MB3793-30A
12
■ OPERATION SEQUENCE
1. Positive clock pulse input
Refer to “1. Basic operation (positive clock pulse)” under “■ DIAGRAM.”
2. Negative clock pulse input
Refer to “2. Basic operation (negative clock pulse)” under “■ DIAGRAM.”
The MB3793 operates in the same way whether it inputs positive or negative pulses.
3. Clock monitoring
To use the MB3793 while monitoring only one clock, connect clock pins CK1 and CK2.
Although the MB3793 operates basically in the same way as when monitoring two clocks, it monitors the clock
signal at every other input pulse.
Refer to “3. Single-clock input monitoring (positive clock pulse)” under “■ DIAGRAM.”
4. Description of Operations
The numbers given to the following items correspond to numbers (1) to (13) used in “■ DIAGRAM.”
(1) The MB3793 outputs a reset signal when the supply voltage (V
CC) reaches about 0.8 V (VCCL)
(2) If V
CC reaches or exceeds the rise-time detected voltage VSH, the MB3793 starts charging the power-on
reset hold time setting capacitor C
TP. At this time, the output remains in a reset state. The VSH value is
3.07 V (Typ) .
(3) When C
TP has been charged for a certain period of time TPR (until the CTP pin voltage exceeds the
threshold voltage (V
th) after the start of charging), the MB3793 cancels the reset (setting the RESET pin
to “H” level from “L” level).
The V
th value is about 2.4 V with VCC = 3.3 V
The power-on reset hold time t
PR is set with the following equation:
t
PR (ms) A × CTP (µF)
The value of A is about 750 with V
CC = 3.3 V. The MB3793 also starts charging the watchdog timer
monitor time setting capacitor (C
TW).
(4) When the voltage at the watchdog timer monitor time setting pin C
TW reaches the “H” level threshold
voltage V
H, the CTW switches from the charge state to the discharge state.
The value of V
H is always about 1.24 V regardless of the detected voltage.
(5) If the CK2 pin inputs a clock pulse (positive edge trigger) when the C
TW is being discharged in the
CK1-CK2 order or simultaneously, the C
TW switches from the discharge state to the charge state.
The MB3793 repeats operations (4) and (5) as long as the CK1/CK2 pin inputs clock pulses with the
system logic circuit operating normally.
(6) If no clock pulse is fed to the CK1 or CK2 pin within the watchdog timer monitor time t
WD due to some
problem with the system logic circuit, the CTW pin is set to the “L” level threshold voltage V
L or less and
the MB3793 outputs a reset signal (setting the RESET
pin to “L” level from “H” level).
The value of V
L is always about 0.24 V regardless of the detected voltage.
The watchdog timer monitor time t
WD is set with the following equation:
t
WD (ms) B × CTW (µF)
The value of B is hardly affected by the power supply voltage; it is about 1600 with V
CC = 3.3 V.
(Continued)
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