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REV. 1.2.1 7/2/09
FAN1581
5A Adjustable/Fixe d Ultra Low Dropout Linear Regulator
Features
• Ultra Low dropout voltage, 0.4V typical at 5A
• 1.2V Versions available for GTL termination
• Remote sense operation
• Fa s t trans ient res p onse
• Load regul at ion: 0.05 % ty pi cal
• 0.5% typical initial accuracy
• On-chip thermal limiting
• TO-263, TO-252 and TO-220 packages
Applications
• Support of GTL+ bus supply
• Low voltage log ic supply
• Embedded Processor supplies
• Split plane regulator
• 2.5V, and 1.8V Logic Families
• DDR Termination Supply
Description
The FAN1581, FAN1581-1.2, FAN1581-1.5, and FAN1581-
2.5 are ultra - low dropou t regulators with 5A output current
capability. These devices have been optimized for low volt-
age applications including VTT bus termination, where tran-
sient response and minimum input voltage are critical. The
FAN1581 is ideal for low voltage microprocessor applica-
tions requiring a regulated 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
VTT termination . Additionall y , the FAN1581-1 .2 of fers fixed
1.2V output for CPU Bus termination. The FAN1581-2.5
off ers fixed 2.5V with 5A current capability for logic IC
operation and processors while minimizing the overall
power dissipation.
Current limit ens ures cont rolled sh ort -circuit current. On-chip
thermal limiting provi des pro tection again st any combi nation
of overload and ambient temperature that would create exces-
sive junction temperatures.
The FAN1581 series regulators are available in the 5-pin
TO-263, TO-252 and TO-220 packages.
Typical Applications
22μF
22μF
V
CNTL
= 5V
2.1V at 5A
10μF
V
IN
= 3.3V
+
10μF+
+
V
IN
V
SENSE
V
CNTL
Adj
V
OUT
FAN1581 22μF
V
CNTL
= 5V
2.5V at 5
A
10μF
V
IN
= 3.3V
+
1μF+
1μF+
1μF+
1μF+
+
V
IN
V
SENSE
V
CNTL
GND
V
OUT
FAN1581–2.5
86.6Ω
124Ω
V
CNTL
= 5V
1.2V at 5A
V
IN
= 3.3V
V
IN
V
SENSE
V
CNTL
Gnd
V
OUT
FAN1581-1.2
22μF
V
CNTL
= 12V
5V at 5A
10μF
V
IN
= 5.75V
+
+
V
IN
V
SENSE
V
CNTL
Adj
V
OUT
FAN1581
374Ω
124Ω
FAN1581 PRODUCT SPECIFICATION
2REV. 1.2.1 7/2/09
Pin Assignments
Pin Definitions
Internal Block Diagram
Pin
Number Pin Name Pin Function Descrition
1VSense Remote Voltage Sense. Connect this pin to the load to permit true remote sensing and
avoid trace drops.
2ADJ/GND Adjust or Groun d. On the FAN1581, this pin forms the feedback to determine the output
voltage. On the FAN1581-1.2, -1.5 and -2.5, connect this pin to ground.
3VOUTOutput 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.
5VINInput Voltage.
FRONT VIEW
1234 5
FRONT VIEW
1234 5
FAN1581M-1.2,
-1.5, -2.5 FAN1581M
FRONT VIEW
FAN1581D
FRONT VIEW
FAN1581D-1.2,
-1.5, -2.5 FRONT VIEW
FAN1581T
5-Lead Plastic TO-263
Θ
JC
=3°C/W*
Tab is out.
5-Lead TO-220
Θ
JC
=3°C/W* Tab is VOUT
.
5-Lead Plastic TO-252 DPAK
Θ
JC
=3°C/W*
Tab is out.
ADJ
CNTL
OUT
S
IN
GND
CNTL
OUT
S
IN
12345 12345
ADJ
CNTL
OUT
S
IN
12345
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, θ
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, Pow
er
Output
Sense
Adj
V
CNTL
, Control
2
1
3
5
4
Voltage Loop
Amplifier
PRODUCT SPECIFICATION FAN1581
REV. 1.2.1 7/2/0 9 3
Absolute Maximum Ratings
Electrical Characteristics
TJ=25°C, VOUT = VSENSE, VADJ = 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.
