Atmel AT01080: XMEGA E Schematic Checklist [APPLICATION NOTE]
42087A
−
AVR
−
04/2013
6
3.2
Crystal oscillator
Figure 3-2. Crystal oscillator example schematic.
Table 3-2. Crystal oscillator checklist.
Signal name
Recommended pin connection
Description
XTAL1
Load capacitor 15pF
(1)(2)
External crystal between 0.4MHz to 16MHz
XTAL2
Load capacitor 15pF
(1)(2)
Notes:
1. These values are given only as a typical example. Please refer to the crystal datasheet to determine the
capacitor value for the crystal used or refer to the applic”.
2.
Load capacitors should be placed close to the device and crystal pins.
3.3
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.
The Atmel AVR XMEGA E oscillator is optimized for very low power consumption, and thus when selecting crystals,
see
for maximum ESR recommendations on 9pF and 12.5pF crystals.
Table 3-3. Maximum ESR recommendation for 32.768kHz watch crystal.
Crystal CL [pF]
Maximum ESR [k
Ω
]
(1)
9.0
65
12.5
30
Note:
1. Maximum ESR is typical value based on characterization.
The low-frequency crystal oscillator provides an internal load capacitance of typical 3.0pF. Crystals with recommended
3.0pF load capacitance can be without external capacitors as shown in
