ATMEGA168PA-PU Atmel, ATMEGA168PA-PU Datasheet - Page 32

• Manufacturer Part Number: ATMEGA168PA-PU
• Description: MCU, 8BIT, AVR, 16K FLASH, 28PDIP
• Manufacturer: Atmel

Specifications of ATMEGA168PA-PU

• Controller Family/series: Atmega
• No. Of I/o's: 23
• Eeprom Memory Size: 512Byte
• Ram Memory Size: 1KB
• Cpu Speed: 20MHz
• No.: RoHS Compliant
• Core Size: 8bit
• Program Memory Size: 16KB
• Oscillator Type: External, Internal
• Rohs Compliant: Yes

8.5
8271C–AVR–08/10
Low Frequency Crystal Oscillator
The Low-frequency Crystal Oscillator is optimized for use with a 32.768 kHz 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/48PA/88A/88PA/168A/168PA/328/328P oscillator is optimized for very low power
consumption, and thus when selecting crystals, see
tions on 6.5 pF, 9.0 pF and 12.5 pF crystals
Table 8-7.
Note:
The Low-frequency Crystal Oscillator provides an internal load capacitance, see
each TOSC pin.
Table 8-8.
The capacitance (Ce+Ci) needed at each TOSC pin can be calculated by using:
where:
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
Table 8-9.
C
ATmega48A/48PA/88A/88PA/168A/168PA/328/328
ATmega48A/48PA/88A/88P
A/168A/168PA/328/328P
=
SUT1...0
– Ce - is optional external capacitors as described in
– Ci - is the pin capacitance in
– CL - is the load capacitance for a 32.768 kHz crystal specified by the crystal vendor
– CS - is the total stray capacitance for one TOSC pin.
2 CL
00
⋅
1. Maximum ESR is typical value based on characterization
Table
Device
–
C
s
Maximum ESR Recommendation for 32.768 kHz Crystal
Capacitance for Low-frequency Oscillator
Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
Additional Delay from Reset (V
Figure 8-2 on page
8-9.
Crystal CL (pF)
Table 8-10 on page
12.5
6.5
9.0
32kHz Osc. Type
4 CK
System Osc.
Timer Osc.
Table 8-8
29.
33. Start-up times are determined by the SUT Fuses as
CC
= 5.0V)
Table 8-7
Cap(Xtal1/Tosc1)
Recommended Usage
Fast rising power or BOD enabled
Figure 8-2 on page 29
18pF
18pF
for maximum ESR recommenda-
Max ESR [kΩ]
75
65
30
Cap(Xtal2/Tosc2)
(1)
8pF
8pF
Table 8-8
32
at