Datasheet LX8554-33CP, LX8554-33CDD, LX8554-00CP, LX8554-00CDD Datasheet (Microsemi Corporation)

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LX8554-xx

5A E

XTREMELY LOW DROPOUT POSITIVE REGULATORS

8554

THE INFINITE POWER OF INNOVATION

DESCRIPTION KEY FEATURES

The LX8554 series ICs are very low dropout three-terminal positive regulators with 5A rated output current. This product family is ideally suited for Pentium sor and Power PC

applications requir-

Proces-

ing fast transient response. The LX8554 is guaranteed to have a dropout volt- age under 1V at 5A load, making it ideal to provide well-regulated outputs of 2.5V to 3.6V with input supply as low as 4.75V. Fixed versions are also available and are specified in the Available Options table below.

Current limit is trimmed above 5.1A to

ensure adequate output current and con-

trolled short-circuit current. On-chip thermal limiting provides protection against any combination of overload that would create excessive junction temperatures.

The LX8554 series products are available in both through-hole and surfacemount versions of industry standard 3-pin TO-220 / TO-263 power packages.

The LX8554 family of products are ideal for use in multiple processor applications where output voltage is jumper selected. The LX8554 ICs offer precision output as well as low supply operation (see application below). For higher current applications see the LX8584 series of products.

PRODUCT HIGHLIGHT

TYPICAL APPLICATION OF THE LX8554 IN A FLEXIBLE MOTHERBOARD WITH

OUTPUT VOLTAGE SELECTABLE VIA JUMPERS "JP1" AND "JP2"

P RODUCTION DATA SHEET

■■

■ THREE-TERMINAL ADJUSTABLE OR FIXED

■■

OUTPUT

■■

■ GUARANTEED

■■

■ OUTPUT CURRENT OF 5A

■■

p FAST TRANSIENT RESPONSE p 1% VOLTAGE REFERENCE INITIAL

ACCURACY

p OUTPUT SHORT-CIRCUIT PROTECTION

p BUILT-IN THERMAL SHUTDOWN

■ EVALUATION BOARD AVAILABLE:

REQUEST LXE9001 EVALUATION KIT

APPLICATIONS

■ PENTIUM PROCESSOR SUPPLIES

■ POWER PC SUPPLIES

■ MICROPROCESSOR SUPPLIES

■ LOW VOLTAGE LOGIC SUPPLIES

■ BATTERY POWERED CIRCUIT

■ POST REGULATOR FOR SWITCHING SUPPLY

≤≤

≤ 1V HEADROOM AT 5A

≤≤

VIN ³ 4.75 IN

1500µF, 6.3V

Sanyo MVGX Series

JP1 JP2 OUTPUT VOLTAGE

Open Open 3.6V Open Short 3.45V

Short Short 3.3V

LX8554

OUT

ADJ

REF

R1 121

200

14.7 1%

JP1

= V

OUT

REF

JP2

1 + + I

PACKAGE ORDER INFORMATION

(°C)

Plastic TO-220

3-pin

0 to 125 LX8554-xxCP LX8554-xxCDD

Note: All surface-mount packages are available in Tape & Reel.

Append the letter "T" to part number. (i.e. LX8554-00CDDT)

"xx" refers to output voltage, please see table above.

(See Table Below)

3x 1500µF

6.3V Sanyo MVGX Series

ADJ

Plastic T0-263

3-pin

AVAILABLE OPTIONS PER PART #

Part #

LX8554-00 Adjustable LX8554-33 3.3V

Other voltage options may be available —

Please contact factory for details.

Output

Voltage

FOR FURTHER INFORMATION CALL (714) 898-8121

11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841

Page 2

LX8554-xx

PRODUCT DATABOOK 1996/1997

5A E

XTREMELY LOW DROPOUT POSITIVE REGULATORS

RODUCTION DATA SHEET

ABSOLUTE MAXIMUM RATINGS (Note 1)

Power Dissipation .................................................................................. Internally Limited

Input Voltage................................................................................................................ 10V

Input to Output Voltage Differential ........................................................................... 10V

Operating Junction Temperature

Plastic (P 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,

θθ

DD PACKAGE:

THERMAL RESISTANCE-JUNCTION TO TAB,

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

Junction Temperature Calculation: TJ = TA + (P

numbers are guidelines for the thermal performance of the device/pc-board system.

