Datasheet

32142D–06/2013

ATUC64/128/256L3/4U

6. Supply and Startup Considerations

6.1 Supply Considerations

6.1.1 Power Supplies

The ATUC64/128/256L3/4U 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, the USB pins, and the internal regulator. Voltage is 1.8 to 3.3V

nominal if USB is not used, and 3.3V nominal when USB is used.

• 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.

Refer to Section 35. on page 897 for power consumption on the various supply pins.

For decoupling recommendations for the different power supplies, please refer to the schematic

checklist.

Refer to Section on page 10 for power supply connections for I/O pins.

6.1.2 Voltage Regulator

The ATUC64/128/256L3/4U embeds a voltage regulator that converts from 3.3V nominal to

1.8V with a load of up to 60 mA. The regulator supplies the output voltage on VDDCORE. The

regulator may only be used to drive internal circuitry in the device. VDDCORE should be exter-

nally 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

and GND as close to the device as possible. Please refer to Section 35.8 on page 911 for

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

IN1

OUT1

OUT2

IN2

IN3