1
Date 5/25/04
SPX1581 5A Ultra Low Dropout Voltage Regulator
Copyright 2004 Sipex Corporation
SPX1581
DESCRIPTION
FEATURES
Low Dropout Voltage 500mV at 5A Full Load Current
Adjustable Ouput Down to 1.2V from ATX Power Supply
Fixed Output Voltages of 3.3V, 2.8V and 2.5V
Extremely Tight Load and Line Regulation
Standard 5-Terminal Low Cost TO-220 and TO-263
The SPX1581 is a 5A Low Dropout Regulator with extremely low dropout voltage. The adjustable version requires only
two external resistors to set the output voltage. The fixed version has a preset output of 3.3V, 2.8V or 2.5V and does
not require any external resistors. The SPX1581 features a low dropout of 400mV(Typ.) and offers fast transient
response. This device is suitable for Pentium applications requiring 2.8V, 2.5V from 3.3V ATX power supplies, where
a low current input voltage 1V greater than the output voltage is needed. With an external sense pin the load regulation
is less than 1mV. This device is an excellent choice for the use of powering low voltage microprocessors that require
a lower dropout, fast transient response to regulate from 3.3V and 5V supplies. The SPX1581 is also an excellent choice
as a post regulator for switching supplies applications.
The SPX1581 offers protection against over-current faults, reversed input polarity, over temperature operation and
positive and negative transient voltage.
The SPX1581 is offered in a 5 pin TO-220 and TO-263 compatible with industry standard 5-terminal regulators. For 7A,
3A and 1.5A ultra low dropout versions refer to SPX1580, SPX1582 and SPX1583 data sheets respectively.
5A Ultra Low Dropout Voltage Regulator
Fast Response, Adjustable & Fixed
APPLICATIONS
3.3V to 2.8V ATX Power Supplies
3.3V to 2.9V for Portable PENTIUM
TM
Processor
5V to 3.5V VRE Supply
High efficiency "Green" Computer Systems
1
3
2
5
4
SPX1581
5 Pin TO-263
SENSE
ADJ OR FIXED
V
OUT
V
CNTRL
V
IN
3
2
1
SPX1581
5 Pin TO-220
SENSE
ADJ OR FIXED
V
OUT
V
CNTRL
V
IN
4 5
C4
2x330F
2.5V
V
OUT
R1
124
R2
124
V
OUT
SENSE
C2
10F
V
CTRL
C1
330F
3.3V
V
IN
5V
V
CTRL
SPX1581
5
4
2
3
1
(1) V
CTRL
needed when V
IN
< 5V.
(2) V
OUT
= V
REF
(1+R
2
/R
1
)+I
ADJ
R
2
.
(3) V
REF
is measured across adjust to sense.
ADJ
V
IN
C3
.033F
C4
2x330F
2.5V
V
OUT
V
OUT
SENSE
C2
10F
V
CTRL
C1
330F
3.3V
V
IN
5V
V
CTRL
SPX1581
5
4
2
3
1
(1) V
CTRL
needed when V
IN
< 5V.
GND
V
IN
Typical Fixed Regulator
Adjustable Regulator
TYPICAL APPLICATIONS CIRCUIT
Now Available in Lead Free Packaging
2
Date 5/25/04
SPX1581 5A Ultra Low Dropout Voltage Regulator
Copyright 2004 Sipex Corporation
Power Dissipation ..................................... Internally Limited
Lead Temp. (Soldering, 10 Seconds) ......................... 300C
Storage Temperature Range ..................... -65C to +150C
Operating Junction Temperature Range
SPX1581 Control Section ............................. 0C to +125C
SPX1581 Power Transistor .......................... 0C to +150C
ELECTRICAL CHARACTERISTICS
Electrical characteristics at V
OUT
= V
SENSE
, V
ADJ
= 0V, T
A
=25
C, C
CTL
= C
PWR
= C
OUT
= 33
F tantalum cap otherwise specified.