6. FAN1581-1.2 only.
Parameter Min. Max. Unit
VIN 7V
VCNTL 13.2 V
Operating Junction Temperature Range 0 125 °C
Lead Temperature (Soldering, 10 sec.) 300 °C
Storage Temp er ature Range -65 150 °C
Parameter Conditions Min. Typ. Max. Units
Reference Voltage32.05V ≤ VIN ≤ 5.5V,
2.7V ≤ VCNTL ≤ 12V ,
10mA ≤ IOUT ≤ 5A
• 1.237 1.250 1.263 V
Adjustable Output Voltage 3V ≤ VIN ≤ 7V (function of Vout),
10mA ≤ IOUT ≤ 5A •Vref 1.5 5.7 V
Output Voltage43V ≤ VIN ≤ 7V, 10mA ≤ IOUT ≤ 5A • 1.47 1.5 1.53 V
Output Voltage54V ≤ VIN ≤ 7V, 10mA ≤ IOUT ≤ 5A • 2.474 2.5 2.526 V
Output Voltage62.7V ≤ VIN ≤ 7V, 10mA ≤ IOUT ≤ 5A • 1.176 1.200 1.224 V
Line Regulation1,2 1.75V ≤ VIN ≤ 5.5V, 2.5V ≤ VCNTL ≤ 12V,
IOUT = 10mA •13mV
Load Regulation1,2 VIN = 2.1V, VCNTL = 2.75V,
10mA ≤ IOUT ≤ 5A •15mV
Dropout Voltage Minimum
(VCNTL–VOUT)VIN = 2.05V, ΔVREF = 1%, IOUT = 5A • 1.05 1.1 8 V
Dropout Voltage Minimum
(VIN–VOUT)VCNTL = 2.75V, ΔVREF = 1%,
IOUT = 5A 0.4 0.5 V
Dropout Voltage Minimum VIN VCNTL = 2.75V, ΔVREF = 1%,
IOUT = 5A •0.50.6V
Current Limit VIN = 2. 05V, VCNTL = 2.75V • 5.2 A
Control Pin Current VIN = 2.05V, VCNTL = 2.75V,
IOUT = 10mA •36mA
Adjust Pin Current3VIN = 2.05V, VCNTL = 2.75V • 50 120 µA
Minimum Load Current VIN = 3.3V, VCNTL = 5V • 5.0 10 mA
Ripple Rejection VIN = 3.7 5V, VCNTL = 3.75V, f = 12 0H z,
COUT = 22µF Tantalum, IOUT = 2.5A 60 80 dB
Thermal Resistance, Junction to
Case TO-263
SPAK 3
2 °C/W
Thermal Regulation TA = 25°C, 30ms pulse 0.002 0.02 %/W
Thermal Shutdown 150 °C
FAN1581 PRODUCT SPECIFICATION
4REV. 1.2.1 7/2/09
T=0C
T=125C
T=25C
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
012 4356
DROPOU T VOLTAGE ( V)
REFERENCE VO LTAGEMINIMUM LOAD CURRENT (mA)
OUTPUT CURRENT (A)
Dropout Voltage vs. Output Current Load Re gulation vs. Tem perature
Refer ence Voltage vs. Temperatur e 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
-50 -25 25 50 75 100 125 1500
OUT PUT VOLTAGE DEVIAT IO N (%)
JUNCTION TEMPERATURE (C)
TJ (C)
DI=5A
1.30
1.28
1.26
1.24
1.22
1.20
OUTPUT VOLTAGE (V)
ADJUST PIN CURRENT (A)
2.60
2.35
2.10
1.85
1.60
1.35
1.10
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 JUNCTIO N TEMPERATURE (C)
-75 -50 -25 0 25 50 75 100 125 150 175
TJ (C)
-75 -50 -25 0 25 50 75 100 125 150 175
10
8
6
4
2
0
1.2V
1.5V
2.5V
Typical Perfomance Characteristics
PRODUCT SPECIFICATION FAN1581
REV. 1.2.1 7/2/0 9 5
11
9
7
SHO RT-CIR CUIT CURREN T (A)
POWE R (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)
(VIN—VOUT) 3V
0.5V VRIPPLE 2V
IOUT = 5A
90
80
70
60
50
40
30
20
10
010 100 1K 10K 100K
Short-Circuit Current vs.Temeperature
1.0
1.5
2.0
2.5
3.0
3.5
CONTROL PIN CURRENT ( mA)
0.5
0-75 -50 -25 25 50 75 100 125 150 1750
JUN C TI O N TEMPERATURE (C )
Control Pin Current vs.Temperature
Ripple Rejection vs. Frequency
MAX. ACCEPTABLE ESR, OHM
LOAD CURRENT, A
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0012345
FAN1581 Stability
Maximum Power Dissipation
10mA Load
Typical Perfomance Characteristics (continued)
FAN1581 PRODUCT SPECIFICATION
6REV. 1.2.1 7/2/09
General
The FAN1581, FAN1581-1.2, FAN1581-1.5, and
FAN1581-2.5 are three-terminal regulato rs op timi zed for
DDR and GTL+ VTT termination and logic applications.
