Datasheet

35
8018P–AVR–08/10
ATmega169P
The capacitance (Ce + Ci) needed at each TOSC pin can be calculated by using:
where
Ce - is optional external capacitors as described in Figure 8-2 on page 33.
Ci - is is the pin capacitance in Table 8-8.
CL - is the load capacitance for a 32.768 kHz crystal specified by the crystal vendor.
C
S
- is the total stray capacitance for one TOSC pin.
Crystals specifying load capacitance (CL) higher than the ones given in the Table 8-8, require
external capacitors applied as described in Figure 8-2 on page 33.
The Low-frequency Crystal Oscillator must be selected by setting the CKSEL Fuses to “0110” or
“0111” as shown in Table 8-10. Start-up times are determined by the SUT Fuses as shown in
Table 8-9.
Note: 1. This option should only be used if frequency stability at start-up is not important for the
application
Table 8-8. Capacitance for Low-Frequency Crystal Oscillator
Device 32 kHz Osc. Type Cap (Xtal1/Tosc1) Cap (Xtal2/Tosc2)
ATmega169P
System Osc. 16 pF 6 pF
Timer Osc. 16 pF 6 pF
Table 8-9. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
SUT1..0 Additional Delay from Reset (V
CC
= 5.0V) Recommended Usage
00 14 CK Fast rising power or BOD enabled
01 14 CK + 4 ms Slowly rising power
10 14 CK + 65 ms Stable frequency at start-up
11 Reserved
Table 8-10. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
CKSEL3..0
Start-up Time from
Power-down and Power-save Recommended Usage
0110
(1)
1K CK
0111 32K CK Stable frequency at start-up
Ce Ci+ 2 CL⋅ C
s
–=