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LM1084

SNVS037G –SEPTEMBER 1999–REVISED JANUARY 2015

LM1084 5-A Low Dropout Positive Regulators

1 Features 3 Description

The LM1084 is a regulator with a maximum dropout

1• Available in 3.3-V, 5.0-V, and Adjustable Versions of 1.5 V at 5 A of load current. The device has the

• Current Limiting and Thermal Protection same pinout as TI's industry standard LM317.

• Output Current 5 A Two resistors are required to set the output voltage of

• Industrial Temperature Range −40°C to 125°C the adjustable output voltage version of the LM1084.

• Line Regulation 0.015% (Typical) Fixed output voltage versions integrate the adjust

resistors.

• Load Regulation 0.1% (Typical) The LM1084 circuit includes a zener trimmed

2 Applications bandgap reference, current limiting, and thermal

shutdown.

• Post Regulator for Switching DC-DC Converter Refer to LM1085 for the 3A version, and the LM1086

• High-Efficiency Linear Regulators for the 1.5A version.

• Battery Chargers

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)

TO-263 (3) 10.18 mm × 8.41 mm

LM1084 TO-220 (3) 14.986 mm × 10.16 mm

(1) For all available packages, see the orderable addendum at

the end of the datasheet.

Typical Application

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,

intellectual property matters and other important disclaimers. PRODUCTION DATA.

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Table of Contents

7.3 Feature Description................................................... 9

1 Features.................................................................. 17.4 Device Functional Modes........................................ 11

2 Applications ........................................................... 18 Application and Implementation ........................ 13

3 Description............................................................. 18.1 Application Information............................................ 13

4 Revision History..................................................... 28.2 Typical Applications ................................................ 13

5 Pin Configuration and Functions......................... 39 Power Supply Recommendations...................... 20

6 Specifications......................................................... 410 Layout................................................................... 20

6.1 Absolute Maximum Ratings ...................................... 410.1 Layout Guidelines ................................................. 20

6.2 ESD Ratings ............................................................ 410.2 Layout Example .................................................... 20

6.3 Recommended Operating Conditions....................... 410.3 Thermal Considerations........................................ 20

6.4 Thermal Information.................................................. 411 Device and Documentation Support................. 22

6.5 Electrical Characteristics........................................... 511.1 Trademarks........................................................... 22

6.6 Typical Characteristics.............................................. 711.2 Electrostatic Discharge Caution............................ 22

7 Detailed Description.............................................. 911.3 Glossary................................................................ 22

7.1 Overview................................................................... 912 Mechanical, Packaging, and Orderable

7.2 Functional Block Diagram......................................... 9Information ........................................................... 22

4 Revision History

Changes from Revision F (March 2013) to Revision G Page

• Added Pin Configuration and Functions section, ESD Ratings table, Feature Description section, Device Functional

Modes,Application and Implementation section, Power Supply Recommendations section, Layout section, Device

and Documentation Support section, and Mechanical, Packaging, and Orderable Information section .............................. 1

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5 Pin Configuration and Functions

3-Pin

TO-220 Package

Top View

3-Pin

TO-263 Package

Top View

Pin Functions

PIN I/O DESCRIPTION

NAME NO.

Adjust pin for the adjustable output voltage version. Ground pin for the fixed output voltage

ADJ/GND 1 - versions.

OUTPUT 2 O Output voltage pin for the regulator.

INPUT 3 I Input voltage pin for the regulator.

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6 Specifications

6.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)(1)(2)

MIN MAX UNIT

Maximum Input to Output Voltage Differential

LM1084-ADJ 29 V

LM1084-3.3 27 V

LM1084-5.0 25 V

Power Dissipation(3) Internally Limited

Junction Temperature (TJ)(4) 150 °C

Lead Temperature 260, to 10 sec °C

Storage temperature, Tstg –65 150 °C

(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Recommended Operating Conditions indicate

conditions for which the device is intended to be functional, but specific performance is not ensured. For ensured specifications and the

test conditions, see the Electrical Characteristics.

(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and

specifications.

(3) Power dissipation is kept in a safe range by current limiting circuitry. Refer to Overload Recovery.