These devices are short-circuit protected, and offer thermal
shutdown to turn off the regulator when the junction temper-
ature exceeds about 150°C. The FAN1581 series provides
low dropou t volt age and fa st tran si en t response. Frequency
compensation uses capacitors with low ESR while still main-
taining stability. This is critical in addressing the needs of
low voltage high speed microprocessor buses like GTL+.
VIN and VCNTL Functions
The FAN1581 utilizes a dual supply approach to maximize
efficiency. The collector of the power device is brought out
to the VIN pin to minimize internal power dissipation under
high current loads. VCNTL provides power for the control
circuitry and the drive for the output NPN transistor.
VCNTL sh ould be at leas t 1.2V high e r than the out put 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 3.0mA 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 o utput 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
to ensure stability. The frequency compensation of these
devices optimizes the frequency response with low ESR capaci-
t or s . In general, it is suggested to use capacitors with an ESR
of < 0.3Ω. It is also recommended to use bypass capacitors
such as a 22µF tantalum or a 100µF aluminum on the
adjust pin of the FAN 1581 for low r ipple and f ast trans ient
response. When these bypassing capacitors are not used at the
adjust pin, smaller values of output capacitors provide equally
good results. A graph showing stability of output capacitance
ESR vs. load current can be found under Typical Performance
Characteristics.
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. Theref ore, even with
bypass capacitors on the adjust pin, no protection diode is
needed to ensure device safety under s hort-circuit condit ions.
A protection diode between the input and output pins is
usually not needed. An internal diode between the input and
the output pins on the FAN1581 series can handle microsec-
ond surge currents of 50A to 100A. Even with large value
output capacitors it is difficult to obtain those values of surg e
currents in normal operation. Only with large values of out-
put capacitance, such as 1000µF to 5000µF, and with the
input pin instantaneously shorted to ground can damage
occur. A crowbar circuit at the input can generate those levels
of current; a diode from output to input is then recommended,
as shown in Figure 1. Usually, normal power supply cycling
or system “hot plugging and unplugging” will not generate
current large enough to do any damage.
Figure 1. Optional Protection Diode
Ripple Rejection
In applications that require improved ripple rejection, a bypass
capacitor from the adjust pin of the FAN1581 to ground
reduces the output ripple by the r atio of VOUT/1.25V. The
impedance of the adjust pin capacitor at the ripple frequ ency
should be less than the value of R1 (typically in the range of
100Ω to 120Ω) in the feedback divider network in Figure 1.
Therefore, the value of the required adjust pin capacitor is a
function of the input ripple frequency . For example, if R1 equals
100Ω and the ripple frequency equals 120Hz, the adjust pin
capacitor should be 22µF. At 10kHz, only 0.22µF is needed.
Output Voltage
The FAN1581 re gulator develops a 1.25V referen ce voltage
between the output pin and the adjust pin (see Figure 2).
Placing a resistor R1 between these two terminals causes a
constan t current to fl ow th rough R1 and down t hrough R2 to
set the overall output voltage. Normally, this current is the
specified minimum load current of 10mA.
