www.fairchildsemi.com
Pentium is a registered trademark of Intel Corporation. PowerPC is a trademark of IBM Corporation.
REV. 1.1.3 2/20/02
Features
Ultra Low dropout voltage, 0.4V typical at 5A
Remote sense operation
Fast transient response
Load regulation: 0.05% typical
0.5% initial accuracy
On-chip thermal limiting
5-Pin SPAK and TO-263 packages
Applications
Pentium
Processors
PowerPC
TM
, AMD K5 and K6 processors
Pentium support of GTL+ bus supply
Low voltage logic supply
Embedded Processor supplies
Split plane regulator
New 2.5V and 1.8V Logic Families
Description
The FAN1581, FAN1581-1.5, and FAN1581-2.5 are ultra-low
dropout regulators with 5A output current capability. These
devices have been optimized for low voltage applications
including V
TT
bus termination, where transient response and
minimum input voltage are critical. The FAN1581 is ideal
for low voltage microprocessor applications requiring a reg-
ulated output from 1.3V to 5.7V with a power input supply
of 1.75V to 6.5V. The FAN1581-1.5 offers fixed 1.5V with
5A current capabilities for GTL+ bus V
TT
termination. The
FAN1581-2.5 offers fixed 2.5V with 5A current capability
for logic IC operation and processors while minimizing the
overall power dissipation.
Current limit ensures controlled short-circuit current. On-chip
thermal limiting provides protection against any combination
of overload and ambient temperature that would create exces-
sive junction temperatures.
The FAN1581 series regulators are available in the 5-Pin
SPAK and TO-263 power packages.
Typical Applications
22
F
V
CNTL
= 5V
2.1V at 5A
10
F
V
IN
= 3.3V
+
+
V
IN
V
SENSE
V
CNTL
Adj
V
OUT
FAN1581
22
F
V
CNTL
= 5V
2.5V at 5A
10
F
V
IN
= 3.3V
+
1
F
+
+
V
IN
V
SENSE
V
CNTL
GND
V
OUT
FAN15812.5
86.6
124
22
F
V
CNTL
= 12V
5V at 5A
10
F
V
IN
= 5.75V
+
+
V
IN
V
SENSE
V
CNTL
Adj
V
OUT
FAN1581
374
124
FAN1581
5A Adjustable/Fixed Ultra Low Dropout
Linear Regulator
FAN1581
PRODUCT SPECIFICATION
2
REV. 1.1.3 2/20/02
Pin Assignments
Pin Definitions
Internal Block Diagram
Pin Number
Pin Name
Pin Function Descrition
1
VSense
Remote Voltage Sense
. Connect this pin to the load to permit true
remote sensing and avoid trace drops.
2
ADJ/GND
Adjust or Ground.
On the FAN1581, this pin forms the feedback to
determine the output voltage. On the FAN1581-1.5 and -2.5, connect this
pin to ground.
3
VOUT
Output Voltage.
This pin and the tab are output.
4
VCNTL
Control Voltage.
This pin draws small-signal power to control the
FAN1581 circuitry. Connect to a voltage higher than VIN, as shown in the
applications circuits.
5
VIN
Input Voltage.
FRONT VIEW
FRONT VIEW
1
2 3 4 5
FRONT VIEW
1
2 3 4 5
FAN1581M-1.5, -2.5
FAN1581M
FAN1581P
FRONT VIEW
FAN1581P-1.5, -2.5
FRONT VIEW
FAN1581D
FRONT VIEW
FAN1581D-1.5, -2.5
5-Lead Plastic TO-263
JC
=3
C/W*
Tab is out.
5-Lead Plastic SPAK
JC
=2
C/W*
Tab is out.
5-Lead Plastic TO-252 DPAK
JC
=3
C/W*
Tab is out.
1
2
3
4 5
ADJ
CNTL
OUT
S
IN
GND
CNTL
OUT
S
IN
ADJ
CNTL
OUT
S
IN
GND
CNTL
OUT
S
IN
1
2
3
4 5
1
2
3
4
5
1
2
3
4
5
GND
CNTL
OUT
S
IN
ADJ
CNTL
OUT
S
IN
*With package soldered to 0.5 square inch copper area over backside ground plane or internal
power plane,
JA
can vary from 30
C/W to more than 40 C/W. Other mounting techniques
can provide a thermal resistance lower than 30
C/W.
