www.fairchildsemi.com
FAN1581
5A Adjustable/Fixed Ultra Low Dropout
Linear Regulator
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
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.
Applications
•
•
•
•
•
•
•
Pentium
®
Processors
PowerPC
™
, 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
Typical Applications
V
IN
= 3.3V
+
10µF
V
IN
= 3.3V
+
10µF
V
CNTL
= 5V
V
CNTL
= 5V
+
1µF
2.1V at 5A
+
124Ω
22µF
V
IN
= 5.75V
+
86.6Ω
10µF
V
CNTL
= 12V
V
IN
V
SENSE
V
IN
V
SENSE
FAN1581–2.5
V
OUT
V
CNTL
GND
2.5V at 5A
+
22µF
V
IN
V
SENSE
FAN1581
V
OUT
V
CNTL
Adj
FAN1581
V
OUT
V
CNTL
Adj
124Ω
+
22µF
5V at 5A
374Ω
Pentium is a registered trademark of Intel Corporation. PowerPC is a trademark of IBM Corporation.
REV. 1.0.2 8/15/01
FAN1581
PRODUCT SPECIFICATION
Pin Assignments
FAN1581M-1.5, -2.5
FRONT VIEW
FAN1581M
FRONT VIEW
FAN1581P
FRONT VIEW
FAN1581P-1.5, -2.5
FRONT VIEW
1 2 3 4 5
1 2 3 4 5
1 2 3
4 5
1 2 3
4 5
CNTL
IN
S
GND
OUT
CNTL
IN
S
ADJ
OUT
CNTL
IN
5-Lead Plastic TO-263
Θ
JC
=3°C/W*
Tab is out.
5-Lead Plastic SPAK
Θ
JC
=2°C/W*
Tab is out.
*With package soldered to 0.5 square inch copper area over backside ground plane or internal
power plane.
Θ
JA
can vary fom 20°C/W to >40°C/W with other mounting techniques.
Pin Definitions
Pin Number
1
Pin Name
VSense
ADJ/GND
Pin Function Descrition
Remote Voltage Sense
. Connect this pin to the load to permit true
remote sensing and avoid trace drops.
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.
Output Voltage.
This pin and the tab are output.
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.
Input Voltage.
2
3
4
VOUT
VCNTL
5
VIN
Internal Block Diagram
4
V
CNTL
, Control
5 Vin, Power
Thermal
Shutdown
Current
Limit
3 Output
1 Sense
2 Adj
Vref
Voltage Loop
Amplifier
2
REV. 1.0.2 8/15/01
CNTL
IN
S
ADJ
OUT
S
GND
OUT
PRODUCT SPECIFICATION
FAN1581
Absolute Maximum Ratings
Parameter
V
IN
V
CNTL
Operating Junction Temperature Range
Lead Temperature (Soldering, 10 sec.)
Storage Temperature Range
-65
0
Min.
Max.
7
13.2
125
300
150
Unit
V
V
°C
°C
°C
Electrical Characteristics
T
J
=25°C, V
OUT
= V
S
, V
ADJ
= 0V unless otherwise specified.
The • denotes specifications which apply over the specified operating temperature range.
Parameter
Reference Voltage
3
Reference Voltage
3
Conditions
V
IN
= 2.0V, V
CNTL
= 2.75V,
I
OUT
= 10mA
2.05V
≤
V
IN
≤
5.5V,
2.7V
≤
V
CNTL
≤
12V,
10mA
≤
I
OUT
≤
5A
3V
≤
V
IN
≤
7V (function of Vout),
10mA
≤
I
OUT
≤
5A
3V
≤
V
IN
≤
7V, 10mA
≤
I
OUT
≤
5A
5.1V
≤
V
IN
≤
7V, 10mA
≤
I
OUT
≤
5A
1.75V
≤
V
IN
≤
5.5V, 2.5V
≤
V
CNTL
≤
12V,
I
OUT
= 10mA
V
IN
= 2.1V, V
CNTL
= 2.75V,
10mA
≤
I
OUT
≤
5A
V
IN
= 2.05V,
∆
V
REF
= 1%, I
OUT
= 5A
V
CNTL
= 2.75V,
∆
V
REF
= 1%,
I
OUT
= 5A
V
CNTL
= 2.75V,
∆
V
REF
= 1%,
I
OUT
= 5A
V
IN
= 2.05V, V
CNTL
= 2.75V
V
IN
= 2.05V, V
CNTL
= 2.75V,
I
OUT
= 10mA
V
IN
= 2.05V, V
CNTL
= 2.75V
V
IN
= 3.3V, V
CNTL
= 5V
V
IN
= 3.75V, V
CNTL
= 3.75V, f = 120Hz,
C
OUT
= 22µF Tantalum, I
OUT
= 2.5A
TO-263
SPAK
T
A
= 25°C, 30ms pulse
Min.
