LX8585A-00CDD [MICROSEMI]
4.6A LOW DROPOUT POSITIVE REGULATORS; 4.6A低压差正稳压器型号: | LX8585A-00CDD |
厂家: | Microsemi |
描述: | 4.6A LOW DROPOUT POSITIVE REGULATORS |
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 #: 8585
LX8585-xx/8585A-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 LX8585/85A Series ICs are low drop-
out three-terminal regulators with a mini-
mum of 4.6A output current. Pentium®
Processor and Power PCTM applications
requiring fast transient response are ide-
ally suited for this product family. The
LX8585A is guaranteed to have < 1.2V
at 4.6A, while the LX8585 are specified
for 1.4V, 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.
trolled short-circuit current. On-chip
OUTPUT
thermal limiting provides protection
against any possible overload that would
create excessive junction temperatures.
The LX8585/85A family is available in
both through-hole and surface-mount
versions of the industry standard 3-pin
TO-220 / TO-263 power packages.
The LX1431 Programmable Reference
and LX8585A Series products offer pre-
cision output voltage and are ideal for
use in VRE applications (see application
below). For higher current applications,
see the LX8584 data sheet.
■
■
GUARANTEED < 1.2V HEADROOM AT 4.6A
(LX8585A)
GUARANTEED < 1.4V HEADROOM AT 4.6A
(LX8585)
■ GUARANTEED < 1.3V HEADROOM AT 3A
■ OUTPUT CURRENT OF 4.6A MINIMUM
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 4.6A to
ensure adequate output current and con-
APPLICATIONS
IMPORTANT: For the most current data, consult LinFinity's web site: http://www.linfinity.com.
■ PENTIUM PROCESSOR SUPPLIES
■ POWER PC SUPPLIES
PRODUCT HIGHLIGHT
■ MICROPROCESSOR SUPPLIES
■ LOW VOLTAGE LOGIC SUPPLIES
■ BATTERY POWERED CIRCUIT
■ POST REGULATOR FOR SWITCHING SUPPLY
■ CYRIX® 6x86TM SUPPLIES
■ AMD-K5TM SUPPLIES
THE APPLICATION OF THE LX8585A & LX1431 IN A
75 & 166MHZ P54C PROCESSORS USING 5V CACHE
VO 4.6A
(See Table Below)
PLACE IN µP SOCKET CAVITY
3
2
VIN
VOUT
LX8585A
5V
2x
330µF, 6.3V
1k
Ω
Low ESR
Oscon Type
from Sanyo
ADJ
1
0.01µF
AVAILABLE OPTIONS PER PAR T #
1kΩ
100µF x 6
10V
AVX TYPE
TPS
Output
250pF
2
Part #
Voltage
1
COL
1k
0.1%
µP
Load
LX8585/85A-00
LX8585/85A-15
LX8585/85A-33
Adjustable
1.5V
3
8
V+
220µF
10V
Low ESR
from
Sanyo
REF
LX1431
2.84k
Ω
0.1%
21k
1%
3.3V
1µF x 10
SMD
Other voltage options may be available —
0.1µF
50V
JP1
Please contact factory for details.
SGND FGND
5
6
VOUT
JP1
TYPICAL APPLICATION
3.50
3.38
Short
Open
120/166MHz, VRE, 5V Cache
75/90/100/133MHz, STND, 5V Cache
Thicktracesrepresenthighcurrenttraceswhichmustbelowresistance/low
inductance traces in order to achieve good transient response.
PACKAGE ORDER INFORMATION
Plastic TO-220
3-pin
Plastic T0-263
Dropout
Voltage
TA (°C)
P
DD
3-pin
0 to 125
1.4V
1.2V
LX8585-xxCP
LX8585-xxCDD
LX8585A-xxCP
LX8585A-xxCDD
Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number. (i.e. LX8585A-00CDDT)
"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
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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
Plastic (P, DD Package) ........................................................................................ 150°C
Storage Temperature Range ...................................................................... -65°C to 150°C
Lead Temperature (Soldering, 10 seconds) ............................................................. 300°C
TAB IS VOUT
3
VIN
2
1
VOUT
ADJ / GND*
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.
