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PDF FAN1084 Data sheet ( Hoja de datos )
| Número de pieza | FAN1084 | |
| Descripción | 4.5A Adjustable/Fixed Low Dropout Linear Regulator | |
| Fabricantes | Fairchild Semiconductor | |
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www.fairchildsemi.com
FAN1084
4.5A Adjustable/Fixed Low Dropout Linear Regulator
Features
• Fast transient response
• Low dropout voltage at up to 4.5A
• Load regulation: 0.5% typical
• On-chip thermal limiting
• Standard TO-220, TO-263 center cut, and TO-252
packages
Applications
• Desktop PCs, RISC and embedded processors’ supply
• GTL, SSTL logic Reference bus supply
• Low voltage VCC logic supply
• Battery-powered circuitry
• Post regulator for switching supply
• Cable and ADSL modems’ DSP core supply
• Set Top Boxes and Web Boxes modules’ supply
Application Diagrams
Description
The FAN1084, FAN1084-1.5, and FAN1084-3.3 are low
dropout three-terminal regulators with 4.5A output current
capability. These devices have been optimized for low voltage
applications including VTT bus termination, where transient
response and minimum input voltage are critical. The
FAN1084 is ideal for low voltage microprocessor applica-
tions requiring a regulated output from 1.5V to 3.6A with an
input supply of 5V or less. The FAN1084-1.5 offers fixed
1.5V with 4.5A current capabilities for GTL+ bus VTT
termination. The FAN1084-3.3 offers a fixed 3.3V output
at 4.5A.
On-chip thermal limiting provides protection against any
combination of overload and ambient temperature that
would create excessive junction temperatures.
The FAN1084 series regulators are available in the industry-
standard TO-220, TO-263 center cut, and TO-252 (DPAK)
power packages.
VIN = 5V
10µF
+
FAN1084
VIN VOUT
ADJ
124Ω
2.5V at 4.5A
+
22µF
124Ω
VIN = 3.3V
10µF
+
FAN1084-1.5
VIN VOUT
GND
1.5V at 4.5A
+
22µF
REV. 1.0.6 11/18/02
1 page  
PRODUCT SPECIFICATION
The current out of the adjust pin adds to the current from R1.
Its output voltage contribution is small and only needs consid-
eration when a very precise output voltage setting is required.
VIN +
C1
10µF
FAN1084
IN OUT
ADJ
IADJ
35µA
VREF
+
R1
VOUT
C2
22µF
R2
FAN1084
FAN1084
RP
Parasitic
Line Resistance
VIN IN
OUT
ADJ
R1*
*Connect R1 to case
Connect R2 to load
R2*
RL
Figure 3. Connection for Best Load Regulation
Load Regulation
It is not possible to provide true remote load sensing because
the FAN1084 series are three-terminal devices. Load regula-
tion is limited by the resistance of the wire connecting the reg-
ulator to the load. Load regulation per the data sheet
specification is measured at the bottom of the package.
For fixed voltage devices, negative side sensing is a true
Kelvin connection with the ground pin of the device returned
to the negative side of the load. This is illustrated in Figure 4.
FAN1084-1.5
RP
Parasitic
Line Resistance
VIN IN
OUT
GND
RL
Figure 5. Connection for Best Load Regulation
Thermal Conditions
The FAN1084 series protect themselves under overload con-
ditions with internal power and thermal limiting circuitry.
However, for normal continuous load conditions, do not
exceed maximum junction temperature ratings. It is impor-
tant to consider all sources of thermal resistance from junc-
tion-to-ambient. These sources include the junction-to-case
resistance, the case-to-heatsink interface resistance, and the
heat sink resistance. Thermal resistance specifications have
been developed to more accurately reflect device tempera-
ture and ensure safe operating temperatures. The electrical
characteristics section provides a separate thermal resistance
and maximum junction temperature for both the control cir-
cuitry and the power transistor. Calculate the maximum junc-
tion temperature for both sections to ensure that both thermal
limits are met.
For example, look at using a FAN1084T to generate 4.5A @
1.5V from a 3.3V source (3.2V to 3.6V).
Figure 4. Connection for Best Load Regulation
For adjustable voltage devices, negative side sensing is a true
Kelvin connection with the bottom of the output divider
returned to the negative side of the load. The best load regula-
tion is obtained when the top of the resistor divider R1 connects
directly to the regulator output and not to the load. Figure 5
illustrates this point.
If R1 connects to the load, then the effective resistance
between the regulator and the load would be:
RP X (1 + R2/R1), RP = Parasitic line Resistance
The connection shown in Figure 5 does not multiply RP by the
divider ration. As an example, RP is about four milliohms per
foot with 16-gauge wire. This translates to 4mV per foot at 1A
load current. At higher load currents, this drop represents a
significant percentage of the overall regulation. It is important
to keep the positive lead between the regulator and the load as
short as possible and to use large wire or PC board traces.
Assumptions
• VIN = 3.4V worst case
• VOUT = 1.475V worst case
• IOUT = 4.5A continuous
• TA = 60°C
• θCase-to-Ambient = 5°C/W (assuming both a heatsink and
a thermally conductive material)
The power dissipation in this application is:
PD = (VIN – VOUT) * (IOUT) = (3.6 – 1.475) * (4.5) = 9.6W
From the specification table:
TJ = TA + (PD) * (θCase-to-Ambient + θJC)
= 60 + (9.6) * (5 + 3) = 137°C
The junction temperature is below the maximum thermal limit.
REV. 1.0.6 11/18/02
5
5 Page 
FAN1084
Ordering Information
Product Number
FAN1084MC
FAN1084T
FAN1084D
FAN1084MC15
FAN1084T15
FAN1084D15
FAN1084MC33
FAN1084M33
FAN1084T33
FAN1084D33
Package
TO-263 Center Cut
TO-220
TO-252
TO-263 Center Cut
TO-220
TO-252
TO-263 Center Cut
TO-263
TO-220
TO-252
PRODUCT SPECIFICATION
DISCLAIMER
FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO
ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME
ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN;
NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
LIFE SUPPORT POLICY
FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES
OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body,
or (b) support or sustain life, and (c) whose failure to
perform when properly used in accordance with
instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of the
user.
2. A critical component in any component of a life support
device or system whose failure to perform can be
reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
www.fairchildsemi.com
11/18/02 0.0m 003
Stock#DS30001084
2001 Fairchild Semiconductor Corporation
11 Page | ||
| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet FAN1084.PDF ] | |
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