34
8018P–AVR–08/10
ATmega169P
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in
TableNotes:
1. These options should only be used when not operating close to the maximum frequency of the
device, and only if frequency stability at start-up is not important for the application. These
options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum fre-
quency of the device, and if frequency stability at start-up is not important for the application.
8.6
Low-frequency Crystal Oscillator
The Low-frequency Crystal Oscillator is optimized for use with a 32.768 kHz 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. ATmega169P
oscillator is optimized for very low power consumption, and thus when selecting crystals, see
Table 8-7 for maximum ESR recommendations on 9 pF and 6.5 pF crystals.
Table 8-7.
Maximum ESR Recommendation for 32.768 kHz Watch Crystal
Note:
1. Maximum ESR is typical value based on characterization
The Low-frequency Crystal Oscillator provides an internal load capacitance, see
Table 8-8 onTable 8-6.
Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0
SUT1:0
Start-up Time from
Power-down and
Power-save
Additional Delay
from Reset
(VCC = 5.0V)
Recommended Usage
0
00
14CK + 4.1 ms
Ceramic resonator, fast
rising power
0
01
14CK + 65 ms
Ceramic resonator, slowly
rising power
010
14CK
Ceramic resonator, BOD
enabled
011
14CK + 4.1 ms
Ceramic resonator, fast
rising power
100
14CK + 65 ms
Ceramic resonator, slowly
rising power
1
01
16K CK
14CK
Crystal Oscillator, BOD
enabled
1
10
16K CK
14CK + 4.1 ms
Crystal Oscillator, fast
rising power
1
11
16K CK
14CK + 65 ms
Crystal Oscillator, slowly
rising power
Crystal CL (pF)
Max ESR [k
6.5
60
935
