U5020M-FP TEMIC [TEMIC Semiconductors], U5020M-FP Datasheet - Page 3

• Manufacturer Part Number: U5020M-FP
• Description: Digital Window Watchdog Timer
• Manufacturer: TEMIC [TEMIC Semiconductors]

TELEFUNKEN Semiconductors
Rev. A3, 27-Feb-97
Supply Voltage Monitoring, Pin 10
The integrated power-on reset (POR) circuitry sets the
internal logic to a defined basic status and generates a
reset pulse at the reset output, Pin 10, during ramp-up of
the supply voltage and in the case of voltage drops of the
supply. A hysteresis in the POR threshold prevents the
circuit from oscillating. During ramp–up of the supply
voltage the reset output stays active for time, t
to bring the microcontroller in its defined reset status (see
figure 4). Pin 10 has an open-drain output.
Switch-over Mode Time, Pin 12
The switch-over mode time enables the synchronous
operation of micro and watchdog. After the power-up
reset time the watchdog has to be switched to its
monitoring mode by the micro with a “low” signal
transmitted to the mode pin (Pin 12) within the time out
period, t
t
1
t (
, (see figure 4) the watchdog generates a reset pulse, t
m
Reset Out
V DD
Mode
s)
1000.00
100.00
1
10.00
,. If the low signal does not occur within time,
1.00
1
t
o
Preliminary Information
Figure 4. Power-up reset and mode switchover
Figure 3. Period t vs. R
10
o
, in order
6
R
,
1
(k
and the time, t
synchronized with the switchover mode time, t
time a reset pulse is generated.
Microcontroller in Active Mode
Monitoring with the “Short” Trigger
Window
After the switch-over mode the watchdog works in the
short watchdog mode and expects a trigger pulse from the
microcontroller within the defined time window, t
(enable time). The watchdog generates a reset pulse
which resets the microcontroller if
D
D
D
Figure 5 shows the pulse diagram with a missing trigger
pulse.
W
1
)
, @ C
the trigger pulse duration is too long,
the trigger pulse is within the disable time, t
there is no trigger pulse
t
1
1
C
= 500 pF
1
= 500 pF
100
1
, starts again. Micro and watchdog are
t
6
U5020M
5.5 V
4.5 V
5.0 V
1000
Pin 13
Pin 10
Pin 12
2
1
95 10637
, each
95 10636
3 (8)
3
,