THERMAL DATA
TAB IS VOUT
P PACKAGE:
VIN
3
2
1
THERMAL RESISTANCE-JUNCTION TO TAB, θJT
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
DD PACKAGE:
3.0°C/W
60°C/W
VOUT
ADJ / GND*
THERMAL RESISTANCE-JUNCTION TO TAB, θJT
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
3.0°C/W
60°C/W*
DD PACKAGE
(Top View)
* Pin 1 is GND for fixed voltage versions.
Junction Temperature Calculation: TJ = TA + (PD x θJA). The θJA numbers are guidelines for the
thermalperformanceofthedevice/pc-boardsystem. Alloftheaboveassumenoambientairflow.
* θJAcan be improved with package soldered to 0.5IN2 copper area over backside ground
plane or internal power plane. θJAcan vary from 20ºC/W to > 40ºC/W depending on
mounting technique.
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ELECTRICAL CHARACTERISTICS
(Unless otherwise specified, these specifications apply over the operating ambient temperatures for the LX8585-xxC/85A-xxC with 0°C ≤ TA ≤ 125°C;
VIN - VOUT = 3V; IOUT = 4.6A. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.)
LX8585-00 / 8585A-00 (Adjustable)
LX8585/85A-00
Parameter
Symbol
Test Conditions
Units
Min. Typ.
Max.
Reference Voltage
LX8585/85A
VREF
IOUT = 10mA, TA = 25°C
10mA ≤ IOUT ≤ 4.6A, 1.5V ≤ (V - VOUT), VIN ≤ 7V, P ≤ PMAX
1.238 1.250 1.262
1.225 1.250 1.275
V
V
IN
Line Regulation (Note 2)
Load Regulation (Note 2)
Thermal Regulation
∆VREF (VIN) IOUT = 10mA, 1.5V ≤ (VIN - VOUT), VIN ≤ 7V
VIN - VOUT = 3V, 10mA ≤ IOUT ≤ 4.6A
∆VOUT(Pwr) TA = 25°C, 20ms pulse
VOUT = 3.3V, f =120Hz, COUT = 100µf Tantalum, VIN = 5V
0.035
0.1
0.01
83
0.2
0.5
0.02
%
∆VREF (IOUT
)
%
%/W
dB
60
Ripple Rejection (Note 3)
CADJ = 10µF, TA = 25°C, IOUT = 4.6A
55
0.2
1.2
1.1
1.1
2
100
5
1.4
1.3
1.2
10
µA
µA
V
Adjust Pin Current
Adjust Pin Current Change
Dropout Voltage
IADJ
∆IADJ
∆V
10mA ≤ IOUT ≤ 4.6A, 1.5V ≤ (V - VOUT), VIN ≤ 7V
IN
LX8585
∆VREF = 1%, IOUT = 4.6A
∆VREF = 1%, IOUT = 3A
∆VREF = 1%, IOUT = 4.6A
V
V
mA
A
%
%
%
LX8585A
Minimum Load Current
IOUT(MIN) VIN ≤ 7V
IOUT(MAX) 1.4V ≤ (VIN - VOUT), VIN ≤ 7V
∆VOUT(t)
4.6
6
Maximum Output Current (Note 4)
Temperature Stability (Note 3)
Long Term Stability (Note 3)
0.25
0.3
0.003
1
∆VOUT (t) TA = 125°C, 1000 hrs
RMS Output Noise (% of VOUT) (Note 3) VOUT (RMS) TA = 125°C, 10Hz £ f £ 10kHz
LX8585-15 / 8585A-15 (1.5V Fixed)
LX8585/85A-15
Min. Typ. Max.
