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Электронный компонент: LX8940

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D E S C R I P T I O N
K E Y F E A T U R E S




s
s
s
s
s 2% Internally Trimmed Output




s
s
s
s
s Output Current In Excess Of 1A




s
s
s
s
s Input-Output Differential
Less Than 0.4V At 1A
p Reverse Battery Protection
p 60V Load Dump Protection
p -50V Reverse Transient Protection
p Short Circuit Protection
p Internal Thermal Overload Protection
p Available In 3-Lead Plastic TO-220
p Drops In Most lM2940 Sockets
The LX8940 is a 5V, low dropout, low
quiescent current regulator rated for 1A
of output current. It can regulate with
as low as 0.4V headroom between the
input and output voltages, thus
minimizing power dissipation. In
addition, it can be used in applications
where worst case supplies require a
low input-output differential to maintain
regulation. This feature makes it ideal
for computer monitors that have to
comply with energy-efficient / "Green
PC" programs, where the input voltage
drops to only a few tenths of a volt
above the output when power supply
enters sleep-mode operation.
P R O D U C T H I G H L I G H T
T
A
(C)
Plastic TO-220
3-pin
0 to 125
LX8940CP
-40 to 125
LX8940IP
P
LX8940
OUT
IN
GND
10F
0.1F
5V/100mA
5.3V
D
R O P O U T
V
O L TA G E
V S
. O
U T P U T
C
U R R E N T
V S
. T
E M P E R AT U R E
L
O A D
T
R A N S I E N T
R
E S P O N S E
100
0
Output Current - (mA)
600
Dropout Voltage - (mV)
200
100
500
1000
400
500
300
125C
25C
-40C
Time - (20s/Div.)
Output Voltage
(20mV / Div.)
0mA
T
A
= 25C
C
IN
= 1F
V
IN
= 5.30V
Output Current
(50mA / Div.)
5.000V
C
O
= 47F Electrolytic
100mA
4.980V
A P P L I C A T I O N S
s Small Headroom Battery Applications
s High Efficiency Linear Regulators
s Post Regulators For Switching Power
Supplies
s Green PC Monitor Applications
5 V L
O W
D
R O P O U T
R
E G U L A T O R
P
R O D U C T I O N
D
A T A
S
H E E T
T
H E
I
N F I N I T E
P
O W E R
O F
I
N N O V A T I O N
LX8940
LIN D
O C
#: 8940
PA C K A G E O R D E R I N F O
Copyright 1999
Rev. 1.3 3/99
1
11861 W
ESTERN
A
VENUE
, G
ARDEN
G
ROVE
, CA. 92841, 714-898-8121, F
AX
: 714-893-2570
L
I N
F
I N I T Y
M
I C R O E L E C T R O N I C S
I
N C
.
NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.
5 V L
O W
D
R O P O U T
R
E G U L A T O R
LX8940
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
Copyright 1999
Rev. 1.3 3/99
2
P
R O D U C T I O N
D
A T A
S
H E E T
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Voltage (V
IN
) .......................................................................................... -15V to 26V
Operating Junction Temperature
Plastic (P Package) ................................................................................................ 150C
Storage Temperature Range ...................................................................... -65C to 150C
Lead Temperature (Soldering, 10 seconds) ............................................................. 300C
PACKAGE PIN OUTS
P PACKAGE
(Top View)
Note 1. Exceeding these ratings could cause damage to the device. All voltages are with respect
to Ground. Currents are positive into, negative out of the specified terminal. Pin
numbers refer to DIL packages only.
P PACKAGE:
THERMAL RESISTANCE-JUNCTION TO TAB,