Current
Limit
Thermal
Shutdown
Vref
Vin, Power
Output
Sense
Adj
V
CNTL
, Control
2
1
3
5
4
Voltage Loop
Amplifier
PRODUCT SPECIFICATION
FAN1581
REV. 1.1.3 2/20/02
3
Absolute Maximum Ratings
Electrical Characteristics
T
J
=25C, V
OUT
= V
S
, V
ADJ
= 0V unless otherwise specified.
The denotes specifications which apply over the specified operating temperature range.
Notes:
1. See thermal regulation specifications for changes in output voltage due to heating effects. Load and line regulation are
measured at a constant junction temperature by low duty cycle pulse testing.
2. Line and load regulation are guaranteed up to the maximum power dissipation (18W). Power dissipation is determined by
input/output differential and the output current. Guaranteed maximum output power will not be available over the full input/
output voltage range.
3. FAN1581 only.
4. FAN1581-1.5 only.
5. FAN1581-2.5 only.
Parameter
Min.
Max.
Unit
V
IN
7
V
V
CNTL
13.2
V
Operating Junction Temperature Range
0
125
C
Lead Temperature (Soldering, 10 sec.)
300
C
Storage Temperature Range
-65
150
C
Parameter
Conditions
Min.
Typ.
Max.
Units
Reference Voltage
3
V
IN
= 2.0V, V
CNTL
= 2.75V,
I
OUT
= 10mA
1.243
1.250
1.257
V
Reference Voltage
3
2.05V
V
IN
5.5V,
2.7V
V
CNTL
12V,
10mA
I
OUT
5A
1.237
1.250
1.263
V
Adjustable Output Voltage
3V
V
IN
7V (function of Vout),
10mA
I
OUT
5A
Vref
1.5
5.7
V
Output Voltage
4
3V
V
IN
7V, 10mA
I
OUT
5A
1.47
1.5
1.53
V
Output Voltage
5
5.1V
V
IN
7V, 10mA
I
OUT
5A
2.474
2.5
2.526
V
Line Regulation
1,2
1.75V
V
IN
5.5V, 2.5V
V
CNTL
12V,
I
OUT
= 10mA
1
3
mV
Load Regulation
1,2
V
IN
= 2.1V, V
CNTL
= 2.75V,
10mA
I
OUT
5A
1
5
mV
Dropout Voltage Minimum
(V
CNTL
V
OUT
)
V
IN
= 2.05V,
V
REF
= 1%, I
OUT
= 5A
1.05
1.18
V
Dropout Voltage Minimum
(V
IN
V
OUT
)
V
CNTL
= 2.75V,
V
REF
= 1%,
I
OUT
= 5A
0.4
0.5
V
Dropout Voltage Minimum V
IN
V
CNTL
= 2.75V,
V
REF
= 1%,
I
OUT
= 5A
0.5
0.6
V
Current Limit
V
IN
= 2.05V, V
CNTL
= 2.75V
5.2
A
Control Pin Current
V
IN
= 2.05V, V
CNTL
= 2.75V,
I
OUT
= 10mA
2
6
mA
Adjust Pin Current
3
V
IN
= 2.05V, V
CNTL
= 2.75V
50
120
A
Minimum Load Current
V
IN
= 3.3V, V
CNTL
= 5V
5.0
10
mA
Ripple Rejection
V
IN
= 3.75V, V
CNTL
= 3.75V, f = 120Hz,
C
OUT
= 22F Tantalum, I
OUT
= 2.5A
60
80
dB
Thermal Resistance, Junction to
Case
TO-263
SPAK
3
2
C/W
Thermal Regulation
T
A
= 25C, 30ms pulse
0.002
0.02
%/W
Thermal Shutdown
150
C
FAN1581
PRODUCT SPECIFICATION
4
REV. 1.1.3 2/20/02
Typical Perfomance Characteristics
T=0
C
T=125
C
T=25
C
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
1
2
4
3
5
DROPOUT VOLTAGE (V)
REFERENCE VOLTAGE
MINIMUM LOAD CURRENT (mA)
OUTPUT CURRENT (A)
Dropout Voltage vs. Output Current
Load Regulation vs. Temperature
Reference Voltage vs. Temperature
Output Voltage vs. Temperature
Mimimum Load Current vs. Temperature
Adjust Pin Current vs. Temperature
0.10
0.05
0
-0.05
-0.10
-0.15
-0.20
-75 -50 -25
25
50
75
100
125 150
175
0
OUTPUT VOLTAGE DEVIATION (%)
