AS1582
3A Ultra Low Dropout Voltage Regulator
Fast Response, Adjustable & Fixed
FEATURES
•
Low Dropout Voltage 500mV at 3A Full Load Current
•
Fixed Output Voltages of 3.3V, 2.8V & 2.5V
•
Adjustable Output Down to 1.2V from ATX Power Supply
•
Extremely Tight Voltage and Line Regulation
•
Standard 5-Terminal Low Cost TO-220 & TO-263
APPLICATIONS
•
3.3V to 2.8V ATX Power Supplies
•
3.3V to 2.9V for Portable PENTIUM Processor
•
5V to 3.5V VRE Supply
•
High Efficiency “Green” Computer Systems
PRODUCT DESCRIPTION
The AS1582 is a 3A 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 AS1582 features a low dropout of less than 400mV(typ.) and offers fast transient response.
This device is suitable for
Pentium applications requiring 2.8V or 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 in powering low voltage microprocessors that require a lower dropout, fast transient response to regulate from 3.3V and 5V
supplies. The AS1582 is also an excellent choice as a post regulator for switching supplies applications.
The AS1582 offers full protection against over-current faults, reversed input polarity, over temperature operation and positive and
negative transient voltage.
The AS1582 is offered in a 5 pin TO-220 and TO-263 compatible with industry standard 5-terminal regulators. For 7A, 5A and 1.5A
ultra low dropout versions refer to AS1580, AS1581 and AS1583 data sheets respectively.
ORDERING INFORMATION
TO-22O
5-PIN
AS1582U
AS1582U-X
TO-263
5-PIN
AS1582T
AS1582T-X
OUTPUT
Adjustable
Fixed
Consult with factory for other fixed output voltages.
X= Output Voltage (3.3V, 2.8V or 2.5V)
PIN CONNECTIONS
TO-263-5 (T)
TO-220-5 (U)
AS1582
1 2 3 4 5
1.
2.
3.
4.
5.
SENSE
ADJ or FIXED
V
OUT
V
CTRL
V
IN
AS1582
1 2 3 4 5
1. SENSE
2. ADJ or FIXED
3. V
OUT
4. V
CTRL
5. V
IN
Top View
Front View
Rev. 10/2/00
AS1582
ABSOLUTE MAXIMUM RATINGS
Power Dissipation.................................................... Internally Limited
Lead Temp (soldering, 10 seconds)........................................... 300°C
Storage Temperature Range ...................................... -65ºC to +150ºC
Operating Junction Temperature Range
AS1582 Control Section................................................0ºC to +125ºC
AS1582 Power Transistor .............................................0ºC to +150ºC
Input Supply Voltage ..........................................................6V
V
CTRL
Input Voltage ..........................................................13V
ELECTRICAL CHARACTERISTICS
at V
S
=14V, Ta=25°C, Io=10mA, C2=100µF, unless otherwise specified. (Note 1)
(Boldface
applies over full temperature range).
Parameters
2.5V Version
Output Voltage
V
CTRL
=6.0V to 12V, V
IN
=3.0V to 5.0V, I
O
=10mA
I
O
=10mA to
3A
V
CTRL
=6.3V to 12V, V
IN
=3.3V to 12V, I
O
=10mA
I
O
=10mA to
3A
V
CTRL
=6.3V to 12V, V
IN
=3.3V to 12V, I
O
=10mA
I
O
=10mA to 3A
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
3A
V
CTRL
=2.5V to 12V, V
IN
=1.75V to 5.5V, I
O
=10mA
V
ADJ
=0V
V
CTRL
=2.75V, V
IN
=2.1V, I
O
=10mA to 3A,V
ADJ
=0V
V
ADJ
=0V
V
IN
=2.05V, I
O
=1A
V
ADJ
=0V
V
IN
=2.75V, I
O
=3A
V
CTRL
=2.75V, V
IN
=2.05V,dV
O
=100mV,V
ADJ
=0V
V
CTRL
=5V, V
IN
=3.3V,V
ADJ
=0V
30ms Pulse
V
CTRL
=3.75V V
IN
=3.75V, I
O
=2.3A,V
ADJ
=0V
T
J
=25, V
RIPPLE
=1Vpp at 120Hz
V
ADJ
=0V
V
CTRL
=2.75V, V
IN
=2.05V, I
O
=3A
V
CTRL
=2.75V, V
IN
=2.05V,V
ADJ
=0V I
O
=10mA
TO-220-5
Junction to Case (θ
JC
)
Junction to Ambient
(θ
JA
)
Junction to Case (θ
JC
)
Junction to Ambient
(θ
JA
)
60
3.1
5
0.002
80
60
50
120
120
3
50
3
60
mA
µA
°C/W
°C/W
°C/W
°C/W
10
0.02
2.450
2.400
2.500
2.550
2.600
V
Conditions
Min
AS1582
Typ
Units
Max
2.8V Version
Output Voltage
2.744
2.688
2.800
2.856
2.912
V
3.3V Version
Output Voltage
All Voltage Options
Reference Voltage
1.238
1.250
1.263
V
3.234
3.168
3.300
3.366
3.432
V
Line Regulation
Load Regulation (Note1)
Dropout Voltage Minimum V
CTRL
(Note2)
(V
CTRL
– V
OUT
)
Dropout Voltage Minimum V
IN
(Note2)
(V
IN
- V
OUT
)
Current Limit
Minimum Load Current
Thermal Regulation
Ripple Rejection
Control Pin Current
Adjustable Pin Current
Thermal Resistance
1.0
1.0
1.05
0.40
3.0
5.0
1.18
0.50
mV
mV
V
V
A
mA
%W
dB
TO-263-5
The
Bold
specifications applying to the over full operating temperature range.
