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LM1085
SNVS038H –JULY 1999–REVISED JANUARY 2015
LM1085 3-A Low Dropout Positive Regulators
1 Features 3 Description
The LM1085 is a regulator with a maximum dropout
1• Available in 3.3-V, 5.0-V, 12-V and Adjustable of 1.5 V at 3 A of load current. It has the same pin-
Versions out as TI's industry standard LM317.
• Current Limiting and Thermal Protection Two resistors are required to set the output voltage of
• Output Current 3 A the adjustable output voltage version of the LM1085.
• Line Regulation 0.015% (typical) Fixed output voltage versions integrate the adjust
• Load Regulation 0.1% (typical) resistors.
The LM1085 circuit includes a zener trimmed
2 Applications bandgap reference, current limiting and thermal
shutdown.
• High Efficiency Linear Regulators
• Battery Charger Refer to the LM1084 for the 5A version, and the
LM1086 for the 1.5A version.
• Post Regulation for Switching Supplies
• Constant Current Regulator Device Information(1)
• Microprocessor Supply PART NUMBER PACKAGE BODY SIZE (NOM)
DDPAK/TO-263 (3) 10.18 mm × 8.41 mm
LM1085 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
1
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.
LM1085
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Table of Contents
7.4 Device Functional Modes........................................ 11
1 Features.................................................................. 18 Application and Implementation ........................ 13
2 Applications ........................................................... 18.1 Application Information............................................ 13
3 Description............................................................. 18.2 Typical Applications ................................................ 13
4 Revision History..................................................... 29 Power Supply Recommendations...................... 20
5 Pin Configuration and Functions......................... 310 Layout................................................................... 20
6 Specifications......................................................... 410.1 Layout Guidelines ................................................. 20
6.1 Absolute Maximum Ratings ...................................... 410.2 Layout Example .................................................... 20
6.2 ESD Ratings ............................................................ 410.3 Thermal Considerations........................................ 20
6.3 Recommended Operating Conditions....................... 411 Device and Documentation Support................. 22
6.4 Thermal Information.................................................. 411.1 Documentation Support ........................................ 22
6.5 Electrical Characteristics........................................... 511.2 Trademarks........................................................... 22
6.6 Typical Characteristics.............................................. 711.3 Electrostatic Discharge Caution............................ 22
7 Detailed Description.............................................. 911.4 Glossary................................................................ 22
7.1 Overview................................................................... 912 Mechanical, Packaging, and Orderable
7.2 Functional Block Diagram......................................... 9Information ........................................................... 22
7.3 Feature Description................................................. 10
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision H (March 2013) to Revision I Page
• Added 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 ................................................................................................. 4
Changes from Revision F (March 2013) to Revision G Page
• Deleted layout of National Data Sheet to TI format.............................................................................................................. 19
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5 Pin Configuration and Functions
3-Pin
TO-220
Top View
3-Pin
DDPAK/TO-263
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
LM1085-ADJ 29 V
LM1085-12 18 V
LM1085-3.3 27 V
LM1085-5.0 25 V
Power Dissipation (3) Internally Limited V
Junction Temperature (TJ)(4) 150 °C
Lead Temperature 260, to 10 sec °C
Storage temperature range, Tstg –65 150 °C
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(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 in the Application Notes.
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) MIN MAX UNIT
Junction Temperature (TJ)(1) −40 125 °C
(1) 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 in the Application Notes.
6.4 Thermal Information LM1085
THERMAL METRIC(1) KTT NDE UNIT
3 PINS 3 PINS
RθJA Junction-to-ambient thermal resistance 40.6 22.8
RθJC(top) Junction-to-case (top) thermal resistance 43.0 15.6
RθJB Junction-to-board thermal resistance 23.1 4.2 °C/W
ψJT Junction-to-top characterization parameter 9.9 2.2
ψJB Junction-to-board characterization parameter 22.1 4.2
RθJC(bot) Junction-to-case (bottom) thermal resistance 0.7 0.7
(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
Minimum and Maximum limits are ensured through test, design, or statistical correlation. Typical values represent the most
likely parametric norm at TJ= 25°C, and are provided for reference purposes only.
PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT
LM1085-ADJ, IOUT = 10 mA, VIN −VOUT = 3 V, 10 mA ≤1.238 1.250 1.262
IOUT ≤IFULL LOAD,1.5 V ≤(VIN−VOUT)≤15 V
Reference Voltage
VREF V
LM1085-ADJ, IOUT = 10 mA, VIN −VOUT = 3 V, 10 mA ≤
(3) IOUT ≤IFULL LOAD,1.5 V ≤(VIN −VOUT)≤15 V, –40°C ≤TJ1.225 1.250 1.270
≤125°C
LM1085-3.3, IOUT = 0 mA, VIN = 5 V, 0 ≤IOUT ≤IFULL 3.270 3.300 3.330
LOAD, 4.8 V ≤VIN ≤15 V V
LM1085-3.3, IOUT = 0 mA, VIN = 5 V, 0 ≤IOUT ≤IFULL 3.235 3.300 3.365
LOAD, 4.8 V ≤VIN ≤15 V, –40°C ≤TJ≤125°C
LM1085-5.0, IOUT = 0 mA, VIN = 8 V, 0 ≤IOUT ≤IFULL 4.950 5.000 5.050
LOAD, 6.5 V ≤VIN ≤20 V
Output Voltage
VOUT V
(3) LM1085-5.0, 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
LM1085-12, IOUT = 0 mA, VIN = 15 V, 0 ≤IOUT ≤IFULL 11.880 12.000 12.120
LOAD, 13.5 V ≤VIN ≤25 V V
LM1085-12, IOUT = 0 mA, VIN = 15 V, 0 ≤IOUT ≤IFULL 11.760 12.000 12.240
LOAD, 13.5 V ≤VIN ≤25 V, –40°C ≤TJ≤125°C
LM1085-ADJ, IOUT =10 mA, 1.5 V ≤(VIN-VOUT)≤15 V 0.015 0.2
LM1085-ADJ, IOUT =10 mA, 1.5 V ≤(VIN-VOUT)≤15 V, 0.035 0.2
–40°C ≤TJ≤125°C
LM1085-3.3, IOUT = 0 mA, 4.8 V ≤VIN ≤15 V 0.5 6 mV
LM1085-3.3, IOUT = 0 mA, 4.8 V ≤VIN ≤15 V, –40°C ≤1.0 6
TJ≤125°C
Line Regulation
ΔVOUT (4) LM1085-5.0, IOUT = 0 mA, 6.5 V ≤VIN ≤20 V 0.5 10 mV
LM1085-5.0, IOUT = 0 mA, 6.5 V ≤VIN ≤20 V, –40°C ≤1.0 10
TJ≤125°C
LM1085-12, I OUT = 0 mA, 13.5 V ≤VIN ≤25 V 1.0 25 mV
LM1085-12, I OUT = 0 mA, 13.5 V ≤VIN ≤25 V, –40°C ≤2.0 25
TJ≤125°C
LM1085-ADJ, (VIN-V OUT) = 3 V, 10 mA ≤IOUT ≤IFULL 0.1 0.3
LOAD
LM1085-ADJ, (VIN-V OUT) = 3 V, 10 mA ≤IOUT ≤IFULL 0.2 0.4
LOAD, –40°C ≤TJ≤125°C
LM1085-3.3, VIN = 5 V, 0 ≤IOUT ≤IFULL LOAD 3 15 mV
LM1085-3.3, VIN = 5 V, 0 ≤IOUT ≤IFULL LOAD, –40°C ≤TJ7 20
Load Regulation ≤125°C
ΔVOUT (4) LM1085-5.0, VIN = 8 V, 0 ≤IOUT ≤IFULL LOAD 5 20 mV
LM1085-5.0, VIN = 8 V, 0 ≤IOUT ≤IFULL LOAD, –40°C ≤TJ10 35
≤125°C
LM1085-12, VIN = 15 V, 0 ≤IOUT ≤IFULL LOAD 12 36 mV
LM1085-12, VIN = 15 V, 0 ≤IOUT ≤IFULL LOAD, –40°C ≤24 72
TJ≤125°C
LM1085-ADJ, 3.3, 5, 12, ΔVREF,ΔVOUT = 1%, IOUT = 3A,
VDO Dropout Voltage (5) 1.3 1.5 V
–40°C ≤TJ≤125°C
(1) All limits are specified by testing or statistical analysis.
