ATMEGA328P-20PU Atmel, ATMEGA328P-20PU Datasheet - Page 32

• Manufacturer Part Number: ATMEGA328P-20PU
• Manufacturer: Atmel

Specifications of ATMEGA328P-20PU

• Cpu Family: ATmega
• Device Core: AVR
• Device Core Size: 8b
• Frequency (max): 20MHz
• Interface Type: SPI/TWI/USART
• Program Memory Type: Flash
• Program Memory Size: 32KB
• Total Internal Ram Size: 2KB
• # I/os (max): 23
• Number Of Timers - General Purpose: 3
• Operating Supply Voltage (typ): 3.3/5V
• Operating Supply Voltage (max): 5.5V
• Operating Supply Voltage (min): 2.7V
• On-chip Adc: 6-chx10-bit
• Instruction Set Architecture: RISC
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Through Hole
• Pin Count: 28
• Package Type: PDIP
• Lead Free Status / Rohs Status: Compliant

8.5
8025K–AVR–10/09
Low Frequency Crystal Oscillator
The Low-frequency Crystal Oscillator is optimized for use with a 32.768 kHz watch crystal.
When selecting crystals, load capasitance and crystal’s Equivalent Series Resistance, ESR
must be taken into consideration. Both values are specified by the crystal vendor.
ATmega48P/88P/168P oscillator is optimized for very low power consumption, and thus when
selecting crystals, see
9.0 pF and 12.5 pF crystals
Table 8-7.
Note:
Table 8-8.
The Low-frequency Crystal Oscillator provides an internal load capacitance of typical 6 pF at
each TOSC pin. The external capacitance (C) needed at each TOSC pin can be calculated by
using:
where CL is the load capacitance for a 32.768 kHz crystal specified by the crystal vendor and C
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
Table
Table 8-9.
ATmega48P/88P/169P
SUT1..0
00
01
10
11
8-9.
1. Maximum ESR is typical value based on characterization
Device
Maximum ESR Recommendation for 32.768 kHz Crystal
Capacitance for the Low-frequency Crystal Oscillator
Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
Additional Delay from Reset (V
Figure 8-2 on page
Crystal CL (pF)
Table
12.5
6.5
9.0
Table 8-7 on page 32
8-10. Start-up times are determined by the SUT Fuses as shown in
4 CK + 4.1 ms
4 CK + 65 ms
System Osc.
32 kHz Osc.
Timer Osc.
4 CK
Type
29.
C
=
CC
2 CL
for maximum ESR recommendations on 6.5 pF,
⋅
= 5.0V)
Reserved
–
C
(Xtal1/Tosc1)
ATmega48P/88P/168P
s
Recommended Usage
Fast rising power or BOD enabled
Slowly rising power
Stable frequency at start-up
18 pF
18 pF
Cap
Max ESR [kΩ]
75
65
30
(Xtal2/Tosc2)
(1)
8 pF
8 pF
Cap
32
S