JUNCTION TEMPERATURE (
C)
JUNCTION TEMPERATURE (
C)
=5A
1.275
1.270
1.265
1.260
1.255
1.250
1.245
1.240
1.235
1.230
1.225
OUTPUT VOLTAGE (V)
ADJUST PIN CURRENT (
A)
3.70
3.65
3.60
3.55
3.50
3.45
3.40
3.35
3.30
3.25
3.20
100
90
80
70
60
50
40
30
20
10
0
-75 -50 -25
0
25
50
75
100 125
150 175
JUNCTION TEMPERATURE (
C)
-75 -50 -25
0
25
50
75
100
125 150 175
JUNCTION TEMPERATURE (
C)
-75 -50
-25
0
25
50
75
100 125 150 175
JUNCTION TEMPERATURE (
C)
-75 -50
-25
0
25
50
75
100 125 150 175
V
OUT
set with
1% resistors
V
OUT
= 3.3V
1
Note:
1. FAN1581 Only
10
8
6
4
2
0
Note:
1. FAN1581 Only
PRODUCT SPECIFICATION
FAN1581
REV. 1.1.3 2/20/02
5
Typical Perfomance Characteristics (continued)
11
9
7
SHORT-CIRCUIT CURRENT (A)
POWER (W)
RIPPLE REJECTIONS (dB)
5
3
-75 -50 -25
25
50
75 100
125 150 175
20
25
45
65
85
105
125
15
10
5
0
0
JUNCTION TEMPERATURE (
C)
CASE TEMPERATURE
FREQUENCY (HZ)
(V
IN
--V
OUT
)
3V
0.5V
V
RIPPLE
2V
I
OUT
= 5A
90
90
70
60
50
40
30
20
10
0
10
100
1K
10K
100K
Short-Circuit Current vs.Temeperature
Ripple Rejection vs. Frequency
Maximum Power Dissipation
General
The FAN1581, FAN1581-1.5, and FAN1581-2.5 are three-
terminal regulators optimized for GTL+ V
TT
termination and
logic applications. These devices are short-circuit protected,
and offer thermal shutdown to turn off the regulator when the
junction temperature exceeds about 150C. The FAN1581
series provides low dropout voltage and fast transient
response. Frequency compensation uses capacitors with low
ESR while still maintaining stability. This is critical in
addressing the needs of low voltage high speed microproces-
sor buses like GTL+.
V
IN
and V
CNTL
Functions
The FAN1581 utilizes a dual supply approach to maximize
efficiency. The collector of the power device is brought out
to the V
IN
pin to minimize internal power dissipation under
high current loads. V
CNTL
provides power for the control
circuitry and the drive for the output NPN transistor.
V
CNTL
should be at least 1.2 V higher than the output volt-
age. Special care was taken to ensure there are no supply-
sequencing problems. The output voltage will not turn on
until both supplies are operating. If the control voltage
comes up first, the output current will be typically limited to
about 3.0 mA until the power input voltage comes up. If the
power input voltage comes up first the output will not turn on
at all until the control voltage comes up. The output can
never come up unregulated.
The FAN1581 can also be used as a single supply device
with the control and power inputs tied together. In this mode,
the dropout is determined by the minimum control voltage.
Stability
The FAN1581 series requires an output capacitor as a part of
the frequency compensation. It is recommended to use a 22F
solid tantalum or a 100F aluminum electrolytic on the output
to ensure stability. The frequency compensation of these
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