LX8117A-25CDT-TR [MICROSEMI]

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型号：	LX8117A-25CDT-TR
厂家：	Microsemi
描述：	暂无描述稳压器
文件：	总9页 (文件大小：223K)
中文：	中文翻译
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LIN DOC #: 8117

LX8117-xx/8117A-xx/8117B-xx

0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS

P R O D U C T I O N D A T A S H E E T

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

DESCRIPTION

KEY FEATURES

■ 0.2% Line Regulation Maximum

The LX8117/8117A/8117B series are

positive Low Dropout (LDO) regulators.

At the designed maximum load current,

theLX8117seriesdropoutvoltageisguar-

anteed to be 1.2V or lower at 0.8A

(LX8117A 1.3V @ 1A). The dropout

voltage decreases with load current.

An adjustable output voltage version

of the LX8117/17A/17B is available, as

well as versions with fixed outputs of

2.5V, 2.85V, 3.3V and 5V. The 2.85V

version is specifically designed for use

as a component of active termination

networks for the SCSI bus. On-chip

trimmingoftheinternalvoltagereference

allows specification of the initial output

voltage to within ±1% of its nominal

value. The output current-limit point is

also trimmed, which helps to minimize

stress on both the regulator and the

system power source when they are

operated under short-circuit conditions.

The regulator's internal circuitry will

operate at input-to-output differential

voltages down to 1V.

■ 0.4% Load Regulation Maximum

■ Output Current Of 800mA

Most regulator circuit designs include

outputcapacitorswithvaluesintherange

of tens to hundreds of microfarads or

more. The LX8117/17A/17B typically

requires at least 10µF of output capaci-

tance for stable operation.

PNP-type regulators can waste current

equal to as much as 10 percent of their

output as a quiescent current which flows

directly to ground, bypassing the load.

Quiescent current from the LX8117/17A/

17B flows through the load, increasing

power-useefficiencyandallowingcooler

operation.

The LX8117 is available in low-profile

plastic SOT-223 and D-Pak packages for

applicationswherespaceisatapremium.

The LX8117 is also available in a plastic

TO-263 package for instances when the

thermal resistance from the circuit die to

the environment must be minimized.

■ Regulates Down To 1.2V Dropout

(LX8117) And 1.3V Dropout (LX8117A)

■ Operates Down To 1V Dropout

■ Space Saving SOT-223 Surface

Mount Package

■ Guaranteed Dropout Voltage At Multiple

Current Levels

■ Three-Terminal Adjustable Or Fixed 2.5V,

2.85V, 3.3V & 5V

APPLICATIONS

■ Battery Chargers

■ Active SCSI Terminators

■ 5V To 3.3V Linear Regulators

■ High-Efficiency Linear Regulators

■ Post Regulators For Switching Supplies

AVAILABLE OPTIONS PER PART #

NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.

Output

Part #

Voltage

PRODUCT HIGHLIGHT

LX8117/8117A/8117B-00 Adjustable

LX8117/8117A/8117B-25

LX8117/8117A/8117B-28

LX8117/8117A/8117B-33

LX8117/8117A/8117B-05

2.5V

2.85V

3.3V

ACTIVE TERMINATOR FOR SCSI-2 BUS

110

Ω

LX8117-28

IN OUT

18 to 27

Lines

GND

4.75V to

5.25V

22µF

10µF

110Ω

PACKAGE ORDER INFORMATION

O/P

Current

Plastic SOT-223

3-pin

Plastic T0-263

3-pin

Plastic T0-252

T_A(°C)

(D-Pak) 3-pin

0.8A

1.0A

1.2A

LX8117-xxCST

LX8117A-xxCST

LX8117B-xxCST

LX8117-xxCDD

LX8117-xxCDT

LX8117A-xxCDT

LX8117B-xxCDT

0 to 125

LX8117A-xxCDD

LX8117B-xxCDD

Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number

(i.e. LX8117-28CSTT). "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

Rev. 1.4 3/99

P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7

LX8117-xx/8117A-xx/8117B-xx

0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS

P R O D U C T I O N D A T A S H E E T

ABSOLUTE MAXIMUM RATINGS (Note 1)

