MB3793-27A Datasheet, PDF (15/30 Pages) Fujitsu Component Limited. – Power Voltage Monitoring IC with Watchdog Timer

MB3793-27A
(7) When a certain period of time t_WR has passed (until the CTP pin voltage reaches or exceeds Vth again after recharging
the C_TP), the MB3793 cancels the reset signal and starts operating the watchdog timer.
The
t_WR
watchdog timer
(ms) ^.=. D x C_TP
monitor
(F)
reset
time
t_WR
is
set
with
the
following
equation:
The value of D is 55 with V_CC = 3.3 V and about 50 with V_CC = 3.0 V.
The MB3793 repeats operations (4) and (5) as long as the CK1/CK2 pin inputs clock pulses. If no clock pulse is input,
the MB3793 repeats operations (6) and (7).
(8) If V_CC is lowered to the fall-time detected voltage (V_SL) or less, the CTP pin voltage decreases and the MB3793 outputs
a reset signal (setting the RESET pin to “L” level from “H” level).
The value of V_SL is 2.7 V
(9) When V_CC reaches or exceeds V_SH again, the MB3793 starts charging the C_TP.
(10) When the CTP pin voltage reaches or exceeds V_th, the MB3793 cancels the reset and restarts operating the watchdog
timer. It repeats operations (4) and (5) as long as the CK1/CK2 pin inputs clock pulses.
(11) Making the inhibit pin active (setting the INH pin to “H” from “L”) forces the watchdog timer to stop operation.
This stops only the watchdog timer, leaving the MB3793 monitoring V_CC (operations (8) to (10)).
The watchdog timer remains inactive unless the inhibit input is canceled.
(12) Canceling the inhibit input (setting the INH pin to “L” from “H”) restarts the watchdog timer.
(13) The reset signal is output when the power supply is turned off to set V_CC to V_SL or less.
Document Number: 002-08550 Rev. *A
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