The
denotes the specifications which apply over full temperature range -40C to +85C, unless otherwise specified.
PARAMETER
MIN
TYP
MAX
UNITS
CONDITIONS
2.5V Version
Output Voltage
2.450
2.5
2.550
V
V
CTRL
= 6.0V to 12V, V
IN
= 3.0V to 5.0V, I
O
=10mA
2.400
2.600
I
O
= 10mA to 5A
2.8V Version
Output Voltage
2.744
2.8
2.856
V
V
CTRL
= 6.3V to 12V, V
IN
=3.3V to 12V, I
O
=10mA
2.688
2.912
I
O
= 10mA to 5A
3.3V Version
Output Voltage
3.234
3.3
3.366
V
V
CTRL
= 6.3V to 12V, V
IN
= 3.3V + 0.8V, I
O
=10mA
3.168
3.3
3.432
I
O
= 10mA to 5A
All Voltage Options
Reference Voltage
1.238
1.25
1.263
V
V
CTRL
= 2.75V, V
IN
= 2.00V, I
O
= 10mA
V
CTRL
=2.7V to 12V,V
IN
= 2.05V to 5.5V,I
O
=10mA to 5A
Line Regulation
mV
V
CTRL
= 2.5V to 12V, V
IN
= 1.75V to 5.5V, I
O
=10mA
1.0
3.0
V
ADJ
=0V
Load Regulation (Note 1)
1.0
5.0
mV
V
CTRL
= 2.75V, V
IN
= 2.1V, I
O
=10mA to 5A, V
ADJ
= 0V
Dropout Voltage Min. V
CTRL
1.10
1.25
V
V
ADJ
= 0V
(Note 2) (V
CTRL
- V
OUT
)
V
IN
= 2.05V, I
O
= 1A
Dropout Voltage Min. V
IN
0.40
0.50
V
V
ADJ
= 0V
(Note 2) (V
IN
- V
OUT
)
V
IN
= 2.75V, I
O
= 5A
Current Limit
5.1
A
V
CTRL
= 2.75V, V
IN
= 2.05V, V
OUT
= 100mV, V
ADJ
= 0V
Minimum Load Current
5
10
mA
V
CTRL
= 5V, V
IN
=3.3V, V
ADJ
=0V
Thermal Regulation
0.002
0.02
%/W
30ms Pulse
Ripple Rejection
60
80
dB
V
CTRL
= 3.75V, V
IN
= 3.75V, I
O
= 2.5A, V
ADJ
=0V
T
J
=25, V
RIPPLE
=1Vpp at 120Hz
Control Pin Current
60
120
mA
V
ADJ
= 0V
V
CTRL
= 2.75V, V
IN
= 2.05V, I
O
= 5A
Adjustble Pin Current
50
A
V
CTRL
= 2.75V, V
IN
= 2.05V, V
ADJ
=0V, I
O
= 10mA
120
Thermal Resistance
3
C/W
Junction to Case (
JC
)
TO-220-5
50
C/W
Junction to Ambient (
JA
)
Thermal Resistance
3
C/W
Junction to Case (
JC
)
TO-263-5
60
C/W
Junction to Ambient (
JA
)
Input Supply Voltage ..................................................... 6V
V
CTRL
Input Voltage ....................................................... 13V
ABSOLUTE MAXIMUM RATINGS
Note 1: Low duty cycle pulse testing with Kelvin connections is required to order to maintain accurate data.
Note 2: Dropout voltage is defined as the minimum differential between V
IN
and V
OUT
or V
CTRL
and V
OUT
required to
maintain regulation at V
OUT
95% Nominal V
OUT
.
Note 3: V
REF
is measured across Adjust pin to Sense pin.
3
Date 5/25/04
SPX1581 5A Ultra Low Dropout Voltage Regulator
Copyright 2004 Sipex Corporation
The SPX1581 is designed as a high performance
and low cost solution for application requiring a
lower dropout than traditional NPN regulators.
