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LT3081

3081fa

For more information www.linear.com/LT3081

Typical applicaTion

FeaTures DescripTion

1.5A Single Resistor

Rugged Linear Regulator

with Monitors

The LT

3081 is a 1.5A low dropout linear regulator de-

signed for rugged industrial applications. Key features of

the IC are the extended safe operating area (SOA), output

current monitor, temperature monitor and programmable

current limit. The LT3081 can be paralleled for higher

output current or heat spreading. The device withstands

reverse input and reverse output-to-input voltages without

reverse current flow.

The LT3081’s precision 50µA reference current source

allows a single resistor to program output voltage to

any level between zero and 34.5V. The current reference

architecture makes load regulation independent of output

voltage. The LT3081 is stable with or without input and

output capacitors.

The output current monitor (I

OUT

/5000) and die junction

temperature output (1µA/°C) provide system monitoring

and debug capability. In addition, a single resistor pro-

grams current limit.

Internal protection circuitry includes reverse-battery and

reverse-current protection, current limiting and thermal

limiting. The LT3081 is offered in the 16-lead TSSOP (with

exposed pad for improved thermal performance), 7-lead

TO-220, 7-lead DD-Pak, and an 12-lead 4mm × 4mm DFN.

Wide Safe Operating Area Supply

applicaTions

Extended Safe Operating Area

Maximum Output Current: 1.5A

Stable with or without Input/Output Capacitors

Wide Input Voltage Range: 1.2V to 36V

Single Resistor Sets Output Voltage

Output Current Monitor: I

MON

= I

OUT

/5000

Junction Temperature Monitor: 1µA/°C

Output Adjustable to 0V

50µA SET Pin Current: 1% Initial Accuracy

Output Voltage Noise: 27µV

RMS

Parallel Multiple Devices for Higher Current or

Heat Spreading

Programmable Current Limit

Reverse-Battery and Reverse-Current Protection

<1mV Load Regulation Typical Independent of V

OUT

<0.001%/V Line Regulation Typical

Available in Thermally-Enhanced 12-Lead 4mm ×

4mm DFN and 16-Lead TSSOP, 7-Lead DD-Pak and

7-Lead TO-220

All Surface Mount Power Supply

Rugged Industrial Power Supply

Post Regulator for Switching Supplies

Low Output Voltage Supply

Intrinsic Safety Applications

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

TEMPERATURE (°C)

–50

49.5

SET PIN CURRENT (µA)

49.6

49.8

49.9

50.0

50.5

50.2

3081 TA01b

49.7

50.3

50.4

50.1

–25 25

100

125

150

= 5mA

SET Pin Current

3081 TA01a

6.04k

10µF*

*OPTIONAL

MON

LIM

OUT

–

LT3081

LOAD

/5000

OUT

1.5V

1.5A

300Ω*

1µA/°C

SET

30.1k

TEMP

50µA

Summary of content (32 pages)

