L4923 datasheet(4/6 Pages) STMICROELECTRONICS

4 / 6 page

The operating principle of the voltage regulator is

basedon thereference,the error amplifier,the driver

and the power PNP. This stage uses an Isolated

Collector Vertical PNP transistor which allows to ob-

tain very low dropout voltage (typ. 450 mV) and low

quiescent current (IQ = 20 mA typically at IO = 1 A).

Thanks to these features the device is particularly

suited when the power dissipation must be limited

as, for example, in automotive or industrial applica-

tions supplied by battery.

The three gain stages (operational amplifier, driver

and power PNP) require the external capacitor

(COmin =22

µF) to guarantee the global stability of

the system.

The antisaturationcircuit allows to reducedrastically

the current peak which takes place during the start

up.

The reset function is LOW active when the output

voltage level is lower than the reset threshold volt-

age VRth (typ.value : VO - 150 mV). When the output

voltage is higher than VRth the reset becomes HIGH

after a delay time settablewith the externalcapacitor

Cd. Typically td = 20 ms, Cd = 0.1

µF. The reset

threshold hysteresis improves the noise immunity

allowing to avoid false switchings. The typical reset

output waveform is shown in fig. 2.

The inhibit circuit acceptsstandardTTL inputlevels :

thisblockswitches off the voltage regulatorwhen the

input signal is HIGH and switches on it when the in-

put signal is LOW. Thanksto inhibit functionthe con-

sumption is drastically reduced (650

µA max) when

no load current is required.

Figure 2 : Typical Reset Output Waveform.

FUNCTIONAL DESCRIPTION

L4923

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