Datasheet LX8585A-15CP, LX8585A-15CDD, LX8585-33CP, LX8585-33CDD, LX8585-15CP Datasheet (Microsemi Corporation)

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Page 1

LIN DOC #:

8585

LX8585-xx/8585A-xx

4.6A LOW D

THE INFINITE POWER OF INNOVATION

DESCRIPTION KEY FEATURES

The LX8585/85A Series ICs are low dropout three-terminal regulators with a minimum of 4.6A output current. Pentium Processor and Power PCTM applications requiring fast transient response are ideally 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.

Current limit is trimmed above 4.6A to

ensure adequate output current and con-

IMPORTANT: For the most current data, consult LinFinity's web site: http://www.linfinity.com.

PRODUCT HIGHLIGHT

THE APPLICATION OF THE LX8585A & LX1431 IN A

75 & 166MHZ P54C PROCESSORS USING 5V CACHE

OUT

250pF

+V+V+

LX1431

SGND FGND

COL

Ω

0.01µF

Ω

REF

2.84k

220µF 10V Low ESR from Sanyo

LX8585A

ADJ

0.1µF 50V

trolled short-circuit current. On-chip 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 precision output voltage and are ideal for use in VRE applications (see application below). For higher current applications, see the LX8584 data sheet.

0.1%

Ω

330µF, 6.3V

Low ESR

Oscon Type

from Sanyo

0.1%

VO 4.6A

(See Table Below)

21k 1%

JP1

PLACE IN µP SOCKET CAVITY

100µF x 6

AVX TYPE

1µF x 10 SMD

10V

TPS

ROPOUT POSITIVE REGULATORS

P RODUCTION DAT A SHEET

■ THREE-TERMINAL ADJUSTABLE OR FIXED

OUTPUT

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

APPLICATIONS

■ PENTIUM PROCESSOR SUPPLIES

■ POWER PC SUPPLIES

■ MICROPROCESSOR SUPPLIES

■ LOW VOLTAGE LOGIC SUPPLIES

■ BATTERY POWERED CIRCUIT

■ POST REGULATOR FOR SWITCHING SUPPLY

6x86TM SUPPLIES

SUPPLIES

Output

Voltage

Please contact factory for details.

µP

Load

■ CYRIX

■ AMD-K5

AVAILABLE OPTIONS PER PART #

Part #

LX8585/85A-00 Adjustable LX8585/85A-15 1.5V LX8585/85A-33 3.3V

Other voltage options may be available —

Thick traces represent high current traces which must be low resistance / low inductance traces in order to achieve good transient response.

OUT

JP1 TYPICAL APPLICATION

3.50 Short 120/166MHz, VRE, 5V Cache

3.38 Open 75/90/100/133MHz, STND, 5V Cache

PACKAGE ORDER INFORMATION

(°C)

Dropout

Voltage

Plastic TO-220

3-pin

Plastic T0-263

3-pin

0 to 125 1.4V LX8585-xxCP LX8585-xxCDD

1.2V 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 INFINITY MICROELECTRONICS INC.

11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570

Page 2

PRODUCT DATABOOK 1996/1997

LX8585-xx/8585A-xx

4.6A LOW D

RODUCTION DATA SHEET

ROPOUT POSITIVE REGULATORS

ABSOLUTE MAXIMUM RATINGS (Note 1)

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

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

P PACKAGE:

THERMAL RESISTANCE-JUNCTION TO TAB,

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

DD PACKAGE:

THERMAL RESISTANCE-JUNCTION TO TAB,

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

Junction Temperature Calculation: TJ = TA + (P thermal performance of the device/pc-board system. All of the above assume no ambient airflow.

can be improved with package soldered to 0.5IN2 copper area over backside ground

* θ

plane or internal power plane. θ mounting technique.

can vary from 20ºC/W to > 40ºC/W depending on

θθ

x θJA). The θ

3.0°C/W

60°C/W

3.0°C/W

60°C/W*

numbers are guidelines for the

PACKAGE PIN OUTS

TAB IS V

OUT

P PACKAGE

* Pin 1 is GND for fixed voltage versions.

