l4979md13tr STMicroelectronics, l4979md13tr Datasheet - Page 6

• Manufacturer Part Number: l4979md13tr
• Description: Low Drop Voltage Regulator
• Manufacturer: STMicroelectronics

L4979MD L4979D
and reset pulse delay trd is given by:
Figure 5. Reset Time Diagram.
4
The watchdog input Wi monitors a connected microcontroller. If pulses are missing, the reset output Res is
set to low. The pulse sequence time can be set within a wide range thorough the external capacitor C
watchdog circuit discharges the capacitor C
reached, a watchdog reset is generated. To prevent this reset, the microcontroller must generate a positive edge
during the discharge of the capacitor before the voltage has reached the threshold V
the minimum time Tdis during which the microcontroller must generate the positive edge, the following equation
can be used:
Each W
lower V
charging to discharging. The result is a saw tooth voltage at the watchdog timer capacitor C
Figure 6. Watchdog time diagram
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WATCHDOG
Wi
Vcw
Res
wlth
i
positive edge switches the current source from discharging to charging; the same happens when the
threshold is reached. When the voltage reaches the upper threshold V
W i
Vo
R es
Vcr
< trr
T
osc
=
----------------------------------------------------- -
V
(V
rhth
trr
whth
tw
–
- V
I
V
cr
with the constant current Icwd. If the lower threshold Vwlth is
twol
t
rlth
rd
wlth
= 512 x T
) x C
C
tr
tw
+
= I
trd = 512 T osc
T osc
osc
----------------------------------------------------- -
cwd
Twop
V
Tdis
rhth
x T
–
dis
I
V
dr
rlth
C
tr
whth
the current switches from
wlth
Vrhth
Vrlth
. In order to calculate
tw
V out_th
.
Vwhth
Vwlth
tw
. The