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FAN1585AT18 Schematic ( PDF Datasheet ) - Fairchild Semiconductor

Teilenummer FAN1585AT18
Beschreibung 5A Adjustable/Fixed Low Dropout Linear Regulator
Hersteller Fairchild Semiconductor
Logo Fairchild Semiconductor Logo 




Gesamt 12 Seiten
FAN1585AT18 Datasheet, Funktion
www.fairchildsemi.com
FAN1585A
5A Adjustable/Fixed Low Dropout Linear Regulator
Features
• Fast transient response
• Low dropout voltage at up to 5A
• Load regulation: 0.05% typical
• Trimmed current limit
• On-chip thermal limiting
• Standard TO-220, TO-263 and TO-263 center cut packages
Applications
• AGTL+ bus supply for FC-PGA
• Low voltage logic supply
• Post regulator for switching supply
• 3.3V to 1.5V linear regulator
• 5V to 1.8V linear regulator
Description
The FAN1585A, FAN1585A-1.5, and FAN1585A-1.8 are
low dropout three-terminal regulators with 5A output current
capability. These devices have been optimized for low volt-
age applications including VTT bus termination for FC-PGA,
where transient response and minimum input voltage are
critical. The FAN1585A-1.5 offers fixed 1.5V with 5A
current capabilities for AGTL+ bus VTT termination for
FC-PGA. The FAN1585A is ideal for low voltage micro-
processor applications requiring a regulated output from
1.5V to 3.6V with an input supply of 5V or less, or for
FC-PGA applications with significant trace resistance.
Current limit is trimmed to ensure specified output current
and controlled short-circuit current. On-chip thermal limit-
ing provides protection against any combination of overload
and ambient temperature that would create excessive junc-
tion temperatures.
The FAN1585A series regulators are available in the industry-
standard TO-220, TO-263 and TO-263 center cut power
packages.
Typical Applications
VIN = 3.3V
22µF
+
FAN1585A
VIN VOUT
ADJ
VOUT = VREF(1 + R2/R1) + IAdj • R2
R1
124
1.5V at 5A
+
22µF
R2
24.9
VIN = 3.3V
22µF
+
FAN1585A-1.5
VIN VOUT
GND
1.5V at 5A
+
22µF
REV. 1.1.5 11/7/03






FAN1585AT18 Datasheet, Funktion
FAN1585A
PRODUCT SPECIFICATION
Applications Information
General
The FAN1585A and FAN1585A-1.5 are three-terminal regu-
lators optimized for GTL+ VTT termination and logic appli-
cations. These devices are short-circuit protected and offer
thermal shutdown to turn off the regulator when the junction
temperature exceeds about 150°C. The FAN1585A 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 microprocessor buses
like GTL+.
Stability
The FAN1585A series requires an output capacitor as a part
of the frequency compensation. It is recommended to use a
22µF solid tantalum or a 100 µF aluminum electrolytic on
the output to ensure stability. The frequency compensation of
these devices optimizes the frequency response with low
ESR capacitors. In general, it is suggested to use capacitors
with an ESR of <300m. It is also recommended to use
bypass capacitors such as a 22µF tantalum or a 100µF alumi-
num on the adjust pin of the FAN1585A for low ripple and
fast transient response. When these bypassing capacitors are
not used at the adjust pin, larger values of output capacitors
provide equally good results. Refer to Typical Performance
Characteristics for graph of stability of output capacitance
ESR vs load current.
Protection Diodes
In normal operation, the FAN1585A series does not require
any protection diodes. For the FAN1585A, 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 condi-
tions.
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 FAN1585A series can handle micro-
second surge currents of 50A to 100A. Even with large value
output capacitors it is difficult to obtain those values of surge
currents in normal operation. Only with large values of output
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 cur-
rent; a diode from output to input is then recommended, as
shown in Figure 10. Usually, normal power supply cycling
or system “hot plugging and unplugging” will not generate
current large enough to do any damage.
The adjust pin can be driven on a transient basis ±7V with
respect to the output, without any device degradation. As
with any IC regulator, exceeding the maximum input-to-
output voltage differential causes the internal transistors to
break down and none of the protection circuitry is then func-
tional.
D1
1N4002
(OPTIONAL)
FAN1585A
VIN + IN OUT
C1 ADJ
22µF
+
CADJ
+
R1
VOUT
C2
22µF
R2
D1
1N4002
(OPTIONAL)
VIN +
C1
22µF
FAN1585A-1.5
IN OUT
GND
+ VOUT
C2
22µF
Figure 10. Optional Protection
Ripple Rejection
In applications that require improved ripple rejection, a
bypass capacitor from the adjust pin of the FAN1585A to
ground reduces the output ripple by the ratio of VOUT/1.25V.
The impedance of the adjust pin capacitor at the ripple
frequency should be less than the value of R1 (typically in
the range of 100to 120) in the feedback divider network
in Figure 10. Therefore, the value of the required adjust pin
capacitor is a function of the input ripple frequency. For
example, if R1 equals 100and the ripple frequency equals
120Hz, the adjust pin capacitor should be 22µF. At 10kHz,
only 0.22µF is needed.
Output Voltage
The FAN1585A regulator develops a 1.25V reference volt-
age between the output pin and the adjust pin (see Figure
11). Placing a resistor R1 between these two terminals
causes a constant current to flow through R1 and down
through R2 to set the overall output voltage. Normally, this
current is the specified minimum load current of 10mA.
The current out of the adjust pin adds to the current from R1
and is typically 35µA. Its output voltage contribution is
small and only needs consideration when a very precise out-
put voltage setting is required.
6 REV. 1.1.5 11/7/03

6 Page









FAN1585AT18 pdf, datenblatt
FAN1585A
Ordering Information
Product Number
FAN1585AMX
FAN1585AMCX
FAN1585AT
FAN1585AM15X
FAN1585AMC15X
FAN1585AT15
FAN1585AM18X
FAN1585AMC18X
FAN1585AT18
Package
TO-263 in Tape and Reel
TO-263 Center Cut in Tape and Reel
TO-220
TO-263 in Tape and Reel
TO-263 Center Cut in Tape and Reel
TO-220
TO-263 in Tape and Reel
TO-263 Center Cut in Tape and Reel
TO-220
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
FAIRCHILDS 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, or (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 significant injury to the user.
2. A critical component is 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
11/7/03 0.0m 001
Stock#DS30001585
2002 Fairchild Semiconductor Corporation

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