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FUNCTIONAL DESCRIPTION
The block diagram shows the basic structure of
the devices : the reference, the error amplifier, the
driver, the power PNP, the protection and reset
functions.
The power stage is a Lateral PNP transistor
which allows a very low dropout voltage (typ.
400mV at T
J
= 25
°
C, max. 750mV over the full
temperature range @ I
O
= 500mA). The typical
curve of the dropout voltage as a function of the
junction temperature is shown in Fig. 1 : that is
the worst case, where I
O
= 500mA.
The current consumption of the devices (quies-
cent current) are maximum 10mA - over full T -
when no load current is required.
The internal antisaturation circuit allows a drastic
reduction in the current peak which takes place
during the start up.
The three gain stages (operational amplifier,
driver and power PNP) require the external ca-
pacitor (C
omin
= 20
µ
F) to guarantee the global
stability of the system.
Load dump and field decay protections (
±
80V, t =
300ms), reverse voltage (– 18V) and short circuit
protection, thermal shutdown are the main fea-
tures that make the devices specially suitable for
applications in the automotive enviroment.
ELECTRICAL CHARACTERISTICS
(refer to the test circuit, V
i
= 14. 4V, C
o
= 47
µ
F, ESR < 10
Ω
,
R
p
= 1K
Ω
, R
L
= 1K
Ω
, –40
°
C
≤
T
J
≤
125
°
C, unless otherwise specified)
Symbol Parameter Test Conditions Min. Typ. Max. Unit
V
o
Output Voltage I
o
= 0mA to 500mA
Over Full T Range
4.80 5.00 5.20 V
T
j
= 25°C 4.90 5.00 5.10 V
V
i
Operating Input Voltage I
o
= 0mA to (*) 500mA 6 26 V
∆V
o
Line Regulation V
i
= 6V to 26V ;
I
o
= 5mA
210mV
∆V
o
Load Regulation I
o
= 5mA to 500mA 15 60 mV
V
i
–V
o
Dropout Voltage I
o
= 500mA, T
J
= 25°C
Over Full T Range
0.40 0.55
0.75
V
V
I
q
Quiescent Current I
o
= 0mA, T
J
= 25°C
I
o
= 0mA Over Full T
I
o
= 500mA Over Full T
5
6.5
110
10
13
180
mA
mA
mA
Temperature Output Voltage
Drift
– 0.5 mV/°C
SVR Supply Volt. Rej. I
o
= 350mA ; f = 120Hz
C
o
= 100µF ;
V
i
= 12V ± 5V
pp
50 60 dB
I
sc
Output Short Circuit Current 0.50 0.80 1.50 A
(*)
For a DC voltage 26 < V
i
< 37V the device is not operating
∆V
o
T
TEST CIRCUIT
L4945
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