MITSUMI
System Reset (Built-in Watch Dog Timer) MM1099
Description of Operation
1. The RESET will become "Low" if V
CC
rises to about 0.8V.
Approximately 1µA (Vcc=0.8V) of pull up current is output from RESET
.
.
2. Charging starts at the capacitor C
T
when V
CC
riset to V
SH
(MM1099A = 3.25V, MM1099B = 4.3V), when the
.
.
output has been reset.
3. The output reset is released after a given interval T
PR
from when the C
T
Starts charging and to when it
discharges (that is, the time from when C
T
voltage takes a given value 1 (. . 1.4V) up until decreases to a
=
given value 2 (. . 0.2V). (RESET will become "High"). The RESET will output a pull up current, about 1µA
=
(V
CC
=0.8V). The reset hold time T
PR
is expressed by the following formula:
T
PR
(ms) . . 5000 C
T
(µF)
=
After the reset release C
T
restarts charging and the watch dog timer begins operating.
Note that input of clock while POWER ON RESET time T
PR
will cause an erroneous operation.
4. If clock is input into CK terminal while C
T
is charging (negative edge trigger), C
T
changes from charging
over to discharging.
.
5. When the C
T
voltage decreases to a given threshold ( = 0.2V), then discharging changes over to charging.
.
Steps 4 and 5 will be repeated while normal clock is input from the logic system.
6. When the clock ceases and C
T
voltage reaches the RESET ON threshold (. . 1.4V), the output enters into
=
reset state (RESET becoming "Low").
The C
T
charging time T
WD
up until the reset is output (watch dog monitoring time) is expressed by the
following formula:
T
WD
(ms) . . 5000 C
T
(µF)
=
7. The reset time at the time of watch dog time T
WR
is the discharging time while the C
T
voltage lowers down
to the reset off threshold (. . 0.2V). The calculation formula:
=
. 100 C
T
(µF)
T
WR
(ms) =
.
After the reset off threshold is reached, the output reset is released and C
T
commences to charge. If
thenceforth the clock is input normally, steps 4 and 5 will be repeated, and setps 6 and 7 repeated if the
clock ceases.
8. When V
CC
lowers down to V
SL
(MM1099A . . 3.2V, MM1099B . . 4.2V), the reset is output. At the same time
=
=
C
T
charged.
9. C
T
discharging starts when V
CC
rises up to V
SH
.
If V
CC
lower instantaneously, charging starts after load discharging of C
T
if the time interval from when V
CC
comes lower than V
SL
up until when it rises to V
SH
or higher is equal or superior to the reference value of
V
CC
input pulse width T
PI
.
10.The output reset is released T
PR
after V
CC
becomes V
SH
or higher, and the watch dog time will start. Then if
V
CC
becomes V
SL
or lower, steps 8 to 10 will be repeated.
11.If power Off occurs, reset is output if V
CC
becomes V
SL
or lower.
12.When V
CC
comes down to 0V, the reset output will hold up until V
CC
becomes 0.8V.
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MITSUMI [ MITSUMI ELECTRONICS, CORP. ]