(2) Typical Values represent the most likely parametric norm.
(3) IFULL LOAD is defined in the current limit curves. The IFULL LOAD Curve defines the current limit as a function of input-to-output voltage.
Note that 30W power dissipation for the LM1085 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.
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Electrical Characteristics (continued)
Minimum and Maximum limits are ensured through test, design, or statistical correlation. Typical values represent the most
likely parametric norm at TJ= 25°C, and are provided for reference purposes only.
PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT
LM1085-ADJ, VIN−VOUT = 5 V, –40°C ≤TJ≤125°C 3.2 5.5 A
LM1085-ADJ, VIN−VOUT = 25 V, –40°C ≤TJ≤125°C 0.2 0.5
ILIMIT Current Limit LM1085-3.3, VIN = 8.0 V, –40°C ≤TJ≤125°C 3.2 5.5 A
LM1085-5.0, VIN = 10 V, –40°C ≤TJ≤125°C 3.2 5.5 A
LM1085-12, VIN = 17 V, –40°C ≤TJ≤125°C 3.2 5.5 A
Minimum Load LM1085-ADJ, VIN −VOUT = 25 V, –40°C ≤TJ≤125°C 5.0 10.0 mA
Current (6)
LM1085-3.3, VIN ≤18 V, –40°C ≤TJ≤125°C 5.0 10.0 mA
IGND Quiescent Current LM1085-5.0, VIN ≤20 V, –40°C ≤TJ≤125°C 5.0 10.0 mA
LM1085-12, VIN ≤25 V, –40°C ≤TJ≤125°C 5.0 10.0 mA
Thermal Regulation TA= 25°C, 30ms Pulse .004 0.02 %/W
fRIPPLE = 120Hz, COUT = 25µF Tantalum, IOUT = 3A,
LM1085-ADJ, CADJ = 25µF, (VIN−VO) = 3 V, –40°C ≤TJ60 75 dB
≤125°C
Ripple Rejection LM1085-3.3, VIN = 6.3 V, –40°C ≤TJ≤125°C 60 72 dB
LM1085-5.0, VIN = 8.0 V, –40°C ≤TJ≤125°C 60 68 dB
LM1085-12, VIN = 15 V, –40°C ≤TJ≤125°C 54 60 dB
LM1085–ADJ 55
IADJ Adjust Pin Current µA
LM1085–ADJ, –40°C ≤TJ≤125°C 120
Adjust Pin Current LM1085–ADJ, 10mA ≤IOUT ≤IFULL LOAD, 1.5 V ≤
ΔIADJ 0.2 5 µA
Change VIN−VOUT ≤25 V, –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 10Hz ≤f≤10 kHz 0.003
(% of VOUT)
(6) The minimum output current required to maintain regulation.
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6.6 Typical Characteristics
Figure 2. Short-Circuit Current vs Input/Output Difference
Figure 1. Dropout Voltage vs Output Current
Figure 4. Adjust Pin Current vs Temperature
Figure 3. Percent Change in Output Voltage vs Temperature
Figure 6. Ripple Rejection vs Frequency (LM1085-Adj.)
Figure 5. Maximum Power Dissipation vs Temperature
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Typical Characteristics (continued)
Figure 7. Ripple Rejection vs Output Current (LM1085-ADJ) Figure 8. Line Transient Response
Figure 9. Load Transient Response
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7 Detailed Description
7.1 Overview
A basic functional diagram for the LM1085-ADJ (excluding protection circuitry) is shown in Figure 10. 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 LM1085 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 LM1085 is ensured to provide a minimum dropout voltage of 1.5V over temperature,
at full load.
Figure 10. Basic Functional Diagram for the LM1085, Excluding Protection Circuitry
7.2 Functional Block Diagram
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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 and Figure 13). The
LM1085 exhibits 75dB of ripple rejection (typ.). When adjusted for voltages higher than VREF, the ripple rejection
decreases as function of adjustment gain: (1+R1/R2) or VO/VREF. Therefore a 5V adjustment decreases ripple
rejection by a factor of four (−12dB); Output ripple increases as adjustment voltage increases.
