ATMEGA48PA-AN Atmel, ATMEGA48PA-AN Datasheet - Page 32

• Manufacturer Part Number: ATMEGA48PA-AN
• Description: MCU AVR 4KB FLASH 20MHZ 32TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA48PA-AN

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 23
• Program Memory Size: 4KB (2K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 512 x 8
• Voltage - Supply (vcc/vdd): 1.8 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

8.5
8161D–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.
ATmega48PA/88PA/168PA/328P oscillator is optimized for very low power consumption, and
thus when selecting crystals, see
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 at each TOSC pin
as specified in the
Table 8-8.
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 the ones given in the
32, 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.
ATmega48PA/88PA/168PA/328P
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 Oscillator
Capacitance for Low-Frequency Crystal Oscillator
Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
Additional Delay from Reset (V
Crystal CL (pF)
Table 8-8 on page
Table
12.5
6.5
9.0
8-10. Start-up times are determined by the SUT Fuses as shown in
4 CK + 4.1 ms
4 CK + 65 ms
4 CK
Table 8-7 on page 32
32 kHz Osc. Type
System Osc.
Timer Osc.
ATmega48PA/88PA/168PA/328P
32.
C
=
CC
2 CL
⋅
= 5.0V)
Reserved
–
C
s
Figure 8-2 on page
for maximum ESR recommendations on
Cap (Xtal1/Tosc1)
Recommended Usage
Fast rising power or BOD enabled
Slowly rising power
Stable frequency at start-up
18 pF
18 pF
Max ESR [kΩ]
75
65
30
29.
Cap (Xtal2/Tosc2)
Table 8-8 on page
(1)
8 pF
8 pF
32
S