Datasheet

33
ATmega169A/PA/329A/PA/649A/P/3290A/PA/6490A/P [DATASHEET]
8284E–AVR–02/2013
Table 9-7. Maximum ESR recommendation for 32.768kHz watch XTAL Atmel ATmega169A/169PA.
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 33 at each
TOSC pin.
The Atmel ATmega169A/169PA/329A/329PA/649A/649P/3290A/3290PA/6490A/6490P oscillator is optimized for
very low power consumption, and thus when selecting XTALs, see Table 9-8 on page 33 for maximum ESR recom-
mendations on 6.5pF, 9.0pF and 12.5pF XTALs.
Table 9-8. Maximum ESR recommendation for 32.768kHz watch XTAL
ATmega329A/329PA/3290A/3290PA/649A/649P/6490A/6490P.
Note: 1. Maximum ESR is typical value based on characterization.
The Low-frequency XTAL Oscillator provides an internal load capacitance, seeTable 9-9 at each TOSC pin.
Table 9-9. Capacitance for low-frequency oscillator.
The capacitance (Ce + Ci) needed at each TOSC pin can be calculated by using:
where
Ce - is optional external capacitors as described in Figure 9-2 on page 31.
Ci - is the pin capacitance in Table 9-10.
CL - is the load capacitance for a 32.768kHz XTAL specified by the XTAL vendor.
C
S
- is the total stray capacitance for one TOSC pin.
XTALs specifying load capacitance (CL) higher than the ones given in the Table 9-9, require external capacitors
applied as described in Figure 9-2 on page 31.
To find suitable load capacitance for a 32.768kHz XTAL, please consult the XTAL datasheet.
XTAL CL [pF] Maximum ESR [k]
(1)
6.5 60
935
XTAL CL [pF] Maximum ESR [k]
(1)
6.5 75
9.0 65
12.5 30
Device 32kHz osc. type Cap(XTAL1/Tosc1) Cap(XTAL2/Tosc2)
ATmega169A/169PA/329A/329PA/3290A
/3290PA/649A/649P/6490A/6490P
System osc. 16pF 6pF
Timer osc. 16pF 6pF
Ce Ci+ 2 CL C
s
–=