Atmel Xplained Pro Evaluation Kit for the ATSAMD21J18A Microcontroller ATSAMD21-XPRO ATSAMD21-XPRO Fiche De Données
Codes de produits
ATSAMD21-XPRO
981
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181C–SAM-D21_Datasheet–07/2014
2. Decoupling capacitor should be placed close to the device for each supply pin pair in the signal group.
38.6.3 External Real Time Oscillator
The low frequency crystal oscillator is optimized for use with a 32.768kHz watch crystal. When selecting crystals, load
capacitance and crystal’s Equivalent Series Resistance (ESR) must be taken into consideration. Both values are
specified by the crystal vendor.
capacitance and crystal’s Equivalent Series Resistance (ESR) must be taken into consideration. Both values are
specified by the crystal vendor.
SAM D21 oscillator is optimized for very low power consumption, hence close attention should be made when selecting
crystals, see
crystals, see
for maximum ESR recommendations on 9pF and 12.5pF crystals.
The Low-frequency Crystal Oscillator provides an internal load capacitance of typical values available in
to use a Crystal inferior to 12.5pF load capacitance without external capacitors as shown in
Note:
Maximum ESR is typical value based on characterization. These values are not covered by test limits in
production.
production.
Figure 38-7. External Real Time Oscillator without Load Capacitor
However, to improve Crystal accuracy and Safety Factor, it can be recommended by crystal datasheet to add external
capacitors as shown in
capacitors as shown in
To find suitable load capacitance for a 32.768kHz crystal, consult the crystal datasheet.
Figure 38-8. External Real Time Oscillator with Load Capacitor
Notes: 1. These values are given only as typical examples.
2. Decoupling capacitor should be placed close to the device for each supply pin pair in the signal group.
Table 38-6. Maximum ESR Recommendation for 32.768kHz Crystal
Crystal C
L
(pF)
Max ESR [k
Ω]
12.5
313
Table 38-7. External Real Time Oscillator Checklist
Signal Name
Recommended Pin Connection
Description
XIN32
Load capacitor 22pF
Timer oscillator input
XOUT32
Load capacitor 22pF
Timer oscillator output
XOUT32
XIN32
32.768kHz
XOUT32
XIN32
32.768kHz
22pF
22pF