(4) The maximum power dissipation is a function of TJ(max) ,θJA, and TA. The maximum allowable power dissipation at any ambient

temperature is PD= (TJ(max)–T A)/θJA. All numbers apply for packages soldered directly into a PC board. Refer to Thermal

Considerations.

6.2 ESD Ratings VALUE UNIT

V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2000 V

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)(1)

MIN MAX UNIT

Junction Temperature Range (TJ)(2)

Control Section –40 125 °C

Output Section –40 150 °C

(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Recommended Operating Conditions indicate

conditions for which the device is intended to be functional, but specific performance is not ensured. For ensured specifications and the

test conditions, see the Electrical Characteristics.

(2) The maximum power dissipation is a function of TJ(max) ,θJA, and TA. The maximum allowable power dissipation at any ambient

temperature is PD= (TJ(max)–T A)/θJA. All numbers apply for packages soldered directly into a PC board. Refer to Thermal

Considerations.

6.4 Thermal Information LM1084

THERMAL METRIC(1) KTT NDE UNIT

3 PINS 3 PINS

RθJA Junction-to-ambient thermal resistance 40.4 22.7

RθJC(top) Junction-to-case (top) thermal resistance 42.6 15.5

RθJB Junction-to-board thermal resistance 23.0 4.1 °C/W

ψJT Junction-to-top characterization parameter 9.8 2.1

ψJB Junction-to-board characterization parameter 22.0 4.1

RθJC(bot) Junction-to-case (bottom) thermal resistance: Control Section/Output 0.65/2.7 0.65/2.7

Section

(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.

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6.5 Electrical Characteristics

Typicals and limits apply for TJ= 25°C unless specified otherwise.

PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT

VREF Reference Voltage LM1084-ADJ, IOUT = 10 mA, VIN −VOUT = 3 V, 10 mA ≤1.238 1.250 1.262

IOUT ≤IFULL LOAD,1.5 V ≤(VIN−VOUT)≤25 V(3)

LM1084-ADJ, IOUT = 10 mA, VIN −VOUT = 3 V, 10 mA ≤

IOUT ≤IFULL LOAD,1.5 V ≤(VIN−VOUT)≤25 V(3), –40°C ≤1.225 1.250 1.270

TJ≤125°C

VOUT Output Voltage(3) LM1084-3.3, IOUT = 0 mA, VIN = 8 V, 0 ≤IOUT ≤IFULL 3.270 3.300 3.330

LOAD, 4.8 V ≤VIN ≤15 V V

LM1084-3.3, IOUT = 0 mA, VIN = 8 V, 0 ≤IOUT ≤IFULL 3.235 3.300 3.365

LOAD, 4.8 V ≤VIN ≤15 V , –40°C ≤TJ≤125°C

LM1084-5.0, IOUT = 0 mA, VIN = 8 V, 0 ≤IOUT ≤IFULL 4.950 5.000 5.050

LOAD, 6.5 V ≤VIN ≤20 V V

LM1084-5.0, IOUT = 0 mA, VIN = 8 V, 0 ≤IOUT ≤IFULL 4.900 5.000 5.100

LOAD, 6.5 V ≤VIN ≤20 V, –40°C ≤TJ≤125°C

ΔVOUT Line Regulation(4) LM1084-ADJ, IOUT = 10 mA, 1.5 V ≤(VIN – VOUT)≤15 V 0.015% 0.2%

LM1084-ADJ, IOUT = 10 mA, 1.5 V ≤(VIN – VOUT)≤15 0.035% 0.2%

V, –40°C ≤TJ≤125°C

LM1084-3.3, IOUT = 0 mA, 4.8 V ≤VIN ≤15 V 0.5 6 mV

LM1084-3.3, IOUT = 0 mA, 4.8 V ≤VIN ≤15 V, –40°C ≤1.0 6

TJ≤125°C

LM1084-5.0, IOUT = 0 mA, 6.5 V ≤VIN ≤20 V 0.5 10 mV

LM1084-5.0, IOUT = 0 mA, 6.5 V ≤VIN ≤20 V, –40°C ≤1.0 10

TJ≤125°C

ΔVOUT Load Regulation(4) LM1084-ADJ, (VIN – V OUT) = 3 V, 10 mA ≤IOUT ≤IFULL 0.1 % 0.3%

