LX8384-15IP-TR [MICROSEMI]
Fixed Positive LDO Regulator, 1.5V, 1.5V Dropout, PSFM3, ROHS COMPLIANT, PLASTIC, TO-220, 3 PIN;
| 型号： | LX8384-15IP-TR |
| 厂家： | 
Microsemi |
| 描述： | Fixed Positive LDO Regulator, 1.5V, 1.5V Dropout, PSFM3, ROHS COMPLIANT, PLASTIC, TO-220, 3 PIN 稳压器 |
| 文件： | 总8页 (文件大小：217K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LIN DOC #: 8384
LX8384-xx/8384A-xx/8384B-xx
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T H E I N F I N I T E P O W E R O F I N N O V A T I O N
P R O D U C T I O N D A T A S H E E T
DESCRIPTION
KEY FEATURES
■ THREE-TERMINAL ADJUSTABLE OR FIXED
The LX8384/84A/84B Series ICs are posi-
tive regulators designed to provide 5A
output current. These regulators yield
higher efficiency than currently available
devices with all internal circuitry designed
to operate down to a 1V input-to-output
differential. In each of these products,
the dropout voltage is fully specified as
a function of load current. Dropout is
guaranteed at a maximum of 1.3V
(8384A) and 1.5V (8384) at maximum
output current, decreasing at lower load
currents.
In addition, on-chip trimming adjusts
the reference voltage tolerance to 1%
maximum at room temperature and 2%
maximum over the 0 to 125°C range
for the LX8384A, making this ideal for
the Pentium P54C-VRE specification.
The LX8384B offers 0.8% tolerance at
room temperature and 1.0% maximum
over line, load and temperature.
Fixed versions are also available and
specified in the Available Options table
below.
The LX8384/84A/84B Series devices
are pin-compatible with earlier 3-
terminalregulators, such as the 117 series
products. While a 10µF output capacitor
is required on both input and output of
these new devices, this capacitor is
generally included in most regulator
designs.
The LX8384/84A/84B Series quiescent
current flows into the load, thereby
increasing efficiency. This feature
constrasts with PNP regulators where up
to 10% of the output current is wasted as
quiescent current. The LX8384-xxI is
specified over the industrial temperature
range of -25°C to 125°C, while the
LX8384-xxC/84A-xxC/84B-xxC is
specified over the commercial range of
0°C to 125°C.
OUTPUT
■ GUARANTEED < 1.3V HEADROOM AT 5A
(LX8384A-xx)
■ GUARANTEED 2.0% MAX. REFERENCE
TOLERANCE (LX8384A-xx)
■ GUARANTEED 1.0% MAX. REFERENCE
TOLERANCE (LX8384B-xx)
■ OUTPUT CURRENT OF 5A MINIMUM
p 0.015% LINE REGULATION
p 0.15% LOAD REGULATION
APPLICATIONS
■ PENTIUM® PROCESSOR VRE APPLICATIONS
■ HIGH EFFICIENCY LINEAR REGULATORS
■ POST REGULATORS FOR SWITCHING POWER
SUPPLIES
■ BATTERY CHARGERS
■ CONSTANT CURRENT REGULATORS
■ CYRIX® 6x86TM
■ AMD-K5TM
IMPORTANT: For the most current data, consult LinFinity's web site: http://www.linfinity.com.
AVAILABLE OPTIONS PER PAR T #
PRODUCT HIGHLIGHT
Output
Part #
Voltage
3.5V, 5A REGULATOR
LX8384/84A/84B-00
LX8384/84A/84B-15
LX8384/84A/84B-33
Other voltage options may be available —
Please contact factory for details.
Adjustable
1.5V
IN
OUT
3.3V
3.5V at 5A
5V
LX8384A
121Ω
0.1%
1500µF
*
*
1500µF
6MV1500GX
Sanyo
ADJ
5x 6MV1500GX
Sanyo
Capacitors must
have < 20mΩ Total ESR.
218
Ω
0.1%
*
An application of the LX8384A for the Pentium P54C processors meeting VRE specfication.
PACKAGE ORDER INFORMATION
Plastic TO-220
3-pin
Plastic TO-263
DD
3-pin
Max. Ref. Max. Dropout
TA (°C)
P
Accuracy
Voltage
2.0%
2.0%
1.0%
2.0%
1.5V
1.3V
1.3V
1.5V
LX8384-xxCP
LX8384A-xxCP
LX8384B-xxCP
LX8384-xxIP
LX8384-xxCDD
LX8384A-xxCDD
LX8384B-xxCDD
LX8384-xxIDD
0 to 125
-25 to 125
Note: All surface-mount packages are available in Tape & Reel, append the letter "T" to part number.