PAGE 1
LT3081 1.5A Single Resistor Rugged Linear Regulator with Monitors Description Features n n n n n n n n n n n n n n n n Extended Safe Operating Area Maximum Output Current: 1.5A Stable with or without Input/Output Capacitors Wide Input Voltage Range: 1.
PAGE 2
LT3081 Absolute Maximum Ratings (Note 1) All voltages Relative to VOUT. IN Pin to OUT Pin Differential Voltage......................±40V SET Pin Current (Note 6)......................................±25mA SET Pin Voltage (Relative to OUT, Note 6)............... ±10V TEMP Pin Voltage (Relative to OUT)..................1V, –40V ILIM Pin Voltage (Relative to OUT)..........................±0.2V IMON Pin Voltage (Relative to OUT)....................1V, –40V Output Short-Circuit Duration........................
PAGE 3
LT3081 Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3081EDF#PBF LT3081EDF#TRPBF 3081 12-Lead (4mm × 4mm) Plastic DFN –40°C to 125°C LT3081IDF#PBF LT3081IDF#TRPBF 3081 12-Lead (4mm × 4mm) Plastic DFN –40°C to 125°C LT3081EFE#PBF LT3081EFE#TRPBF 3081FE 16-Lead Plastic TSSOP –40°C to 125°C LT3081IFE#PBF LT3081IFE#TRPBF 3081FE 16-Lead Plastic TSSOP –40°C to 125°C LT3081HFE#PBF LT3081HFE#TRPBF 3081FE 16-Lead Plastic TSSOP –40°
PAGE 4
LT3081 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. (Note 2) PARAMETER CONDITIONS TEMP Output Current (Note 9) TJ > 5°C TEMP Output Current Absolute Error (Note 9) 0°C
PAGE 5
LT3081 Typical Performance Characteristics SET Pin Current 50.5 50.4 TJ = 25°C unless otherwise specified. Offset Voltage (VOUT – VSET) SET Pin Current ILOAD = 5mA 2.0 N = 3195 OFFSET VOLTAGE (mV) SET PIN CURRENT (µA) 50.3 50.2 50.1 50.0 49.9 49.8 49.7 49.5 –50 –25 0 49 25 50 75 100 125 150 TEMPERATURE (°C) 50.5 49.5 50 SET PIN CURRENT DISTRIBUTION (µA) 0.5 0 –0.5 –1.0 –2.0 –50 –25 51 Offset Voltage 1.0 Offset Voltage (VOUT – VSET) 0.2 ILOAD = 5mA 0.
PAGE 6
LT3081 Typical Performance Characteristics Internal Current Limit 1.5 3.0 2.5 CURRENT LIMIT (A) DROPOUT VOLTAGE (V) 1.4 1.3 ILOAD = 1.5A 1.2 ILOAD = 5mA 1.1 Internal Current Limit 2.0 VIN = 7V VOUT = 0V 1.8 1.6 CURRENT LIMIT (A) Dropout Voltage TJ = 25°C unless otherwise specified. 2.0 1.5 1.0 TO-220 AND DD-PAK 1.4 1.2 TSSOP AND DFN 1.0 0.8 0.6 0.4 0.5 0.2 1.
PAGE 7
LT3081 Typical Performance Characteristics Linear Regulator Load Transient Response OUTPUT VOLTAGE DEVIATION (mV) 35 30 25 20 10 5 0 –50 36 6 18 24 0 30 12 INPUT-TO-OUTPUT DIFFERENTIAL VOLTAGE (V) ∆ILOAD = 100mA TO 500mA 200 0 20 40 60 80 100 120 140 160 180 200 TIME (µs) 400 tr = tf = 1µs 0 5 0 10 15 20 25 30 35 40 45 50 TIME (µs) 1.0 0.
PAGE 8
LT3081 Typical Performance Characteristics Current Source Turn-On Response 3 2 1 1.0 RSET = 20k RLOAD = 0.67Ω COUT = 2.2µF CERAMIC CSET = 0.1µF 0 0 2 4 6 8 10 12 14 16 18 20 TIME (ms) OUTPUT CURRENT (mA) OUTPUT VOLTAGE (V) 100mA CURRENT SOURCE CONFIGURATION 3 2 1 RSET = 6.04k ROUT = 3.01Ω COUT = 0 CSET = 20pF 0 0 –0.
PAGE 9
LT3081 Typical Performance Characteristics Ripple Rejection (1MHz) Ripple Rejection (10kHz) 65 26 63 RIPPLE REJECTION (dB) RIPPLE REJECTION (dB) 61 59 57 55 53 51 49 47 TJ = 25°C unless otherwise specified. VIN = VOUT(NOMINAL) + 2V RIPPLE = 500mVP-P f = 10kHz ILOAD = 0.1A COUT = 2.2µF CSET = 0.1µF 45 –50 –25 0 VIN = VOUT(NOMINAL) + 2V 24 RIPPLE = 200mVP-P f = 1MHz 22 ILOAD = 0.1A COUT = 2.2µF CERAMIC 20 CSET = 0.
PAGE 10
