Rev. 10/30/00
SPX1587
3A Low Dropout Voltage Regulator
Adjustable & Fixed Output,
Fast Response
FEATURES
APPLICATIONS
Adjustable Output Down To 1.2V
Powering VGA & Sound Card
Fixed Output Voltages 1.5, 2.5, 3.3, 5.0V
Power PC Supplies
Output Current Of 3A
SMPS Post-Regulator
Low Dropout Voltage 1.1V Typ.
High Efficiency "Green" Computer Systems
Extremely Tight Load And Line Regulation
High Efficiency Linear Power Supplies
Current & Thermal Limiting
Portable Instrumentation
Standard 3-Terminal Low Cost TO-220, TO-263 & TO-252
Constant Current Regulators
Similar To Industry Standard LT1085/LT1585
Adjustable Power Supplies
Battery charger
PRODUCT DESCRIPTION
The SPX1587 is a low power 3A adjustable and fixed voltage regulator that is very easy to use. It requires only 2 external resistors to
set the output voltage for adjustable version. The SPX1587 are designed for low voltage applications that offers lower dropout voltage
and faster transient response. This device is an excellent choice for use in powering low voltage microprocessor that require a lower
dropout, faster transient response to regulate from +2.5V to 3.8V supplies and as a post regulator for switching supplies applications.
The SPX1587 features low dropout of a maximum 1.2 volts.
The SPX1587 offers over current limit and full protection against reversed input polarity, reversed load insertion, and positive and
negative transient voltage. On-Chip trimming adjusts the reference voltage to 1%. The I
Q
of this device flows into the load, which
increases efficiency.
The SPX1587 are offered in a 3-pin TO-220, TO-263 & TO-252 packages compatible with other 3 terminal regulators. For a 5A low
dropout regulator refer to the SPX1585 data sheet.
PIN CONNECTIONS
Front View
TO-220-3 (U)
SPX1587
1
2
3
ADJ/GND V
OUT
V
IN
Top View
TO-263-3 (T)
1
SPX1587
2
3
ADJ/GND V
OUT
V
IN
Front View
TO-252 (R)
ADJ/GND
V
IN
V
OUT
3
2
1
SPX1587
Rev. 10/30/00
SPX1587
ABSOLUTE MAXIMUM RATINGS
Lead Temp. (Soldering, 10 Seconds) .............................. 300C
Maximum Input Voltage ...................................... 10V
Storage Temperature Range ............................ -65 to +150C
Input to Output Voltage Differential Max ........... 8.8V
Operating Junction Temperature Range ......................
SPX1587 Control Section.......................... -45C +125C
SPX1587 Power Transistor.........................-45C +150C
ELECTRICAL CHARACTERISTICS
(NOTE 1) at I
OUT
= 10mA, T
A
=25
C, unless otherwise
specified.
PARAMETER
CONDITIONS Typ
SPX1587A
Min Max
SPX1587
Min Max
Units
1.5V Version
Output Voltage (Note 2)
SPX1587-1.5V, 0
I
OUT
3A, 2.75VV
IN
10V
1.5
1.5
1.485
1.470
1.515
1.530
1.470
1.455
1.530
1.545
V
2.5V Version
Output Voltage (Note 2)
SPX1587-2.5V, 0
I
OUT
3A, 4.0VV
IN
10V
2.5
2.5
2.475
2.450
2.525
2.550
2.450
2.425
2.550
2.575
V
3.3V Version
Output Voltage (Note 2)
SPX1587-3.3V, 0
I
OUT
3A, 4.75VV
IN
10V
3.3
3.3
3.270
3.240
3.330
3.360
3.230
3.201
3.370
3.399
V
5.0V Version
Output Voltage (Note 2)
SPX1587-5.0V, 0
I
OUT
3A, 6.5VV
IN
10V
5.0
5.0
4.95
4.90
5.05
5.10
4.900
4.850
5.100
5.150
V
All Voltage Options
Reference Voltage (V
REF
)
V
IN
7V, P P
MAX
1.5V
(V
IN -
V
OUT
)
(V
IN
-V
OUT
)
MAX
,
10mA
I
OUT
3A
1.250
1.238
1.225
1.263
1.270
1.225
1.212
1.270
1.288
V
