LM334H - National Semiconductor

LM134,LM234,LM334

LM134/LM234/LM334 3-Terminal Adjustable Current Sources

Literature Number: SNVS746C

LM134/LM234/LM334

3-Terminal Adjustable Current Sources

General Description

The LM134/LM234/LM334 are 3-terminal adjustable current

sources featuring 10,000:1 range in operating current, excel-

lent current regulation and a wide dynamic voltage range of

1V to 40V. Current is established with one external resistor

and no other parts are required. Initial current accuracy is

±3%. The LM134/LM234/LM334 are true floating current

sources with no separate power supply connections. In ad-

dition, reverse applied voltages of up to 20V will draw only a

few dozen microamperes of current, allowing the devices to

act as both a rectifier and current source in AC applications.

The sense voltage used to establish operating current in the

LM134 is 64mV at 25˚C and is directly proportional to abso-

lute temperature (˚K). The simplest one external resistor

connection, then, generates a current with ≈+0.33%/˚C tem-

perature dependence. Zero drift operation can be obtained

by adding one extra resistor and a diode.

Applications for the current sources include bias networks,

surge protection, low power reference, ramp generation,

LED driver, and temperature sensing. The LM234-3 and

LM234-6 are specified as true temperature sensors with

guaranteed initial accuracy of ±3˚C and ±6˚C, respectively.

These devices are ideal in remote sense applications be-

cause series resistance in long wire runs does not affect

accuracy. In addition, only 2 wires are required.

The LM134 is guaranteed over a temperature range of

−55˚C to +125˚C, the LM234 from −25˚C to +100˚C and the

LM334 from 0˚C to +70˚C. These devices are available in

TO-46 hermetic, TO-92 and SO-8 plastic packages.

Features

nOperates from 1V to 40V

n0.02%/V current regulation

nProgrammable from 1µA to 10mA

nTrue 2-terminal operation

nAvailable as fully specified temperature sensor

n±3% initial accuracy

Connection Diagrams

SO-8

Surface Mount Package

SO-8 Alternative Pinout

Surface Mount Package

00569724

Order Number LM334M or LM334MX

See NS Package Number M08A

00569725

Order Number LM334SM or LM334SMX

See NS Package Number M08A

TO-46

Metal Can Package TO-92 Plastic Package

00569712

V−Pin is electrically connected to case.

Bottom View

Order Number LM134H,

LM234H or LM334H

See NS Package

Number H03H

00569710

Bottom View

Order Number LM334Z, LM234Z-3 or LM234Z-6

See NS Package Number Z03A

March 2005

LM134/LM234/LM334 3-Terminal Adjustable Current Sources

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

to V

−

Forward Voltage

LM134/LM234/LM334 40V

LM234-3/LM234-6 30V

to V

−

Reverse Voltage 20V

R Pin to V

−

Voltage 5V

Set Current 10 mA

Power Dissipation 400 mW

ESD Susceptibility (Note 6) 2000V

Operating Temperature Range (Note

LM134 −55˚C to +125˚C

LM234/LM234-3/LM234-6 −25˚C to +100˚C

LM334 0˚C to +70˚C

Soldering Information

TO-92 Package (10 sec.) 260˚C

TO-46 Package (10 sec.) 300˚C

SO Package

Vapor Phase (60 sec.) 215˚C

Infrared (15 sec.) 220˚C

See AN-450 “Surface Mounting Methods and Their Effect on

Product Reliability” (Appendix D) for other methods of sol-

dering surface mount devices.

Electrical Characteristics (Note 2)

Parameter Conditions LM134/LM234 LM334 Units

Min Typ Max Min Typ Max

Set Current Error, V

=2.5V, 10µA ≤I

SET

≤1mA 3 6 %

(Note 3) 1mA <I

SET

≤5mA 5 8 %

2µA ≤I

SET

<10µA 8 12 %

Ratio of Set Current to 100µA ≤I

SET

≤1mA 14 18 23 14 18 26

Bias Current 1mA ≤I

SET

≤5mA 14 14

2µA≤I

SET

≤100 µA 18 23 18 26

Minimum Operating Voltage 2µA ≤I

SET

≤100µA 0.8 0.8 V

100µA <I

SET

≤1mA 0.9 0.9 V

1mA <I

SET

≤5mA 1.0 1.0 V

Average Change in Set Current 2µA ≤I

SET

≤1mA

with Input Voltage 1.5 ≤V

≤5V 0.02 0.05 0.02 0.1 %/V

5V ≤V

≤40V 0.01 0.03 0.01 0.05 %/V

1mA <I

SET

≤5mA

1.5V ≤V≤5V 0.03 0.03 %/V

5V ≤V≤40V 0.02 0.02 %/V

Temperature Dependence of 25µA ≤I

SET

≤1mA 0.96T T 1.04T 0.96T T 1.04T

Set Current (Note 4)

Effective Shunt Capacitance 15 15 pF

Note 1: .“Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

functional, but do not guarantee specific performance limits.