(i.e. LX8384A-xxCDDT) "xx" refers to output voltage, please see table above.
L I N F I N I T Y M I C R O E L E C T R O N I C S I N C .
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
Copyright © 1997
Rev. 1.9 12/97
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ABSOLUTE MAXIMUM RATINGS (Note 1)
PACKAGE PIN OUTS
Power Dissipation ..................................................................................Internally Limited
Input Voltage................................................................................................................ 10V
Input to Output Voltage Differential........................................................................... 10V
Operating Junction Temperature
TAB IS VOUT
3
V
IN
2
VOUT
1
ADJ / GND*
Hermetic (K - Package) ........................................................................................ 150°C
Plastic (DD - Package).......................................................................................... 150°C
Storage Temperature Range ...................................................................... -65°C to 150°C
Lead Temperature (Soldering, 10 seconds)............................................................. 300°C
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 VOUT
THERMAL DATA
V
3
2
1
IN
P PACKAGE:
VOUT
ADJ / GND*
THERMAL RESISTANCE-JUNCTION TO TAB, θJT
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
DD PACKAGE:
2.7°C/W
60°C/W
DD PACKAGE
(Top View)
THERMAL RESISTANCE-JUNCTION TO TAB, θJT
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
Junction Temperature Calculation: TJ = TA + (PD x θJA).
2.7°C/W
60°C/W*
* Pin 1 is GND for fixed voltage versions.
The θJA numbers are guidelines for the thermal performance of the device/pc-board system.
All of the above assume no ambient airflow.
* θ can be improved with package soldered to 0.5IN2 copper area over backside ground
pJlAane or internal power plane. θJAcan vary from 20ºC/W to > 40ºC/W depending on
mounting technique.
BLOCK DIAGRAM
VIN
Bias
Circuit
Bandgap
Circuit
Control
Circuit
Output
Circuit
Thermal
Limit Circuit
VOUT
SOA Protection
Circuit
ADJ or
GND*
Current
Limit Circuit
* This pin GND for fixed voltage versions.
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ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, these specifications apply over the operating ambient temperatures for the LX8384-xxC/8384A-xxC/8384B-xxC with
0°C ≤ TA ≤ 125°C, and the LX8384-xxI with -25°C ≤ TA ≤ 125°C; VIN - VOUT = 3V; IOUT = 5A. Low duty cycle pulse testing techniques are used which
maintains junction and case temperatures equal to the ambient temperature.)
LX8384-00 / 8384A-00 / 8384B-00 (Adjustable)
LX8384/84A/84B-00
Parameter
Symbol
Test Conditions
Units
Min. Typ.
Max.
1.238
1.250
1.262
V
V
V
Reference Voltage
(Note 4)
LX8384/84A-00
LX8384B-00
VREF
IOUT = 10mA, TA = 25°C
10mA ≤ IOUT ≤ 5A, 1.5V ≤ (V - VOUT), V ≤ 10V, P ≤ PMAX
1.225 1.250 1.270
1.240 1.250 1.260
1.238 1.250 1.262
IN
IN
IOUT = 10mA, TA = 25°C
10mA ≤ IOUT ≤ 5A, 1.5V ≤ (V - VOUT), V ≤ 10V, P ≤ PMAX
V
IN
IN
0.015
0.035
0.15
0.01
83
0.2
0.3
%
%
%
%/W
dB
Line Regulation (Note 2)
∆VREF 1.3V ≤ (VIN - VOUT), VIN ≤ 7V, IOUT = 10mA
(VIN)
1.3V ≤ (VIN - VOUT), VIN ≤ 10V, IOUT = 10mA
0.5
0.02
Load Regulation (Note 2)
Thermal Regulation
∆VREF (IOUT
)
VOUT ≥ VREF, VIN - VOUT = 3V, 10mA ≤ IOUT ≤ 5A
∆VOUT(Pwr) TA = 25°C, 20ms pulse
VOUT = 5V, f =120Hz, COUT = 100µf Tantalum, VIN = 6.5V
65
20
Ripple Rejection (Note 3)
CADJ = 10µF, IOUT = 5A
55
0.2
1.2
1.1
2
100
5
µA
µA
V
Adjust Pin Current
Adjust Pin Current Change (Note 4)
IADJ
∆IADJ
∆V
10mA ≤ IOUT ≤ IOUT (MAX) , 1.3V ≤ (V - VOUT), V ≤ 10V
IN
IN
1.5
1.3
10
Dropout Voltage
LX8384-00
∆VREF = 1%, IOUT = 5A
∆VREF = 1%, IOUT = 5A
LX8384A/84B-00
V
mA
A
Minimum Load Current
IOUT (MIN)
V ≤ 10V
IN
5
3
6
Maximum Output Current
IOUT (MAX) (VIN - VOUT) ≤ 7V
(VIN - VOUT) ≤ 10V
4
A
0.25
0.3
0.003
%
%
%
Temperature Stability (Note 3)
Long Term Stability (Note 3)
∆VOUT (T)
∆VOUT (t) TA = 125°C, 1000 hours
1
RMS Output Noise (% of VOUT) (Note 3) VOUT (RMS) TA = 25°C, 10Hz ≤ f ≤ 10kHz
LX8384-15 / 8384A-15 / 8384B-15 (1.5V Fixed)
LX8384/84A/84B-15
Parameter
Symbol
Test Conditions
Units
Min. Typ.
