Microsemi LX8587A-15 3a low dropout positive regulator Datasheet

LIN D O C #: 8587
LX8587-xx/8587A-xx
3 A L O W D R O P O U T P O S I T I V E R E G U L AT O R S
T
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N F I N I T E
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N N O VA T I O N
DESCRIPTION
The LX8587/8587A series ICs are low
dropout three-terminal positive regulators
with a nominal 3A output current. Pentium® Processor and Power PCTM applications requiring fast transient response
are ideally suited for this product family.
The LX8587A is guaranteed to have
< 1.2V dropout at 3A and the LX8587
< 1.3V at the same current, making
them ideal to provide well-regulated outputs of 2.5V to 3.6V using a 5V input
supply. Fixed versions are also available
and specified in the Available Options
table below.
A T A
S
H E E T
K E Y F E AT U R E S
■ Three-Terminal Adjustable Or Fixed
Output
■ Guaranteed ≤ 1.2V Headroom At 3A
(LX8587A)
■ Guaranteed ≤ 1.3V Headroom At 3A
(LX8587)
■ Output Current Of 3A
p Fast Transient Response
p 1% Voltage Reference Initial Accuracy
p Output Short Circuit Protection
p Built-In Thermal Shutdown
Current limit is trimmed above 3.1A to
ensure adequate output current and controlled short-circuit current. On-chip
thermal limiting provides protection
against any combination of overload conditions that would create excessive junction temperatures.
The LX8587/87A family of products are
available in both TO-220 through-hole
as well as TO-263 surface-mount packages. For higher current applications,
see the LX8585 and LX8584 data sheets.
APPLICATIONS
■
■
■
■
■
■
■
■
IMPORTANT: For the most current data, consult LinFinity's web site: http://www.linfinity.com.
PRODUCT HIGHLIGHT
TYPICAL APPLICATION OF THE LX8587/87A IN
VIN ³ 4.75
D
R O D U C T I O N
A
5V TO 3.3V MOTHERBOARD APPLICATION
LX8587A
3.3V/3A
121W
1500µF
6MV1500GX
2x 1500µF
Sanyo
6MV1500GX
Pentium Processor Supplies
Power PC Supplies
Microprocessor Supplies
Low Voltage Logic Supplies
Post Regulator For Switching Supply
ASIC & Low Voltage Chipset Supplies
Graphics & Sound Cards
Processor I/O Supply
A VA I L A B L E O P T I O N S
Part #
200W
PER
PAR T #
Output
Voltage
LX8587/87A-00
Adjustable
LX8587/87A-15
LX8587/87A-33
1.5V
3.3V
Other voltage options may be available —
Please contact factory for details.
The output capacitors must be low ESR and low ESL type for good transient response.
PA C K A G E O R D E R I N F O R M AT I O N
TO-220
TO-263
Dropout
TA (°C)
P Plastic
DD Plastic
Voltage
3-pin
3-pin
0 to 125
1.3V
LX8587-xxCP
LX8587-xxCDD
1.2V
LX8587A-xxCP
LX8587A-xxCDD
Note: All surface-mount packages are available in Tape & Reel.
Append the letter "T" to part number. (i.e. LX8587A-00CDDT)
"xx" refers to output voltage, please see table above.
Copyright © 1998
Rev. 1.2 3/98
LINFINITY MICROELECTRONICS INC.
11861 W ESTERN A VENUE, G ARDEN G ROVE, CA. 92841, 714-898-8121, F AX: 714-893-2570
1
PRODUCT DATABOOK 1996/1997
LX8587-xx/8587A-xx
3 A L O W D R O P O U T P O S I T I V E R E G U L AT O R S
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R O D U C T I O N
A B S O L U T E M A X I M U M R AT I N G S
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A T A
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H E E T
PACKAGE PIN OUTS
(Note 1)
Power Dissipation ................................................................................ Internally Limited
Input Voltage ............................................................................................................... 10V
Input to Output Voltage Differential .......................................................................... 10V
Maximum Output Current ............................................................................................. 5A
Operating Junction Temperature
Plastic (P Package) ............................................................................................... 150°C
Storage Temperature Range ...................................................................... -65°C to 150°C
Lead Temperature (Soldering, 10 seconds) ............................................................ 300°C
TAB IS VOUT
3
VIN
VOUT
ADJ /
GND*
2
1
P PACKAGE
(Top View)
* Pin 1 is GND for fixed voltage versions.