Note 2: Unless otherwise specified, tests are performed at Tj= 25˚C with pulse testing so that junction temperature does not change during test

Note 3: Set current is the current flowing into the V+pin. For the Basic 2-Terminal Current Source circuit shown on the first page of this data sheet. ISET is

determined by the following formula: ISET = 67.7 mV/RSET (@25˚C). Set current error is expressed as a percent deviation from this amount. ISET increases at

0.336%/˚C @Tj= 25˚C (227 µV/˚C).

LM134/LM234/LM334

www.national.com 2

Electrical Characteristics (Note 2) (Continued)

Note 4: ISET is directly proportional to absolute temperature (˚K). ISET at any temperature can be calculated from: ISET =I

o(T/To) where Iois ISET measured at To

(˚K).

Note 5: For elevated temperature operation, TJmax is:

LM134 150˚C

LM234 125˚C

LM334 100˚C

Thermal Resistance TO-92 TO-46 SO-8

(Junction to

Ambient)

180˚C/W (0.4" leads) 440˚C/W 165˚C/W

160˚C/W (0.125"

leads)

(Junction to Case) N/A 32˚C/W 80˚C/W

Note 6: Human body model, 100pF discharged through a 1.5kΩresistor.

Electrical Characteristics (Note 2)

Parameter Conditions LM234-3 LM234-6 Units

Min Typ Max Min Typ Max

Set Current Error, V

=2.5V, 100µA ≤I

SET

≤1mA ±1±2%

(Note 3) T

= 25˚

Equivalent Temperature Error ±3±6˚C

Ratio of Set Current to 100µA ≤I

SET

≤1mA 14 18 26 14 18 26

Bias Current

Minimum Operating Voltage 100µA I

SET

≤1mA 0.9 0.9 V

Average Change in Set Current 100µA ≤I

SET

≤1mA

with Input Voltage 1.5 ≤V

≤5V 0.02 0.05 0.02 0.01 %/V

5V ≤V

≤30V 0.01 0.03 0.01 0.05 %/V

Temperature Dependence of 100µA ≤I

SET

≤1mA 0.98T T 1.02T 0.97T T 1.03T

Set Current (Note 4) and

Equivalent Slope Error ±2±3%

Effective Shunt Capacitance 15 15 pF

LM134/LM234/LM334

www.national.com3

Typical Performance Characteristics

Output Impedance

Maximum Slew Rate

Linear Operation

00569730 00569731

Start-Up Transient Response

00569732 00569733

Voltage Across R

SET

) Current Noise

00569734 00569735

LM134/LM234/LM334

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Typical Performance Characteristics (Continued)

Turn-On Voltage Ratio of I

SET

to I

BIAS

00569729 00569703

Application Hints

The LM134 has been designed for ease of application, but a

general discussion of design features is presented here to

familiarize the designer with device characteristics which

may not be immediately obvious. These include the effects

of slewing, power dissipation, capacitance, noise, and con-

tact resistance.

CALCULATING R

SET

The total current through the LM134 (I

SET

) is the sum of the

current going through the SET resistor (I

) and the LM134’s

bias current (I

BIAS

), as shown in Figure 1.

A graph showing the ratio of these two currents is supplied

under Ratio of I

SET

to I

BIAS

in the Typical Performance

Characteristics section. The current flowing through R

SET

determined by V

, which is approximately 214µV/˚K (64

mV/298˚K ∼214µV/˚K).

Since (for a given set current) I

BIAS

is simply a percentage of

SET

, the equation can be rewritten

where n is the ratio of I

SET

to I

BIAS

as specified in the

Electrical Characteristics Section and shown in the graph.

Since n is typically 18 for 2µA ≤I

SET

≤1mA, the equation can

be further simplified to

for most set currents.

SLEW RATE

At slew rates above a given threshold (see curve), the

LM134 may exhibit non-linear current shifts. The slewing

rate at which this occurs is directly proportional to I

SET

.At

SET

= 10µA, maximum dV/dt is 0.01V/µs; at I

SET

= 1mA, the

limit is 1V/µs. Slew rates above the limit do not harm the

LM134, or cause large currents to flow.