Max.
Output Voltage
(Note 4)
LX8384/84A-15
LX8384B-15
VOUT
VIN = 5V, IOUT = 0mA, TA = 25°C
1.485
1.470
1.488
1.485
1.50
1.50
1.50
1.50
1
1.515
1.530
1.512
1.515
3
V
V
4.75V ≤ VIN ≤ 10V, 0mA ≤ IOUT ≤ 5A, P ≤ PMAX
VIN = 5V, IOUT = 0mA, TA = 25°C
4.75V ≤ VIN ≤ 10V, 0mA ≤ IOUT ≤ 5A, P ≤ PMAX
V
V
Line Regulation (Note 2)
∆VOUT 4.75V ≤ VIN ≤ 7V
(VIN)
mV
mV
mV
% / W
dB
mA
V
4.75V ≤ VIN ≤ 10V
1
5
7
2.5
0.01
83
Load Regulation (Note 2)
Thermal Regulation
Ripple Rejection (Note 3)
Quiescent Current
∆VOUT (IOUT
)
VIN = 5V, 0mA ≤ IOUT ≤ IOUT (MAX)
∆VOUT(Pwr) TA = 25°C, 20ms pulse
COUT = 100µF (Tantalum), IOUT = 5A
0.02
60
5
IQ
∆V
0mA ≤ IOUT ≤ IOUT (MAX) , 4.75V ≤ VIN ≤ 10V
∆VOUT = 1%, IOUT ≤ IOUT (MAX)
4
1.2
1
10
1.5
1.3
Dropout Voltage
LX8384-15
LX8384A/84B-15
V
∆VOUT = 1%, IOUT ≤ IOUT (MAX)
6
A
Maximum Output Current
IOUT (MAX) VIN ≤ 7V
0.25
0.3
0.003
%
Temperature Stability (Note 3)
Long Term Stability (Note 3)
RMS Output Noise (% of VOUT) (Note 3) VOUT (RMS) TA = 25°C, 10Hz ≤ f ≤ 10kHz
∆VOUT (T)
1
%
%
∆VOUT (t) TA = 125°C, 1000 hours
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.
Note 4. See Maximum Output Current Section above.
Copyright © 1997
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ELECTRICAL CHARACTERISTICS (Continued)
LX8384-33 / 8384A-33 / 8384B-33 (3.3V Fixed)
LX8384/84A/84B-33
Parameter
Symbol
Test Conditions
Units
Min. Typ.
Max.
