L4979D STMicroelectronics, L4979D Datasheet - Page 6

• Manufacturer Part Number: L4979D
• Description: IC VOLTAGE REG LDO SO-8
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L4979D

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 150mA
• Voltage - Input: 5.6 ~ 31 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Polarity: Positive
• Input Voltage Max: 31 V
• Output Voltage: 5 V
• Output Type: Fixed
• Dropout Voltage (max): 0.4 V at 150 mA
• Output Current: 300 mA
• Line Regulation: 25 mV
• Load Regulation: 25 mV
• Voltage Regulation Accuracy: 2 %
• Maximum Operating Temperature: + 150 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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
V o
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
) C
) x 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