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 LM1085 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 11 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 terminal on the positive side and directly tied to the ground terminal on the negative side.
Figure 11. Typical Application Using Fixed Output Regulator
When the adjustable regulator is used (Figure 12), the best performance is obtained with the positive side of the
resistor R1 tied directly to the output terminal 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 5V regulator with
0.05Ωresistance between the regulator and load will have a load regulation due to line resistance of 0.05Ωx 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 12. 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 since 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 LM1085 adjustable version develops a 1.25V reference voltage, (VREF), between the output and the adjust
terminal. As shown in Figure 13, 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 since it is small (120uA max), it
becomes negligible when R1 is in the 100 Ωrange.
For fixed voltage devices, R1 and R2 are integrated inside the devices.
Figure 13. 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 LM1085 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 10uF tantalum or a 50uF 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 10uF 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:
V = 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 LM1085 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 terminal. 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 LM1085 regulator, the internal diode between the output and
input pins can withstand microsecond surge currents of 10 A to 20 A. 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 14.
Figure 14. 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 LM1085 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 LM1085 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 15 based on the LM1085-ADJ.
Figure 15. 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 in Figure 15, where R1 is the upper feedback
resistor 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 16 outlines a simple 5 V output application made possible by the LM1085-ADJ.
This application can provide 3 A at high efficiencies and very low drop-out.
Figure 16. Adjustable @ 5V
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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 17 based on the
LM1085-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 17. 5-V Regulator with Shutdown
8.2.4 Battery Charger
The LM1085-ADJ can be used as a battery charger to regulate the charging current required by the battery bank
as shown in Figure 18. In this application the LM1085 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 18. 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 19 based on the fixed output voltage LM1085-5.0. 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 19. Adjustable Fixed Regulator
8.2.6 Regulator with Reference
A fixed output voltage version of the LM1085-5.0 can be employed to provide an output rail and a reference rail
at the same time as shown in Figure 20. 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 20. 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 LM1085-ADJ shown in Figure 21 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 21. 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 22. 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
LM1085-5.0. The diodes prevent the rails from back feeding into the supply and batteries.
Figure 22. 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 23 using the LM1085-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 23. Ripple Rejection Enhancement
8.2.10 Automatic Light Control
A common street light control or automatic light control circuit is designed in Figure 24 based on the LM1085-
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 LM1085 regulates the voltage to 1.25V between OUT and ADJ,
ensuring the lamp remains on.
Figure 24. 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 25 using the LM1085 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 25. 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 26 using the LM1085-
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 26. Remote Sensing
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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 connections. 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 27. 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 LM1085 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:
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Thermal Considerations (continued)
IIN = IL+ IG(4)
PD= (VIN−VOUT) IL+ VINIG(5)
Figure 28 shows the voltages and currents which are present in the circuit.
Figure 28. 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
The LM1085 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(6)
θJA (max, OUTPUT SECTION) = (150°C - TA(max))/PD(7)
The required heat sink is determined by calculating its required thermal resistance (θHA (max)).
θHA (max) =θJA (max) −(θJC +θCH) (8)
(θHA (max)) should also be calculated twice as follows:
(θHA (max)) = θJA (max, CONTROL SECTION) - (θJC (CONTROL SECTION) + θCH) (9)
(θHA (max)) = θJA(max, OUTPUT SECTION) - (θJC (OUTPUT SECTION) + θCH) (10)
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 29 can be used to determine the appropriate
area (size) of copper foil required.
Figure 29. Heat Sink Thermal Resistance vs Area
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11 Device and Documentation Support
11.1 Documentation Support
11.1.1 Related Documentation
Application Note 1520 A Guide to Board Layout for Best Thermal Resistance for Exposed Packages,SNVA183
11.2 Trademarks
All trademarks are the property of their respective owners.
11.3 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.
11.4 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.
