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L4949EP

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P19
Application information L4949E
10/19 Doc ID 4275 Rev 6
3 Application information
Figure 3. Application circuit
(1)
1. For stability: C
S
≥ 1µF, C
O
≥ 4.7µF, ESR < 10Ω at 10KHz
Recommended for application: C
S
= C
O
= 10 µF to 100 µF
3.1 Supply voltage transient
High supply voltage transients can cause a reset output signal disturbance. 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 transients of more
than 0.4V/µs can cause a reset signal disturbance.
To improve the transient behaviour for supply voltages less than 8V a capacitor at pin V
Z
can
be used.
This capacitor (C3 ≤ 1 µF) reduces also the output noise.
3.2 Functional description
The L4949E is a monolithic integrated voltage regulator, based on the STM modular voltage
regulator approach. 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
Obsolete Product(s) - Obsolete Product(s)
L4949E Application information
Doc ID 4275 Rev 6 11/19
required. The modular approach of this device allows to get easily also other features and
functions when required.
3.3 Voltage regulator
The voltage regulator uses an Isolated Collector Vertical PNP transistor as a regulating
element.
Figure 4. Foldback characteristic of V
O
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 voltage is regulated up to the transient input supply voltage of 40V. With this
feature no functional interruption 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
Figure 5. The current consumption of the device (quiescent current) is less than 300 µA.
To reduce the quiescent current peak in the undervoltage region and to improve the
transient response in this region, the dropout voltage is controlled, the quiescent current as
a function of the supply input voltage is shown in Figure 6.
Obsolete Product(s) - Obsolete Product(s)
Application information L4949E
12/19 Doc ID 4275 Rev 6
Figure 5. Output voltage vs input voltage
Figure 6. Quiescent current vs supply voltage
3.4 Preregulator
To improve the transient immunity a preregulator stabilizes the internal supply voltage to 5 V.
This internal voltage is present at Pin 3 (V
Z
). This voltage should not be used as an output
because the output capability is very small (≤ 10 µA).
This output may be used as an option when a better transient behaviour for supply voltages
less than 8 V is required (see also application note).
In this case a capacitor (100 nF - 1 µF) must be connected between pin V
Z
and GND. If this
feature is not used pin V
Z
must be left open.
Obsolete Product(s) - Obsolete Product(s)
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P19

L4949EP

Mfr. #:
Buy L4949EP
Manufacturer:
STMicroelectronics
Description:
LDO Voltage Regulators 5V Multifunction LDO
Lifecycle:
New from this manufacturer.
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