JT
3.0C/W
THERMAL RESISTANCE-JUNCTION TO AMBIENT,




JA
60C/W
Junction Temperature Calculation: T
J
= T
A
+ (P
D
x
JA
).
The
JA
numbers are guidelines for the thermal performance of the device/pc-board system.
All of the above assume no ambient airflow.
THERMAL DATA
BLOCK DIAGRAM
* Required if regulator is located far from power supply filter.
C2
10F
INPUT VOLTAGE
LX8940
1 (INPUT)
3 (OUTPUT)
2 (GND)
C1*
0.1F
OVERVOLTAGE
THERMAL
SHUTDOWN
REGULATOR
BIAS
1.23V
REFERENCE
OUTPUT VOLTAGE
Tab is GROUND
OUTPUT
GND
INPUT
3
2
1
5 V L
O W
D
R O P O U T
R
E G U L A T O R
LX8940
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
3
Copyright 1999
Rev. 1.3 3/99
P
R O D U C T I O N
D
A T A
S
H E E T
Input Voltage
V
IN
Load Current (with adequate heatsinking)
Maximum Line Transient (Load Dump), V
O
5.5V
Input Capacitor (V
IN
to GND)
Output Capacitor with ESR of 10
max., (V
OUT
to GND & V
SB
to GND)
R E C O M M E N D E D O P E R A T I N G C O N D I T I O N S
Parameter
Symbol
Units
Recommended Operating Conditions
Min.
Typ.
Max.
Note 2
26
V
5
1000
mA
60
V
0.1
F
10
F
Note 2. V
IN (MIN)
= 1.2
V
(MAX)
. See Dropout Voltage maximum limit.
E L E C T R I C A L C H A R A C T E R I S T I C S
Unless otherwise specified, these specifications apply over the operating ambient temperatures of -40C to +125C for LX8940IP, and 0C to +125C
for LX8940CP; V
IN
= 10V, I
O
= 1A, C
OUT
= 22F, and are for DC characteristics only. (Low duty cycle pulse testing techniques are used which maintains
junction and case temperatures equal to the ambient temperature.)
Parameter
Symbol
Test Conditions
Units
Output Voltage
V
O
I
O
= 0A, T
A
= 25C
Line Regulation
V
OI
7V
V
IN
26V, I
O
= 5mA
Load Regulation
V
OL
50mA
I
O
1A
Output Impedance (Note 3)
r
O
100mA
DC
and 20mA
RMS
, f
O
= 120Hz
Quiescent Current
I
Q
I
O
5mA, 7
V
IN
26V
I
O
= 500mA
I
O
= 1000mA
Output Noise Voltage (Note 3)
V
O RMS
10Hz - 100kHz, I
O
= 5mA
Long Term Stability (Note 3)
Ripple Rejection (Note 3)
R
R
f
O
= 120Hz, 1V
RMS
, I
O
= 100mA
Dropout Voltage
V
I
O
= 100mA
I
O
= 500mA
I
O
= 1A
Current Limit
I
CL
V
IN
= 26V
Maximum Operational Input Voltage
V
IN (MAX)
Maximum Line Transient
V
IN
(TR)
R
O
= 100
, T
100ms
4.85
5
5.15
V
1
50
mV
10
50
mV
200
m
3
15
mA
30
50
mA
115
180
mA
150
V
RMS
20
mV/1000hr
66
dB
150
300
mV
275
500
mV
400
800
mV
1
1.2
A
26
31
V
60
V
LX8940
Min.
Typ.
Max.
Note 3. These parameters, although guaranteed, are not tested in production.
5 V L
O W
D
R O P O U T
R
E G U L A T O R
LX8940
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
Copyright 1999
Rev. 1.3 3/99
4
P
R O D U C T I O N
D
A T A
S
H E E T
A P P L I C A T I O N N O T E S
The advantages of using a low-dropout regulator such as the
LX8940 is the need for less "headroom" for full regulation, and the
inherent reverse polarity protection provided by the PNP output
device. A typical NPN regulator design requires an input to output
differential of approximately two volts minimum. This is due to
the 2Vbe + Vcesat of the NPN Darlington used in the output,
coupled with the voltage drop across the current limit resistor. In
contrast, the "PNP Regulator" uses a single series pass transistor
with its single Vcesat, thus the lower input to output voltage
differential or dropout voltage.
In some applications the regulator output voltage is used not
only as a power supply but also as a voltage reference for control
systems. In such cases not just the temperature stability of the
output is important but also the initial accuracy. LX8940 fills this
need as the internal bandgap reference is trimmed allowing a
typical output voltage tolerance of 1%.
EXTERNAL CAPACITORS
To stabilize the outputs and prevent oscillation (perhaps by many
volts) external capacitors are required. The minimum recom-
mended value for the output capacitors is 10F, although the
actual size and type will likely vary according to the particular
application, e.g., operating temperature range and load. Another
consideration is the effective series resistance (ESR) of the
capacitor. Capacitor ESR will vary by manufacturer. Conse-
quently, some evaluation may be required to determine the
minimum value of the output capacitors. Generally worst case
occurs at the maximum load and minimum ambient temperature.
The size of the output capacitor can be increased to any value
above the minimum. One possible advantage of this would be to
maintain the output voltage during brief periods of negative input
transients
The output capacitors chosen should be rated for the full range
of ambient temperature over which the circuit will be exposed and
expected to operate. For example, many aluminum type electro-
lytic capacitors change values at cold temperatures. The effective
capacitance is reduced and regulator stability is effected. Tanta-
lum capacitors are a good choice for these types of environments.
OUTPUT PROTECTION
The output features fault protection against overvoltage as well as
a thermal shutdown feature. If the input voltage rises above 33V
(load dump), the output shuts down automatically. The internal
circuitry is thus protected and the IC is able to survive higher
voltage transients than might otherwise be expected. The thermal
shutdown output effectively guards against overheating of the die
and protects the device from being damaged.
PRODUCTION DATA - Information contained in this document is proprietary to Lin Finity, and is current as of publication date. This document
may not be modified in any way without the express written consent of LinFinity. Product processing does not necessarily include testing of
all parameters. Linfinity reserves the right to change the configuration and performance of the product and to discontinue product at any time.