Note 1: Low duty cycle pulse testing with Kelvin connections are 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
99% Nominal V
OUT.
Note 3: V
REF
is measured across Adjust pin to Sense pin.
Rev. 10/2/00
AS1582
PIN DESCRIPTION
1.
2.
3.
4.
5.
Sense = Allows Kelvin sense of V
OUT
at the load. (Positive side of the reference voltage of the
device).
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.
V
OUT
= Power output of the device.
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.
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 the device to regulate.
BLOCK DIAGRAM
(4) V
CTRL
S.O.A
V
IN
(5)
CURRENT
LIMIT
AMPLIFIER
LIMIT
SENSE
V
OUT
(3)
THERMAL OVERLOAD
SENSE (1)
VOLTAGE
REGULATION
AMPLIFIER
V
REF
ADJ (2)
APPLICATIONS NOTES
The AS1582 is designed as a high performance and low cost
solution for application requiring a lower dropout than
traditional NPN regulators.
The AS1582 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 dissipation, and
lower heatsink and cooling fan cost. A typical application
would use 5V for Vin and 3.3V for V
CTRL
from a motherboard
power supply to provide a nominal 2.5V output. Using the
sense pin allows to Kelvin measure the output, reducing
resistive-associated errors.
The AS1582 can power the 2.5V core voltage for
microprocessors such as Pentium, P55C, AMD5k86
and K6 and the IBM PowerPC 603EV and 604EV
processors.
*The reduction of heat dissipation is a result of the increase of the regulator
efficiency (efficiency = V
OUT
/ V
IN
).
Adjustable Regulator Design
1.25V reference voltage is being developed between the
SENSE pin and the ADJ pin of the AS1582. 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 typically 50µA. This ADJ pin
contributes to the final VOUT but is usually neglected.
Connecting the sense pin to the top of the resistor divider will
improve load regulation.
Lowering Noise
Using the SENSE pin to Kelvin the load will increase accuracy
of the output voltage during load regulation. For the fixed
voltage devices, adding a capacitor at the GND pin will
improve transient response. This capacitor is chosen in the
range of 1µF to 0.1µF and will depend on the amount of
output capacitance in the system.
Rev. 10/2/00
AS1582
TYPICAL APPLICATION
Fig. 1 Adjustable Regulator
3.3V
V
IN
5V
V
CTRL
C1
330uF
V
IN
V
OUT
AS1582
V
CTRL
ADJ
C2
10uF
2.5V
V
OUT
SENSE
R1
124
Ω
C4
2 X 330uF
C3
.033uF
R2
124
Ω
(1) V
CTRL
needed when V
IN
< 5V.
(2) V
OUT
= V
REF
(1 + R2/ R1) + I
ADJ
R2.
(3) V
REF
is measured across adjust to sense.
Fig.2 Typical Fixed Regulator
3.3V
V
IN
C1
5V
V
CTRL
330uF
V
IN
V
OUT
AS1582
2.5V
V
OUT
V
CTRL
GND
C2
10uF
SENSE
C4
2 X 330uF
(1) V
CTRL
is needed when V
IN
<5V.
Rev. 10/2/00
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