3.267
3.235
3.274
3.267
3.30
3.30
3.30
3.30
1
3.333
3.365
3.326
3.333
6
V
V
V
Output Voltage
(Note 4)
LX8384/84A-33
LX8384B-33
VOUT
VIN = 5V, IOUT = 0mA, TA = 25°C
4.75V ≤ VIN ≤ 10V, 0mA ≤ IOUT ≤ 5A, P ≤ PMAX
VIN = 5V, IOUT = 0mA, TA = 25°C
4.75V ≤ VIN ≤ 10V, 0mA ≤ IOUT ≤ 5A, P ≤ PMAX
V
Line Regulation (Note 2)
∆VOUT 4.75V ≤ VIN ≤ 7V
(VIN)
mV
mV
mV
% / W
dB
mA
V
2
10
4.75V ≤ VIN ≤ 10V
Load Regulation (Note 2)
Thermal Regulation
∆VOUT (IOUT
)
VIN = 5V, 0mA ≤ IOUT ≤ IOUT (MAX)
∆VOUT(Pwr) TA = 25°C, 20ms pulse
COUT = 100µF (Tantalum), IOUT = 5A
5
0.01
83
4
1.2
1
15
0.02
Ripple Rejection (Note 3)
Quiescent Current
60
5
IQ
0mA ≤ IOUT ≤ IOUT (MAX) , 4.75V ≤ VIN ≤ 10V
∆VOUT = 1%, IOUT ≤ IOUT (MAX)
∆VOUT = 1%, IOUT ≤ IOUT (MAX)
10
1.5
1.3
Dropout Voltage
LX8384-33
LX8384A/84B-33
∆V
V
A
6
Maximum Output Current
IOUT (MAX) VIN ≤ 7V
0.25
0.3
0.003
%
%
%
Temperature Stability (Note 3)
Long Term Stability (Note 3)
∆VOUT (T)
∆VOUT (t) TA = 125°C, 1000 hours
1
RMS Output Noise (% of VOUT) (Note 3) VOUT (RMS) TA = 25°C, 10Hz ≤ f ≤ 10kHz
Copyright © 1997
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APPLICATION NOTES
Minumum Load
(Larger resistor)
TheLX8384/84A/84BSeriesICsareeasytouseLow-Dropout(LDO)
Power Supply
LX8384/84A
/84B
ADJ
IN
OUT
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 LX8384/84A/
84B series. Please see the table below for recommended minimum
capacitor values.
Full Load
(Smaller resistor)
RDSON << RL
1 sec
10ms
Star Ground
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.
FIGURE 1 — DYNAMIC INPUT and OUTPUT TEST
OVERLOAD RECOVERY
Like almost all IC power regulators, the LX8384/84A/84B regulators
are equipped with Safe Operating Area (SOA) protection. The SOA
circuitlimitstheregulator'smaximumoutputcurrenttoprogressively
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
rangeoftheregulator. TheLX8384/84A/84BSOAprotectionsystem
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 opera-
tion 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 toa resistive load under steadystateconditions. Amoderate
input-to-output voltage appears across the regulator but the voltage
difference is small enough that the SOA circuitry allows sufficient
currenttoflowthroughtheregulatortodevelopthedesignedoutput
voltage across the load resistance. If the output resistor is short-
circuitedtoground,theinput-to-outputvoltagedifferenceacrossthe
regulatorsuddenlybecomeslargerbytheamountofvoltagethathad
appeared across the load resistor. The SOA circuit reads the
increased input-to-output 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, alltheregulatoroutputcurrentwillagainflowthroughthe
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. If this limited current is not
sufficient to develop the designedvoltageacrosstheoutputresistor,
STABILITY
The output capacitor is part of the regulator’s frequency compen-
sation 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
pinbypassingisused,therequiredoutputcapacitorvalueincreases.
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.
Thetablebelowshowsrecommendedminimumcapacitancevalues
for stable operation.
RECOMMENDED CAPACITOR VALUES
INPUT
10µF
10µF
OUTPUT
15µF Tantalum, 100µF Aluminum
47µF Tantalum, 220µF Aluminum
ADJ
None
15µF
To ensure good transient response from the power supply system
underrapidlychangingcurrentloadconditions,designersgenerally
use several output capacitors connected in parallel. Such an
arrangementservestominimizetheeffectsoftheparasiticresistance
(ESR) and inductance (ESL) that are present in all capacitors. Cost-
effective solutions that sufficiently limit ESR and ESL effects gener-
ally 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.
ThecircuitshowninFigure1canbeusedtoobservethetransient
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 under-
shoot, can be compared quickly in order to develop an optimum
solution.
Copyright © 1997
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APPLICATION NOTES
OVERLOAD RECOVERY (continued)
the voltage will stabilize at some lower value, and will never reach
thedesignedvalue. Underthesecircumstances, itmaybenecessary
to cycle the input voltage down to zero in order to make the
regulator output voltage return to regulation.
LX8384/84A/84B
IN
OUT
VIN
VOUT
ADJ
VREF
R1
R2
IADJ
50µA
RIPPLE REJECTION
Ripple rejection can be improved by connecting a capacitor
betweentheADJpinandground. Thevalueofthecapacitorshould
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:
R2
R1
VOUT = VREF 1 +
+ IADJ R2
FIGURE 2 — BASIC ADJUSTABLE REGULATOR
C = 1 / (6.28 F R1)
*
*
R
LOAD REGULATION
where: C ≡ the value of the capacitor in Farads;
select an equal or larger standard value.