The θ

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 θ

2.7°C/W

60°C/W

2.7°C/W

60°C/W *

PACKAGE PIN OUTS

TAB IS V

OUT

P PACKAGE

(Top View)

* Pin 1 is GND for fixed voltage versions.

TAB IS V

OUT

DD PACKAGE

* Pin 1 is GND for fixed voltage versions.

(Top View)

ADJ / GND*

OUT

ADJ / GND*

OUT

Rev. 1.1 1/97

Page 3

PRODUCT DATABOOK 1996/1997

LX8554-xx

5A E

XTREMELY LOW DROPOUT POSITIVE REGULATORS

P RODUCTION DATA SHEET

ELECTRICAL CHARACTERISTICS

(Unless otherwise specified, these specifications apply over the operating ambient temperatures for the LX8554-xxC with 0°C ≤ TA ≤ 125°C; V

= 5A. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.)

OUT

LX8554-00 (Adjustable)

Parameter

Reference Voltage V

Symbol

REFIOUT

10mA ≤ I

Line Regulation (Note 2)

Load Regulation (Note 2)

Thermal Regulation

∆V

)

REF(VIN

)

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 ∆V ∆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

1.4V ≤ (V

OUT(MAX)

(T)

OUT

(t) TA = 125°C, 1000 hrs

OUT

OUT (RMS)TA

Test Conditions Units

= 10mA, TA = 25°C

≤ 5A, 1.5V ≤ (V

OUT

= 10mA, 1.5V ≤ (V

OUT

= 3V, 10mA ≤ I

OUT

= 3.3V, f =120Hz, C

OUT

= 10µF, I

ADJ

= 1%, I

REF

OUT

≤ 5A, 1.5V ≤ (V

OUT

≤ 7V

- V

OUT

= 125°C, 10Hz ≤ f ≤ 10kHz

= 5A

), V

≤ 7V

- V

OUT

- V

), V

OUT

≤ 7V

≤ 7V, P ≤ P

MAX

OUT

), V

≤ 5A

= 100µf Tantalum, VIN = 5V

- V

), V

OUT

≤ 7V

LX8554-00

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

0.8 1 V 210mA

5.1 7 A

0.25 %

0.003 %

- V

= 3V;

OUT

LX8554-33 (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 ∆V ∆V

Maximum Output Current I

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 (MAX)VIN

OUT

OUT (RMS)TA

= 5V, I

OUT

4.75V ≤ VIN ≤ 10V, 0mA ≤ I

4.75V ≤ VIN ≤ 7V

OUT

)

4.75V ≤ VIN ≤ 10V

)

= 5V, 10mA ≤ I

(Pwr)

TA = 25°C, 20ms pulse

= 100µF (Tantalum), I

OUT

0mA ≤ I

= 1%, I

OUT

≤ 7V

(T)

(t) TA = 125°C, 1000 hours

= 25°C, 10Hz ≤ f ≤ 10kHz

Test Conditions Units

= 0mA, TA = 25°C

≤ I

OUT

OUT (MAX)

≤ I

, 4.75V ≤ VIN ≤ 10V

OUT (MAX)

≤ I

OUT

OUT (MAX)

≤ 5A, TA = 25°C, P ≤ P

OUT

= 5A

OUT

, VIN - V

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

LX8554-33

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

0.8 1 V

5.1 7 A

0.25 %

0.3 1 %

0.003 %

Page 4

PRODUCT DATABOOK 1996/1997

LX8554-xx

5A E

XTREMELY LOW DROPOUT POSITIVE REGULATORS

RODUCTION DATA SHEET

The LX8554 is an easy to use Low-Dropout (LDO) voltage regulator. It has 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 LX8554A. Please see the table below for recommended minimum capacitor values.

