FUNCTIONAL DESCRIPTION

The L4938E/ED/EPD is a monolithic integrated

dual voltage regulator, based on the STM modu-

lator voltage regulator approach. Several out-

standing features and auxiliary functions are im-

plemented to meet the requirements of supplying

microprocessor systems in automotive applica-

tions. Nevertheless, it is suitable also in other ap-

plications where two stabilized voltages are re-

quired. The modular approach of this device

allows to get easly also other features and func-

tions when required.

Standby Regulator

The standby regulator uses an Isolated collector

Vertical PNP transistor as a regulating element.

With this structure very low dropout volotage 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.

In the standby mode when the output 2 is dis-

abled, the current consumption of the device (qui-

escent current) is less than 90

µA (14V supply

voltage).

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. A second regulation path will keep the

output voltage without load below 5.5V even at

high temperatures.

Output 2 Voltage

The output 2 regulator uses the same output

structure as the standby regulator but rated for

the output current of 400mA. The output voltage

is internally fixed to 5V if ADJ is connected to

The output 2 regulator can be switches OFF via

the enable input.

REG1

1.23V

REFERENCE

REG2

1.23V

RESET

1.4V

1.23V

1.23V

SENSE

VS1

VS2

EN

PR

SI

SO

RES

CT

ADJ

OUT2

OUT1

GND

D94AT079A

15V

100K

(Note 8)

for example

BZX97C15

CT (Note 7)

Figure 1. Application Diagram.

1.23V

D94AT080

-

+

OUT2

ADJ

total 100K

typical

Figure 2.

L4938E - L4938ED - L4938EPD

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