LOAD

LM1084-ADJ, (VIN – V OUT) = 3 V, 10 mA ≤IOUT ≤IFULL 0.2% 0.4%

LOAD, –40°C ≤TJ≤125°C

LM1084-3.3, VIN = 5 V, 0 ≤IOUT ≤IFULL LOAD 3 15 mV

LM1084-3.3, VIN = 5 V, 0 ≤IOUT ≤IFULL LOAD, –40°C ≤TJ7 20

≤125°C

LM1084-5.0, VIN = 8 V, 0 ≤IOUT ≤IFULL LOAD 5 20 mV

LM1084-5.0, VIN = 8 V, 0 ≤IOUT ≤IFULL LOAD, –40°C ≤TJ10 35

≤125°C

Dropout Voltage(5) LM1084-ADJ, 3.3, 5, 12, ΔVREF,ΔVOUT = 1%, IOUT = 5A, 1.3 1.5 V

–40°C ≤TJ≤125°C

ILIMIT Current Limit LM1084-ADJ, VIN−VOUT = 5 V, –40°C ≤TJ≤125°C 5.5 8.0 A

LM1084-ADJ, VIN−VOUT = 25 V, –40°C ≤TJ≤125°C 0.3 0.6

LM1084-3.3, VIN = 8 V, –40°C ≤TJ≤125°C 5.5 8.0 A

LM1084-5.0, VIN = 10 V, –40°C ≤TJ≤125°C 5.5 8.0 A

Minimum Load LM1084-ADJ, VIN −VOUT = 25 V 5 10.0 mA

Current(6)

Quiescent Current LM1084-3.3, VIN = 18 V 5.0 10.0 mA

LM1084-5.0, VIN ≤20 V 5.0 10.0 mA

Thermal Regulation TA= 25°C, 30 ms Pulse 0.003 0.015 %/W

(1) All limits are specified by testing or statistical analysis.

(2) Typical Values represent the most likely parametric norm.

(3) IFULLLOAD is defined in the current limit curves. The IFULLLOAD Curve defines the current limit as a function of input-to-output voltage.

Note that 30W power dissipation for the LM1084 is only achievable over a limited range of input-to-output voltage.

(4) Load and line regulation are measured at constant junction temperature, and are ensured up to the maximum power dissipation of 30W.

Power dissipation is determined by the input/output differential and the output current. ensured maximum power dissipation will not be

available over the full input/output range.

(5) Dropout voltage is specified over the full output current range of the device.

(6) The minimum output current required to maintain regulation.

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Electrical Characteristics (continued)

Typicals and limits apply for TJ= 25°C unless specified otherwise.

PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT

Ripple Rejection fRIPPLE = 120 Hz, = COUT = 25 µF Tantalum, IOUT = 5A dB

LM1084-ADJ, CADJ, = 25 µF, (VIN −VO) = 3 V, –40°C ≤60 75

TJ≤125°C

LM1084-3.3, VIN = 6.3 V, –40°C ≤TJ≤125°C 60 72 dB

LM1084-5.0, VIN = 8 V, –40°C ≤TJ≤125°C 60 68 dB

Adjust Pin Current LM1084 55 µA

LM1084, –40°C ≤TJ≤125°C 120

Adjust Pin Current 10 mA ≤IOUT ≤IFULL LOAD, 1.5 V ≤VIN −VOUT ≤25 V, 0.2 5 µA

Change –40°C ≤TJ≤125°C

Temperature Stability –40°C ≤TJ≤125°C 0.5%

Long Term Stability TA=125°C, 1000 Hrs 0.3% 1.0%

RMS Output Noise 10 Hz ≤f≤10 kHz 0.003%

(% of VOUT)

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6.6 Typical Characteristics

Figure 2. Short-Circuit Current

Figure 1. Dropout Voltage (VIN−VOUT)

Figure 4. LM1084-ADJ Ripple Rejection

Figure 3. Load Regulation

Figure 5. LM1084-ADJ Ripple Rejection vs Current Figure 6. Temperature Stability

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Typical Characteristics (continued)

Figure 8. LM1084-ADJ Load Transient Response

Figure 7. Adjust Pin Current

Figure 10. Maximum Power Dissipation

Figure 9. LM1084-ADJ LineTransient Response

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7 Detailed Description

7.1 Overview

A basic functional diagram for the LM1084-ADJ (excluding protection circuitry) is shown in Figure 11. The

topology is basically that of the LM317 except for the pass transistor. Instead of a Darlington NPN with its two

diode voltage drop, the LM1084 uses a single NPN. This results in a lower dropout voltage. The structure of the

pass transistor is also known as a quasi LDO. The advantage of a quasi LDO over a PNP LDO is its inherently

lower quiescent current. The LM1084 is ensured to provide a minimum dropout voltage of 1.5-V over

temperature, at full load.

