SPX3940
1A Low Dropout Voltage Regulator
February 2012
Rev. 1.0.0
GENERAL DESCRIPTION
The SPX3940 is a 1A, accurate voltage
regulator with a low drop out voltage of
280mV (typical) at 1A.
These regulators are specifically designed for
low voltage applications that require a low
dropout voltage and a fast transient response.
They are fully fault protected against over-
current, reverse battery, and positive and
negative voltage transients.
The SPX3940 is offered in 3-pin SOT223 and
TO-263 packages. For a 3A version, refer to
the SPX29300 data sheet.
APPLICATIONS
Power Supplies
LCD Monitors
Portable Instrumentation
Medical and Industrial Equipments
FEATURES
Guaranteed 1.5A Peak Current
1% Output Accuracy SPX3940A
Low Quiescent Current
Low Dropout Voltage of 280mV at 1A
Extremely Tight Load and Line
Regulation
Extremely Fast Transient Response
Reverse-battery Protection
Internal Thermal Protection
Internal Short Circuit Current Limit
Replacement for LM3940
Standard SOT223 & TO-263 packages
TYPICAL APPLICATION DIAGRAM
Fig. 1: SPX3940 Application Diagram – Fixed Output Linear Regulator
Exar Corporation
48720 Kato Road, Fremont CA 94538, USA
www.exar.com
Tel. +1 510 668-7000 – Fax. +1 510 668-7001
SPX3940
1A Low Dropout Voltage Regulator
ABSOLUTE MAXIMUM RATINGS
These are stress ratings only and functional operation of
the device at these ratings or any other above those
indicated in the operation sections of the specifications
below is not implied. Exposure to absolute maximum
rating conditions for extended periods of time may affect
reliability.
Input Voltage V
IN
................................................... 20V
1
Storage Temperature .............................. -65°C to 150°C
Lead Temperature (Soldering, 5 sec) ..................... 260°C
OPERATING RATINGS
Input Voltage V
IN
.................................................... 16V
Junction Temperature Range ....................-40°C to 125°C
Packages Thermal Resistance
SOT-223 Junction to Case (at T
A
) ..................... 15°C/W
SOT-223 Junction to Ambient ........................62.3°C/W
TO-263 Junction to Case (at T
A
) ......................... 3°C/W
TO-263 Junction to Ambient ..........................31.4°C/W
Note 1: Maximum positive supply voltage of 20V must be
of limited duration (<100ms) and duty cycle (<1%). The
maximum continuous supply voltage is 16V.
ELECTRICAL SPECIFICATIONS
Specifications with standard type are for an Operating Ambient Temperature of T
A
= 25°C only; limits applying over the full
Operating Junction Temperature range are denoted by a “•”. Minimum and Maximum limits are guaranteed through test,
design, or statistical correlation. Typical values represent the most likely parametric norm at T
A
= 25°C, and are provided
for reference purposes only. Unless otherwise indicated, V
IN
= V
IN
+1V, I
OUT
= 10mA, C
IN
= 6.8µF, C
OUT
= 10µF, T
A
= 25°C.
Parameter
1.8V version
Output Voltage -
Output Voltage -
2.5V version
Output Voltage -
Output Voltage -
3.3V version
Output Voltage -
Output Voltage -
5.0V version
Output Voltage -
Output Voltage -
SPX3940A (1%)
SPX3940A (1%)
SPX3940A (1%)
SPX3940A (1%)
Min.
1.782
1.755
1.764
1.737
2.475
2.437
2.450
2.412
3.267
3.217
3.234
3.184
4.950
4.875
4.900
4.825
Typ.
1.8
1.8
1.8
1.8
2.5
2.5
2.5
2.5
3.3
3.3
3.3
3.3
5.0
5.0
5.0
5.0
0.2
0.3
20
70
280
12
18
1.2
Max.
1.818
1.845
1.836
1.863
2.525
2.563
2.550
2.588
3.333
3.383
3.366
3.416
5.050
5.125
5.100
5.175
1.0
1.5
100
200
550
25
Units
Conditions
V
V
•
•
SPX3940 (2%)
I
OUT
=10mA
10mA≤I
OUT
≤1A, 6V≤V
IN
≤16V
V
V
•
•
SPX3940 (2%)
I
OUT
=10mA
10mA≤I
OUT
≤1A, 6V≤V
IN
≤16V
V
V
•
•
SPX3940 (2%)
I
OUT
=10mA
10mA≤I
OUT
≤1A, 6V≤V
IN
≤16V
V
V
•
•
SPX3940 (2%)
I
OUT
=10mA
10mA≤I
OUT
≤1A, 6V≤V
IN
≤16V
All Voltage Options
Line Regulation
Load Regulation
- Output Voltage
temperature Coefficient
Dropout Voltage
2
(except 1.8V version)
Ground Current
3
I
GNDDO
Ground Pin Current at
Dropout
Current Limit
Output Noise Voltage
1.5
%
%
ppm/°C
mV
mV
mA
mA
mA
A
µV
RMS
µV
RMS
•
•
•
•
I
OUT
=100mA
I
OUT
=1A
I
OUT
=750mA, V
IN
= V
OUT
+1V
I
OUT
=1A
V
IN
= 0.1V less than specified V
OUT
I
OUT
=10mA,
V
OUT
= 0V
4
10Hz-100KHz, I
L
=100mA, C
L
=10µF
10Hz-100KHz, I
L
=100mA, C
L
=33µF
I
OUT
=10mA, (V
OUT
+1V)≤V
IN
≤16V
V
IN
= V
OUT
+1V,10mA≤I
OUT
≤1A
2.2
400
260
© 2012 Exar Corporation
2/11
Rev. 1.0.0
SPX3940
1A Low Dropout Voltage Regulator
Note 2: Dropout voltage is defined as the input to output differential when the output voltage drops to 99% of its normal
value.