PACKAGE PIN OUTS

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

Input Voltage

TAB IS V_OUT

LX8117-00/8117A-00/8117B-00 (Adj.) ..................................................................... 15V

LX8117-33/8117A-33/8117B-33 (3.3V), LX8117-05/8117A-05/8117B-05 (5.0V).... 15V

LX8117-25/8117A-25/8117B-25 (2.5V), LX8117-28/8117A-28/8117B-28 (2.85V).. 12V

Surge Voltage ............................................................................................................... 15V

Operating Junction Temperature

3. IN

2. OUT

1. ADJ / GND

Plastic (ST, DD & DT Packages) .......................................................................... 150°C

Storage Temperature Range ...................................................................... -65°C to 150°C

Lead Temperature (Soldering, 10 seconds) ............................................................. 300°C

Short-Circuit Protection....................................................................................... Indefinite

ST PACKAGE

(Top View)

TAB IS V_OUT

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.

OUT

THERMAL DATA

ADJ / GND

ST PACKAGE:

THERMAL RESISTANCE-JUNCTION TO TAB, θ_JT

THERMAL RESISTANCE-JUNCTION TO AMBIENT, θ_JA

DD PACKAGE:

15°C/W

DD PACKAGE (D²Pak)

*150°C/W

(Top View)

THERMAL RESISTANCE-JUNCTION TO TAB, θ_JT

THERMAL RESISTANCE-JUNCTION TO AMBIENT, θ_JA

DT PACKAGE:

10°C/W

TAB IS V_OUT

*60°C/W

3. IN

2. OUT

THERMAL RESISTANCE-JUNCTION TO TAB, θ_JC

THERMAL RESISTANCE-JUNCTION TO AMBIENT, θ_JA

9°C/W

*80°C/W

1. ADJ / GND

Junction Temperature Calculation: T_J= T_A+ (P_Dx θ_JA). The θ_JAnumbers are guidelines for the

thermalperformanceofthedevice/pc-boardsystem. Alloftheaboveassumenoambientairflow.

* θ_JAcan be improved with package soldered to 0.5IN²copper area over backside ground

plane or internal power plane. θ_JAcan vary from 20ºC/W to > 40ºC/W depending on

mounting technique. (See Application Notes Section: Thermal Considerations)

DT PACKAGE (D-Pak)

(Top View)

BLOCK DIAGRAM

V_IN

Bias

Circuit

Bandgap

Circuit

Control

Circuit

Output

Circuit

Thermal

Limit Circuit

V_OUT

Current

Limit Circuit

ADJ

Rev. 1.4 3/99

P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7

LX8117-xx/8117A-xx/8117B-xx

0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS

P R O D U C T I O N D A T A S H E E T

RECOMMENDED OPERATING CONDITIONS

(Note 2)

Recommended Operating Conditions

Parameter

Symbol

Units

Min.

Typ.

Max.

Input Voltage

Operating Voltage

LX8117(A/B)-00 / 8117(A/B)-05

LX8117(A/B)-25 / -28 / -33

LX8117(A/B)-00

Input-Output Differential

125

°C

Operating Ambient Temperature Range

Note 2. Range over which the device is functional.

ELECTRICAL CHARACTERISTICS

(Unless otherwise specified: 0°C ≤ T ≤ 125°C, I_MAX= 0.8A for the LX8117-xx, I_MAX= 1.0A for the LX8117A-xx, and I_MAX= 1.2A for the LX8117B-xx.)

LX8117-00 / 8117A-00 / 8117B-00 (Adjustable)

LX8117 / 17A / 17B-00

Parameter

Symbol

Test Conditions

Units

Min. Typ.

Max.