FAN1581
Adj C2
22μF
V
OU
T
+
C1
10μF
+
C
ADJ
+
Vcntl Vsense
Vin Vout R1
R2
D1
1N4002
(OPTIONAL)
V
IN
V
OUT
FAN1581
Gnd C2
22μF
V
OU
T
+
C1
10μF
+
Vcntl Vsense
Vin Vout
D1
1N4002
(OPTIONAL)
V
IN
V
CNTL
PRODUCT SPECIFICATION FAN1581
REV. 1.2.1 7/2/0 9 7
The current out of the ad just pin adds to the curr ent fro m R1
and is typically 50µA. Its output voltage contribution is
small and only needs consideration when a very precise out-
put voltage setting is required.
Figure 2. Basic Regul ator Circuit
Load Regulation
The FAN1581 family provides true remote sensing, eliminat-
ing output voltage errors due to trace resistance. To utilize
remote sensing, connect the VSENSE pin directly to the
load, rather than at the VOUT pin. If the load is more than 1"
away from the FAN1581, it may be necessary to increase the
load capacitance to ensure stability.
Thermal Considerations
The FAN1581 series protect themselves under overload con-
ditions with internal power and thermal limiting circuitry.
However , for normal continuous load conditions, do n ot exceed
maximum junction temperature ratings. It is important to
consider all sources of thermal resistance from junction-to-
ambient. These sources include the junction-to-case resistance,
the case-to-heat sink interface resistance, and the heat sink
resistance. Thermal resistance specifications have been
developed to mo re accu rately reflect d evice temp erature and
ensure safe operating temperatures. The electrical character-
istics section provides a separate thermal resistance and
maximum junction tem perature for both the con trol circuitry
and the power transistor. Calculate the maximum junction
temperature for both sections to ensure that both thermal
limits are met.
For example, look at using an FAN1581M-1.5 to generate
5A @ 1.5V ± 2% from a 3.3V source (3.2V to 3.6V).
Assumptions:
•V
in = 3.6V worst case
•V
OUT = 1.47V worst case
•I
OUT = 5A continuous
•T
A = 40°C
•Θ Case-to-Ambient = 5°C/W (assuming both a heatsink and a
thermally conductive material)
The power dissipation in this application is:
PD = (VIN - VOUT) * (I OUT) = (3.6-1.47) * (5) = 10.65W
From the specification table,
TJ = TA + (PD) * (Θ Case-to-Ambient + ΘJC)
= 40 + (10.65) * (5 + 3) = 125°C
The junction temperature is within the maximum rating.
Junction-to-case thermal resistance is specified from the IC
junction to the bottom of the case directly below the die.
This is the lowest resistance path for heat flow. Proper
mounting ensures the best thermal flow from this area of the
package to the heat sink. Use of a thermally conductive
material at the case-to-heat sink interface is recommended.
Use a thermally conductive spacer if the case of the device
must be electrically isolated and include its contribution to
the total thermal resistance.
C2
22μF
V
IN
V
OU
T
V
REF
C1
10μF
V
cntl
++
Vcntl Vsense
Vin Adj Vout
FAN1581
R1
R2
I
ADJ
50μA
V
OUT
= V
REF
(1+R2/R1) + I
ADJ
(R2)
FAN1581 PRODUCT SPECIFICATION
8REV. 1.2.1 7/2/09
Figure 3. Application Circuit (FAN1581)
