ATmega169P datasheet(34/393 Pages) ATMEL

34 / 393 page

8018N–AVR–08/09

ATmega169P

The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table

8-6.

Notes:

1. These options should only be used when not operating close to the maximum frequency of the

device, and only if frequency stability at start-up is not important for the application. These

options are not suitable for crystals.

2. These options are intended for use with ceramic resonators and will ensure frequency stability

at start-up. They can also be used with crystals when not operating close to the maximum fre-

quency of the device, and if frequency stability at start-up is not important for the application.

8.6

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. ATmega169P

oscillator is optimized for very low power consumption, and thus when selecting crystals, see

Table 8-7 on page 34 for maximum ESR recommendations on 9 pF and 6.5 pF crystals

Table 8-7.

Maximum ESR Recommendation for 32.768 kHz Watch Crystal

Note:

1. Maximum ESR is typical value based on characterization

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:

Table 8-6.

Start-up Times for the Crystal Oscillator Clock Selection

CKSEL0

SUT1:0

Start-up Time from

Power-down and

Power-save

Additional Delay

from Reset

(VCC = 5.0V)

Recommended Usage

258 CK(1)

14CK + 4.1 ms

Ceramic resonator, fast

rising power

258 CK(1)

14CK + 65 ms

Ceramic resonator, slowly

rising power

010

1K CK(2)

14CK

Ceramic resonator, BOD

enabled

011

1K CK(2)

14CK + 4.1 ms

Ceramic resonator, fast

rising power

100

1K CK(2)

14CK + 65 ms

Ceramic resonator, slowly

rising power

16K CK

14CK

Crystal Oscillator, BOD

enabled

16K CK

14CK + 4.1 ms

Crystal Oscillator, fast

rising power

16K CK

14CK + 65 ms

Crystal Oscillator, slowly

rising power

Crystal CL (pF)

Max ESR [k

Ω](1)

6.5

935

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