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6175H–ATARM–03-Dec-07
AT91SAM7S Series Preliminary
5.
Power Considerations
5.1
Power Supplies
The AT91SAM7S Series 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.
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 or from 1.65V to 1.95V, 1.8V 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.
During startup, core supply voltage (VDDCORE) slope must be superior or equal to 6V/ms.
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.
In order to decrease current consumption, if the voltage regulator and the ADC are not used,
VDDIN, ADVREF, AD4, AD5, AD6 and AD7 should be connected to GND. In this case VDDOUT
should be left unconnected.
5.2
Power Consumption
The AT91SAM7S Series has a static current of less than 60 A on VDDCORE at 25°C, including
the RC oscillator, the voltage regulator and the power-on reset. When the brown-out detector is
activated, 20 A static current is added.
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 AT91SAM7S Series embeds a voltage regulator that is managed by the System Controller.
In Normal Mode, the voltage regulator consumes less than 100 A 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 A
static current and draws 1 mA of output current.
Adequate output supply decoupling is mandatory for VDDOUT to reduce ripple and avoid oscil-
lations. 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 F (or 3.3 F) X7R capacitor must be connected between VDDOUT
and GND.