MB3793-30A Fujitsu Media Devices, MB3793-30A Datasheet - Page 12

• Manufacturer Part Number: MB3793-30A
• Description: POWER-VOLTAGE MONITORING IC WITH WATCHDOG TIMER
• Manufacturer: Fujitsu Media Devices

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