Note 1. Exceeding these ratings could cause damage to the device. All voltages are with
respect to Ground. Currents are positive into, negative out of the specified terminal.
TAB IS V OUT
T H E R M A L D ATA
P PACKAGE:
THERMAL RESISTANCE-JUNCTION TO TAB, θJT
3.0°C/W
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
60°C/W
DD PACKAGE:
3
VIN
2
V OUT
1
ADJ / GND*
THERMAL RESISTANCE-JUNCTION TO TAB, θJT
3.0°C/W
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
DD PACKAGE
(Top View)
60°C/W*
* Pin 1 is GND for fixed voltage versions.
Junction Temperature Calculation: TJ = TA + (PD x θJA).
The θJA numbers are guidelines for the thermal performance of the device/pc-board system.
All of the above assume no ambient airflow.
* With package soldered to 0.5 in. 2 copper area over back-side ground plane or internal
power plane, θJA can vary from 20°C/W to 40°C/W, depending on mounting technique.
2
Copyright © 1998
Rev. 1.2 3/98
PRODUCT DATABOOK 1996/1997
LX8587-xx/8587A-xx
3 A L O W D R O P O U T P O S I T I V E R E G U L AT O R S
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ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, these specifications apply over the operating ambient temperatures for the LX8587-xx/87A-xx with 0°C ≤ TA ≤ 125°C;
VIN - VOUT = 3V; IOUT = 3A. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.)
LX8587-00/87A-00 (Adjustable)
Parameter
Reference Voltage
Symbol
Test Conditions
V REF
IOUT = 10mA, TA = 25°C
10mA ≤ IOUT ≤ 3A, 1.5V ≤ (V IN - V OUT), V IN ≤ 7V, P ≤ PMAX
Line Regulation (Note 2)
∆VREF (VIN) IOUT = 10mA, 1.5V ≤ (VIN - V OUT), V IN ≤ 7V
Load Regulation (Note 2)
∆VREF (IOUT) VIN - VOUT = 3V, 10mA ≤ I OUT ≤ 3A
∆V OUT (Pwr) TA = 25°C, 20ms pulse
Thermal Regulation
Ripple Rejection (Note 3)
VOUT = 3.3V, f =120Hz, COUT = 100µf Tantalum, VIN = 5V
CADJ = 10µF, IOUT = 3A
Adjust Pin Current
IADJ
Adjust Pin Current Change
∆IADJ
10mA ≤ IOUT ≤ 3A, 1.5V ≤ (VIN - V OUT), V IN ≤ 7V
Dropout Voltage
LX8587-00
∆V
∆VREF = 1%, IOUT = 3A
LX8587A-00
∆VREF = 1%, IOUT = 3A
Minimum Load Current
IOUT(MIN) VIN ≤ 7V
Maximum Output Current
IOUT(MAX) 1.4V ≤ (VIN - VOUT ), VIN ≤ 7V
Temperature Stability
∆VOUT (T)
Long Term Stability
∆VOUT (t) TA = 125°C, 1000 hrs
VOUT (RMS) TA = 25°C, 10Hz £ f £ 10kHz
RMS Output Noise (% of VOUT)
LX8587/87A-00
Min. Typ.
Max.