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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
LM1085IS-12/NOPB ACTIVE DDPAK/
TO-263 KTT 3 45 RoHS-Exempt
& Green SN Level-3-245C-168 HR -40 to 125 LM1085
IS-12
LM1085IS-3.3 NRND DDPAK/
TO-263 KTT 3 45 Non-RoHS
& Green Call TI Call TI -40 to 125 LM1085
IS-3.3
LM1085IS-3.3/NOPB ACTIVE DDPAK/
TO-263 KTT 3 45 RoHS-Exempt
& Green SN Level-3-245C-168 HR -40 to 125 LM1085
IS-3.3
LM1085IS-5.0/NOPB ACTIVE DDPAK/
TO-263 KTT 3 45 RoHS-Exempt
& Green SN Level-3-245C-168 HR -40 to 125 LM1085
IS-5.0
LM1085IS-ADJ NRND DDPAK/
TO-263 KTT 3 45 Non-RoHS
& Green Call TI Call TI LM1085
IS-ADJ
LM1085IS-ADJ/NOPB ACTIVE DDPAK/
TO-263 KTT 3 45 RoHS-Exempt
& Green SN Level-3-245C-168 HR -40 to 125 LM1085
IS-ADJ
LM1085ISX-3.3 NRND DDPAK/
TO-263 KTT 3 500 Non-RoHS
& Green Call TI Call TI LM1085
IS-3.3
LM1085ISX-3.3/NOPB ACTIVE DDPAK/
TO-263 KTT 3 500 RoHS-Exempt
& Green SN Level-3-245C-168 HR -40 to 125 LM1085
IS-3.3
LM1085ISX-5.0/NOPB ACTIVE DDPAK/
TO-263 KTT 3 500 RoHS-Exempt
& Green SN Level-3-245C-168 HR -40 to 125 LM1085
IS-5.0
LM1085ISX-ADJ NRND DDPAK/
TO-263 KTT 3 500 Non-RoHS
& Green Call TI Call TI -40 to 125 LM1085
IS-ADJ
LM1085ISX-ADJ/NOPB ACTIVE DDPAK/
TO-263 KTT 3 500 RoHS-Exempt
& Green SN Level-3-245C-168 HR -40 to 125 LM1085
IS-ADJ
LM1085IT-12/NOPB ACTIVE TO-220 NDE 3 45 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LM1085
IT-12
LM1085IT-3.3/NOPB ACTIVE TO-220 NDE 3 45 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LM1085
IT-3.3
LM1085IT-5.0 NRND TO-220 NDE 3 45 Non-RoHS
& Green Call TI Call TI LM1085
IT-5.0
LM1085IT-5.0/NOPB ACTIVE TO-220 NDE 3 45 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LM1085
IT-5.0
LM1085IT-ADJ NRND TO-220 NDE 3 45 Non-RoHS
& Green Call TI Call TI -40 to 125 LM1085
IT-ADJ
LM1085IT-ADJ/NOPB ACTIVE TO-220 NDE 3 45 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LM1085
PACKAGE OPTION ADDENDUM
www.ti.com 11-Jan-2021
Addendum-Page 2
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
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.
(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)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LM1085ISX-3.3 DDPAK/
TO-263 KTT 3 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
LM1085ISX-3.3/NOPB DDPAK/
TO-263 KTT 3 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
LM1085ISX-5.0/NOPB DDPAK/
TO-263 KTT 3 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
LM1085ISX-ADJ DDPAK/
TO-263 KTT 3 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
LM1085ISX-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 29-Sep-2019
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM1085ISX-3.3 DDPAK/TO-263 KTT 3 500 367.0 367.0 45.0
LM1085ISX-3.3/NOPB DDPAK/TO-263 KTT 3 500 367.0 367.0 45.0
LM1085ISX-5.0/NOPB DDPAK/TO-263 KTT 3 500 367.0 367.0 45.0
LM1085ISX-ADJ DDPAK/TO-263 KTT 3 500 367.0 367.0 45.0
LM1085ISX-ADJ/NOPB DDPAK/TO-263 KTT 3 500 367.0 367.0 45.0
PACKAGE MATERIALS INFORMATION
www.ti.com 29-Sep-2019
Pack Materials-Page 2
MECHANICAL DATA
NDE0003B
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MECHANICAL DATA
KTT0003B
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BOTTOM SIDE OF PACKAGE
TS3B (Rev F)
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