ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 28

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

9.3
28
Low Power Crystal Oscillator
Atmel ATmega48PA/88PA/168PA [Preliminary]
Table 9-2.
Main purpose of the delay is to keep the AVR in reset until it is supplied with minimum V
The delay will not monitor the actual voltage and it will be required to select a delay longer
than the V
should be used. A BOD circuit will ensure sufficient V
time-out delay can be disabled. Disabling the time-out delay without utilizing a Brown-Out
Detection circuit is not recommended.
The oscillator is required to oscillate for a minimum number of cycles before the clock is con-
sidered stable. An internal ripple counter monitors the oscillator output clock, and keeps the
internal reset active for a given number of clock cycles. The reset is then released and the
device will start to execute. The recommended oscillator start-up time is dependent on the
clock type, and varies from 6 cycles for an externally applied clock to 32K cycles for a low fre-
quency crystal.
The start-up sequence for the clock includes both the time-out delay and the start-up time
when the device starts up from reset. When starting up from Power-save or Power-down
mode, V
Pins XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can
be configured for use as an On-chip Oscillator, as shown in
quartz crystal or a ceramic resonator may be used.
This Crystal Oscillator is a low power oscillator, with reduced voltage swing on the XTAL2 out-
put. It gives the lowest power consumption, but is not capable of driving other clock inputs, and
may be more susceptible to noise in noisy environments. In these cases, refer to the
Swing Crystal Oscillator” on page
C1 and C2 should always be equal for both crystals and resonators. The optimal value of the
capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and
the electromagnetic noise of the environment. Some initial guidelines for choosing capacitors
for use with crystals are given in
values given by the manufacturer should be used.
Figure 9-2.
Typ Time-out (V
CC
CC
is assumed to be at a sufficient level and only the start-up time is included.
4.1ms
rise time. If this is not possible, an internal or external Brown-Out Detection circuit
65ms
0ms
Number of Watchdog Oscillator Cycles
Crystal Oscillator Connections
CC
= 5.0V)
Table 9-3 on page
30.
C2
C1
Typ Time-out (V
4.3ms
69ms
0ms
CC
XTAL2 (TOSC2)
XTAL1 (TOSC1)
GND
29. For ceramic resonators, the capacitor
= 3.0V)
CC
before it releases the reset, and the
Figure 9-2 on page
Number of Cycles
8K (8,192)
512
0
9223B–AVR–09/11
28. Either a
“Full
CC
.