Figure 11. Basic Functional Diagram for the LM1084, Excluding Protection Circuitry

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Ripple Rejection

Ripple rejection is a function of the open loop gain within the feed-back loop (refer to Figure 11 and Figure 14).

The LM1084 exhibits 75dB of ripple rejection (typ.). When adjusted for voltages higher than VREF, the ripple

rejection decreases as a function of adjustment gain: (1+R1/R2) or VO/VREF. Therefore a 5-V adjustment

decreases ripple rejection by a factor of four (−12dB); Output ripple increases as adjustment voltage increases.

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Feature Description (continued)

However, the adjustable version allows this degradation of ripple rejection to be compensated. The adjust

terminal can be bypassed to ground with a capacitor (CADJ). The impedance of the CADJ should be equal to or

less than R1 at the desired ripple frequency. This bypass capacitor prevents ripple from being amplified as the

output voltage is increased.

1/(2π× fRIPPLE*CADJ)≤R1(1)

7.3.2 Load Regulation

The LM1084 regulates the voltage that appears between its output and ground pins, or between its output and

adjust pins. In some cases, line resistances can introduce errors to the voltage across the load. To obtain the

best load regulation, a few precautions are needed.

Figure 12 shows a typical application using a fixed output regulator. Rt1 and Rt2 are the line resistances. VLOAD

is less than the VOUT by the sum of the voltage drops along the line resistances. In this case, the load regulation

seen at the RLOAD would be degraded from the data sheet specification. To improve this, the load should be tied

directly to the output pin on the positive side and directly tied to the ground pin on the negative side.

Figure 12. Typical Application Using Fixed Output Regulator

When the adjustable regulator is used (Figure 13), the best performance is obtained with the positive side of the

resistor R1 tied directly to the output pin of the regulator rather than near the load. This eliminates line drops

from appearing effectively in series with the reference and degrading regulation. For example, a 5-V regulator

with 0.05Ωresistance between the regulator and load will have a load regulation due to line resistance of 0.05Ω

× IL. If R1 (= 125Ω) is connected near the load the effective line resistance will be 0.05Ω(1 + R2/R1) or in this

case, it is 4 times worse. In addition, the ground side of the resistor R2 can be returned near the ground of the

load to provide remote ground sensing and improve load regulation.

Figure 13. Best Load Regulation Using Adjustable Output Regulator

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Feature Description (continued)

7.3.3 Overload Recovery

Overload recovery refers to regulator's ability to recover from a short circuited output. A key factor in the recovery

process is the current limiting used to protect the output from drawing too much power. The current limiting circuit

reduces the output current as the input to output differential increases. Refer to short circuit curve in the Typical

Characteristics section.

During normal start-up, the input to output differential is small because the output follows the input. But, if the

output is shorted, then the recovery involves a large input to output differential. Sometimes during this condition

the current limiting circuit is slow in recovering. If the limited current is too low to develop a voltage at the output,

the voltage will stabilize at a lower level. Under these conditions it may be necessary to recycle the power of the

regulator in order to get the smaller differential voltage and thus adequate start up conditions. Refer to Typical

Characteristics section for the short circuit current vs. input differential voltage.

7.4 Device Functional Modes

7.4.1 Output Voltage

The LM1084 adjustable version develops a 1.25-V reference voltage, (VREF), between the output and the adjust

pin. As shown in Figure 14, this voltage is applied across resistor R1 to generate a constant current I1. This

constant current then flows through R2. The resulting voltage drop across R2 adds to the reference voltage to

sets the desired output voltage.

The current IADJ from the adjustment terminal introduces an output error. But because it is small (120 uA max), it

becomes negligible when R1 is in the 100 Ωrange.

