2.3.1 Requirements

As described in the Electrical Characteristics chapter of the SAM9X7 Series data sheet, low impedance decoupling of the device power supply inputs must be provided. A 10 nF to 220 nF ceramic X7R (or X5R) capacitor placed very close to each power supply input is a minimum requirement.

In the example below, 100 nF 0201, X5R rated at 16V multilayer ceramic capacitors were used with good results. Using small footprint capacitors enabled an optimal placement on the bottom of the PCB, very close to vias connected to the power pins of the MPU.

Additionally, the internal LDO that generates VDDOUT25 requires two extra capacitors. As stated in table “VDDOUT25 Voltage Regulator Characteristics” in the SAM9X7 Series data sheet Electrical Characteristics chapter:

• A 2.2 µF (min) capacitor should be connected at its input (at VDDIN33).
• A 1 to 2.7 µF (typ) capacitor should be connected at its output (at VDDOUT25).
• The output capacitor should have a low ESR, between 0.01 and 0.3 ohm.