THERMAL EFFECTS

Internal heating can have a significant effect on current

regulation for I

SET

greater than 100µA. For example, each

1V increase across the LM134 at I

SET

= 1 mA will increase

junction temperature by ≈0.4˚C in still air. Output current

SET

) has a temperature coefficient of ≈0.33%/˚C, so the

change in current due to temperature rise will be (0.4)

(0.33) = 0.132%. This is a 10:1 degradation in regulation

compared to true electrical effects. Thermal effects, there-

fore, must be taken into account when DC regulation is

critical and I

SET

exceeds 100µA. Heat sinking of the TO-46

package or the TO-92 leads can reduce this effect by more

than 3:1.

SHUNT CAPACITANCE

In certain applications, the 15 pF shunt capacitance of the

LM134 may have to be reduced, either because of loading

problems or because it limits the AC output impedance of the

current source. This can be easily accomplished by buffering

the LM134 with an FET as shown in the applications. This

can reduce capacitance to less than 3 pF and improve

00569727

FIGURE 1. Basic Current Source

LM134/LM234/LM334

www.national.com5

Application Hints (Continued)

regulation by at least an order of magnitude. DC character-

istics (with the exception of minimum input voltage), are not

affected.

NOISE

Current noise generated by the LM134 is approximately 4

times the shot noise of a transistor. If the LM134 is used as

an active load for a transistor amplifier, input referred noise

will be increased by about 12dB. In many cases, this is

acceptable and a single stage amplifier can be built with a

voltage gain exceeding 2000.

LEAD RESISTANCE

The sense voltage which determines operating current of the

LM134 is less than 100mV. At this level, thermocouple or

lead resistance effects should be minimized by locating the

current setting resistor physically close to the device. Sock-

ets should be avoided if possible. It takes only 0.7Ωcontact

resistance to reduce output current by 1% at the 1 mA level.

SENSING TEMPERATURE

The LM134 makes an ideal remote temperature sensor be-

cause its current mode operation does not lose accuracy

over long wire runs. Output current is directly proportional to

absolute temperature in degrees Kelvin, according to the

following formula:

Calibration of the LM134 is greatly simplified because of the

fact that most of the initial inaccuracy is due to a gain term

(slope error) and not an offset. This means that a calibration

consisting of a gain adjustment only will trim both slope and

zero at the same time. In addition, gain adjustment is a one

point trim because the output of the LM134 extrapolates to

zero at 0˚K, independent of R

SET

or any initial inaccuracy.

This property of the LM134 is illustrated in the accompanying

graph. Line abc is the sensor current before trimming. Line

a'b'c' is the desired output. A gain trim done at T2 will move

the output from b to b' and will simultaneously correct the

slope so that the output at T1 and T3 will be correct. This

gain trim can be done on R

SET

or on the load resistor used

to terminate the LM134. Slope error after trim will normally

be less than ±1%. To maintain this accuracy, however, a low

temperature coefficient resistor must be used for R

SET

A 33 ppm/˚C drift of R

SET

will give a 1% slope error because

the resistor will normally see about the same temperature

variations as the LM134. Separating R

SET

from the LM134

requires 3 wires and has lead resistance problems, so is not

normally recommended. Metal film resistors with less than

20 ppm/˚C drift are readily available. Wire wound resistors

may also be used where best stability is required.

APPLICATION AS A ZERO TEMPERATURE

COEFFICENT CURRENT SOURCE

Adding a diode and a resistor to the standard LM134 con-

figuration can cancel the temperature-dependent character-

istic of the LM134. The circuit shown in Figure 3 balances

the positive tempco of the LM134 (about +0.23 mV/˚C) with

the negative tempco of a forward-biased silicon diode (about

−2.5 mV/˚C).

00569704

FIGURE 2. Gain Adjustment

LM134/LM234/LM334

www.national.com 6

Application Hints (Continued)

The set current (I

SET

) is the sum of I

and I

, each contrib-

uting approximately 50% of the set current, and I

BIAS

usually included in the I

term by increasing the V

value

used for calculations by 5.9%. (See CALCULATING R

SET

The first step is to minimize the tempco of the circuit, using

the following equations. An example is given using a value of

+227µV/˚C as the tempco of the LM134 (which includes the

BIAS

component), and −2.5 mV/˚C as the tempco of the

diode (for best results, this value should be directly mea-

sured or obtained from the manufacturer of the diode).

With the R

to R

ratio determined, values for R

and R

should be determined to give the desired set current. The

formula for calculating the set current at T = 25˚C is shown

below, followed by an example that assumes the forward

voltage drop across the diode (V

) is 0.6V, the voltage

across R

is 67.7mV (64 mV + 5.9% to account for I

BIAS

and R

= 10 (from the previous calculations).

