Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet
Product codes
MEGA328P-XMINI
33
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
9.5
Low Frequency Crystal Oscillator
The Low-frequency Crystal Oscillator is optimized for use with a 32.768kHz 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. ATmega48A/PA/88A/PA/168A/PA/328/P oscillator is optimized
for very low power consumption, and thus when selecting crystals, see
crystals, load capacitance and crystal’s Equivalent Series Resistance, ESR must be taken into consideration.
Both values are specified by the crystal vendor. ATmega48A/PA/88A/PA/168A/PA/328/P oscillator is optimized
for very low power consumption, and thus when selecting crystals, see
for maximum ESR
recommendations on 6.5pF, 9.0pF and 12.5pF crystals
Note:
1. Maximum ESR is typical value based on characterization
The Low-frequency Crystal Oscillator provides an internal load capacitance, see
at each TOSC pin.
The capacitance (Ce+Ci) needed at each TOSC pin can be calculated by using:
where:
̶
̶
Ci - is the pin capacitance in
̶
CL - is the load capacitance for a 32.768kHz crystal specified by the crystal vendor
̶
CS - is the total stray capacitance for one TOSC pin.
Crystals specifying load capacitance (CL) higher than 6 pF, require external capacitors applied as described in
The Low-frequency Crystal Oscillator must be selected by setting the CKSEL Fuses to “0110” or “0111”, as
shown in
shown in
. Start-up times are determined by the SUT Fuses as shown in
Table 9-7.
Maximum ESR Recommendation for 32.768kHz Crystal
Crystal CL (pF)
Max ESR [k
]
6.5
75
9.0
65
12.5
30
Table 9-8.
Capacitance for Low-frequency Oscillator
Device
32kHz Osc. Type
Cap(Xtal1/Tosc1)
Cap(Xtal2/Tosc2)
ATmega48A/PA/88A/PA/168A/PA/3
28/P
System Osc.
18pF
8pF
Timer Osc.
18pF
8pF
Table 9-9.
Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
SUT1...0
Additional Delay from Reset (V
CC
= 5.0V)
Recommended Usage
00
4 CK
Fast rising power or BOD enabled
01
4 CK + 4.1ms
Slowly rising power
10
4 CK + 65ms
Stable frequency at start-up
11
Reserved
C
2 CL
C
s
–
=