Parameter
Symbol
Test Conditions
Units
Output Voltage (Note 4)
VOUT
VIN = 5V, IOUT = 0mA, TA = 25°C
4.75V ≤ VIN ≤ 10V, 0mA ≤ IOUT ≤ 7A, TA = 25°C, P ≤ PMAX
∆VOUT 4.75V ≤ VIN ≤ 7V
1.485
1.470
1.50
1.50
1
1.515
1.530
3
V
V
Line Regulation (Note 2)
mV
mV
mV
% / W
dB
mA
V
(VIN)
4.75V ≤ VIN ≤ 10V
1
5
Load Regulation (Note 2)
Thermal Regulation (Note 3)
Ripple Rejection (Note 3)
Quiescent Current
∆VOUT (IOUT
)
VIN = 5V, 10mA ≤ IOUT ≤ IOUT (MAX)
2.5
0.01
83
7
0.02
∆VOUT(Pwr) TA = 25°C, 20ms pulse
COUT = 100µF (Tantalum), IOUT = 4.6A, TA = 25°C
65
IQ
0mA ≤ IOUT ≤ IOUT (MAX) , 4.75V ≤ VIN ≤ 10V
∆VOUT = 1%, IOUT ≤ IOUT (MAX) , VIN - VOUT ≤ 7V
∆VOUT = 1%, IOUT ≤ 3A, VIN - VOUT ≤ 7V
∆VOUT = 1%, IOUT ≤ IOUT (MAX) , VIN - VOUT ≤ 7V
4
10
1.4
1.3
1.2
1.2
1.1
1.1
0.25
0.3
0.003
Dropout Voltage
LX8585-15
∆V
V
V
%
LX8585A-15
Temperature Stability (Note 3)
Long Term Stability (Note 3)
∆VOUT (T)
1
%
%
∆VOUT (t) TA = 125°C, 1000 hours
RMS Output Noise (% of VOUT) (Note 3) VOUT (RMS) TA = 25°C, 10Hz ≤ f ≤ 10kHz
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. IOUT (MAX) is measured under the condition that VOUT is forced below its nominal value by 100mV.
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ELECTRICAL CHARACTERISTICS (Continued)
LX8585-33 / 8585A-33 (3.3V Fixed)
LX8585/85A-33
Min. Typ. Max.
Parameter
Symbol
Test Conditions
Units
Output Voltage (Note 4)
VOUT
VIN = 5V, IOUT = 0mA, TA = 25°C
4.75V ≤ VIN ≤ 10V, 0mA ≤ IOUT ≤ 7A, TA = 25°C, P ≤ PMAX
∆VOUT 4.75V ≤ VIN ≤ 7V
3.267
3.235
3.3
3.3
1
2
5
3.333
3.365
6
10
15
V
V
Line Regulation (Note 2)
mV
mV
mV
% / W
dB
mA
V
(VIN)
4.75V ≤ VIN ≤ 10V
Load Regulation (Note 2)
Thermal Regulation (Note 3)
Ripple Rejection (Note 3)
Quiescent Current
∆VOUT (IOUT
)
VIN = 5V, 10mA ≤ IOUT ≤ IOUT (MAX)
∆VOUT(Pwr) TA = 25°C, 20ms pulse
COUT = 100µF (Tantalum), IOUT = 4.6A, TA = 25°C
0.01
83
0.02
65
IQ
∆V
0mA ≤ IOUT ≤ IOUT (MAX) , 4.75V ≤ VIN ≤ 10V
∆VOUT = 1%, IOUT ≤ IOUT (MAX) , VIN - VOUT ≤ 7V
∆VOUT = 1%, IOUT ≤ 3A, VIN - VOUT ≤ 7V
∆VOUT = 1%, IOUT ≤ IOUT (MAX) , VIN - VOUT ≤ 7V
4
10
1.4
1.3
1.2
Dropout Voltage
LX8585-33
1.2
1.1
1.1
0.25
0.3
0.003
V
V
%
LX8585A-33
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
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APPLICATION NOTES
Minumum Load
(Larger resistor)
The LX8585/85A Series ICs are easy to use Low-Dropout (LDO)
Power Supply
IN
OUT
LX8585/85A
voltage regulators. They have all of the standard self-protection
featuresexpectedofavoltageregulator:shortcircuitprotection,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 LX8585/85A
series. Please see the table below for recommended minimum
capacitor values.