1.238
1.225
65
3.0
Units
1.250
1.250
0.035
0.1
0.01
83
1.262
1.275
0.2
0.5
0.02
V
V
%
%
%/W
dB
55
0.2
1.1
1
2
5
0.25
100
5
1.3
1.2
10
µA
µA
V
V
mA
A
%
%
%
1
0.003
LX8587-15/87A-15 (1.5V Fixed)
Parameter
Output Voltage
Symbol
VOUT
Test Conditions
VIN = 5V, IOUT = 0mA, TA = 25°C
3.0V ≤ V IN ≤ 7V, 0mA ≤ IOUT ≤ 3A, P ≤ PMAX
Line Regulation (Note 2)
∆VOUT 4.75V ≤ V IN ≤ 7V
(VIN )
4.75V ≤ VIN ≤ 10V
Load Regulation (Note 2)
∆VOUT (IOUT) VIN = 5V, 0mA ≤ IOUT ≤ IOUT (MAX)
Thermal Regulation (Note 3)
∆VOUT (Pwr) TA = 25°C, 20ms pulse
Ripple Rejection (Note 3)
COUT = 100µF (Tantalum), IOUT = 3A
Quiescent Current
IQ
0mA ≤ IOUT ≤ IOUT (MAX) , 4.75V ≤ VIN ≤ 10V
Dropout Voltage
LX8587-15
∆V
∆VOUT = 1%, IOUT ≤ IOUT (MAX)
LX8587A-15
∆VOUT = 1%, IOUT ≤ IOUT (MAX)
Maximum Output Current
IOUT (MAX) VIN ≤ 7V
Temperature Stability (Note 3)
∆VOUT (T)
Long Term Stability (Note 3)
∆VOUT (t) TA = 125°C, 1000 hours
RMS Output Noise (% of VOUT) (Note 3) VOUT (RMS) TA = 25°C, 10Hz ≤ f ≤ 10kHz
LX8587-15/87A-15
Min. Typ.
Max.
1.485
1.470
60
3.0
1.5
1.5
1
2
5
0.01
75
4
1.1
1
5.0
0.25
0.3
0.003
1.515
1.530
6
10
7.5
0.02
10
1.3
1.2
1
Units
V
V
mV
mV
mV
%/W
dB
mA
V
V
A
%
%
%
Note 2. Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to
heating effects are covered under the specification for thermal regulation.
Note 3. These parameters, although guaranteed, are not tested in production.
Copyright © 1998
Rev. 1.2 3/98
3
PRODUCT DATABOOK 1996/1997
LX8587-xx/8587A-xx
3 A L O W D R O P O U T P O S I T I V E R E G U L AT O R S
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ELECTRICAL CHARACTERISTICS
LX8587-33/87A-33 (3.3V Fixed)
Parameter
Output Voltage
Symbol
VOUT
Test Conditions
VIN = 5V, IOUT = 0mA, TA = 25°C
4.75V ≤ V IN ≤ 10V, 0mA ≤ IOUT ≤ 3A, P ≤ PMAX
Line Regulation (Note 2)
∆VOUT 4.75V ≤ VIN ≤ 7V
(VIN )
4.75V ≤ VIN ≤ 10V
∆VOUT (IOUT) VIN = 5V, 0mA ≤ IOUT ≤ IOUT (MAX)
Load Regulation (Note 2)
Thermal Regulation (Note 3)
∆VOUT (Pwr) TA = 25°C, 20ms pulse
Ripple Rejection (Note 3)
COUT = 100µF (Tantalum), IOUT = 3A
0mA ≤ IOUT ≤ IOUT (MAX) , 4.75V ≤ VIN ≤ 10V
Quiescent Current
IQ
Dropout Voltage
LX8587-33
∆V
∆VOUT = 1%, IOUT ≤ IOUT (MAX)
LX8587A-33
∆VOUT = 1%, IOUT ≤ IOUT (MAX)
Maximum Output Current
IOUT (MAX) VIN ≤ 7V
Temperature Stability (Note 3)
∆VOUT (T)
Long Term Stability (Note 3)
∆VOUT (t) TA = 125°C, 1000 hours
RMS Output Noise (% of VOUT) (Note 3) VOUT (RMS) TA = 25°C, 10Hz ≤ f ≤ 10kHz
LX8587-33/87A-33
Min. Typ.
