ATMEGA644PV ATMEL [ATMEL Corporation], ATMEGA644PV Datasheet - Page 34

• Manufacturer Part Number: ATMEGA644PV
• Description: 8-bit Microcontroller with 16/32/64K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

7.5
34
Low Frequency Crystal Oscillator
ATmega164P/324P/644P
Table 7-6.
Notes:
The Low-frequency Crystal Oscillator is optimized for use with a 32.768 kHz watch crystal.
When selecting crystals, load capasitance and crystal’s Equivalent Series Resistance, ESR
must be taken into consideration. Both values are specified by the crystal vendor.
ATmega164P/324P/644P oscillator is optimized for very low power consumption, and thus when
selecting crystals, see
12.5 pF crystals
Table 7-7.
Note:
The Low-frequency Crystal Oscillator provides an internal load capacitance of typical 8.0 pF.
Crystals with recommended 8.0 pF load capacitance can be without external capacitors as
shown in
Oscillator Source /
Power Conditions
Ceramic resonator, fast
rising power
Ceramic resonator, slowly
rising power
Crystal Oscillator, BOD
enabled
Crystal Oscillator, fast
rising power
Crystal Oscillator, slowly
rising power
1. These options should only be used when not operating close to the maximum frequency of the
2. These options are intended for use with ceramic resonators and will ensure frequency stability
1. Maximum ESR is typical value based on characterization
Figure 7-3 on page
device, and only if frequency stability at start-up is not important for the application. These
options are not suitable for crystals.
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.
Start-up Times for the Full Swing Crystal Oscillator Clock Selection
Maximum ESR Recommendation for 32.768 kHz Watch Crystal
Crystal CL (pF)
12.5
9.0
Table 7-7 on page 34
Start-up Time from
35.
Power-down and
Power-save
16K CK
16K CK
16K CK
1K CK
1K CK
for maximum ESR recommendations on 9 pF and
Additional Delay
14CK + 4.1 ms
14CK + 65 ms
14CK + 4.1 ms
14CK + 65 ms
(V
from Reset
CC
14CK
= 5.0V)
Max ESR [kΩ]
(2)
(2)
65
30
CKSEL0
(1)
0
1
1
1
1
8011D–AVR–02/07
SUT1..0
11
00
01
10
11