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L4925
(Rev.:2000)

VERY LOW DROP VOLTAGE REGULATOR

STMicroelectronics 

L4925

APPLICATION NOTE

SUPPLY VOLTAGE TRANSIENTS

High supply voltage transients can cause a reset

output signal disturbation.

For supply voltage greater than 8V the circuit

shows a high immunity of the reset output against

supply transients of more than 100V/µs.

For supply voltage lower than 8V, supply tran-

sients of more than 0.4V/µs. can cause a reset

signal disturbation.

Foldback Characteristics Of Vo

FUNCTIONAL DESCRIPTION

The L4925 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.

Nevetrheless, it is suitable also in other applica-

tions where the present functions are required.

The modular approach of this device allows to get

easily also other features and functions when re-

quired.

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 500mA is obtained.

Figure 1: Output Voltage vs. Input Voltage

The dropout operation of the standby regulator is

maintained down to 3V input supply voltage. The

output voltage is regulated up to the transient in-

put supply voltage of 35V. 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 fig. 1.

The current consumption of the device (quiescent

current) is less than 250µA.

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.

The quiescent current as a function of the supply

input voltage is shown in fig. 2.

Figure 2: Quiescent Current vs. Supply Voltage

4/8

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