(Top View)

TAB IS V

OUT

DD PACKAGE

(Top View)

OUT

ADJ / GND*

OUT

ADJ / GND*

Rev. 2.2 12/97

Page 3

PRODUCT DATABOOK 1996/1997

LX8585-xx/8585A-xx

4.6A LOW D

ROPOUT POSITIVE REGULATORS

P RODUCTION DATA SHEET

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 - V

LX8585-00 / 8585A-00 (Adjustable)

= 3V; I

OUT

Reference Voltage LX8585/85A V

= 4.6A. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.)

OUT

Parameter

Symbol

REFIOUT

10mA ≤ I

Line Regulation (Note 2)

Load Regulation (Note 2) Thermal Regulation

∆V

(VIN)

REF

)

VIN - V

REF(IOUT

(Pwr)

TA = 25°C, 20ms pulse

OUT

Ripple Rejection (Note 3) V

Adjust Pin Current I

Adjust Pin Current Change ∆I

ADJ

10mA ≤ I

Dropout Voltage LX8585 ∆V ∆V

∆V

LX8585A ∆V

Minimum Load Current I Maximum Output Current (Note 4) I

Temperature Stability (Note 3) ∆V Long Term Stability (Note 3) ∆V

RMS Output Noise (% of V

) (Note 3) V

OUT

OUT(MIN)VIN

OUT(MAX)

OUT (RMS)TA

1.4V ≤ (V

(t)

OUT

(t) TA = 125°C, 1000 hrs

OUT

Test Conditions Units

= 10mA, TA = 25°C

≤ 4.6A, 1.5V ≤ (V

OUT

= 10mA, 1.5V ≤ (V

OUT

= 3V, 10mA ≤ I

OUT

= 3.3V, f =120Hz, C

OUT

= 10µF, TA = 25°C, I

ADJ

≤ 4.6A, 1.5V ≤ (V

OUT

= 1%, I

REF

= 1%, I = 1%, I

OUT

≤ 7V

- V

OUT

= 125°C, 10Hz £ f £ 10kHz

= 4.6A

= 3A = 4.6A

), V

- V

≤ 7V

OUT

- V

), V

OUT

≤ 7V

≤ 7V, P ≤ P

OUT

), V

≤ 4.6A

= 100µf Tantalum, VIN = 5V

OUT

= 4.6A

OUT

- V

), V

OUT

≤ 7V

MAX

LX8585/85A-00

Min. Typ. Max.

1.238 1.250 1.262 V

1.225 1.250 1.275 V

0.035 0.2 %

0.1 0.5 %

0.01 0.02 %/W

60 83 dB

55 100 µA

0.2 5 µA

1.2 1.4 V

1.1 1.3 V

1.1 1.2 V 210mA

4.6 6 A

0.25 %

0.3 1 %

0.003 %

LX8585-15 / 8585A-15 (1.5V Fixed)

Parameter

Output Voltage (Note 4) V

Line Regulation (Note 2) ∆V

Load Regulation (Note 2) Thermal Regulation (Note 3)

Ripple Rejection (Note 3) C Quiescent Current I

Dropout Voltage LX8585-15 ∆V ∆V

LX8585A-15 ∆V Temperature Stability (Note 3) ∆V Long Term Stability (Note 3) ∆V

RMS Output Noise (% of V

) (Note 3) V

OUT

Symbol

OUTVIN

∆V

OUT(IOUT

∆V

OUT

OUT (RMS)TA

= 5V, I

4.75V ≤ V

4.75V ≤ VIN ≤ 7V

OUT

)

4.75V ≤ V

)

(Pwr)

TA = 25°C, 20ms pulse

0mA ≤ I

∆V

OUT

= 5V, 10mA ≤ I

= 100µF (Tantalum), I

OUT

= 1%, I

OUT

= 1%, I

OUT

= 1%, I

OUT

(T)

(t) TA = 125°C, 1000 hours

= 25°C, 10Hz ≤ f ≤ 10kHz

Test Conditions Units

= 0mA, TA = 25°C

≤ 10V, 0mA ≤ I

≤ 10V

≤ I

OUT

OUT (MAX)

≤ I

, 4.75V ≤ VIN ≤ 10V

OUT (MAX)

≤ I

OUT

OUT (MAX)

≤ 3A, V

OUT

≤ I

OUT

OUT (MAX)

≤ 7A, TA = 25°C, P ≤ P

OUT

= 4.6A, TA = 25°C

OUT

, VIN - V

- V

, VIN - V

OUT

≤ 7V

OUT

≤ 7V

MAX

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. I

is measured under the condition that V

OUT (MAX)

is forced below its nominal value by 100mV.