1.238 1.250 1.262

1.225 1.250 1.270

Reference Voltage

V_REF

I_OUT= 10mA, (V_IN- V_OUT) = 2V, T_J= 25°C

10mA ≤ I_OUT≤ I_{OUT (MAX)}, 1.4V ≤ (V - V_OUT) ≤ 10V

0.05

0.15

0.97

1.00

1.05

1.15

950

1200

1500

0.5

0.2

0.4

1.10

1.15

1.20

1.30

Line Regulation (Note 3)

Load Regulation (Note 3)

∆V_REF(V ) I_OUT= 10mA, 1.5V ≤ (V_IN- V_OUT) ≤ 7V

∆V_REF(I_OUT

)

(V_IN- V_OUT) = 3V, 10mA ≤ I_OUT≤ I_{OUT (MAX)}

I_OUT= 100mA

Dropout Voltage

(Note 4)

∆V

I_OUT= 500mA

LX8117-00

I_OUT= I_{OUT (MAX)}

LX8117A/B-00

LX8117-00

I_OUT= I_{OUT (MAX)}

I_{OUT (MAX)}(V_IN- V_OUT) = 5V, T_J= 25°C

(V_IN- V_OUT) = 5V, T_J= 25°C

800

1000

1200

%/W

µA

Current Limit

LX8117A-00

LX8117B-00

Minimum Load Current (Note 5)

Thermal Regulation

(V_IN- V_OUT) = 5V, T_J= 25°C

0.2

I_{OUT (MIN)}

V ≤ 10V

0.08

∆V_OUT(Pwr) T_A= 25°C, 30ms pulse

Ripple Rejection

Adjust Pin Current

f_RIPPLE=120Hz, (V - V_OUT) = 3V, V_RIPPLE= 1Vp-p

100

I_ADJ

∆I_ADJ

0.2

Adjust Pin Current Change

Temperature Stability

Long Term Stability

10mA ≤ I_OUT≤ I_{OUT (MAX)}, 1.4V ≤ (V - V_OUT) ≤ 10V

0.5

0.3

∆V_OUT(T)

∆V_OUT(t) T_A= 125°C, 1000 hours

V_{OUT (RMS)}10Hz ≤ f ≤ 10kHz

0.003

RMS Output Noise (% of V_OUT

)

Notes: 3. See thermal regulation specification for changes in output voltage due to heating effects. Load regulation and line regulation are measured at a constant junction

temperature by low duty cycle pulse testing.

4. Dropout voltage is specified over the full output current range of the device. Dropout voltage is defined as the minimum input/output differential measured

at the specified output current. Test points and limits are also shown on the Dropout Voltage Curve.

5. Minimum load current is defined as the minimum output current required to maintain regulation.

(Other Voltage Options on following pages.)

Rev. 1.4 3/99

P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7

LX8117-xx/8117A-xx/8117B-xx

0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS

P R O D U C T I O N D A T A S H E E T

ELECTRICAL CHARACTERISTICS (continued)

LX8117-25 / 8117A-25 / 8117B-25 (2.5V Fixed)

LX8117 / 17A / 17B-25

Min. Typ. Max.

Parameter

Symbol

Test Conditions

Units

2.475 2.500 2.525

2.450 2.500 2.550

Output Voltage

V_OUT

I_OUT= 10mA, V_IN= 5V, T_A= 25°C

0mA ≤ I_OUT≤ I_{OUT (MAX)}, 4.75V ≤ V_IN≤ 10V

I_OUT= 0mA, 4.25V ≤ V_IN≤ 10V

V_IN= 4.25V, 0mA ≤ I_OUT≤ I_{OUT (MAX)}

I_OUT= 100mA

(V_IN)

∆V_OUT

Line Regulation (Note 3)

Load Regulation (Note 3)

Dropout Voltage

(Note 4)

∆V_OUT(I_OUT

)

