Datasheet

48
4317K–AVR–03/2013
AT90PWM2/3/2B/3B
Figure 9-3. MCU Start-up, RESET Extended Externally
9.0.4 External Reset
An External Reset is generated by a low level on the RESET
pin. Reset pulses longer than the
minimum pulse width (see Table 9-1) will generate a reset, even if the clock is not running.
Shorter pulses are not guaranteed to generate a reset. When the applied signal reaches the
Reset Threshold Voltage – V
RST
– on its positive edge, the delay counter starts the MCU after
the Time-out period – t
TOUT
– has expired.
Figure 9-4. External Reset During Operation
9.0.5 Brown-out Detection
AT90PWM2/2B/3/3B has an On-chip Brown-out Detection (BOD) circuit for monitoring the V
CC
level during operation by comparing it to a fixed trigger level. The trigger level for the BOD can
be selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike free
Brown-out Detection. The hysteresis on the detection level should be interpreted as V
BOT+
=
V
BOT
+ V
HYST
/2 and V
BOT-
= V
BOT
- V
HYST
/2.
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST
V
CC
CC
Table 9-2. BODLEVEL Fuse Coding
(1)(2)
BODLEVEL 2..0 Fuses Min V
BOT
Typ V
BOT
Max V
BOT
Units
111 BOD Disabled
110 4.5 V
101 2.7 V
100 4.3 V
011 4.4 V