L4945
5V VERY LOW DROP VOLTAGE REGULATOR
5V
4% PRECISE OUTPUT VOLTAGE
OVER FULL TEMPERATURE RANGE
( 40 / 125
C)
VERY LOW VOLTAGE DROP (0.75Vmax)
OVER FULL TEMPERATURE RANGE
OUTPUT CURRENT UP TO 500mA
OVERVOLTAGE AND REVERSE VOLTAGE
PROTECTIONS
REVERSE VOLTAGE PROTECTION
SHORT CIRCUIT PROTECTION AND THER-
MAL SHUT-DOWN (with hysteresis)
LOW START UP CURRENT
DESCRIPTION
The L4945 is a monolithic integrated circuit in
Versawatt package specially designed to provide
a stabilized supply voltage for automotive and in-
dustrial electronic systems. Thanks to their very
low voltage drop, in automotive applications the
devices can work correctly even during the crank-
ing phase, when the battery voltage could fall as
low as 6V. Furthermore, they incorporate a com-
plete range of protection circuits against the dan-
gerous overvoltages always present on the bat-
tery rail of the car.
This is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
March 1999
BLOCK DIAGRAM
TO220
ORDERING NUMBER: L4945
1/6
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Value
Unit
V
i
DC Input Voltage
DC Reverse Input Voltage
Transient Input Overvoltages :
Load Dump :
5ms
t
rise
10ms
f
Fall Time Constant = 100ms
R
SOURCE
0.5
Field Decay :
5ms
t
fall
10ms, R
SOURCE
10
r
Rise Time Constant = 33ms
Low Energy Spike :
t
rise
= 1
s, t
fall
= 500
s, R
SOURCE
10
f
r
Repetition Frequency = 5Hz
35
18
80
80
100
V
V
V
V
V
T
J
Junction Temperature Range
40 to 150
C
T
OP
Operating Temperature Range
40 to 125
C
T
stg
Storage Temperature Range
55 to 150
C
Note: The circuit is ESD protected according to MIL-STD-883C.
THERMAL DATA
Symbol
Parameter
Value
Unit
R
th j-case
Thermal Resistance Junction-case
Max
3
C/W
PIN CONNECTION (Top view)
L4945
2/6
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
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
F, ESR < 10
,
R
p
= 1K
, R
L
= 1K
, 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
2
10
mV
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
= 100
F ;
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
3/6
EXTERNAL COMPENSATION
Since the purpose of a voltage regulator is to sup-
ply and load variations, the open loop gain of the
regulators must be very high at low frequencies.
This may cause instability as a result of the vari-
ous poles present in the loop. To avoid this insta-
bility dominant pole compensation is used to re-
duce phase shift due to other poles at the unity
gain frequency. The lower the frequency of these
others poles at the unity gain frequency. The
lower the frequency of these other poles, the
greater must be capacitor esed to create the
dominant pole for the same DC gain.
Where the output transistor is a lateral PNP type
there is a pole in the regulation loop at a fre-
quencybtoo low to be compensated by a capaci-
tor which can be integrated. An external compen-
sation is therefore necessary so a very high value
capacitor must be connected from the output to
ground.
The paeassitic equivalent series resistance of the
capacitor used adds a zero to the regulation loop.
This zero may compromise the stability of the
system since its effect tends to cancel the effect
of the pole added. In regulators this ESR must be
less than 3
and the minimum capacitor value is
47
F.
Figure 1: Typical Dropout Voltage vs. T
j
(I
o
= 500mA).
L4945
4/6
Versawatt (TO220)
DIM.
mm
inch
MIN.
TYP.
MAX.
MIN.
TYP.
MAX.
A
4.40
4.60
0.173
0.181
C
1.23
1.32
0.048
0.051
D
2.40
2.72
0.094
0.107
E
0.49
0.70
0.019
0.027
F
0.61
0.88
0.024
0.034
F1
1.14
1.70
0.044
0.067
F2
1.14
1.70
0.044
0.067
G
4.95
5.15
0.194
0.203
G1
2.40
2.70
0.094
0.106
H2
10.0
10.4
0.393
0.409
L2
16.4
0.645
L4
13.0
14.0
0.511
0.551
L5
2.65
2.95
0.104
0.116
L6
15.25
15.75
0.600
0.620
L7
6.20
6.60
0.244
0.260
L9
3.50
3.93
0.137
0.154
M
2.6
0.102
Dia
3.75
3.85
0.147
0.151
M
TO220MEC
OUTLINE AND
MECHANICAL DATA
L4945
5/6
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