Min. Load Current (Note 3)
1.5V
(V
IN -
V
OUT
)
(V
IN
-V
OUT
)
MAX
5 10 10
mA
Line Regulation (
V
REF
(V
IN
)) 2.75V
V
IN
7V, I
OUT
=10mA, T
J
=25
C
(Note 3)
0.005 0.2
0.2
%
V
IN
7V, I
OUT
=0mA, T
J
=25
C
(Note 2)
0.005 0.2
0.2
%
Load Regulation (
V
REF
(I
OUT
))
10mA
I
OUT
3A, (V
IN
-V
OUT
)=3V, T
J
=25
C
(Note 3)
0.05 0.3
0.3
%
0
I
OUT
3A, V
IN
=7V, T
J
=25
C
(Note 2)
0.05 0.3
0.3
%
Dropout Voltage
V
REF
=1% I
OUT
=3A
I
OUT
3A
1.1 1.2 1.2
V
Current Limit
I
OUT
(
MAX
)
V
IN
=7V
1.4V
(V
IN
-
V
OUT
) (Note3)
4.0
3.2
3.2
A
Long Term Stability
T
A
=125
C, 1000 Hrs.
0.3
(Note 2)
1 1 %
Thermal Regulation
(
V
OUT
(Pwr))
T
A
=25
C, 20 ms pulse
0.01 0.020 0.020
%/W
Temperature Stability
(
V
OUT
(T))
0.25
%
Output Noise, RMS
10Hz to 10kHz T
A
= 25
c
0.003
%V
Thermal Resistance
TO-220
DD Package
Junction to Tab
Junction to Ambient
Junction to Tab
Junction to Ambient
3.0
60
3.0
60
3.0
60
3.0
60
C/W
The Bold specifications apply to the full operating temperature range.
Note 1: Changes in output voltage due to heating effects are covered under the specification for thermal regulation.
Note 2: Fixed Version Only
Note 3: Adjustable Version Only
Rev. 10/30/00
SPX1587
APPLICATION HINTS
The SPX1587 incorporates protection against over-current
faults, reversed load insertion, over temperature operation, and
positive and negative transient voltage. However, the use of
an output capacitor is required in order to improve the stability
and the performances.
Stability
The output capacitor is part of the regulator's frequency
compensation system. Either a 22
F aluminum electrolytic
capacitor or a 10
F solid tantalum capacitor between the
output terminal and ground guarantees stable operation for all
operating conditions.
However, in order to minimize overshoot and undershoot, and
therefore optimize the design, please refer to the section
`Ripple Rejection'.
Ripple Rejection
Ripple rejection can be improved by adding a capacitor
between the ADJ pin and ground as shown in figure 6. When
ADJ pin bypassing is used, the value of the output capacitor
required increases to its maximum (22
F for an aluminum
electrolytic capacitor, or 10
F for a solid tantalum capacitor).
If the ADJ pin is not bypass, the value of the output capacitor
can be lowered to 10
F for an electrolytic aluminum capacitor
or 4.7
F for a solid tantalum capacitor.
However the value of the ADJ-bypass capacitor should be
chosen with respect to the following equation:
C = 1 / (6.28 * F
R
* R
1
)
Where C
= value of the capacitor in Farads (select an
equal or larger standard value),
F
R
= ripple frequency in Hz,
R
1
= value of resistor R
1
in Ohms.
If an ADJ-bypass capacitor is use, the amplitude of the output
ripple will be independent of the output voltage. If an ADJ-
bypass capacitor is not used, the output ripple will be
proportional to the ratio of the output voltage to the reference
voltage:
M = V
OUT
/ V
REF
Where M = multiplier for the ripple seen when the ADJ pin
is optimally bypassed.
V
REF
= Reference Voltage
Reducing parasitic resistance and inductance
One solution to minimize parasitic resistance and inductance is
to connect in parallel capacitors. This arrangement will
improve the transient response of the power supply if your
system requires rapidly changing current load condition.