∆V

0.97

1.00

1.05

1.15

950

1200

1500

4.5

1.10

1.15

1.20

1.30

I_OUT= 500mA

I_OUT= I_{OUT (MAX)}

LX8117-25

LX8117A/B-25

LX8117-25

LX8117A-25

LX8117B-25

I_OUT= I_{OUT (MAX)}

800

1000

1200

%/W

Current Limit

I_{OUT (MAX)}(V_IN- V_OUT) = 5V, T_J= 25°C

(V_IN- V_OUT) = 5V, T_J= 25°C

Quiescent Current

Thermal Regulation

Ripple Rejection

Temperature Stability

Long Term Stability

I_Q

∆V_OUT(Pwr) T_A= 25°C, 30ms pulse

f_RIPPLE=120Hz, (V_IN- V_OUT) = 3V, V_RIPPLE= 1Vp-p

V_IN≤ 10V

0.08

0.2

0.5

0.3

∆V_OUT(T)

∆V_OUT(t) T_A= 125°C, 1000 hours

V_{OUT (RMS)}10Hz ≤ f ≤ 10kHz

0.003

RMS Output Noise (% of V_OUT

)

LX8117-28 / 8117A-28 / 8117B-28 (2.8V Fixed)

LX8117 / 17A / 17B-28

Min. Typ. Max.

Parameter

Symbol

Test Conditions

Units

2.820 2.850 2.880

2.790 2.850 2.910

Output Voltage

V_OUT

I_OUT= 10mA, V_IN= 4.85V, T_A= 25°C

0mA ≤ I_OUT≤ I_{OUT (MAX)}, 4.25V ≤ V_IN≤ 10V

0mA ≤ I_OUT≤ 500mA, V_IN= 3.95V

I_OUT= 0mA, 4.25V ≤ V_IN≤ 10V

V_IN= 4.25V, 0mA ≤ I_OUT≤ I_{OUT (MAX)}

I_OUT= 100mA

(V_IN)

∆V_OUT

Line Regulation (Note 3)

Load Regulation (Note 3)

∆V_OUT(I_OUT

)

0.97

1.00

1.05

1.15

950

1200

1500

4.5

1.10

1.15

1.20

1.30

Dropout Voltage

(Note 4)

∆V

I_OUT= 500mA

LX8117-28

LX8117A/B-28

LX8117-28

LX8117A-28

LX8117B-28

I_OUT= I_{OUT (MAX)}

800

1000

1200

%/W

Current Limit

I_{OUT (MAX)}(V_IN- V_OUT) = 5V, T_J= 25°C

(V_IN- V_OUT) = 5V, T_J= 25°C

V_IN≤ 10V

Quiescent Current

Thermal Regulation

Ripple Rejection

I_Q

∆V_OUT(Pwr) T_A= 25°C, 30ms pulse

f_RIPPLE=120Hz, (V_IN- V_OUT) = 3V, V_RIPPLE= 1Vp-p

0.08

0.2

0.5

Temperature Stability

Long Term Stability

∆V_OUT(T)

∆V_OUT(t) T_A= 125°C, 1000 hours

V_{OUT (RMS)}10Hz ≤ f ≤ 10kHz

0.3

0.003

RMS Output Noise (% of V_OUT

)

Notes: 3. See thermal regulation specification for changes in output voltage due to heating effects. Load regulation and line regulation are measured at a constant junction

temperature by low duty cycle pulse testing.

4. Dropout voltage is specified over the full output current range of the device. Dropout voltage is defined as the minimum input/output differential measured

at the specified output current. Test points and limits are also shown on the Dropout Voltage Curve.

5. Minimum load current is defined as the minimum output current required to maintain regulation.

Rev. 1.4 3/99

P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7

LX8117-xx/8117A-xx/8117B-xx

0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS

P R O D U C T I O N D A T A S H E E T

ELECTRICAL CHARACTERISTICS (continued)

LX8117-33 / 8117A-33 / 8117B-33 (3.3V Fixed)

LX8117 / 17A / 17B-33

Min. Typ. Max.

