ground pins GND are common to VDDCORE, VDDIO, and VDDIN. The ground pin for
VDDANA is GNDANA.
When VDDCORE is not connected to VDDIN, the VDDIN voltage must be higher than 1.98V.
For decoupling recommendations for the different power supplies, please refer to the schematic
checklist.
6.1.2
Voltage Regulator
The AT32UC3L0128/256 embeds a voltage regulator that converts from 3.3 V nominal to 1.8V
with a load of up to 60mA. The regulator supplies the output voltage on VDDCORE. The regula-
tor may only be used to drive internal circuitry in the device. VDDCORE should be externally
connected to the 1.8V domains. See
Section 6.1.3 for regulator connection figures.
Adequate output supply decoupling is mandatory for VDDCORE to reduce ripple and avoid
oscillations. The best way to achieve this is to use two capacitors in parallel between VDDCORE
decoupling capacitors values and regulator characteristics.
Figure 6-1.
Supply Decoupling
The voltage regulator can be turned off in the shutdown mode to power down the core logic and
keep a small part of the system powered in order to reduce power consumption. To enter this
mode the 3.3V supply mode, with 1.8V regulated I/O lines power supply configuration must be
used.
3.3V
1.8V
VDDIN
VDDCORE
1.8V
Regulator
C
IN1
C
OUT1
C
OUT2
C
IN2
IN3
C