For fixed voltage devices, R1 and R2 are integrated inside the devices.

Figure 14. Basic Adjustable Regulator

7.4.2 Stability Consideration

Stability consideration primarily concerns the phase response of the feedback loop. In order for stable operation,

the loop must maintain negative feedback. The LM1084 requires a certain amount series resistance with

capacitive loads. This series resistance introduces a zero within the loop to increase phase margin and thus

increase stability. The equivalent series resistance (ESR) of solid tantalum or aluminum electrolytic capacitors is

used to provide the appropriate zero (approximately 500 kHz).

Aluminum electrolytics are less expensive than tantalums, but their ESR varies exponentially at cold

temperatures; therefore requiring close examination when choosing the desired transient response over

temperature. Tantalums are a convenient choice because their ESR varies less than 2:1 over temperature.

The recommended load/decoupling capacitance is a 10-uF tantalum or a 50-uF aluminum. These values will

assure stability for the majority of applications.

The adjustable versions allow an additional capacitor to be used at the ADJ pin to increase ripple rejection. If this

is done the output capacitor should be increased to 22 uF for tantalum or to 150 uF for aluminum.

Capacitors other than tantalum or aluminum can be used at the adjust pin and the input pin. A 10-uF capacitor is

a reasonable value at the input. See Ripple Rejection section regarding the value for the adjust pin capacitor.

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Device Functional Modes (continued)

It is desirable to have large output capacitance for applications that entail large changes in load current

(microprocessors for example). The higher the capacitance, the larger the available charge per demand. It is also

desirable to provide low ESR to reduce the change in output voltage:

ΔV = ΔI x ESR (2)

It is common practice to use several tantalum and ceramic capacitors in parallel to reduce this change in the

output voltage by reducing the overall ESR.

Output capacitance can be increased indefinitely to improve transient response and stability.

7.4.3 Protection Diodes

Under normal operation, the LM1084 regulator does not need any protection diode. With the adjustable device,

the internal resistance between the adjustment and output terminals limits the current. No diode is needed to

divert the current around the regulator even with a capacitor on the adjustment pin. The adjust pin can take a

transient signal of ±25 V with respect to the output voltage without damaging the device.

When an output capacitor is connected to a regulator and the input is shorted, the output capacitor will discharge

into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage

of the regulator, and rate of decrease of VIN. In the LM1084 regulator, the internal diode between the output and

input pins can withstand microsecond surge currents of 10A to 20A. With an extremely large output capacitor (≥

1000 µf), and with input instantaneously shorted to ground, the regulator could be damaged. In this case, an

external diode is recommended between the output and input pins to protect the regulator, shown in Figure 15.

Figure 15. Regulator with Protection Diode

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LM1084 is versatile in its applications, including uses in programmable output regulation and local on-card

regulation. Or, by connecting a fixed resistor between the ADJUST and OUTPUT terminals, the LM1084 can

function as a precision current regulator. An optional output capacitor can be added to improve transient

response. The ADJUST terminal can be bypassed to achieve very high ripple-rejection ratios, which are difficult

to achieve with standard three-terminal regulators. Please note, in the following applications, if ADJ is mentioned,

it makes use of the adjustable version of the part, however, if GND is mentioned, it is the fixed voltage version of

the part.

8.2 Typical Applications

8.2.1 1.2-V to 15-V Adjustable Regulator

This part can be used as a simple low drop out regulator to enable a variety of output voltages needed for

demanding applications. By using an adjustable R2 resistor a variety of output voltages can be made possible as

shown in Figure 16 based on the LM1084-ADJ.

Figure 16. 1.2-V to 15-V Adjustable Regulator

8.2.1.1 Design Requirements

The device component count is very minimal, employing two resistors as part of a voltage divider circuit and an

output capacitor for load regulation.

8.2.1.2 Detailed Design Procedure

The voltage divider for this part is set based on the equation shown in Figure 16, where R1 is the upper feedback

resistor and R2 is the lower feedback resistor.

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Typical Applications (continued)

8.2.1.3 Application Curve

8.2.2 Adjustable at 5 V

The application shown in Figure 17 outlines a simple 5 V output application made possible by the LM1084-ADJ.

This application can provide 5 A at high efficiencies and very low drop-out.

