Datasheet

The typical parasitic load capacitance values are available in the Electrical Characteristics section. This
capacitance and PCB capacitance can allow using a crystal inferior to 12.5pF load capacitance without
external capacitors as shown in the next figure.
Figure 59-10. External Real Time Oscillator without Load Capacitor
XOUT32
XIN32
32.768kHz
To improve accuracy and Safety Factor, the crystal datasheet can recommend adding external capacitors
as shown the figure below.
To find suitable load capacitance for a 32.768kHz crystal, consult the crystal datasheet.
Figure 59-11. External Real Time Oscillator with Load Capacitor
XOUT32
XIN32
32.768kHz
18pF
18pF
Table 59-5. External Real Time Oscillator Checklist
Signal Name Recommended Pin Connection Description
XIN32 Load capacitor 18pF
(1)(2)
Timer oscillator input
XOUT32 Load capacitor 18pF
(1)(2)
Timer oscillator output
1. These values are only given as typical examples.
2. The capacitors should be placed close to the device for each supply pin pair in the signal group.
Note: In order to minimize the cycle-to-cycle jitter of the external oscillator, keep the neighboring pins as
steady as possible. For neighboring pin details, refer to the Oscillator Pinout section.
59.6.4 Calculating the Correct Crystal Decoupling Capacitor
The model shown in Figure 59-12 can be used to calculate correct load capacitor for a given crystal. This
model includes internal capacitors C
Ln
, external parasitic capacitance C
ELn
and external load capacitance
C
Pn
.
SAM D5x/E5x Family Data Sheet
Schematic Checklist
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 2104