Parameter

Symbol

Test Conditions

Units

3.267 3.300 3.333

3.235 3.300 3.365

Output Voltage

V_OUT

I_OUT= 10mA, V = 5V, T_A= 25°C

0mA ≤ I_OUT≤ I_{OUT (MAX)}, 4.75V ≤ V_IN≤ 10V

(V_IN)

∆V_OUT

Line Regulation (Note 3)

Load Regulation (Note 3)

Dropout Voltage

(Note 4)

I_OUT= 0mA, 4.25V ≤ V_IN≤ 10V

V_IN= 4.25V, 0mA ≤ I_OUT≤ I_{OUT (MAX)}

I_OUT= 100mA

∆V_OUT(I_OUT

)

∆V

0.97

1.00

1.05

1.15

950

1200

1500

4.5

1.10

1.15

1.20

1.30

I_OUT= 500mA

I_OUT= I_{OUT (MAX)}

LX8117-33

LX8117A/B-33

LX8117-33

I_OUT= I_{OUT (MAX)}

800

1000

1200

%/W

Current Limit

I_{OUT (MAX)}(V_IN- V_OUT) = 5V, T_J= 25°C

(V_IN- V_OUT) = 5V, T_J= 25°C

LX8117A-33

LX8117B-33

(V_IN- V_OUT) = 5V, T_J= 25°C

0.2

Quiescent Current

Thermal Regulation

Ripple Rejection

Temperature Stability

Long Term Stability

I_Q

∆V_OUT(Pwr) T_A= 25°C, 30ms pulse

f_RIPPLE=120Hz, (V_IN- V_OUT) = 3V, V_RIPPLE= 1Vp-p

V_IN≤ 10V

0.08

0.5

∆V_OUT(T)

0.3

∆V_OUT(t) T_A= 125°C, 1000 hours

V_{OUT (RMS)}10Hz ≤ f ≤ 10kHz

0.003

RMS Output Noise (% of V_OUT

)

LX8117-05 / 8117A-05 / 8117B-05 (5.0V Fixed)

LX8117 / 17A / 17B-05

Min. Typ. Max.

Parameter

Symbol

Test Conditions

Units

4.950 5.000 5.050

4.900 5.000 5.100

Output Voltage

V_OUT

I_OUT= 10mA, V = 7V, T_A= 25°C

0mA ≤ I_OUT≤ I_{OUT (MAX)}, 6.50V ≤ V_IN≤ 10V

(V_IN)

∆V_OUT

Line Regulation (Note 3)

Load Regulation (Note 3)

Dropout Voltage

(Note 4)

I_OUT= 0mA, 6.5V ≤ V_IN≤ 10V

V_IN= 6.5V, 0mA ≤ I_OUT≤ I_{OUT (MAX)}

I_OUT= 100mA

∆V_OUT(I_OUT

)

2.5

∆V

0.97

1.00

1.05

1.15

950

1200

1500

4.5

1.10

1.15

1.20

1.30

I_OUT= 500mA

I_OUT= I_{OUT (MAX)}

LX8117-05

LX8117A/B-05

LX8117-05

I_OUT= I_{OUT (MAX)}

800

1000

1200

%/W

Current Limit

I_{OUT (MAX)}(V_IN- V_OUT) = 5V, T_J= 25°C

(V_IN- V_OUT) = 5V, T_J= 25°C

LX8117A-05

LX8117B-05

(V_IN- V_OUT) = 5V, T_J= 25°C

0.2

Quiescent Current

Thermal Regulation

Ripple Rejection

Temperature Stability

Long Term Stability

I_Q

∆V_OUT(Pwr) T_A= 25°C, 30ms pulse

f_RIPPLE=120Hz, (V_IN- V_OUT) = 3V, V_RIPPLE= 1Vp-p

V_IN≤ 10V

0.08

0.5

∆V_OUT(T)

0.3

∆V_OUT(t) T_A= 125°C, 1000 hours

V_{OUT (RMS)}10Hz ≤ f ≤ 10kHz

0.003

RMS Output Noise (% of V_OUT

)

Notes: 3. See thermal regulation specification for changes in output voltage due to heating effects. Load regulation and line regulation are measured at a constant junction

temperature by low duty cycle pulse testing.