Figure 17. Adjustable @ 5 V

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Typical Applications (continued)

8.2.3 5-V Regulator With Shutdown

A variation of the 5 V output regulator application with shutdown control is shown in Figure 18 based on the

LM1084-ADJ. It uses a simple NPN transistor on the ADJ pin to block or sink the current on the ADJ pin. If the

TTL logic is pulled high, the NPN transistor is activated and the part is disabled, outputting approximately 1.25 V.

If the TTL logic is pulled low, the NPN transistor is unbiased and the regulator functions normally.

Figure 18. 5-V Regulator with Shutdown

8.2.4 Battery Charger

The LM1084-ADJ can be used as a battery charger to regulate the charging current required by the battery bank

as shown in Figure 19. In this application the LM1084 acts as a constant voltage, constant current part by

sensing the voltage potential across the battery and compensating it to the current voltage. To maintain this

voltage, the regulator delivers the maximum charging current required to charge the battery. As the battery

approaches the fully charged state, the potential drop across the sense resistor, RS,reduces and the regulator

throttles back the current to maintain the float voltage of the battery.

Figure 19. Battery Charger

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Typical Applications (continued)

8.2.5 Adjustable Fixed Regulator

A simple adjustable, fixed range output regulator can be made possible by placing a variable resistor on the

ground of the device as shown in Figure 20 based on the fixed output voltage LM1084-5.0. The GND pin has a

small quiescent current of 5 mA typical. Increasing the resistance on the GND pin increases the voltage potential

across the resistor. This potential is then mirrored on to the output to increase the total output voltage by the

potential drop across the GND resistor.

Figure 20. Adjustable Fixed Regulator

8.2.6 Regulator with Reference

A fixed output voltage version of the LM1084-5.0 can be employed to provide an output rail and a reference rail

at the same time as shown in Figure 21. This simple application makes use of a reference diode, the LM136-5,

to regulate the GND voltage to a fixed 5 V based on the quiescent current generated by the GND pin. This

voltage is then added onto the output to generate a total of 10 V out.

Figure 21. Regulator with Reference

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Typical Applications (continued)

8.2.7 High Current Lamp Driver Protection

A simple constant current source with protection can be designed by controlling the impedance between the

lamp and ground. The LM1084-ADJ shown in Figure 22 makes use of an external TTL or CMOS input to drive

the NPN transistor. This pulls the output of the regulator to a few tenths of a volt and puts the part into current

limit. Releasing the logic will reduce the current flow across the lamp into the normal operating current thereby

protecting the lamp during startup.

Figure 22. High Current Lamp Driver Protection

8.2.8 Battery Backup Regulated Supply

A regulated battery backup supply can be generated by using two fixed output voltage versions of the part as

shown in Figure 23. The top regulator supplies the Line voltage during normal operation, however when the input

is not available, the second regulator derives power from the battery backup and regulates it to 5 V based on the

LM1084-5.0. The diodes prevent the rails from back feeding into the supply and batteries.

Figure 23. Battery Backup Regulated Supply

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Typical Applications (continued)

8.2.9 Ripple Rejection Enhancement

A very simple ripple rejection circuit is shown in Figure 24 using the LM1084-ADJ. The capacitor C1 smooths out

the ripple on the output by cleaning up the feedback path and preventing excess noise from feeding back into the

regulator. Please remember XC1 should be approximately equal to R1 at the ripple frequency.

Figure 24. Ripple Rejection Enhancement

8.2.10 Automatic Light Control

A common street light control or automatic light control circuit is designed in Figure 25 based on the LM1084-

ADJ. The photo transistor conducts in the presence of light and grounds the ADJ pin preventing the lamp from

turning on. However, in the absence of light, the LM1084 regulates the voltage to 1.25V between OUT and ADJ,

ensuring the lamp remains on.

Figure 25. Automatic Light Control

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Typical Applications (continued)

8.2.11 Generating Negative Supply Voltage

A quick inverting output rail or negative output rail is shown in Figure 26 using the LM1084 fixed output part. By

tying the output to GND, the GND node is at a relatively more negative potential than the output. This is then

interfaced to the negative application such as an operational amplifier or any other rail needing negative voltage.