The regulator offers a more tightly controlled reference voltage tolerance and superior reference stability when measured against the older pin-compatible regulator types that it replaces.

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

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.

APPLICATION NOTES

Power Supply

FIGURE 1 — DYNAMIC INPUT and OUTPUT TEST

OVERLOAD RECOVERY

Like almost all IC power regulators, the LX8554 is 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 LX8554 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.

Minumum Load

LX8554

ADJ

OUT

Star Ground

(Larger resistor)

Full Load (Smaller resistor)

<< R

DSON

1 sec

10ms

Rev. 1.1 1/97

Page 5

PRODUCT DATABOOK 1996/1997

LX8554

OUT

ADJ

Parasitic

Line Resistance

Connect R1 to Case of Regulator

Connect R2 to Load

5A E

XTREMELY LOW DROPOUT POSITIVE REGULATORS

P RODUCTION DATA SHEET

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

F R1 ≡ the value of resistor R1 in ohms

At a ripple frequency of 120Hz, with R1 = 100Ω:

C = 1 / (6.28 * 120Hz

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

For example, if V

M = 2.5V/1.25V= 2

* R1)

select an equal or larger standard value.

≡ the ripple frequency in Hz

100Ω) = 13.3µF

ADJ pin is optimally bypassed.

= 1.25V.

REF

= 2.5V the output ripple will be:

OUT

LX8554-xx

LX8554

ADJ

R2 R1

OUT

ADJ

OUT

REF

Peff

ADJ

50µA

= V

OUT

FIGURE 2 — BASIC ADJUSTABLE REGULATOR

1 + + I

REF

LOAD REGULATION

Because the LX8554 is a three-terminal device, 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

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

LX8554

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

is very small and constant when compared with the current

ADJ

FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION

Page 6

PRODUCT DATABOOK 1996/1997

LX8554-xx

5A E

XTREMELY LOW DROPOUT POSITIVE REGULATORS

RODUCTION DATA SHEET

LOAD REGULATION (continued)

Even when the circuit is optimally configured, 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.

APPLICATION NOTES

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

OUT

Ambient Temp., T R

θJT

300 ft/min airflow available

Find: Proper Heat Sink to keep IC's junction

temperature below 125°C.**

Solution: The junction temperature is:

= PD (R

where: P

IN (MIN)

θJT

θCS

θSA

= 2.8V, I

OUT

= 5.0A

= 50°C

= 2.7°C/W for TO-220

+ 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 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 LX8554 regulator has internal power and thermal limiting circuitry designed to protect the 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

θJT

OUT

+ 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.

Rev. 1.1 1/97

Page 7

PRODUCT DATABOOK 1996/1997

LX8554

OUT

ADJ

OUT

R1 121W

R2 1k

C1* 10µF

* Needed if device is far from filter capacitors.

** V

OUT

= 1.25V 1 +

C2 100µF

R2 R1

(Note A)

5A E

XTREMELY LOW DROPOUT POSITIVE REGULATORS

P RODUCTION DATA SHEET

TYPICAL APPLICATIONS

LX8554-xx

(Note A)

10µF

* C1 improves ripple rejection. X

should be » R1 at ripple

frequency.

LX8554

ADJ

OUT

365W

(Note A)

TTL

utput

R1 121 1%

OUT

150µF

C1 10µF*

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

LX8554

ADJ

OUT

121W

10µF

2N3904

365 1%

100µF

Note A: V

= (Intended V

IN (MIN)

10µF Tantalum

or 100µF Aluminum

OUT

) + (V

FIGURE 6 — 5V REGULATOR WITH SHUTDOWN

LX8554-33

OUT

GND

FIGURE 7 — FIXED 3.3V OUTPUT REGULATOR

DROPOUT (MAX)

Power PC is a trademark of International Business Machines Corporation.

)

Pentium is a registered trademark of Intel Corporation.

3.3V

Min. 15µF Tantalum or 100µF Aluminum capacitor. May be increased without limit. ESR must be less than 50mW .