Table 1. Bill of Materials for Application Circuit for the FAN1581
Figure 4. Application Circuit (FAN1581-1.5)
Table 2. Bill of Materials for Application Circuit for the FAN1581-1.5
Item Quantity Manufacturer Part Number Description
C1, C3 2 Xicon L10V10 10µF, 10V Aluminum
C2 1 Xicon L10V100 100µF, 10V Aluminum
C4 1 Any 1µF Ceramic
R1 1 Generic 124Ω, 1%
R2 1 Generic 86.6Ω, 1%
U1 1 Fairchild FAN1581P 5A Regulator
Item Quantity Manufacturer Part Number Description
C1 1 Xicon L10V10 10µF, 10V Aluminum
C2 1 Any 1µF Ceramic
C3 1 Xicon L10V100 100µF, 10V Aluminum
U1 1 Fairchild FAN1581P-1.5 5A Regulator
100μF
C2
10μF
C3
V
CNTL = 5V
2.1V at 5
A
V
IN = 3.3V
+
10μFC1
1μF
C4
+
V
IN
V
SENSE
V
CNTL
Adj
V
OUT
FAN1581
124Ω
86.6ΩR2
R1
U1
100μF
C3
V
CNTL
= 3.3V
1.5V at 5
A
10μF
C1
V
IN
= 2.5V
+
1μFC2
+
V
IN
V
SENSE
V
CNTL
GND
U1
V
OUT
FAN1581–1.5
PRODUCT SPECIFICATION FAN1581
REV. 1.2.1 7/2/0 9 9
Figure 5. Application Circuit (FAN1581-2.5)
Table 3. Bill of Materials for Application Circuit for the FAN1581-2.5
Orderi ng Info r mat io n
Item Quantity Manufacturer Part Number Description
C1 1 Xicon L10V10 10µF, 10V Aluminum
C2 1 Any 1µF Ceramic
C3 1 Xicon L10V100 100µF, 10V Aluminum
U1 1 Fairchild FAN1581P-2.5 5A Regulator
Produc t Number Packag e
FAN1581MX TO-263 in Tape and Reel
FAN1581DX TO-252 DPAK in Tape and Reel
FAN1581M12X TO-263 in Tape and Reel
FAN1581D15X TO-252 DPAK in Tape and Reel
FAN1581M25X TO-263 in Tape and Reel
FAN1581D25X TO-252 DPAK in Tape and Reel
FAN1581T TO-220 in Tape and Reel
100μF
C3
V
CNTL
= 5V 2.5V at 5
A
10μF
C1
V
IN
= 3.3V +
1μF
C2
++
V
IN
V
SENSE
V
CNTL
GND
U1
V
OUT
FAN1581–2.5
PRODUCT SPECIFICATION FAN1581
REV. 1.2.1 7/2/0 9 10
Mechanical Dimensions
5-Lead TO-263 Package
10.20
9.80 1.40
1.00
9.40
9.00
9.50 MIN
9.00 MIN
4.00 MIN
1.20 MIN
LAND PATTERN RECOMMENDATION
10.00
1.70
6.80
5.10
4.70
(1.28)
(8.00)
(4.40)
1.70
6.80
(1.75)
(0.90)
R0.45
–B–
(6.80)
0.25 B A
MM
1.37
1.17
0.90
0.70
15.60
15.00
2.84
2.24
8°
0°
0.10 B
EATING
PLANE
0.75
0.45 0.25
GAGE PLANE
NOTES: UNLESS OTHERWISE SPECIFIED
A) ALL DIMENSIONS ARE IN MILLIMETERS.
B) STANDARD LEAD FINISH: 200 MICROINCHE
5.08 MICROMETERS MIN. LEAD/TIN 15/85
ON COPPER.
C) NO PACKAGE STANDARD REFERENCE AS
OF JUNE 2002.
D) DIMENSIONING AND TOLERANCING PER
ANSI Y14.5M – 1982.
DETAIL A, ROTATED 90°
R0.56
1.40
1.14
4.70
4.30
SEE
DETAIL A
5
5
1
1
A
FAN1581 PRODUCT SPECIFICATION
11 REV. 1.2.1 7/2/09
Mechanical Dimensions (conti nue d)
5-Lead TO-252 Package
FAN1581 PRODUCT SPECIFICATION
12 REV. 1.2.1 7/2/09
Mechanical Dimensions (continued)
TO-220 Package
10.54
9.90
15.87
14.47 13.69
11.81
26.54
24.00
9.39
8.38
5°
3°
3°
NOTES: UNLESS OTHERWISE SPECIFIED
STANDARD LEAD FINISH: 200 MICROINCHES /
5.08 MICROMETERS MIN. LEAD/TIN 15/85 ON
COPPER.
A)
REFERENCE JEDEC, TS–001, ISSUE A,
VARIATION AA, DATED AUGUST 1989
B)
ALL DIMENSIONS ARE IN MILLIMETERS.C)
DIMENSIONING AND TOLERANCING PER
ASME Y14.5M–1994.
D)
7°
5°
(1.30) 1.01
0.50
0.635
0.304
2.92
2.15
1.70
6.80
0.36 ABM
3.96
3.53 4.82
4.19
1.39
0.88
Ø
L
A
B
FAN1581 PRODUCT SPECIFICATION
13 REV. 1.2.1 7/2/09