L4938E STMicroelectronics, L4938E Datasheet - Page 6

• Manufacturer Part Number: L4938E
• Description: IC REG LDO DUAL 5V/ADV 16DIP
• Manufacturer: STMicroelectronics

Specifications of L4938E

• Regulator Topology: Positive Fixed and Adjustable
• Voltage - Output: 5V, 4.9 ~ 5.1 V
• Voltage - Input: Up to 28V
• Voltage - Dropout (typical): 0.2V @ 100mA, 0.3V @ 400mA
• Number Of Regulators: 2
• Current - Output: 100mA, 400mA
• Current - Limit (min): 100mA, 450mA
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Through Hole
• Package / Case: 20-SOIC (7.5mm Width)
• Polarity: Positive
• Number Of Outputs: 2
• Output Type: Fixed
• Output Voltage: 5.1 V
• Output Current: 5 mA
• Line Regulation: 20 mV
• Load Regulation: 50 mV
• Dropout Voltage (max): 0.2 V
• Input Voltage Max: 20 V
• Maximum Operating Temperature: + 150 C
• Minimum Operating Temperature: - 40 C
• Maximum Power Dissipation: 875 mW
• Mounting Style: Through Hole
• Reference Voltage: 1.23 V
• Voltage Regulation Accuracy: 2 %
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: 497-3355-5; 497-3914-5; 497-3914-5

L4938E - L4938ED - L4938EPD
Connecting a resistor divider R
OUT2 pin the output voltage 2 can be pro-
grammed to the value of
with R
5.05V.
For an exact calculation the temperature coeffi-
cient (Tc -2000pprm) of the internal resistor
(R
mode should not have a capacitive burden be-
cause this would reduce the phase margin of the
regulator loop.
Reset circuit
The reset circuit supervises the standby output
voltage. The reset output (RES) is defined from
V
Even if V
plied by the output voltage V
The reset threshold of 4.7V is defined with the in-
ternal reference voltage (note 9) and standby out-
put divider, when pin PR is left open. The reset
threshold voltage can be programmed in the
range from 3.8V to 4.7V by connecting an exter-
nal resistor from pin PR to GND.
The value of the programming resistor R
be calculated with:
The reset pulse delay time t
charge time of an external capacitor C
The reaction time of the reset circuit originates
from the noise immunity. Standby output voltage
drops below the reset threshold only a bit longer
than the reaction time results in a shorter reset
delay time. The nominal reset delay time will be
generated for standby output voltage drops longer
6/12
OUT
ADJ
R
PR
) must be taken into account. Pin ADJ in this
V
ADJ
1V.
OUT2
S
4.7K
V
= 60K to 150K and V
is lacking, the reset generator is sup-
t
t
22K
RT
RDnom
RDmin
V
OUT1
1
C
C
92.9K,
T
T
1
1 A
1 A
0.6V
1.4V
R
1E
3.8V
RD
OUT1
R
(note 5)
, is defined with the
(note 6)
R
2E
1E
2E
.
, R
OUT1
R
V
2E
ADJ
R
RT
T
ADJ
to the ADJ,
:
= 4.95 to
4.7V
PR
can
than approximately 50 s.
The minimum rset time is generated if reset con-
dition only occures for a short time triggering a re-
set pulse but not completely discharging C
reset can be related to output2 on request. If
higher charge currents for the reset capacitor are
required a resistors from Pin C
used to increase the current. We recommended
the use of 10K to 5V as an output pull up.
Sense Comparator
The sense comparator compares an input signal
with an internal voltage reference of typical 1.23V.
The use of an external voltage divider makes this
comparator very flexible in the application. It can
be used to supervise the input voltage either be-
fore or after the protection diode and to give addi-
tional information to the microprocessor like low
voltage warnings. We recommended the use of
10K to 5V as an output pull up.
Note 9:
The reference is alternatively supplied from V
is present, the reference is operating.
Thermal Protection
Both outputs are provided with an overtempera-
ture shut down regulation power dissipation down
to uncritical values.
Output 2 will shut down approximately 10K before
output 1.
Under normal conditions shut down of output 2
will allow the chip to cool down again. Thus out-
put 1 will be unaffected.
The thermal shut down reduces the output volt-
ages until power dissipation and the flow of ther-
mal energy out of the chip balance.
Transient Sensitivity
In proper operation (V
supplied by V
put transients.
Precise Data will be issued as soon as samples
are available.
OUT1
thus reducing sensitivity to in-
OUT
> 4.5V) the reference is
T
to OUT1, may be
S
or V
OUT1
. If one supply
T
. The