SAM7S256_14 Datasheet, PDF (12/775 Pages) ATMEL Corporation – ARM-based Flash MCU

5. Power Considerations
5.1 Power Supplies
The SAM7S 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:
z VDDIN pin. It powers the voltage regulator and the ADC; voltage ranges from 3.0V to 3.6V, 3.3V nominal.
z VDDOUT pin. It is the output of the 1.8V voltage regulator.
z 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.
z 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.
z 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.
z 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.
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 SAM7S Series 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 activated, 20 µA 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 SAM7S Series 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.
5.4 Typical Powering Schematics
The SAM7S Series supports a 3.3V single supply mode. The internal regulator is connected to the 3.3V source and its
output feeds VDDCORE and the VDDPLL. Figure 5-1 shows the power schematics to be used for USB bus-powered
systems.
SAM7S Series [DATASHEET] 12
6175M–ATARM–26-Oct-12