4. Dropout voltage is specified over the full output current range of the device. Dropout voltage is defined as the minimum input/output differential measured

at the specified output current. Test points and limits are also shown on the Dropout Voltage Curve.

5. Minimum load current is defined as the minimum output current required to maintain regulation.

Rev. 1.4 3/99

P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7

LX8117-xx/8117A-xx/8117B-xx

0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS

P R O D U C T I O N D A T A S H E E T

APPLICATION NOTES

Minumum Load

(Larger resistor)

The LX8117 series ICs are easy to use Low-Dropout (LDO) voltage

Power Supply

OUT

LX8117-xx

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 LX8117 series.

Please see the table below for recommended minimum capacitor

values.

Full Load

(Smaller resistor)

ADJ

R_DSON<< R_L

C₁

C₂

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 LX8117 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 LX8117 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. Now consider the

casewheretheregulatorissupplyingregulatedvoltagetoaresistive

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

throughtheregulatortodevelopthedesignedoutputvoltageacross

theloadresistance. Iftheoutputresistorisshort-circuitedtoground,

theinput-to-outputvoltagedifferenceacrosstheregulatorsuddenly

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

permittheregulatortosupplytoitsoutputterminal. Whentheshort

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

bytheSOAcircuit,basedonthelargeinput-to-outputvoltageacross

theregulatoratthetimetheshortcircuitisremovedfromtheoutput.

RECOMMENDED CAPACITOR VALUES

INPUT

OUTPUT

ADJ

None

15µF

10µF

15µF Tantalum, 100µF Aluminum

47µF Tantalum, 220µF Aluminum

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.

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 quickly compared in order to develop an optimum

solution.

Rev. 1.4 3/99

P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7

LX8117-xx/8117A-xx/8117B-xx

0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS

P R O D U C T I O N D A T A S H E E T

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.

LX8117-xx

OUT

V_IN

V_OUT

ADJ

V_REF

I_ADJ

50µA

RIPPLE REJECTION

V_OUT= V_REF1 +

+ I_ADJR2

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 LX8117 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

connectedtotheload,theeffectiveresistancebetweentheregulator

and the load would be:

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

select an equal or larger standard value.

F_R≡ the ripple frequency in Hz

R1 ≡ the value of resistor R1 in ohms

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

R_Peff= R_P

where: R_P≡ Actual parasitic line resistance.

M = V_OUT/V_REF

When the circuit is connected as shown in Figure 3, the parasitic

resistance appears as its actual value, rather than the higher R_Peff.

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

ADJ pin is optimally bypassed.

V_REF= 1.25V.

Para^Psitic

LX8117-xx

OUT

Line Resistance

For example, if V_OUT= 2.5V the output ripple will be:

M = 2.5V/1.25V= 2

V_IN

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.

R_L

OUTPUT VOLTAGE

Connect

The LX8117 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.

BecauseI_ADJisverysmallandconstantwhencomparedwiththecurrent

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

to Load

FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION

Rev. 1.4 3/99

P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7

LX8117-xx/8117A-xx/8117B-xx

0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS

P R O D U C T I O N D A T A S H E E T

APPLICATION NOTES

LOAD REGULATION (continued)

THERMAL CONSIDERATIONS (continued)

Example

Given: V_IN= 5.0V ±5%, V_OUT= 2.5V ±3%

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

roomtemperature. Ifa3-terminalregulatorusedtosupply2.50volts

is connected by 2 inches of this trace to a load which draws 5 amps

of current, a50 millivoltdrop will appear between 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.

I_OUT= 0.5A, T_A= 55°C, T_J= 125°C

R_θJT= 15°C/W, R_θTS= 5°C/W

Find: The size of a square area of 1oz. copper circuit-

board trace-foil that will serve as a heatsink,

adequate to maintain the junction temperature of the

LX8117 in the ST (SOT-223) package within

specified limits.