OUT

LX8585/85A-15

Min. Typ. Max.

1.485 1.50 1.515 V

1.470 1.50 1.530 V

13mV 15mV

2.5 7 mV

0.01 0.02 % / W

65 83 dB

410mA

1.2 1.4 V

1.1 1.3 V

1.1 1.2 V

0.25 %

0.3 1 %

0.003 %

Page 4

PRODUCT DATABOOK 1996/1997

LX8585-xx/8585A-xx

4.6A LOW D

ELECTRICAL CHARACTERISTICS (Continued)

LX8585-33 / 8585A-33 (3.3V Fixed)

Parameter

Output Voltage (Note 4) V

Line Regulation (Note 2) ∆V

Load Regulation (Note 2) Thermal Regulation (Note 3) Ripple Rejection (Note 3) C

Quiescent Current I

Dropout Voltage LX8585-33 ∆V ∆V

LX8585A-33 ∆V Temperature Stability (Note 3) ∆V Long Term Stability (Note 3) ∆V

RMS Output Noise (% of V

) (Note 3) V

OUT

Symbol

OUTVIN

OUT

)

∆V

)

OUT(IOUT

∆V

(Pwr)

OUT

(T)

OUT

(t) TA = 125°C, 1000 hours

OUT

OUT (RMS)TA

ROPOUT POSITIVE REGULATORS

RODUCTION DATA SHEET

Test Conditions Units

= 5V, I

4.75V ≤ VIN ≤ 10V, 0mA ≤ I

4.75V ≤ VIN ≤ 7V

4.75V ≤ V

= 5V, 10mA ≤ I

TA = 25°C, 20ms pulse

OUT

0mA ≤ I

OUT

∆V

OUT

= 25°C, 10Hz ≤ f ≤ 10kHz

= 0mA, TA = 25°C

OUT

≤ 10V

OUT

≤ I

= 100µF (Tantalum), I

≤ I

OUT

= 1%, I

, 4.75V ≤ VIN ≤ 10V

OUT (MAX)

≤ I

OUT

OUT (MAX)

≤ 3A, V

OUT

≤ I

OUT

OUT (MAX)

≤ 7A, TA = 25°C, P ≤ P

OUT

OUT (MAX)

= 4.6A, TA = 25°C

OUT

, VIN - V

- V

, VIN - V

OUT

≤ 7V

OUT

≤ 7V

MAX

LX8585/85A-33

Min. Typ. Max.

3.267 3.3 3.333 V

3.235 3.3 3.365 V

16mV 210mV 515mV

0.01 0.02 % / W

65 83 dB

410mA

1.2 1.4 V

1.1 1.3 V

1.1 1.2 V

0.25 %

0.3 1 %

0.003 %

Rev. 2.2 12/97

Page 5

PRODUCT DATABOOK 1996/1997

LX8585-xx/8585A-xx

4.6A LOW D

ROPOUT POSITIVE REGULATORS

P RODUCTION DATA SHEET

APPLICATION NOTES

The LX8585/85A 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 LX8585/85A 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 15µF Tantalum, 100µF Aluminum None 10µF 47µF Tantalum, 220µF Aluminum 15µF

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. Costeffective 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 compared quickly in order to develop an optimum solution.

Minumum Load

Power Supply

LX8585/85A

ADJ

FIGURE 1 — DYNAMIC INPUT and OUTPUT TEST

OUT

Star Ground

(Larger resistor)

Full Load (Smaller resistor)

<< R

DSON

1 sec

10ms

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 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 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.

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 shortcircuited 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-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, 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.

Page 6

PRODUCT DATABOOK 1996/1997

LX8585/85A

OUT

ADJ

Parasitic

Line Resistance

Connect R1 to Case of Regulator

Connect R2 to Load

LX8585-xx/8585A-xx

4.6A LOW D

RODUCTION DATA SHEET

ROPOUT POSITIVE REGULATORS

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 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.

