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6117BS–ATARM–07-Apr-05

AT91SAM7S256

5.

Power Considerations

5.1

Power Supplies

The AT91SAM7S256 has six types of power supply pins and integrates a voltage regulator,

allowing the device to be supplied with only one voltage. The six power supply pin types are:

• VDDIN pin. It powers the voltage regulator and the ADC; voltage ranges from 3.0V to 3.6V,

3.3V nominal. If the voltage regulator is not used, VDDIN should be connected to GND.

• VDDOUT pin. It is the output of the 1.8V voltage regulator.

• VDDIO pin. It powers the I/O lines and the USB transceivers; dual voltage range is

supported. Ranges from 3.0V to 3.6V, 3.3V nominal. Note that supplying less than 3.0V to

VDDIO prevents any use of the USB transceivers.

• VDDFLASH pin. It powers a part of the Flash and is required for the Flash to operate

correctly; voltage ranges from 3.0V to 3.6V, 3.3V nominal.

• VDDCORE pins. They power the logic of the device; voltage ranges from 1.65V to 1.95V,

1.8V typical. It can be connected to the VDDOUT pin with decoupling capacitor.

VDDCORE is required for the device, including its embedded Flash, to operate correctly.

• VDDPLL pin. It powers the oscillator and the PLL. It can be connected directly to the

VDDOUT pin.

No separate ground pins are provided for the different power supplies. Only GND pins are pro-

vided and should be connected as shortly as possible to the system ground plane.

5.2

Power Consumption

The AT91SAM7S256 has a static current of less than 60 µA on VDDCORE at 25°C, including

the RC oscillator, the voltage regulator and the power-on reset when the brown-out detector is

deactivated. Activating the brown-out detector adds 20 µA static current.

The dynamic power consumption on VDDCORE is less than 50 mA at full speed when running

out of the Flash. Under the same conditions, the power consumption on VDDFLASH does not

exceed 10 mA.

5.3

Voltage Regulator

The AT91SAM7S256 embeds a voltage regulator that is managed by the System Controller.

In Normal Mode, the voltage regulator consumes less than 100 µA static current and draws

100 mA of output current.

The voltage regulator also has a Low-power Mode. In this mode, it consumes less than 25 µA

static current and draws 1 mA of output current.

Adequate output supply decoupling is mandatory for VDDOUT to reduce ripple and avoid

oscillations. The best way to achieve this is to use two capacitors in parallel: one external 470

pF (or 1 nF) NPO capacitor must be connected between VDDOUT and GND as close to the

chip as possible. One external 2.2 µF (or 3.3 µF) X7R capacitor must be connected between

VDDOUT and GND.

Adequate input supply decoupling is mandatory for VDDIN in order to improve startup stability

and reduce source voltage drop. The input decoupling capacitor should be placed close to the

chip. For example, two capacitors can be used in parallel: 100 nF NPO and 4.7 µF X7R.