FR ≡ the ripple frequency in Hz
Because the LX8384/84A/84B 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:
R1 ≡ the value of resistor R1 in ohms
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:
R2+R1
RPeff = RP
*
R1
M = VOUT/VREF
where: RP ≡ Actual parasitic line resistance.
where: M ≡ a multiplier for the ripple seen when the
ADJ pin is optimally bypassed.
When the circuit is connected as shown in Figure 3, the parasitic
resistance appears as its actual value, rather than the higher RPeff.
VREF = 1.25V.
For example, if VOUT = 2.5V the output ripple will be:
M = 2.5V/1.25V= 2
R
ParaPsitic
LX8384/84A/84B
IN
Line Resistance
OUT
VIN
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.
Connect
ADJ
R1 to Case
of Regulator
R1
OUTPUT VOLTAGE
The LX8384/84A/84B 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.
RL
R2
Connect
R2
to Load
FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION
Copyright © 1997
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APPLICATION NOTES
LOAD REGULATION (continued)
Even when the circuit is configured optimally, 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, a50 millivolt dropwill appearbetween theregulatorand
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.
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.**
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 capaci-
tance, 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
enoughthatthevoltageattheinputpindoesnotdropbelowVIN(MIN)
during transients.
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 TC TS
TA
VIN (MIN) = VOUT + VDROPOUT (MAX)
RθJT
RθCS
RθSA
where: VIN (MIN)
VOUT
≡ the lowest allowable instantaneous
voltage at the input pin.
≡ the designed output voltage for the
power supply system.
First, find the maximum allowable thermal resistance of the
heat sink:
TJ - TA
RθSA
=
- (RθJT + RθCS)
PD
VDROPOUT (MAX) ≡ the specified dropout voltage
for the installed regulator.
PD = (VIN(MAX) - VOUT) IOUT = (5.0V-2.8V) 5.0A
*
= 11.0W
THERMAL CONSIDERATIONS
125°C - 50°C
RθSA
=
- (2.7°C/W+ 1.0°C/W)
The LX8384/84A/84B 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-to-
heat-sink interface is strongly recommended. If the case of the
device must be electrically isolated, a thermally conductive spacer
(5.0V-2.8V) 5.0A
*
= 3.1°C/W
Next,selectasuitableheatsink. Theselectedheatsinkmusthave
RθSA≤ 3.1°C/W. Thermalloyheatsink6296BhasRθSA =3.0°C/Wwith
300ft/min air flow.
Finally, verify that junction temperature remains within speci-
fication 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 recom-
mended for long term reliability to keep the junction temperature
below 125°C whenever possible.
Copyright © 1997
Rev. 1.9 12/97
7
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
LX8384-xx/8384A-xx/8384B-xx
5 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 A T A S H E E T
TYPICAL APPLICATIONS
LX8384/84A/84B
OUT
LX8384/84A/84B
OUT
VIN
(Note A)
(Note A)
VIN
IN
VOUT**
5V
VOUT
IN
ADJ
R1
121Ω
R1
121Ω
1%
ADJ
10µF
C2
100µF
C1*
10µF
150µF
R2
1k
R2
C1
10µF*
* C1 improves ripple rejection.
XC should be ≈ R1 at ripple
frequency.
365Ω
1%
* Needed if device is far from filter capacitors.
R2
R1
**VOUT = 1.25V 1 +
FIGURE 4 — IMPROVING RIPPLE REJECTION
FIGURE 5 — 1.2V - 8V ADJUSTABLE REGULATOR
LX8384/84A/84B
VIN
(Note A)
OUT
IN
5V
ADJ
121Ω
1%
100µF
10µF
1k
TTL
Output
2N3904
365Ω
1%
1k
FIGURE 6 — 5V REGULATOR WITH SHUTDOWN
LX8384/84A/84B-33
VIN
OUT
IN
3.3V
GND
10µF Tantalum
or 100µF Aluminum
Min. 15µF Tantalum or
100µF Aluminum capacitor.
May be increased without
limit. ESR must be less
than 50mΩ.
FIGURE 7 — FIXED 3.3V OUTPUT REGULATOR
Note A: VIN (MIN) = (Intended VOUT) + (VDROPOUT (MAX)
)
Pentium is a registered trademark of Intel Corporation.
Cyrix is a registered trademark and 6x86 is a trademark of Cyrix Corporation. K5 is a trademark of AMD.
PRODUCTION DATA - Information contained in this document is proprietary to Linfinity, 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.
Copyright © 1997
Rev. 1.9 12/97
8
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