Note 3: Ground pin current is the regulator quiescent current. The total current drawn from the source is the sum of the
load current to the ground current.
Note 4: V
IN
=V
OUT(NOMINAL)
+1V. For example, use V
IN
=4.3V for a 3.3V regulator. Employ pulse-testing procedures to minimize
temperature rise.
BLOCK DIAGRAM
Fig. 2: SPX3940 Block Diagram
PIN ASSIGNMENT
Fig. 3: SPX3940 Pin Assignment
© 2012 Exar Corporation
3/11
Rev. 1.0.0
SPX3940
1A Low Dropout Voltage Regulator
ORDERING INFORMATION
Part Number
SPX3940AM3-L-1-8
SPX3940AM3-L-1-8/TR
SPX3940AM3-L-2-5
SPX3940AM3-L-2-5/TR
SPX3940AM3-L-3-3
SPX3940AM3-L-3-3/TR
SPX3940AM3-L-5-0
SPX3940AM3-L-5-0/TR
SPX3940AT-L-1-8
SPX3940AT-L-1-8/TR
SPX3940AT-L-3-3
SPX3940AT-L-3-3/TR
SPX3940AT-L-5-0
SPX3940AT-L-5-0/TR
SPX3940M3-L-2-5
SPX3940M3-L-2-5/TR
SPX3940M3-L-3-3
SPX3940M3-L-3-3/TR
SPX3940M3-L-5-0
SPX3940M3-L-5-0/TR
SPX3940T-L-3-3
SPX3940T-L-3-3/TR
SPX3940T-L-5-0
SPX3940T-L-5-0/TR
Temperature
Range
-40°C≤T
J
≤+125°C
-40°C≤T
J
≤+125°C
Marking
3940A
18YYWWL
XXX
3940A
25YYWWL
XXX
3940A
33YYWWL
XXX
3940A
50YYWWL
XXX
SPX3940AT
18YYWWLX
SPX3940AT
33YYWWLX
SPX3940AT
50YYWWLX
3940M3
25YYWWL
3940M3
33YYWWL
3940M3
50YYWWL
SPX3940T
33YYWWLX
SPX3940T
33YYWWLX
Package
3-pin
SOT-223
3-pin
SOT-223
3-pin
SOT-223
3-pin
SOT-223
3-pin
TO-263
3-pin
TO-263
3-pin
TO-263
3-pin
SOT-223
3-pin
SOT-223
3-pin
SOT-223
3-pin
TO-263
3-pin
TO-263
Packing
Quantity
2.5K/Tape & Reel
Bulk
2.5K/Tape & Reel
Bulk
2.5K/Tape & Reel
Bulk
2.5K/Tape & Reel
Bulk
500/Tape & Reel
Bulk
500/Tape & Reel
Bulk
500/Tape & Reel
Bulk
2.5K/Tape & Reel
Bulk
2.5K/Tape & Reel
Bulk
2.5K/Tape & Reel
Bulk
500/Tape & Reel
Bulk
500/Tape & Reel
Bulk
Lead Free
Lead Free
Lead Free
Lead Free
Lead Free
Lead Free
Lead Free
Lead Free
Lead Free
Lead Free
Lead Free
Lead Free
Note 1
Note 2
1.8V Output
Voltage – 1%
2.5V Output
Voltage – 1%
3.3V Output
Voltage – 1%
5.0V Output
Voltage – 1%
1.8V Output
Voltage – 1%
3.3V Output
Voltage – 1%
5.0V Output
Voltage – 1%
2.5V Output
Voltage – 2%
3.3V Output
Voltage – 2%
5.0V Output
Voltage – 2%
3.3V Output
Voltage – 2%
5.0V Output
Voltage – 2%
-40°C≤T
J
≤+125°C
-40°C≤T
J
≤+125°C
-40°C≤T
J
≤+125°C
-40°C≤T
J
≤+125°C
-40°C≤T
J
≤+125°C
-40°C≤T
J
≤+125°C
-40°C≤T
J
≤+125°C
-40°C≤T
J
≤+125°C
-40°C≤T
J
≤+125°C
-40°C≤T
J
≤+125°C
“YY” = Year – “WW” = Work Week – “X” = Lot Number – when applicable.
© 2012 Exar Corporation
4/11
Rev. 1.0.0
SPX3940
1A Low Dropout Voltage Regulator
TYPICAL PERFORMANCE CHARACTERISTICS
Schematic and BOM from Application Information section of this datasheet.
Fig. 4: Line Regulation
Fig. 5: Load Regulation
Fig. 6: Ground Current vs Load Current
Fig. 7: Ground Current vs Input Voltage
Fig. 8: Ground Current vs Load Current in Dropout
Fig. 9: Dropout Voltage vs Load Current
© 2012 Exar Corporation
5/11
Rev. 1.0.0
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