Max.
3.267
3.235
60
3.0
3.3
3.3
1
2
5
0.01
75
4
1.1
1
5.0
0.25
0.3
0.003
3.333
3.365
6
10
15
0.02
10
1.3
1.2
1
Units
V
V
mV
mV
mV
%/W
dB
mA
V
V
A
%
%
%
Note 2. Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to
heating effects are covered under the specification for thermal regulation.
Note 3. These parameters, although guaranteed, are not tested in production.
4
Copyright © 1998
Rev. 1.2 3/98
PRODUCT DATABOOK 1996/1997
LX8587-xx/8587A-xx
3 A L O W D R O P O U T P O S I T I V E R E G U L AT O R S
P
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A T A
H E E T
A P P L I C AT I O N N O T E S
The LX8587/87A series ICs are easy to use Low-Dropout (LDO)
voltage regulators. They have all of the standard self-protection
features expected of a voltage regulator: short circuit protection,
safe operating area protection and automatic thermal shutdown if
the device temperature rises above approximately 165°C.
Use of an output capacitor is REQUIRED with the LX8587/87A
series. Please see the table below for recommended minimum
capacitor values.
These regulators offer a more tightly controlled reference voltage
tolerance and superior reference stability when measured against
the older pin-compatible regulator types that they replace.
STABILITY
The output capacitor is part of the regulator’s frequency compensation system. Many types of capacitors are available, with different
capacitance value tolerances, capacitance temperature coefficients,
and equivalent series impedances. For all operating conditions,
connection of a 220µF aluminum electrolytic capacitor or a 47µF
solid tantalum capacitor between the output terminal and ground
will guarantee stable operation.
If a bypass capacitor is connected between the output voltage
adjust (ADJ) pin and ground, ripple rejection will be improved
(please see the section entitled “RIPPLE REJECTION”). When ADJ
pin bypassing is used, the required output capacitor value increases.
Output capacitor values of 220µF (aluminum) or 47µF (tantalum)
provide for all cases of bypassing the ADJ pin. If an ADJ pin bypass
capacitor is not used, smaller output capacitor values are adequate.
The table below shows recommended minimum capacitance values
for stable operation.
RECOMMENDED CAPACITOR VALUES
INPUT
OUTPUT
ADJ
10µF
10µF
15µF Tantalum, 100µF Aluminum
47µF Tantalum, 220µF Aluminum
None
15µF
In order to ensure good transient response from the power supply
system under rapidly changing current load conditions, designers
generally use several output capacitors connected in parallel. Such
an arrangement serves to minimize the effects of the parasitic
resistance (ESR) and inductance (ESL) that are present in all
capacitors. Cost-effective solutions that sufficiently limit ESR and
ESL effects generally result in total capacitance values in the range
of hundreds to thousands of microfarads, which is more than
adequate to meet regulator output capacitor specifications. Output
capacitance values may be increased without limit.
The circuit shown in Figure 1 can be used to observe the transient
response characteristics of the regulator in a power system under
changing loads. The effects of different capacitor types and values
on transient response parameters, such as overshoot and undershoot, can be quickly compared in order to develop an optimum
solution.
Copyright © 1998
Rev. 1.2 3/98
Power Supply
IN
LX8587/87A
OUT
ADJ
Minumum Load
(Larger resistor)
Full Load
(Smaller resistor)
RDSON << RL
Star Ground
10ms
1 sec
FIGURE 1 — Dynamic Input And Output Test
OVERLOAD RECOVERY
Like almost all IC power regulators, the LX8587/87A regulators are
equipped with Safe Operating Area (SOA) protection. The SOA
circuit limits the regulator's maximum output current to progressively lower values as the input-to-output voltage difference
increases. By limiting the maximum output current, the SOA circuit
keeps the amount of power that is dissipated in the regulator itself
within safe limits for all values of input-to-output voltage within the
operating range of the regulator. The LX8587/87A SOA protection
system is designed to be able to supply some output current for all
values of input-to-output voltage, up to the device breakdown
voltage.