1.243
•
1.237
Typ.
1.250
1.250
Max.
1.257
1.263
Units
V
V
Adjustable Output Voltage
Output Voltage
4
Output Voltage
5
Line Regulation
1,2
Load Regulation
1,2
Dropout Voltage Minimum
(V
CNTL
–V
OUT
)
Dropout Voltage Minimum
(V
IN
–V
OUT
)
Dropout Voltage Minimum V
IN
Current Limit
Control Pin Current
Adjust Pin Current
3
Minimum Load Current
Ripple Rejection
Thermal Resistance, Junction to
Case
Thermal Regulation
Thermal Shutdown
•
•
•
•
•
•
Vref
1.47
2.474
1.5
1.5
2.5
1
1
1.05
0.4
5.7
1.53
2.526
3
5
1.18
0.5
0.6
V
V
V
mV
mV
V
V
V
A
mA
µA
mA
dB
°C/W
•
•
•
•
•
60
5.2
0.5
2
50
5.0
80
3
2
0.002
150
6
120
10
0.02
%/W
°C
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.
REV. 1.0.2 8/15/01
3
FAN1581
PRODUCT SPECIFICATION
Typical Perfomance Characteristics
OUTPUT VOLTAGE DEVIATION (%)
1.0
0.9
DROPOUT VOLTAGE (V)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
1
2
3
OUTPUT CURRENT (A)
Dropout Voltage vs. Output Current
0.10
0.05
0
-0.05
-0.10
-0.15
-0.20
-75 -50 -25
0
25 50 75 100 125 150 175
JUNCTION TEMPERATURE (°C)
Load Regulation vs. Temperature
∆Ι=5A
T=0°C
T=25°C
T=125°C
4
5
1.275
REFERENCE VOLTAGE
1.265
1.260
1.255
1.250
1.245
1.240
1.235
1.230
1.225
-75 -50 -25
0
25 50 75 100 125 150 175
JUNCTION TEMPERATURE (°C)
Reference Voltage vs. Temperature
OUTPUT VOLTAGE (V)
1.270
3.70
3.65
3.60
3.55
3.50
3.45
3.40
3.35
3.30
3.25
3.20
V
OUT
set with
1% resistors
V
OUT
= 3.3V
1
-75 -50
Note:
1. FAN1581 Only
-25 0
25 50 75 100 125 150 175
JUNCTION TEMPERATURE (°C)
Output Voltage vs. Temperature
MINIMUM LOAD CURRENT (mA)
10
ADJUST PIN CURRENT (µA)
8
6
4
2
0
-75 -50 -25 0
25 50 75 100 125 150 175
JUNCTION TEMPERATURE (°C)
Mimimum Load Current vs. Temperature
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)
Adjust Pin Current vs. Temperature
Note:
1. FAN1581 Only
4
REV. 1.0.2 8/15/01
PRODUCT SPECIFICATION
FAN1581
Typical Perfomance Characteristics (continued)
11
SHORT-CIRCUIT CURRENT (A)
90
90
9
RIPPLE REJECTIONS (dB)
70
60
50
40
30
20
10
3
-75 -50 -25 0 25 50 75 100 125 150 175
JUNCTION TEMPERATURE (°C)
Short-Circuit Current vs.Temeperature
20
0
10
100
1K
10K
FREQUENCY (HZ)
100K
(V
IN
—V
OUT
)
≤
3V
0.5V
≤
V
RIPPLE
≤
2V
I
OUT
= 5A
7
5
Ripple Rejection vs. Frequency
15
POWER (W)
10
5
0
25
45
65
85
105
CASE TEMPERATURE
125
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 150°C. 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+.
to ensure stability. The frequency compensation of these
devices optimizes the frequency response with low ESR capaci-
tors. In general, it is suggested to use capacitors with an ESR
of <1Ω. It is also recommended to use bypass capacitors such
as a 22µF tantalum or a 100µF aluminum on the adjust pin of
the FAN1581 for low ripple and fast transient response. When
these bypassing capacitors are not used at the adjust pin, smaller
values of output capacitors provide equally good results.
Protection Diodes
In normal operation, the FAN1581 series does not require any
protection diodes. For the FAN1581, internal resistors limit
internal current paths on the adjust pin. Therefore, even with
bypass capacitors on the adjust pin, no protection diode is
needed to ensure device safety under short-circuit conditions.
Stability
The FAN1581 series requires an output capacitor as a part of
the frequency compensation. It is recommended to use a 22µF
solid tantalum or a 100µF aluminum electrolytic on the output
REV. 1.0.2 8/15/01
5
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