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. Nevertheless, it is suitable also in other

applications where the present 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 the transient input supply voltage

of 35 V. 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 14.

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 15.

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 13.

0

5.0

20

100

200

10

5.0 V

35 V

5.0 V

2.0 V

0 V

Figure 14. Output Voltage versus Supply Voltage

3.0

Figure 15. Quiescent Current versus Supply Voltage

2.5

2.0

1.5

1.0

0

5.0

10

15

20

25

30

0.5

0

Preregulator

To improve the transient immunity a preregulator

stabilizes the internal supply voltage to 6.0 V. This internal

used as an output because the output capability is very small

(

≤ 100 mA).

This output may be used as an option when better transient

behavior for supply voltages less than 8.0 V is required. 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.