Full Load
(Smaller resistor)
ADJ
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 LX8585/85A regulators are
equipped with Safe Operating Area (SOA) protection. The SOA
circuit limits the regulator's maximum output current to progres-
sively 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 LX8585/85A 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.
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.
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.
RECOMMENDED CAPACITOR VALUES
INPUT
OUTPUT
ADJ
None
15µF
10µF
10µF
15µF Tantalum, 100µF Aluminum
47µF Tantalum, 220µF Aluminum
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.
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
appearedacrosstheloadresistor. TheSOAcircuitreadstheincreased
input-to-outputvoltage,andcutsbacktheamountofcurrentthatitwill
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.
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APPLICATION NOTES
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 willnever 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.
LX8585/85A
OUT
IN
VIN
VOUT
ADJ
VREF
R1
R2
IADJ
50µA
RIPPLE REJECTION
R2
R1
VOUT = VREF 1 +
+ IADJ R2
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:
FIGURE 2 — BASIC ADJUSTABLE REGULATOR
LOAD REGULATION
C = 1 / (6.28 F R1)
*
*
Because the LX8585/85A regulators are three-terminal devices, it is
not possible to provide true remote load sensing. Load regulation
willbelimitedbytheresistanceofthewireconnectingtheregulator
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
connectedtotheload,theeffectiveresistancebetweentheregulator
and the load would be:
R
where: C ≡ the value of the capacitor in Farads;
select an equal or larger standard value.
FR ≡ the ripple frequency in Hz
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
R1
RPeff = RP
*
where: RP ≡ Actual parasitic line resistance.
M = VOUT/VREF
When the circuit is connected as shown in Figure 3, the parasitic
resistance appears as its actual value, rather than the higher RPeff.
where: M ≡ a multiplier for the ripple seen when the
ADJ pin is optimally bypassed.
VREF = 1.25V.
R
ParaPsitic
LX8585/85A
OUT
Line Resistance
For example, if VOUT = 2.5V the output ripple will be:
M = 2.5V/1.25V= 2
IN
VIN
ADJ
Connect
R1 to Case
of Regulator
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
R2
RL
OUTPUT VOLTAGE
Connect
R2
The LX8585/85A 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.
BecauseIADJisverysmallandconstantwhencomparedwiththecurrent
through R1, it represents a small error and can usually be ignored.
to Load
FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION
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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 (2.54 mm) 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
roomtemperature. Ifa3-terminalregulatorusedtosupply2.50volts
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)
Rq JT
RqCS
RqSA
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 LX8585/85A 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. 2.2 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
LX8585-xx/8585A-xx
4 . 6 A LO W
D
R O P O U T
P
O S I T I V E
R
E G U L A T O R S
P R O D U C T I O N D A T A S H E E T
TYPICAL APPLICATIONS
LX8585/85A
OUT
LX8585/85A
OUT
VIN
(Note A)
(Note A)
VIN
IN
VOUT**
5V
VOUT
IN
ADJ
R1
121W
R1
ADJ
10µF
121W
C2
100µF
C1*
1%
10µF
150µF
R2
1k
R2
365W
1%
C1
* C1 improves ripple rejection.
XC should be » R1 at ripple
frequency.
10µF*
* 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
LX8585/85A
OUT
VIN
(Note A)
IN
5V
ADJ
121W
1%
100µF
10µF
1k
TTL
Output
2N3904
365W
1%
1k
FIGURE 6 — 5V REGULATOR WITH SHUTDOWN
LX8585-33/85A-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 50mW.
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. Power PC is a trademark of International Business Machines Corporation.
PRODUCTIONDATA-InformationcontainedinthisdocumentisproprietarytoLinFinity, andiscurrentasofpublicationdate. Thisdocument
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. 2.2 12/97
8
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