MB3793-42PF FUJITSU [Fujitsu Component Limited.], MB3793-42PF Datasheet - Page 13

• Manufacturer Part Number: MB3793-42PF
• Description: POWER-VOLTAGE MONITORING IC WITH WATCHDOG TIMER
• Manufacturer: FUJITSU [Fujitsu Component Limited.]

OPERATION SEQUENCE
The operation sequence is explained by using “ TIMING DIAGRAM 1. Basic operation (Positive clock pulse)”.
The following item numbers correspond to the numbers in “
clock pulse)”.
(1) When the power voltage (V
(2) When V
(3) When the voltage at the CTP terminal setting the power-on reset hold time exceeds the threshold voltage
(4) When the voltage at the CTW terminal setting the monitoring time reaches High level (V
(5) When clock pulses are input to the CK2 terminal during C
(6) If clock pulse input does not occur at either the CK1 or CK2 clock terminals during the watchdog timer
(7) When the voltage of the CTP terminal exceeds V
(8) When V
(9) When V
(10)When the voltage of the CTP terminal exceeds V
(11)When an inhibition signal is input (INH terminal is High level), the watchdog timer is halted forcibly.
(12)When the inhibition input is canceled (INH terminal is Low level), the watchdog timer restarts.
(13)When the V
(14)When the power voltage (V
Similar operation is also performed for negative clock-pulse input (“
(Negative clock pulse)”).
Short-circuit the clock terminals CK1 and CK2 to monitor a single clock. The basic operation is the same but
the clock pulses are monitored at every other pulse ( TIMING Diagram 3. Single-clock input monitoring).
Hence, when C
Where, B is about 1500. C is about 3; it is much smaller than B.
The power-on reset hold time (t
Where, A is about 1300.
The watchdog timer reset time (t
Where, D is about 100.
In this case, V
The watchdog timer does not function unless this inhibition input is canceled.
capacitance (C
(V
the watchdog timer monitoring time setting capacitance (C
discharging from charging. V
CK1 terminal—positive-edge trigger, C
monitoring time (t
the RESET terminal changes to Low level. V
and the watchdog timer restarts monitoring.
signal is output, and the voltage at the RESET terminal changes to Low level. V
th
t
t
t
t
t
), resetting is canceled and the voltage at the RESET terminal changes to High level to start charging of
WD
WR
PR
WD
WD
(ms) ≈ A × C
(ms) ≈ B × C
(ms) ≈ D × C
can be calculated from the following equation.
(ms) ≈ B × C
CC
CC
CC
falls below the rising-edge detection voltage (V
exceeds V
exceeds the rising-edge detection voltage (V
CC
CC
TP
TP
voltage falls below V
monitoring is continued without the watchdog timer.
) is started. V
WD
/ C
TP
TW
TP
TW
), the CTW voltage falls below Low level (V
TW
SH
(µF)
(µF)
(µF)
(µF) + C × C
≤ 10, the calculation can be simplified as follows:
, C
TP
CC)
begins charging.
CC
H
reaches about 0.8 V (V
SH
is about 1.24 V (reference value).
) falls below about 0.8 V (V
PR
WR
is about 4.3 V.
) can be calculated by the following equation.
) can be calculated by the following equation.
TP
SL
(µF)
after power-off, a reset signal is output.
TW
switches to charging.
L
is about 0.24 V.
th
th
again as a result of recharging C
, resetting is canceled and the watchdog timer restarts.
CCL
), a reset signal is output.
SL
SH
TW
), the voltage of the CTP terminal falls and a reset
CCL
TW
), charging of power-on reset hold time setting
TIMING DIAGRAM 1. Basic operation (Positive
). Vth is about 3.6 V.
discharging after clock pulses are input to the
) , a reset signal is released.
L
), a reset signal is output, and the voltage at
TIMING DIAGRAM 2. Basic operation
SL
is about 4.2 V.
MB3793-42
TP
, resetting is canceled
H
), C
TW
switches to
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