Solution: The junction temperature is:

T_J= P_D(R_θJT+ R_θCS+ R_θSA) + T_A

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

enoughthatthevoltageattheinputpindoesnotdropbelowV_IN(MIN)

during transients.

where: P_D≡ Dissipated power.

R_θJT≡ Thermal resistance from the junction to the

mounting tab of the package.

R_θTS≡ Thermal resistance through the interface

between the IC and the surface on which

it is mounted.

R_θSA

≡

Thermal resistance from the mounting surface

of the heatsink to ambient.

T_S≡ Heat sink temperature.

T_JT_CT_S

T_A

R_qJT

R_qCS

R_qSA

First, find the maximum allowable thermal resistance of the

heat sink:

V_{IN (MIN)}= V_OUT+ V_{DROPOUT (MAX)}

P_D= [[V_IN(1 + Tol )] - [V

(1 - Tol )]] I

VOUT OUT

VIN

OUT

where: V_{IN (MIN)}

V_OUT

≡ the lowest allowable instantaneous

voltage at the input pin.

≡ the designed output voltage for the

power supply system.

P_D= 1.4W

T_J- T_A

R_θSA

- (R_θJT+ R_θTS) ,

R_θSA= 29.6°C/W

P_D

V_{DROPOUT (MAX)}≡ the specified dropout voltage

for the installed regulator.

A test was conducted to determine the thermal characteristics of

1 oz. copper circuit-board trace material. The following equation

describes the observed relationship between the area of a square

copper pad, and the thermal resistance from the tab of a SOT-223

package soldered at the center of the pad to ambient.

THERMAL CONSIDERATIONS

The LX8117 regulators have internal power and thermal limiting

circuitrydesignedtoprotecteachdeviceunderoverloadconditions.

For continuous normal load conditions, however, maximum junc-

tion temperature ratings must not be exceeded. It is important to

give careful consideration to all sources of thermal resistance from

junctiontoambient. Thisincludesjunctiontocase, casetoheatsink

interface, and heat sink thermal resistance itself.

3.1°C/W

Area_SINK

in²

R_θSA- 22.3°C/W

Substituting the value for R_θSAcalculated above, we find that a

square pad with area:

Area_SINK= 0.43 in²(0.66" x 0.66"), 280mm²(17 x 17 mm)

will be required to maintain the LX8117 junction temperature

within specified limits.

Rev. 1.4 3/99

P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7

LX8117-xx/8117A-xx/8117B-xx

0.8, 1 & 1.2A LOW DROPOUT POSITIVE REGULATORS

P R O D U C T I O N D A T A S H E E T

TYPICAL APPLICATIONS

LX8117-xx

OUT

LX8117-xx

OUT

V_IN

(Note A)

V_IN

V_OUT**

V_OUT

ADJ

121

ADJ

Ω

10µF

121

Ω

100µF

C1*

10µF

150µF

10µF*

* C1 improves ripple rejection.

365

Ω

X_Cshould be

frequency.

≈ R1 at ripple

* Needed if device is far from filter capacitors.

**V_OUT= 1.25V 1 +

FIGURE 4 — IMPROVING RIPPLE REJECTION

FIGURE 5 — 1.2V - 8V ADJUSTABLE REGULATOR

LX8117-33

V_IN

OUT

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 6 — FIXED 3.3V OUTPUT REGULATOR

Note A: V_{IN (MIN)}= (Intended V_OUT) + (V_{DROPOUT (MAX)}

)

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.

Rev. 1.4 3/99

LX8117A-25CDT-TR [MICROSEMI]

相关型号：

LX8117A-25CDTT

LX8117A-25CST

LX8117A-25CST-TR

LX8117A-25CSTT

LX8117A-28

LX8117A-28CDD

LX8117A-28CDD-TR

LX8117A-28CDDT

LX8117A-28CDT

LX8117A-28CDT-TR

LX8117A-28CDTT

LX8117A-28CST