Under some conditions, a correctly operating SOA circuit may
prevent a power supply system from returning to regulated
operation after removal of an intermittent short circuit at the output
of the regulator. This is a normal mode of operation which can be
seen in most similar products, including older devices such as 7800
series regulators. It is most likely to occur when the power system
input voltage is relatively high and the load impedance is relatively
low.
When the power system is started “cold”, both the input and
output voltages are very close to zero. The output voltage closely
follows the rising input voltage, and the input-to-output voltage
difference is small. The SOA circuit therefore permits the regulator
to supply large amounts of current as needed to develop the
designed voltage level at the regulator output. Now consider the
case where the regulator is supplying regulated voltage to a resistive
load under steady state conditions. A moderate input-to-output
voltage appears across the regulator but the voltage difference is
small enough that the SOA circuitry allows sufficient current to flow
through the regulator to develop the designed output voltage across
the load resistance. If the output resistor is short-circuited to ground,
the input-to-output voltage difference across the regulator suddenly
becomes larger by the amount of voltage that had appeared across
the load resistor. The SOA circuit reads the increased input-tooutput voltage, and cuts back the amount of current that it will
permit the regulator to supply to its output terminal. When the short
circuit across the output resistor is removed, all the regulator output
current will again flow through the output resistor. The maximum
current that the regulator can supply to the resistor will be limited
by the SOA circuit, based on the large input-to-output voltage across
the regulator at the time the short circuit is removed from the output.
5
PRODUCT DATABOOK 1996/1997
LX8587-xx/8587A-xx
3 A L O W D R O P O U T P O S I T I V E R E G U L AT O R S
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OVERLOAD RECOVERY (continued)
If this limited current is not sufficient to develop the designed
voltage across the output resistor, the voltage will stabilize at some
lower value, and will never reach the designed value. Under these
circumstances, it may be necessary to cycle the input voltage down
to zero in order to make the regulator output voltage return to
regulation.
C = 1 / (6.28 * FR * R1)
≡ the value of the capacitor in Farads;
select an equal or larger standard value.
F R ≡ the ripple frequency in Hz
R1 ≡ the value of resistor R1 in ohms
where: C
At a ripple frequency of 120Hz, with R1 = 100Ω:
C = 1 / (6.28 * 120Hz * 100Ω) = 13.3µF
The closest equal or larger standard value should be used, in this
case, 15µF.
When an ADJ pin bypass capacitor is used, output ripple
amplitude will be essentially independent of the output voltage. If
an ADJ pin bypass capacitor is not used, output ripple will be
proportional to the ratio of the output voltage to the reference
voltage:
M = VOUT/VREF
where: M
VREF
≡ a multiplier for the ripple seen when the
ADJ pin is optimally bypassed.
= 1.25V.
For example, if VOUT = 2.5V the output ripple will be:
M = 2.5V/1.25V= 2
VOUT
VREF
R1
R2
VOUT = VREF 1 + R2 + IADJ R2
R1
FIGURE 2 — Basic Adjustable Regulator
LOAD REGULATION
Because the LX8587/87A regulators are three-terminal devices, it is
not possible to provide true remote load sensing. Load regulation
will be limited by the resistance of the wire connecting the regulator
to the load. The data sheet specification for load regulation is
measured at the bottom of the package. Negative side sensing is a
true Kelvin connection, with the bottom of the output divider
returned to the negative side of the load. Although it may not be
immediately obvious, best load regulation is obtained when the top
of the resistor divider, (R1), is connected directly to the case of the
regulator, not to the load. This is illustrated in Figure 3. If R1 were
connected to the load, the effective resistance between the regulator
and the load would be:
RPeff = RP *
 R2+R1
 R1 
where: R P ≡ Actual parasitic line resistance.