LT3081 Pin Functions IN: Input. This pin supplies power to regulate internal circuitry and supply output load current. For the device to operate properly and regulate, the voltage on this pin must be between the dropout voltage and 36V above the OUT pin (depending on output load current, see Dropout Voltage Specifications). IMON: Output Current Monitor. The IMON pin sources a current typically equal to ILOAD/5000 or 200µA per amp of output current.
PAGE 11
LT3081 Applications Information Introduction The LT3081 regulator is easy to use and has all the protection features expected in high performance regulators. Included are short-circuit protection, reverse-input protection and safe operating area protection, as well as thermal shutdown with hysteresis. Safe operating area (SOA) for the LT3081 is extended, allowing for use in harsh industrial and automotive environments where sudden spikes in input voltage lead to high power dissipation.
PAGE 12
LT3081 Applications Information Table 1 lists many common output voltages and the closest standard 1% resistor values used to generate that output voltage. Regulation of the output voltage requires a minimum load current of 5mA. For true zero voltage output operation, return this 5mA load current to a negative output voltage. Table 1. 1% Resistors for Common Output Voltages VOUT (V) RSET (kΩ) 1 20 1.2 24.3 1.5 30.1 1.8 35.7 2.5 49.9 3.3 66.
PAGE 13
LT3081 Applications Information Again, the lower current levels used in the LT3081 necessitate attention to board leakages as error sources (see the Programming Linear Regulator Output Voltage section). In a current source configuration, programmable current limit and current monitoring functions are often unused. When not used, tie IMON to OUT and leave ILIM open. The TEMP pin is still available for use, if unused tie TEMP to OUT.
PAGE 14
LT3081 Applications Information The self-inductance, or isolated inductance, of a wire is directly proportional to its length. Wire diameter is not a major factor on its self-inductance. For example, the selfinductance of a 2-AWG isolated wire (diameter = 0.26") is about half the self-inductance of a 30-AWG wire (diameter = 0.01"). One foot of 30-AWG wire has about 465nH of self inductance. One of two ways reduces a wire’s self-inductance.
PAGE 15
LT3081 Applications Information In LT3081 applications with long wires or PCB traces, the inductive reactance may cause instability. In some cases, adding series resistance to the input and output lines (as shown in Figure 4) may sufficiently dampen these possible high-Q lines and provide stability. The user must evaluate the required resistor values against the design’s headroom constraints.
PAGE 16
LT3081 Applications Information In some extreme cases, capacitors or series RC networks may be required on both the LT3081’s input and output to stabilize the circuit. Figure 6 depicts a general application using input and output capacitor networks rather than an input-to-output capacitor. As the input of the current source tends to be high impedance, placing a capacitor on the input does not have the same effect as placing a capacitor on the lower impedance output. Capacitors in the range of 0.
PAGE 17
