L4938N STMicroelectronics, L4938N Datasheet - Page 7

• Manufacturer Part Number: L4938N
• Description: Linear Regulators - Standard Dual 5V Very LDO
• Manufacturer: STMicroelectronics

Specifications of L4938N

• Polarity: Positive
• Number Of Outputs: 2
• Output Type: Selectable
• Output Voltage: 5 V
• Output Current: 5 mA
• Line Regulation: 20 mV
• Load Regulation: 50 mV
• Dropout Voltage (max): 0.4 V
• Input Voltage Max: 28 V
• Maximum Operating Temperature: + 150 C
• Minimum Operating Temperature: - 55 C
• Package / Case: PDIP-16
• Maximum Power Dissipation: 875 mW
• Mounting Style: Through Hole
• Reference Voltage: 1.23 V
• Voltage Regulation Accuracy: 2 %
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

RESET CIRCUIT
The block circuit diagram of the reset circuit is shown
in fig. 4. The reset circuit supervises the standby out-
put voltage. The reset threshold of 4.7V is defined
by the internal reference voltage and the standby
output divider.
The reset pulse delay time t
charge time of an external capacitor C
The reaction time of the reset circuit depends on the
discharge time limitation of the reset capacitor C
and is proportional to the value of C
The reaction time of the reset circuit increases the
noise immunity. In fact, if the standby output voltage
drops below the reset threshold for a time shorter
than the reaction time t
Figure 4: Block Diagram of the Reset Circuit.
t
RD
=
C
RR
T
2 A
x 2V
, no reset output variation
RD
, is defined by the
T
.
T
:
T
occurs. The nominal reset delay is generated for
standby output voltage drops longer than the time
necessary for the complete discharging of the ca-
pacitor C
C
shown in fig. 5.
SENSE COMPARATOR
This circuit compares an input signal with an internal
voltage reference of typically 1.23V. The use of an
external voltage divider makes the comparator very
flexible in the application. This function can be used
to supervise the input voltage - either before or after
the protection diode - and to give additional informa-
tion to the microprocessor such as low voltage warn-
ings.
If this feature is not used SI and SO have to con-
nected to GND. In this case the St-by quiescent cur-
rent (14V) increases from 290 A to 300 A.
T
= 100nF. The typical reset output waveforms are
T
. This time is typically equal to 50 s if
L4938N - L4938ND - L4938NPD
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