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L4949E-L4949ED-L4949EP
MULTIFUNCTION VERY LOW DROP VOLTAGE REGULATOR
L4949EMULTIFUNCTION VERY LOW DROP
VOLTAGE REGULATOR
OPERATING DC SUPPLY VOLTAGE RANGE
5V - 28V
TRANSIENT SUPPLY VOLTAGE UP TO 40V
EXTREMELY LOW QUIESCENT CURRENT
IN STANDBY MODE
HIGH PRECISION STANDBY OUTPUT VOLT-
AGE 5V±1%
OUTPUT CURRENT CAPABILITY UP TO
100mA
VERY LOW DROPOUT VOLTAGE LESS
THAN 0.5V
RESET CIRCUIT SENSING THE OUTPUT
VOLTAGE
PROGRAMMABLE RESET PULSE DELAY
WITH EXTERNAL CAPACITOR
VOLTAGE SENSE COMPARATOR
THERMAL SHUTDOWN AND SHORT CIR-
CUIT PROTECTIONS
DESCRIPTIONThe L4949E is a monolithic integrated 5V voltage
regulator with a very low dropout output and addi-
tional functions as power-on reset and input volt-
age sense. It is designed for supplying the micro-
computer controlled systems especially in
automotive applications.
BLOCK DIAGRAM
ABSOLUTE MAXIMUM RATINGSNote: The circuit is ESD protected according to MIL-STD-883C
THERMAL DATA
PIN CONNECTIONS
L4949E2/10
ELECTRICAL CHARACTERISTICS (VS = 14V; -40°C < Tj < 125°C unless otherwise specified)** With this test we guarantee that with no output current the output voltage will not exceed 5.5V
RESET
SENSE
PREREGULATOR
Note 1: Foldback characteristic
L4949E3/10
APPLICATION INFORMATION
Supply Voltage TransientHigh supply voltage transients can cause a reset
output signal disturbation.
For supply voltages greater than 8V the circuit
shows a high immunity of the reset output against
supply transients of more than 100V/μs.
For supply voltages less than 8V supply tran-
sients of more than 0.4V/μs can cause a reset
signal disturbation.
To improve the transient behaviour for supply
voltages less than 8V a capacitor at pin 3 can be
used.
A capacitor at pin 3 (C3 ≤ 1μF) reduces also the
output noise.
FUNCTIONAL DESCRIPTIONThe L4949E is a monolithic integrated voltage
regulator, based on the STM modular voltage
regulator approch. Several outstanding features
and auxiliary functions are implemented to meet
the requirements of supplying microprocessor
systems in automotive applications. Nevertheless,
it is suitable also in other applications where the
present functions are required. The modular ap-
proach of this device allows to get easily also
other features and functions when required.
Voltage RegulatorThe voltage regulator uses an Isolated Collector
Vertical PNP transistor as a regulating element.
Figure 1: Foldback Characteristic of VO
APPLICATION CIRCUIT
L4949E4/10
With this structure very low dropout voltage at
currents up to 100mA is obtained. The dropout
operation of the standby regulator is maintained
down to 3V input supply voltage. The output volt-
age is regulated up to the transient input supply
voltage of 40V. With this feature no functional in-
terruption due to overvoltage pulses is generated.
The typical curve showing the standby output
voltage as a function of the input supply voltage is
shown in Fig. 2. The current consumption of the
device (quiescent current) is less than 300μA.
To reduce the quiescent current peak in the un-
dervoltage region and to improve the transient re-
sponse in this region, the dropout voltage is con-
trolled, the quiescent current as a function of the
supply input voltage is shown in Fig. 3.
PreregulatorTo improve the transient immunity a preregulator
stabilized the internal supply voltage to 5V. This
internal voltage is present at Pin 3 (VZ). This volt-
age should not be used as an output because the
output capability is very small (≤10μA).
This output may be used as an option when a
better transient behaviour for supply voltages less
than 8V is required (see also application note).
In this case a capacitor (100nF - 1μF) must be
connected between Pin 3 and GND. If this feature
is not used Pin 3 must be left open.
Reset CircuitThe block circuit diagram of the reset circuit is
shown in Fig. 4. The reset circuit supervises the
output voltage.
The reset thereshold of 4.5V is defined with the
internal reference voltage and standby output
drivider.
The reset pulse delay time tRD, is defined with the
charge time of an external capacitor CT:
tRD = CT • 2V
2μA
The reaction time of the reset circuit originates
from the discharge time limitation of the reset ca-
pacitor CT and is proportional to the value of CT.
The reaction time of the reset circuit increases the
noise immunity. Standby output voltage drops be-
low 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 than approxi-
mately 50μs.
The typical reset output waveforms are shown in
Fig. 5.
Sense ComparatorThe 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 before or after the protection diode and to
give additional informations to the microprocessor
like low voltage warnings.
Figure 3: Quiescent Current vs. Supply Voltage
Figure 2: Output Voltage vs. Input Voltage
L4949E5/10
Figure 5
Figure 4
L4949E6/10
