FUNCTIONAL DESCRIPTION

The L4938N is based on the STMicroelectronics

modular voltage regulator approach. Several out-

standing features and auxiliary functions are pro-

vided to meet the requirements of supplying the mi-

croprocessor systems used in automotive applica-

tions.

Furthermore the device is suitable also in other ap-

plications requiring two stabilized voltages.

The modular approach allows other features and

functions to be realized easily when required.

STANDBY REGULATOR

The standby regulator uses an Isolated Collector

Vertical PNP transistor as the regulating element.

This structure allows a very low dropout voltage at

currents up to 50mA. The dropout operation of the

standby regulator is maintained down to 2V input

supply voltage. The output voltage is regulated up

to the transientinput supplyvoltageof 40V.This fea-

ture avoids functional interruptions which could be

generated by overvoltage pulses.

The typical curve of the standby output voltage as a

functionof theinput supply voltage is shown in fig. 1.

The current consumption of the device (quiescent

current) is less than 250

µA when output 2 is dis-

abled (standby mode). The dropout voltage is con-

trolled to reduce the quiescent current peak in the

undervoltage region and to improve the transient

response in this region.

The quiescentcurrent is shown in fig. 2 as a function

of the supply input voltage 2.

OUTPUT 2 VOLTAGE

The output 2 regulator uses the same output struc-

ture as the standbyregulator, but rated for an output

current of 500mA.

The output 2 regulator works in tracking mode with

the standby output voltage as a reference voltage

when the output 2 programming pin ADJ is con-

age 2 can be programmed to the value :

The output 2 regulator can be switched off via the

Enable input.

If a fixed 5 regulation is required ADJ Pin has to be

2 : Foldback characteristic

ELECTRICAL CHARACTERISTICS (continued)

RESET

Symbol

Parameter

Test Conditions

Min.

Typ.

Max.

Unit

Reset Low Threshold Voltage

4.7

V

Reset Threshold Hysteresis

50

100

200

mV

Reset Pulse Delay

µs

55

100

180

mV

Reset Reaction Time

1

10

50

µs

Reset Output LOW Voltage

0.4

V

Reset Output HIGH Leakage

1

µA

Delay Comparator Threshold

2.0

V

Delay Comparator Threshold

Hysteresis

100

mV

SENSE

Sense Threshold Voltage

1.16

1.23

1.35

V

Sense Threshold Hysteresis

40

100

200

mV

Sense Output LOW Voltage

≥ 3V

0.4

V

Sense Output Leakage

≥ 1.5V

1

µA

L4938N - L4938ND - L4938NPD

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