The SPX1581 uses a separate input voltage V
CTRL
( V
CTRL
V
OUT
+ 1.3V) to minimize the dropout
voltage. This allows the 2.5V power for the load
to come from a 3.3V system supply.
As added benefit this will reduce the heat dissi-
pation*, and lower heatsink and cooling fan cost.
A typical application would use 5V for V
IN
and
3.3V for V
CTRL
from a motherboard power
supply to provide a nominal 2.5V output. Using
the sense pin allows Kelvin measure the output,
reducing resistance-associated errors.
The SPX1581 can power the 2.5V core voltage
for microprocessors such as a Pentium
TM
,
P55C
TM
, AMD5k86
TM
and K6
TM
and the IBM
PowerPC
TM
603EV and 604EV processors.
CURRENT
LIMIT
AMPLIFIER
THERMAL OVERLOAD
V
REF
VOLTAGE
REGULATION
AMPLIFIER
LIMIT
SENSE
(4) V
CTRL
V
IN
(5)
V
OUT
(3)
SENSE (1)
ADJ (2)
S.O.A
PIN NUMBER
PIN NAME
DESCRIPTION
1
SENSE
Allows Kelvin sense of V
OUT
at the load. (Positive side of the reference
voltage of the device).
2
ADJ
Negative side of the reference voltage for the device. Adding a small
bypass capacitor from the ADJ pin to ground will improve the transient
response.
3
V
OUT
Power output of the device.
4
V
CTRL
Supply pin for the control circuitry of the device. The current flow into this
pin will be about 1% of the output current. V
CTRL
must be between 1.0V
and 1.3V greater than the output voltage for the
device to regulate.
5
V
IN
Output load current is supplied through this pin. V
IN
must be between 0.1V
and 0.8V greater than the output voltage for this device to regulate.
PIN DESCRIPTION
FUNCTIONAL DIAGRAM
APPLICATION NOTES
* The reduction of heat dissipation is a result of the
increase of the regulator efficiency (efficiency = V
OUT
/V
IN
).
4
Date 5/25/04
SPX1581 5A Ultra Low Dropout Voltage Regulator
Copyright 2004 Sipex Corporation
Adjustable Regulator Design
1.25V reference voltage is being developed be-
tween the SENSE pin and the ADJ pin of the
SPX1581. Adding two external resistors (see fig
1.) will allow setting the output voltage from
1.25V to 6V. R
1
is chosen so that this current is
specified minimum load current of 10mA. R
2
is
given by the formula: V
OUT
= V
REF
(1+ R
2
/R
1
)
+ I
ADJ
(R
2
). The current flowing from the ADJ
pin is typicaly 50
A. This ADJ pin contributes
to the final V
OUT
but is usually neglected.
Connecting the sense pin to the top of the resis-
tor divider will improve load regualtion.
Lowering Noise
Using the SENSE pin to Kelvin the load will
increase accuracy of the output voltage during
load regulation. For the fixed voltage device,
adding a capacitor at the GND pin will improve
transient response. This capacitor is chosen in
the range of 1
F to 0.1F and will depend on the
amount of output capacitance in the system.
APPLICATION NOTES: Continued
5
Date 5/25/04
SPX1581 5A Ultra Low Dropout Voltage Regulator
Copyright 2004 Sipex Corporation
PACKAGE: 5 Pin TO-220
.160 - .190
Dimensions in
(inches)
5 PIN TO-220
.015 - .040
A
b
C1
D
E
MIN NOM MAX
e
e1
F
H1
J1
P
Q
U
V
L
.014 - .022
.560 - .590
.385 - .415
.385 - .415
.062 - .072
.045 - .055
.234 - .258
.090 - .115
.540 - .560
.146 - .156
.103 - .113
- .30 -
- .24 -
L1
- .250
D
B
SEATING
PLANE
F
A
CHAMFER
OPTIONAL
C1
J1
A
A
E
P
Q
D
D1
E/2
L
L1
C C
D
D
b
e1
H1
e
5 PIN TO-220
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