LT3081 Applications Information Voltage and temperature coefficients are not the only sources of problems. Some ceramic capacitors have a piezoelectric response. A piezoelectric device generates voltage across its terminals due to mechanical stress. In a ceramic capacitor, the stress can be induced by vibrations in the system or thermal transients. LT3081 IN 50µA + – OUT SET Paralleling Devices Higher output current is obtained by paralleling multiple LT3081s together.
PAGE 18
LT3081 Applications Information The LT3081 uses a unity-gain follower from the SET pin to the OUT pin. Therefore, multiple possibilities exist (besides a SET pin resistor) to set output voltage. For example, using a high accuracy voltage reference from SET to GND removes the errors in output voltage due to reference current tolerance and resistor tolerance. Active driving of the SET pin is acceptable.
PAGE 19
LT3081 Applications Information Connecting a resistor from IMON to ground converts the IMON pin current into a voltage to allow for monitoring by an ADC. With a 1k resistor, 0mV to 300mV indicates 0A to 1.5A of load current. Compensating for Cable Drops with IMON The IMON pin can compensate for resistive drops in wires or cables between the LT3081 and the load. Breaking the SET resistor into two pieces adjusts the output voltage as a function of load current.
PAGE 20
LT3081 Applications Information T7 Package, 7-Lead TO-220 Reducing Power Dissipation Thermal Resistance (Junction-to-Case) = 3°C/W In some applications it may be necessary to reduce the power dissipation in the LT3081 package without sacrificing output current capability. Two techniques are available. The first technique, illustrated in Figure 12, employs a resistor in series with the regulator’s input.
PAGE 21
LT3081 Applications Information The second technique for reducing power dissipation, shown in Figure 13, uses a resistor in parallel with the LT3081. This resistor provides a parallel path for current flow, reducing the current flowing through the LT3081. This technique works well if input voltage is reasonably constant and output load current changes are small. This technique also increases the maximum available output current at the expense of minimum load requirements.
PAGE 22
LT3081 Applications Information The LT3081’s IN pin withstands ±40V voltages with respect to the OUT and SET pins. Reverse current flow, if OUT is greater than IN, is less than 1mA (typically under 100µA), protecting the LT3081 and sensitive loads. Clamping diodes and 400Ω limiting resistors protect the LT3081’s SET pin relative to the OUT pin voltage. These protection components typically only carry current under transient overload conditions.
PAGE 23
LT3081 Typical Applications Load Sharing Without Ballast Resistors VIN 3V TO 18V 22µF IN OUT IN 22µF LT3081 SET 0.1µF 20k OUT OUT LT3081 IMON 5.1k 20k 0.1µF LT3081 IMON SET 1k IN SET 1k 0.1µF 100k 20k VOUT 1V 4.5A IMON 1k 100k + + 1/2 LT1638 1/2 LT1638 5.1k – – 0.47µF 0.47µF 5.1k 5.1k 3081 TA05 Load Current Sharing Without Ballasting VOUT 1V 3A VIN 3V TO 36V 4.7µF IN OUT LT3081 100Ω IMON SET 0.1µF ILIM OUT 2.
PAGE 24
VIN 30V 24 For more information www.linear.com/LT3081 LT8612 PG BIAS SW BST OUT 562Ω 49.9K 60.4k TR/SS FB RT PGND GND INTVCC SYNC EN/UV VIN SET + – IN 0.1µF 1µF 10µF 10µA LT3092 22µF 1k 4.99k 10nF TPO610T 10µF ×2 10k ARDUINO A3 PORT ARDUINO A2 PORT 10k 6V 47µF 20k 10k IMON LT3081 IMON LT3081 IN 0.01µF ×2 ARDUINO A5 PORT 4.99k SET TEMP + – ISET 50µA IN ARDUINO A4 PORT 4.99k SET TEMP + – ISET 50µA www.linear.com/product/LT3081#demoboards 10µH 100k 49.
PAGE 25