When the circuit is connected as shown in Figure 3, the parasitic
resistance appears as its actual value, rather than the higher RPeff.
VIN
IN
LX8587/87A
OUT
ADJ
RP
Parasitic
Line Resistance
Output ripple will be twice as bad as it would be if the ADJ pin
were to be bypassed to ground with a properly selected capacitor.
R1
OUTPUT VOLTAGE
R2
The LX8587/87A ICs develop a 1.25V reference voltage between the
output and the adjust terminal (See Figure 2). By placing a resistor, R1,
between these two terminals, a constant current is caused 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.
Because IADJ is very small and constant when compared with the current
through R1, it represents a small error and can usually be ignored.
6
LX8587/87A
OUT
ADJ
IADJ
50µA
RIPPLE REJECTION
Ripple rejection can be improved by connecting a capacitor
between the ADJ pin and ground. The value of the capacitor should
be chosen so that the impedance of the capacitor is equal in
magnitude to the resistance of R1 at the ripple frequency. The
capacitor value can be determined by using this equation:
IN
VIN
Connect
R1 to Case
of Regulator
RL
Connect
R2
to Load
FIGURE 3 — Connections For Best Load Regulation
Copyright © 1998
Rev. 1.2 3/98
PRODUCT DATABOOK 1996/1997
LX8587-xx/8587A-xx
3 A L O W D R O P O U T P O S I T I V E R E G U L AT O R S
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A P P L I C AT I O N N O T E S
LOAD REGULATION (continued)
Even when the circuit is optimally configured, parasitic resistance
can be a significant source of error. A 100 mil wide PC trace built
from 1 oz. copper-clad circuit board material has a parasitic
resistance of about 5 milliohms per inch of its length at room
temperature. If a 3-terminal regulator used to supply 2.50 volts is
connected by 2 inches of this trace to a load which draws 5 amps
of current, a 50 millivolt drop will appear between the regulator and
the load. Even when the regulator output voltage is precisely
2.50 volts, the load will only see 2.45 volts, which is a 2% error. It
is important to keep the connection between the regulator output
pin and the load as short as possible, and to use wide traces or
heavy-gauge wire.
The minimum specified output capacitance for the regulator
should be located near the reglator package. If several capacitors
are used in parallel to construct the power system output capacitance, any capacitors beyond the minimum needed to meet the
specified requirements of the regulator should be located near the
sections of the load that require rapidly-changing amounts of
current. Placing capacitors near the sources of load transients will
help ensure that power system transient response is not impaired
by the effects of trace impedance.
To maintain good load regulation, wide traces should be used on
the input side of the regulator, especially between the input
capacitors and the regulator. Input capacitor ESR must be small
enough that the voltage at the input pin does not drop below VIN (MIN)
during transients.
can be used, as long as its added contribution to thermal resistance
is considered. Note that the case of all devices in this series is
electrically connected to the output.
Example
Given: VIN = 5V
VOUT = 2.8V, IOUT = 5.0A
Ambient Temp., TA = 50°C
RθJT = 2.7°C/W for TO-220
300 ft/min airflow available
Find: Proper Heat Sink to keep IC's junction
temperature below 125°C.**
Solution: The junction temperature is:
TJ = PD (RθJT + RθCS + RθSA) + TA
where: PD ≡ Dissipated power.
RθJT ≡ Thermal resistance from the junction to the
mounting tab of the package.
RθCS ≡ Thermal resistance through the interface
between the IC and the surface on which
it is mounted. (1.0°C/W at 6 in-lbs
mounting screw torque.)
RθSA ≡ Thermal resistance from the mounting surface
to ambient (thermal resistance of the heat sink).
TS ≡ Heat sink temperature.
TJ
VIN (MIN) = VOUT + VDROPOUT (MAX)
where: VIN (MIN)
VOUT
VDROPOUT (MAX)
≡ the lowest allowable instantaneous
voltage at the input pin.
