The SAM L22 Xplained Pro has a backup super capacitor for use with the SAM L22 backup system. The super capacitor can be connected to the device by placing a jumper over pin 1-2 on the 3-pin VBAT SELECT header.
By default the jumper is placed over pin 2-3 to select the board power supply. This configuration is selected to avoid draining the super capacitor and can be used during development.
Due to the high capacitive load represented by the super capacitor, a 220Ω limiting resistor is added to reduce inrush current. The charging supply is the targets main supply and a low-power opamp is used for disconnecting the charger input when removing power. This is added to avoid a current leak back to the main supply from the super capacitor when power is removed.
A full charge of the super capacitor from empty will take approximately 45 seconds and can supply the target device in backup mode with ULP running for up to 24 hours. Other modes are not characterized, but will reduce the available time in backup mode respectively. For more information about the current consumption in other modes, refer to the electrical characteristics chapter in the SAM L22 datasheet.
| VBAT SELECT pin | Function |
|---|---|
| 1 | Power from super capacitor (47mF) |
| 2 | PB03/VBAT pin on SAM L22 |
| 3 | Power from board supply |