31
ATmega165A/PA/325A/PA/3250A/PA/645A/P/6450A/P [DATASHEET]
8285E–AVR–02/2013
Notes:
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 XTALs.
2. These options are intended for use with ceramic resonators and will ensure frequency stability at start-up. They can
also be used with XTALs when not operating close to the maximum frequency of the device, and if frequency stabil-
ity at start-up is not important for the application.
9.6
Low-frequency XTAL Oscillator
The Low-frequency XTAL Oscillator is optimized for use with a 32.768kHz watch XTAL. When selecting XTALs,
load capacitance and XTAL’s Equivalent Series Resistance, ESR must be taken into consideration. Both values
ar e
spe c if ie d
by
the
XT AL
v end or .
Atm e l
ATmega165A/165PA/325A/325PA/3250A/3250PA/645A/645P/6450A/6450P oscillator is optimized for very low
power consumption, and thus when selecting XTALs, see
Table 9-7 for maximum ESR recommendations on 9pF
and 6.5pF XTALs.
Note:
1. Maximum ESR is typical value based on characterization.
The low-frequency XTAL oscillator provides an internal load capacitance, see
Table 9-9 on page 32 at each TOSC
pin.
ATmega325A/325PA/3250A/3250PA/645A/645P/6450A/6450P oscillator is optimized for very low power con-
sumption, and thus when selecting XTALs, see
Table 9-8 on page 31 for maximum ESR recommendations on
6.5 pF, 9.0 pF and 12.5 pF XTALs.
Table 9-8.
Maximum ESR recommendation for 32.768kHz watch XTAL Atmel
ATmega325A/325PA/3250A/3250PA/645A/645P/6450A/6450P.
Note:
1. Maximum ESR is typical value based on characterization.
101
16K CK
14CK
XTAL Oscillator, BOD
enabled
1
10
16K CK
14CK + 4.1ms
XTAL Oscillator, fast rising
power
1
11
16K CK
14CK + 65ms
XTAL Oscillator, slowly
rising power
Table 9-6.
Start-up times for the XTAL oscillator clock selection. (Continued)
CKSEL0
SUT1:0
Start-up time from
power-down and
power-save
Additional delay
from reset
(V
CC = 5.0V)
Recommended usage
Table 9-7.
Maximum ESR recommendation for 32.768kHz watch XTAL ATmega165A/ATmega165PA.
XTAL CL [pF]
Max ESR [k
6.5
60
935
XTAL CL [pF]
Max ESR [k
6.5
75
9.0
65
12.5
30