MB3793-34A Datasheet, PDF (15/26 Pages) Cypress Semiconductor – Precise detection of power voltage fall: 2.5%

MB3793-34A
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
(wmastc) ^{h.=.dDog×tiCm}_T^e_P^r
monitor
(F)
reset
time
t_WR
is
set
with
the
following
equation:
The value of D is 100 with V_CC = 5.0 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 3.40 V (Typ).
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.
The inhibition (INH) pin must be connecting a voltage of more low impedance, to evade of the noise.
12.Cancelling 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.
1. Equation of time-setting capacitances (C_TP and C_TW) and set time
t_PR [ms] ^.=. A × C_TP [μF]
t_WD [ms] ^.=. B × C_TW [μF] + C × C_TP [μF]
However, when C_TP/C_TW ^.=. 10 or less, t_WD [ms] ^.=. B × C_TW [μF]
t_WR [ms] ^.=. D × C_TP [μF]
Values of A, B, C, and D
A
B
C
D
Remark
1300
1500
0
100
V_CC = 5.0 V
Note: The width of value of t_PR, t_WD and t_WR becomes the same ratio as width (Min, Max) of each
specification value.
2. Example (when C_TP = 0.1 μF and C_TW = 0.01 μF)
Symbol
V_CC = 5.0 V
time
t_PR
130
(ms)
t_WD
15
t_WR
10
Document Number: 002-08556 Rev. *A
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