LT3081 Typical Applications Boosting Fixed Output Regulators IN LT3081 ISET 50µA + – IMON 5V OUT 20mΩ ILIM SET TEMP 20mΩ LT1963-3.3 8.2Ω* 10µF 47µF 3.3VOUT 3A 47µF 3081 TA08 6.2k *4mV DROP ENSURES LT3081 IS OFF WITH NO LOAD MULTIPLE LT3081s CAN BE USED Reference Buffer VIN IN LT3081 ISET 50µA + – IMON SET TEMP 1k INPUT LT1019 OUT VOUT ILIM 1k 1k* 47µF OUTPUT 1µF GND *MIN LOAD 5mA 3081 TA09 Adding Soft-Start VIN 4.
PAGE 26
LT3081 Typical Applications Using a Lower Value Set Resistor VIN 12V 4.7µF IN LT3081 ISET 50µA + – IMON OUT SET TEMP 1k 4.02k VOUT 0.2V TO 10V ILIM 1k 40.2Ω 4.7µF 3081 TA11 RSET 2k VOUT = 0.2V + 5mA • RSET Using an External Reference Current VIN 1µF LT3092 IN 10µA ISET 50µA + – SET 20k IN LT3081 + – OUT OUT 215Ω IMON SET TEMP 1k 1k ILIM VOUT 0V TO 20V 1µF 3081 TA12 20k 26 1mA 3081fa For more information www.linear.
PAGE 27
LT3081 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DF Package 12-Lead Plastic DFN (4mm × 4mm) (Reference LTC DWG # 05-08-1733 Rev A) 2.50 REF 0.70 ±0.05 3.38 ±0.05 4.50 ±0.05 3.10 ±0.05 2.65 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (4 SIDES) 2.50 REF 7 12 0.40 ±0.10 3.38 ±0.10 2.65 ±0.10 PIN 1 NOTCH R = 0.20 TYP OR 0.
PAGE 28
LT3081 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. FE Package 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663 Rev J) Exposed Pad Variation BB 4.70 (.185) 3.58 (.141) DETAIL A 4.90 – 5.10* (.193 – .201) 0.56 (.022) REF 3.58 (.141) NOTE 5 16 1514 13 12 1110 9 NOTE 5 6.60 ±0.10 2.94 3.05 (.116) (.120) 4.50 ±0.10 DETAIL A SEE NOTE 4 2.94 6.40 (.116) (.252) BSC 0.53 (.
PAGE 29
LT3081 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. T7 Package 7-Lead Plastic TO-220 (Straight Lead) (Nonstandard Flow 06) (Reference LTC DWG # 05-08-1422) .390 – .415 (9.906 – 10.541) .147 – .155 (3.734 – 3.937) DIA .165 – .180 (4.191 – 4.572) .045 – .055 (1.143 – 1.397) .230 – .270 (5.842 – 6.858) .460 – .500 (11.684 – 12.700) .570 – .620 (14.478 – 15.748) .330 – .370 (8.382 – 9.398) .980 – 1.070 (24.892 – 27.178) .520 – .
PAGE 30
LT3081 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. R Package 7-Lead Plastic DD Pak (Reference LTC DWG # 05-08-1462 Rev F) .256 (6.502) .060 (1.524) TYP .060 (1.524) .390 – .415 (9.906 – 10.541) .165 – .180 (4.191 – 4.572) .045 – .055 (1.143 – 1.397) 15° TYP .060 (1.524) .183 (4.648) +.008 .004 –.004 +0.203 0.102 –0.102 .059 (1.499) TYP .330 – .370 (8.382 – 9.398) ( ) .095 – .115 (2.413 – 2.921) .075 (1.
PAGE 31
LT3081 Revision History REV DATE DESCRIPTION A 11/13 Modified Typical Application circuit for more detail PAGE NUMBER Added H- and MP-grade references Changed TJMAX to 150°C on the FE and T7 packages 1 Throughout 2 Changed specs to TEMP Output Current Absolute Error 4 Modified Block Diagram 10 Modified Paralleling Regulators Circuit 22 Modified Arduino Supply Circuit 24 Added new Typical Application circuits 25, 26 Modified High Efficiency Adjustable Supply circuit 32 Updated Related Pa
PAGE 32
LT3081 Typical Application High Efficiency Adjustable Supply VIN 6.3V TO 36V 15k 63.4k 1000pF VIN BD RUN/SS BOOST VC RT PG LT3680 SYNC GND 0.47µF SW IN 6.8µH 47µF MBRA340T3 590k 6.04k 6V MTD2955 FB LT3081 OUT 1k IMON TEMP 1k 15k 22µF VOUT 0V TO 25V, 1.5A SET ILIM 500k 0.1µF 10k 1µF 1k 2N3904 3081 TA13 1µF CMDSH-4E Related Parts PART NUMBER DESCRIPTION COMMENTS LT1185 3A Negative Low Dropout Regulator VIN: –4.5V to –35V, 0.