Figure 26. Generating Negative Supply Voltage

8.2.12 Remote Sensing

Remote sensing is a method of compensating the output voltage to a very precise degree by sensing the output

and feeding it back through the feedback. The circuit implementing this is shown in Figure 27 using the LM1084-

ADJ. The output of the regulator is fed into a voltage follower to avoid any loading effects and the output of the

op-amp is injected into the top of the feedback resistor network. This has the effect of modulating the voltage to a

precise degree without additional loading on the output.

Figure 27. Remote Sensing

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SNVS037G –SEPTEMBER 1999–REVISED JANUARY 2015

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9 Power Supply Recommendations

The linear regulator input supply should be well regulated and kept at a voltage level such that the maximum

input to output voltage differential allowed by the device is not exceeded. The minimum dropout voltage (VIN –

VOUT) should be met with extra headroom when possible in order to keep the output well regulated. A 10 μF or

higher capacitor should be placed at the input to bypass noise.

10 Layout

10.1 Layout Guidelines

For the best overall performance, some layout guidelines should be followed. Place all circuit components on the

same side of the circuit board and as near as practical to the respective linear regulator pins. Traces should be

kept short and wide to reduce the amount of parasitic elements into the system. The actual width and thickness

of traces will depend on the current carrying capability and heat dissipation required by the end system. An array

of plated vias can be placed on the pad area underneath the TAB to conduct heat to any inner plane areas or to

a bottom-side copper plane.

10.2 Layout Example

Figure 28. Layout Example

10.3 Thermal Considerations

ICs heats up when in operation, and power consumption is one factor in how hot it gets. The other factor is how

well the heat is dissipated. Heat dissipation is predictable by knowing the thermal resistance between the IC and

ambient (θJA). Thermal resistance has units of temperature per power (C/W). The higher the thermal resistance,

the hotter the IC.

The LM1084 specifies the thermal resistance for each package as junction to case (θJC). In order to get the total

resistance to ambient (θJA), two other thermal resistance must be added, one for case to heat-sink (θCH) and one

for heatsink to ambient (θHA). The junction temperature can be predicted as follows:

TJ= TA+ PD(θJC +θCH +θHA)=TA+ PDθJA (3)

TJis junction temperature, TAis ambient temperature, and PDis the power consumption of the device. Device

power consumption is calculated as follows:

Product Folder Links: LM1084

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SNVS037G –SEPTEMBER 1999–REVISED JANUARY 2015

Thermal Considerations (continued)

IIN = IL+ IG(4)

PD= (VIN−VOUT) IL+ VINIG(5)

Figure 29 shows the voltages and currents which are present in the circuit.

Figure 29. Power Dissipation Diagram

Once the devices power is determined, the maximum allowable (θJA (max)) is calculated as:

θJA (max) = TR(max)/PD= TJ(max) −TA(max)/PD(6)

The LM1084 has different temperature specifications for two different sections of the IC: the control section and

the output section. The Thermal Information table shows the junction to case thermal resistances for each of

these sections, while the maximum junction temperatures (TJ(max)) for each section is listed in the Absolute

Maximum Ratings section of the datasheet. TJ(max) is 125°C for the control section, while TJ(max) is 150°C for the

output section.

θJA (max) should be calculated separately for each section as follows:

θJA (max, CONTROL SECTION) = (125°C - TA(max))/PD(7)

θJA (max, OUTPUT SECTION) = (150°C - TA(max))/PD(8)

The required heat sink is determined by calculating its required thermal resistance (θHA (max)).

θHA (max) =θJA (max) −(θJC +θCH) (9)

(θHA (max)) should also be calculated twice as follows:

(θHA (max)) = θJA (max, CONTROL SECTION) - (θJC (CONTROL SECTION) + θCH) (10)

(θHA (max)) = θJA(max, OUTPUT SECTION) - (θJC (OUTPUT SECTION) + θCH) (11)

If thermal compound is used, θCH can be estimated at 0.2 C/W. If the case is soldered to the heat sink, then a

θCH can be estimated as 0 C/W.

After, θHA (max) is calculated for each section, choose the lower of the two θHA (max) values to determine the

appropriate heat sink.

If PC board copper is going to be used as a heat sink, then Figure 30 can be used to determine the appropriate

area (size) of copper foil required.