≡ the designed output voltage for the
power supply system.
≡ the specified dropout voltage
for the installed regulator.
THERMAL CONSIDERATIONS
The LX8587/87A regulators have internal power and thermal
limiting circuitry designed to protect each device under overload
conditions. For continuous normal load conditions, however,
maximum junction temperature ratings must not be exceeded. It is
important to give careful consideration to all sources of thermal
resistance from junction to ambient. This includes junction to case,
case to heat sink interface, and heat sink thermal resistance itself.
Junction-to-case thermal resistance is specified from the IC
junction to the back surface of the case directly opposite the die.
This is the lowest resistance path for heat flow. Proper mounting
is required to ensure the best possible thermal flow from this area
of the package to the heat sink. Thermal compound at the case-toheat-sink interface is strongly recommended. If the case of the
device must be electrically isolated, a thermally conductive spacer
Copyright © 1998
Rev. 1.2 3/98
TC
Rq JT
TS
Rq CS
TA
Rq SA
First, find the maximum allowable thermal resistance of the
heat sink:
TJ - TA
- (RθJT + RθCS )
RθSA =
PD
5.0A
PD
= (VIN(MAX) - VOUT) I OUT =
(5.0V-2.8V) *
RθSA
125°C - 50°C = 11.0W
(5.0V-2.8V) * 5.0A
=
- (2.7°C/W + 1.0°C/W)
= 3.1°C/W
Next, select a suitable heat sink. The selected heat sink must have
RθSA ≤ 3.1°C/W. Thermalloy heatsink 6296B has RθSA = 3.0°C/W with
300ft/min air flow.
Finally, verify that junction temperature remains within specification using the selected heat sink:
TJ = 11W (2.7°C/W + 1.0°C/W + 3.0°C/W) + 50°C = 124°C
** Although the device can operate up to 150°C junction, it is recommended for long term reliability to keep the junction temperature
below 125°C whenever possible.
7
PRODUCT DATABOOK 1996/1997
LX8587-xx/8587A-xx
3 A L O W D R O P O U T P O S I T I V E R E G U L AT O R S
P
R O D U C T I O N
D
S
A T A
H E E T
T Y P I C A L A P P L I C AT I O N S
(Note A)
VIN
10µF
LX8587/87A
OUT
IN
ADJ
* C1 improves ripple rejection.
XC should be » R1 at ripple
frequency.
5V
R1
121W
1%
R2
365W
1%
VIN
VOUT
IN
(Note A)
LX8587/87A
OUT
ADJ
C1*
10µF
150µF
VOUT**
R1
121W
R2
1k
C1
10µF*
C2
100µF
* Needed if device is far from filter capacitors.
** VOUT = 1.25V 1 + R2
R1
FIGURE 4 — Improving Ripple Rejection
FIGURE 5 — 1.2V - 8V Adjustable Regulator
VIN
IN
(Note A)
LX8587/87A
OUT
ADJ
5V
121W
1%
100µF
10µF
1k
TTL
Output
2N3904
365W
1%
1k
FIGURE 6 — 5V Regulator With Shutdown
LX8587-33/87A-33
VIN
OUT
IN
10µF Tantalum
or 100µF Aluminum
GND
3.3V
Min. 15µF Tantalum or
100µF Aluminum capacitor.
May be increased as needed.
ESR must be less than 50mW .
FIGURE 7 — Fixed 3.3V Output Regulator
Note A: V IN (MIN) = (Intended V OUT) + (VDROPOUT (MAX))
Pentium is a registered trademark of Intel Corporation.
Power PC is a trademark of International Business Machines Corporation.
PRODUCTION DATA - Information contained in this document is proprietary to Lin Finity, and is current as of publication date. This document
may not be modified in any way without the express written consent of LinFinity. Product processing does not necessarily include testing of
all parameters. Linfinity reserves the right to change the configuration and performance of the product and to discontinue product at any time.
8
Copyright © 1998
Rev. 1.2 3/98
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