51.2.1 Power Supply Connections

The following figures shows the recommended power supply connections for switched/linear mode, linear mode only and with battery backup.

Table 51-1. Power Supply Connections, V_DDCORE or V_SW From Internal Regulator
Signal Name	Recommended Pin Connection	Description
V_DDIO	1.6V to 3.6V Decoupling/filtering capacitors 100 nF⁽¹⁾⁽²⁾ and 10 µF⁽¹⁾ Decoupling/filtering inductor 10 µH⁽¹⁾⁽³⁾	Digital supply voltage
V_DDANA	1.6V to 3.6V Decoupling/filtering capacitors 100 nF⁽¹⁾⁽²⁾ and 10 µF⁽¹⁾ Ferrite bead⁽⁴⁾ prevents the V_DD noise interfering with V_DDANA	Analog supply voltage
V_DDIN	1.6V to 3.6V Decoupling/filtering capacitors 100 nF⁽¹⁾⁽²⁾ and 10 µF⁽¹⁾ Decoupling/filtering inductor 10 µH⁽¹⁾⁽³⁾	Digital supply voltage
V_BAT	1.6V to 3.6V when connected	External battery supply input
V_DDCORE	0.9V to 1.2V typical Decoupling/filtering capacitors 100 nF⁽¹⁾⁽²⁾ and 1 µF⁽¹⁾	Linear regulator mode: Core supply voltage output/ external decoupling pin Switched regulator mode: Core supply voltage input, must be connected to V_SW via inductor
V_SW	Switching regulator mode: 10 µH inductor with saturation current above 150 mA and DCR<1Ω Linear regulator mode: Not connected	On-chip switching mode regulator output
GND	-	Ground
GND_ANA	-	Ground for the analog power domain

Note:

These values are only given as a typical example.
Decoupling capacitors must be placed close to the device for each supply pin pair in the signal group, low ESR capacitors must be used for better decoupling.
An inductor must be added between the external power and the V_DD for power filtering.
A ferrite bead has better filtering performance compared to standard inductor at high frequencies. A ferrite bead can be added between the main power supply (V_DD) and V_DDANA to prevent digital noise from entering the analog power domain. The bead should provide enough impedance (e.g. 50Ω at 20 MHz and 220Ω at 100 MHz) to separate the digital and analog power domains. Make sure to select a ferrite bead designed for filtering applications with a low DC resistance to avoid a large voltage drop across the ferrite bead.
When the VBAT pin is used for battery supply, PB03 (VBAT) cannot be used as PORT I/O pin or for any other multiplexed peripheral signal. The VBAT pin should not be powered before it has been properly configured by software for battery supply. Till its configuration, PB03 will behave as a standard I/O regarding leakage.

SAM L21