This circuit will eliminate most of the LM134’s temperature

coefficient, and it does a good job even if the estimates of the

diode’s characteristics are not accurate (as the following

example will show). For lowest tempco with a specific diode

at the desired I

SET

, however, the circuit should be built and

tested over temperature. If the measured tempco of I

SET

positive, R

should be reduced. If the resulting tempco is

negative, R

should be increased. The recommended diode

for use in this circuit is the 1N457 because its tempco is

centered at 11 times the tempco of the LM134, allowing R

10 R

. You can also use this circuit to create a current source

with non-zero tempcos by setting the tempco component of

the tempco equation to the desired value instead of 0.

EXAMPLE: A 1mA, Zero-Tempco Current Source

First, solve for R

and R

The values of R

and R

can be changed to standard 1%

resistor values (R

= 133Ωand R

= 1.33kΩ) with less than

a 0.75% error.

00569728

FIGURE 3. Zero Tempco Current Source

LM134/LM234/LM334

www.national.com7

Application Hints (Continued)

If the forward voltage drop of the diode was 0.65V instead of

the estimate of 0.6V (an error of 8%), the actual set current

will be

an error of less than 5%.

If the estimate for the tempco of the diode’s forward voltage

drop was off, the tempco cancellation is still reasonably

effective. Assume the tempco of the diode is 2.6mV/˚C in-

stead of 2.5mV/˚C (an error of 4%). The tempco of the circuit

is now:

A 1mA LM134 current source with no temperature compen-

sation would have a set resistor of 68Ωand a resulting

tempco of

So even if the diode’s tempco varies as much as ±4% from

its estimated value, the circuit still eliminates 98% of the

LM134’s inherent tempco.

Typical Applications

Ground Referred Fahrenheit Thermometer

00569715

*Select R3 = VREF/583µA. VREF may be any stable positive voltage ≥2V

Trim R3 to calibrate

Terminating Remote Sensor for Voltage Output

00569714

Low Output Impedance Thermometer

00569706

*Output impedance of the LM134 at the “R” pin is approximately

where R2is the equivalent external resistance connected from the V−pin

to ground. This negative resistance can be reduced by a factor of 5 or

more by inserting an equivalent resistor R3=(R

2/16) in series with the

output.

Low Output Impedance Thermometer

00569716

LM134/LM234/LM334

www.national.com 8

Typical Applications (Continued)

Higher Output Current

00569705

*Select R1 and C1 for optimum stability

Basic 2-Terminal Current Source

00569701

Micropower Bias Low Input Voltage Reference Driver

00569717

00569718

LM134/LM234/LM334

www.national.com9

Typical Applications (Continued)

Ramp Generator

00569719

1.2V Reference Operates on 10 µA and 2V

00569720

*Select ratio of R1 to R2 to obtain zero temperature drift

1.2V Regulator with 1.8V Minimum Input

00569707

*Select ratio of R1 to R2 for zero temperature drift

Zener Biasing

00569749

Alternate Trimming Technique

00569750

*For ±10% adjustment, select RSET10% high, and make R1 ≈3R

SET

LM134/LM234/LM334

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Typical Applications (Continued)

Buffer for Photoconductive Cell

00569751

Generating Negative Output Impedance

00569723

*ZOUT ≈−16 •R1 (R1/VIN must not exceed ISET)

In-Line Current Limiter

00569709

*Use minimum value required to ensure stability of protected device. This

minimizes inrush current to a direct short.

Schematic Diagram

FET Cascoding for Low Capacitance and/or Ultra High Output Impedance

00569721

*Select Q1 or Q2 to ensure at least 1V across the LM134. Vp(1 −

ISET/IDSS)≥1.2V. 00569722

FIGURE 4.

LM134/LM234/LM334

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Schematic Diagram (Continued)

00569711

LM134/LM234/LM334

www.national.com 12

Physical Dimensions inches (millimeters)

unless otherwise noted

Order Number LM134H, LM234H or LM334H

NS Package Number H03H

SO Package (M)

Order Number LM334M, LM334MX,

LM334SM or LM334SMX

NS Package Number M08A

LM134/LM234/LM334

www.national.com13

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

Order Number LM334Z, LM234Z-3 or LM234Z-6

NS Package Number Z03A

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves

the right at any time without notice to change said circuitry and specifications.

For the most current product information visit us at www.national.com.

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2. A critical component is any component of a life support

device or system whose failure to perform can be reasonably

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LM134/LM234/LM334 3-Terminal Adjustable Current Sources

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