Thermal Consideration
Although the SPX1587 offers some limiting circuitry for
overload conditions, it is necessary not to exceed the
maximum junction temperature, and therefore to be careful
about thermal resistance. The heat flow will follow the lowest
resistance path, which is the Junction-to-case thermal
resistance. In order to insure the best thermal flow of the
component, a proper mounting is required. Note that the case
of the device is electrically connected to the output. In case
the case has to be electrically isolated, a thermally conductive
spacer can be used. However do not forget to consider its
contribution to thermal resistance.
Assuming:
V
IN
= 10V, V
OUT
= 5V, I
OUT
= 1.5A, T
A
= 50
C/W,
Heatsink Case
= 6
C/W,
Heatsink Case
= 0.5
C/W,
JC
= 3
C/W
Power dissipation under this condition
P
D
= (V
IN
V
OUT
) * I
OUT
= 7.5W
Junction Temperature
T
J
= T
A
+ P
D
* (
Case - HS
+
HS
+
JC
)
For the Control Sections
T
J
= 50 + 7.5*(0.5 +6=3) = 121.25
C
121.25
C < T
J (max)
for the Control & Power Sections.
In both case reliable operation is insured by adequate junction
temperature.
Rev. 10/30/00
SPX1587
Basic Adjustable Regulator
Output Voltage
Consider Figure 2. The resistance R
1
generates a constant
current flow, normally the specified load current of 10mA.
This current will go through the resistance R
2
to set the overall
output voltage. The current I
ADJ
is very small and constant.
Therefore its contribution to the overall output voltage is very
small and can generally be ignored.
Load Regulation
Parasitic line resistance can degrade load regulation. In order
not to affect the behavior of the regulator, it is best to connect
directly the R
1
resistance from the resistor divider to the case,
and not to the load. For the same reason, it is best to connect
the resistor R
2
to the Negative side of the load.
Output Voltage
The fixed voltage LDO voltage regulators are simple to use
regulators since the V
OUT
is preset to the specifications. It is
important however, to provide the proper output capacitance
for stability and improvement. For most operating conditions
a capacitance of 22uF tantalum or 100uF electrolytic will
ensure stability and prevent oscillation.
SPX1587
Fig.2 Basic Adjustable Regulator
V
OUT
V
IN
V
REF
R
1
R
2
V
OUT
= V
REF
* ( 1 + R
2
/R
1
) + I
ADJ
* R
2
I
ADJ
50A
SPX1587
Fig.3 Basic Adjustable Regulator
V
IN
R
2
R
1
Connect R
2
to Load
R
L
Connect R
1
to
Case of Regulator
R
P
Parasitic Line
Resistance
SPX1587
Basic Fixed Regulator
V
IN
V
OUT
5V
C1
10uF
C2
10uF
3.3V
Rev. 10/30/00
SPX1587
TYPICAL APPLICATIONS
IN
OUT
ADJ
SPX1587
C
1
R
1
V
OUT
Fig. 5 Typical Adjustable Regulator
V
IN
LOAD
ADJ
SPX1587
Fig. 4 3A Current output Regulator
V
IN
C
1
OUT
IN
R
2
C
2
V
OUT
= V
REF
(1 + R
2
) + I
ADJ
R
2
R
1
R
1
Note A: V
IN(MIN)
= (Intended V
OUT
) + (V
DROPOUT (MAX)
)
SPX1587
Fig. 6 Improving Ripple Rejection
V
IN
R
1
R
2
150F
10F*
121
1%
365
1%
+
+
10F
C
1
*C
1
improves ripple rejection.
should be ~ R
1
at ripple frequency.
5V
ADJ
IN
OUT
(Note A)
V
OUT
SPX1587
Fig.7 5V Regulator with Shutdown
V
IN
100F
121
1%
365
1%
+
+
10F
5V
ADJ
IN
OUT
(Note A)
1k
1k
TTL
Input
2N3904
Note A: V
IN(MIN)
= (Intended V
OUT
) + (V
DROPOUT (MAX)
)
X
C
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