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:

C = 1 / (6.28 * F

* R1)

where: C ≡ the value of the capacitor in Farads;

select an equal or larger standard value.

≡ 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:

M = V

OUT/VREF

where: M ≡ a multiplier for the ripple seen when the

ADJ pin is optimally bypassed.

= 1.25V.

REF

For example, if V

= 2.5V the output ripple will be:

OUT

M = 2.5V/1.25V= 2

LX8585/85A

ADJ

OUT

REF

ADJ

50µA

= V

OUT

REF

FIGURE 2 — BASIC ADJUSTABLE REGULATOR

1 + + I

ADJ

LOAD REGULATION

Because the LX8585/85A 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:

R2+R1

= RP

Peff

where: R





≡ 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 R

Peff

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.

OUTPUT VOLTAGE

The

LX8585/85A

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 I through R1, it represents a small error and can usually be ignored.

ICs develop a 1.25V reference voltage between the

is very small and constant when compared with the current

ADJ

FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION

Rev. 2.2 12/97

Page 7

PRODUCT DATABOOK 1996/1997

LX8585-xx/8585A-xx

4.6A LOW D

ROPOUT POSITIVE REGULATORS

P RODUCTION DATA SHEET

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 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 V during transients.

IN (MIN)

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: V

= 5V

= 2.8V, I

OUT

Ambient Temp., T R

= 2.7°C/W for TO-220

θJT

300 ft/min airflow available

OUT

= 5.0A

= 50°C

Find: Proper Heat Sink to keep IC's junction

temperature below 125°C.**

Solution: The junction temperature is:

where: P

= PD (R

θJT

θCS

+ R

θJT

θCS

θSA

) + T

≡ Dissipated power.

≡ Thermal resistance from the junction to the

mounting tab of the package.

≡ 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.)

≡

Thermal resistance from the mounting surface

θSA

to ambient (thermal resistance of the heat sink).

≡ Heat sink temperature.

= V

IN (MIN)

where: V

+ V

OUT

IN (MIN)

OUT

DROPOUT (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 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-toheat-sink interface is strongly recommended. If the case of the device must be electrically isolated, a thermally conductive spacer

First, find the maximum allowable thermal resistance of the

heat sink:

TJ - T

IN(MAX)

- V

OUT

θJT

+ R

) I

125°C - 50°C

(5.0V-2.8V) * 5.0A

)

θCS

= (5.0V-2.8V) * 5.0A

OUT

= 11.0W

= - (R

θSA

=(V

= - (2.7°C/W + 1.0°C/W)

θSA

= 3.1°C/W

Next, select a suitable heat sink. The selected heat sink must have

≤ 3.1°C/W. Thermalloy heatsink 6296B has R

θSA

300ft/min air flow.

= 3.0°C/W with

θSA

Finally, verify that junction temperature remains within speci-

fication using the selected heat sink:

= 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.

Page 8

PRODUCT DATABOOK 1996/1997

LX8585-xx/8585A-xx

(Note A)

10µF

LX8585/85A

ADJ

* C1 improves ripple rejection. X

should be » R1 at ripple

frequency.

4.6A LOW D

OUT

365W

(Note A)

R1 121 1%

ROPOUT POSITIVE REGULATORS

RODUCTION DATA SHEET

TYPICAL APPLICATIONS

OUT

(Note A)

150µF

C1 10µF*

* Needed if device is far from filter capacitors.

** V

FIGURE 5 — 1.2V - 8V ADJUSTABLE REGULATORFIGURE 4 — IMPROVING RIPPLE REJECTION

LX8585/85A

OUT

ADJ

10µF

C1* 10µF

= 1.25V 1 +

OUT

121W 1%

LX8585/85A

ADJ

R2 1k

R2 R1

100µF

OUT

R1 121W

OUT

C2 100µF

Note A: V

= (Intended V

IN (MIN)

TTL

utput

FIGURE 6 — 5V REGULATOR WITH SHUTDOWN

2N3904

365 1%

LX8585-33/85A-33

10µF Tantalum

or 100µF Aluminum

GND

OUT

3.3V

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

) + (V

OUT

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.

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.

DROPOUT (MAX)

)

Rev. 2.2 12/97