l4923 STMicroelectronics, l4923 Datasheet - Page 4

• Manufacturer Part Number: l4923
• Description: With Reset And Inhibit 5v.1a Very Low Drop Regulator
• Manufacturer: STMicroelectronics

L4923
FUNCTIONAL DESCRIPTION
The operating principle of the voltage regulator is
basedon thereference,the error amplifier,the driver
and the power PNP. This stage uses an Isolated
CollectorVertical PNP transistor which allowsto ob-
tain very low dropout voltage (typ. 450 mV) and low
quiescent current (I
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
(C
the system.
The antisaturationcircuit allows to reducedrastically
the current peak which takes place during the start
up.
4/6
Figure 2 : Typical Reset Output Waveform.
Omin
= 22 F) to guarantee the global stability of
Q
= 20 mA typically at I
O
= 1 A).
The reset function is LOW active when the output
voltage level is lower than the reset threshold volt-
age V
voltage is higher than V
aftera delay time settablewith the externalcapacitor
C
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 :
thisblockswitchesoff 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 A max) when
no load current is required.
d
. Typically t
Rth
(typ.value : V
d
= 20 ms, C
O
Rth
- 150 mV). When the output
the reset becomes HIGH
d
= 0.1 F. The reset