Figure 30. Heat Sink Thermal Resistance vs Area

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11 Device and Documentation Support

11.1 Trademarks

All trademarks are the property of their respective owners.

11.2 Electrostatic Discharge Caution

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

11.3 Glossary

SLYZ022 —TI Glossary.

This glossary lists and explains terms, acronyms, and definitions.

12 Mechanical, Packaging, and Orderable Information

The following pages include mechanical, packaging, and orderable information. This information is the most

current data available for the designated devices. This data is subject to change without notice and revision of

this document. For browser-based versions of this data sheet, refer to the left-hand navigation.

Product Folder Links: LM1084

PACKAGE OPTION ADDENDUM

www.ti.com 11-Jan-2021

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead finish/

Ball material

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM1084IS-3.3/NOPB ACTIVE DDPAK/

TO-263 KTT 3 45 RoHS-Exempt

& Green SN Level-3-245C-168 HR -40 to 125 LM1084

IS-3.3

LM1084IS-5.0/NOPB ACTIVE DDPAK/

TO-263 KTT 3 45 RoHS-Exempt

& Green SN Level-3-245C-168 HR -40 to 125 LM1084

IS-5.0

LM1084IS-ADJ NRND DDPAK/

TO-263 KTT 3 45 Non-RoHS

& Green Call TI Call TI -40 to 125 LM1084

IS-ADJ

LM1084IS-ADJ/NOPB ACTIVE DDPAK/

TO-263 KTT 3 45 RoHS-Exempt

& Green SN Level-3-245C-168 HR -40 to 125 LM1084

IS-ADJ

LM1084ISX-3.3/NOPB ACTIVE DDPAK/

TO-263 KTT 3 500 RoHS-Exempt

& Green SN Level-3-245C-168 HR -40 to 125 LM1084

IS-3.3

LM1084ISX-5.0/NOPB ACTIVE DDPAK/

TO-263 KTT 3 500 RoHS-Exempt

& Green SN Level-3-245C-168 HR -40 to 125 LM1084

IS-5.0

LM1084ISX-ADJ/NOPB ACTIVE DDPAK/

TO-263 KTT 3 500 RoHS-Exempt

& Green SN Level-3-245C-168 HR -40 to 125 LM1084

IS-ADJ

LM1084IT-3.3/NOPB ACTIVE TO-220 NDE 3 45 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LM1084

IT-3.3

LM1084IT-5.0/NOPB ACTIVE TO-220 NDE 3 45 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LM1084

IT-5.0

LM1084IT-ADJ/NOPB ACTIVE TO-220 NDE 3 45 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LM1084

IT-ADJ

(1) The marketing status values are defined as follows:

ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.

PREVIEW: Device has been announced but is not in production. Samples may or may not be available.

OBSOLETE: TI has discontinued the production of the device.

(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance

do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may

reference these types of products as "Pb-Free".

RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.

Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based

flame retardants must also meet the <=1000ppm threshold requirement.

PACKAGE OPTION ADDENDUM

www.ti.com 11-Jan-2021

Addendum-Page 2

(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation

of the previous line and the two combined represent the entire Device Marking for that device.

(6) Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two

lines if the finish value exceeds the maximum column width.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information

provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and

continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.

TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

Type Package

Drawing Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

Quadrant

LM1084ISX-3.3/NOPB DDPAK/

TO-263 KTT 3 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2

LM1084ISX-5.0/NOPB DDPAK/

TO-263 KTT 3 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2

LM1084ISX-ADJ/NOPB DDPAK/

TO-263 KTT 3 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2

PACKAGE MATERIALS INFORMATION

www.ti.com 8-Sep-2014

Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

LM1084ISX-3.3/NOPB DDPAK/TO-263 KTT 3 500 367.0 367.0 45.0

LM1084ISX-5.0/NOPB DDPAK/TO-263 KTT 3 500 367.0 367.0 45.0

LM1084ISX-ADJ/NOPB DDPAK/TO-263 KTT 3 500 367.0 367.0 45.0

PACKAGE MATERIALS INFORMATION

www.ti.com 8-Sep-2014

Pack Materials-Page 2

MECHANICAL DATA

NDE0003B

www.ti.com

MECHANICAL DATA

KTT0003B

www.ti.com

BOTTOM SIDE OF PACKAGE

TS3B (Rev F)

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