L4949, NCV4949
http://onsemi.com
7
OPERATING DESCRIPTION
The L4949 is a monolithic integrated low dropout voltage
regulator. Several outstanding features and auxiliary
functions are implemented to meet the requirements of
supplying microprocessor systems in automotive
applications. It is also suitable in other applications where
the included functions are required. The modular approach
of this device allows the use of other features and functions
independently when required.
Voltage Regulator
The voltage regulator uses an isolated collector vertical
PNP transistor as a regulating element. With this structure,
very low dropout voltage at currents up to 100 mA is
obtained. The dropout operation of the standby regulator is
maintained down to 3.0 V input supply voltage. The output
voltage is regulated up to a transient input supply voltage of
35 V.
A typical curve showing the standby output voltage as a
function of the input supply voltage is shown in Figure 16.
The current consumption of the device (quiescent current)
is less than 200 mA.
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 17.
Short Circuit Protection:
The maximum output current is internally limited. In case
of short circuit, the output current is foldback current limited
as described in Figure 15.
0
5.0
20 100 200
I
out
(mA)
Figure 15. Foldback Characteristic of V
out
V
out
(V)
10
V
out
5.0 V
35 V5.0 V2.0 V0 V
V
out
V
CC
Figure 16. Output Voltage versus Supply Voltage
3.0
Figure 17. Quiescent Current versus Supply Voltage
2.5
2.0
1.5
1.0
0 5.0 10 15 20 25 30
V
CC
, SUPPLY VOLTAGE (V)
0.5
0
R
L
= 5.0 k
R
L
= 100 W
T
J
= 25°C
I
Q
, QUIESCENT CURRENT (mA)
Preregulator
To improve transient immunity a preregulator stabilizes
the internal supply voltage to 6.0 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 (≤ 100
mA).
This output may be used to improve transient behavior for
supply voltages less than 8.0 V. In this case a capacitor (100
nF − 1.0 mF) must be connected between Pin 3 and GND. If
this feature is not used Pin 3 must be left open.
