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AT91SAM7S128 Summary Preliminary

6116AS–ATARM–20-Oct-04

Power Considerations

Power Supplies

The AT91SAM7S128 has six types of power supply pins and integrates a voltage regu-

lator, allowing the device to be supplied with only one voltage. The six power supply pin

types are:

•

VDDIN pin. It powers the voltage regulator; 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.

•

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 provided and should be connected as shortly as possible to the system ground

plane.

Power Consumption

The AT91SAM7S128 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.

Voltage Regulator

The AT91SAM7S128 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

20 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.