Datasheet LM334Z, LM334SMX, LM334SM, LM334MX, LM334M Datasheet (NSC)

LM134/LM234/LM334
3-Terminal Adjustable Current Sources

General Description

The LM134/LM234/LM334 are 3-terminal adjustable current
sources featuring10,000:1 range in operating current, excel­lent 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. Inaddi­tion, 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 abso­lute temperature (˚K). The simplest one external resistor
connection, then, generates a current with ≈+0.33%/˚C tem­perature 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 be­cause 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

n Operates from 1V to 40V
n 0.02%/V current regulation
n Programmable from 1µA to 10mA
n True 2-terminal operation
n Available as fully specified temperature sensor

n

±

3% initial accuracy

Connection Diagrams

SO-8

Surface Mount Package

DS005697-24

Order Number LM334M or

LM334MX

See NS Package Number M08A

SO-8 Alternative Pinout
Surface Mount Package

DS005697-25

Order Number LM334SM or

LM334SMX

See NS Package Number M08A

TO-46

Metal Can Package

DS005697-12

V−Pin is electrically connected to case.

Bottom View

Order Number LM134H,

LM234H or LM334H

See NS Package

Number H03H

TO-92 Plastic Package

DS005697-10

Bottom View

Order Number LM334Z, LM234Z-3 or LM234Z-6

See NS Package Number Z03A

March 2000

LM134/LM234/LM334 3-Terminal Adjustable Current Sources

© 2000 National Semiconductor Corporation DS005697 www.national.com

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

V

+

to V−Forward Voltage
LM134/LM234/LM334 40V
LM234-3/LM234-6 30V

V

+

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 5)

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 sol­dering 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 T

j

= 25˚C with pulse testing so that junction temperature does not change during test

Note 3: Set current is thecurrentflowingintotheV

+

pin. For the Basic 2-TerminalCurrentSourcecircuitshownonthefirst page of this data sheet. I

SET

is determined

by the following formula: I

SET

= 67.7 mV/R

SET

(@25˚C). Set current error is expressed as a percent deviation from this amount. I

SET

increases at 0.336%/˚C@T

j

= 25˚C (227 µV/˚C).
Note 4: I

SET

is directly proportional to absolute temperature (˚K). I

SET

at any temperature can be calculated from: I

SET=Io

(T/To) where Iois I

SET

measured at T

o

(˚K).
Note 5: For elevated temperature operation, T

J

max is:

LM134 150˚C
LM234 125˚C
LM334 100˚C

Thermal Resistance TO-92 TO-46 SO-8

θ

ja

(Junction to Ambient) 180˚C/W (0.4" leads) 440˚C/W 165˚C/W

160˚C/W (0.125" leads)

θ

jc

(Junction to Case) N/A 32˚C/W 80˚C/W

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

LM134/LM234/LM334

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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

J

= 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

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Typical Performance Characteristics

Output Impedance

DS005697-30

Maximum Slew Rate
Linear Operation

DS005697-31

Start-Up

DS005697-32

Transient Response

DS005697-33

Voltage Across R

SET(VR

)

DS005697-34

Current Noise

DS005697-35

LM134/LM234/LM334

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Typical Performance Characteristics (Continued)

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 con­tact resistance.

CALCULATING R

SET

The total current through the LM134 (I

SET

) is the sum of the

current going through the SET resistor (I

R

) 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

is

determined by V

R

, which is approximately 214µV/˚K (64 mV/

298˚K ∼ 214µV/˚K).

Since (for a given set current) I

BIAS

is simply a percentage of

I

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

I

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 effecton currentregu­lation for I

SET

greater than 100µA. For example, each 1V in-

crease across the LM134 at I

SET

= 1 mA will increase junc-

tion temperature by ≈0.4˚C in still air. Output current (I

SET

)
has a temperature coefficient of≈0.33%/˚C, sothe changein
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, therefore, 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 limitsthe AC outputimpedance 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 regu­lation by at least an order of magnitude. DC characteristics
(with the exception of minimum input voltage), are not af­fected.

Turn-On Voltage

DS005697-29

Ratio of I

SET

to I

BIAS

DS005697-3

DS005697-27

FIGURE 1. Basic Current Source

LM134/LM234/LM334

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Application Hints (Continued)

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. Sock­ets should be avoided if possible. It takes only 0.7Ω contact
resistance to reduce output current by 1% at the 1 mA level.

SENSING TEMPERATURE

The LM134 makes an ideal remote temperature sensor be­cause 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 LM134is illustrated in the accompanying
graph. Line abc is the sensor current before trimming. Line
a'b'c' is the desired output. Again 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 con­figuration can cancel the temperature-dependent character­istic 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).

The set current (I

SET

) is the sum of I1and I2, each contribut-

ing approximately 50% of the set current, and I

BIAS.IBIAS

is

usually included in the I

1

term by increasing the VRvalue

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
I

BIAS

component), and −2.5 mV/˚C as the tempco of the di­ode (for best results, this value should be directly measured
or obtained from the manufacturer of the diode).

With the R1to R2ratio determined, values for R1and R

2

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

D

) is 0.6V, the voltage

across R

1

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

BIAS

),

and R

2/R1

= 10 (from the previous calculations).

DS005697-4

FIGURE 2. Gain Adjustment

DS005697-28

FIGURE 3. Zero Tempco Current Source

LM134/LM234/LM334

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Application Hints (Continued)

This circuit will eliminate most of the LM134’s temperature
coefficient, and itdoes a goodjob even if the estimatesof 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

is

positive, R

2

should be reduced. If the resulting tempco is

negative, R

2

should be increased. The recommended diode
for use in thiscircuit is the 1N457 because its tempco is cen­tered at 11 times the tempco of the LM134, allowing R

2

=10

R

1

. 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

1

and R2:

The values of R1and R2can be changed to standard 1% re­sistor values (R

1

= 133Ω and R2= 1.33kΩ) with less than a

0.75% error.
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 instead
of 2.5mV/˚C (an error of 4%). The tempco of the circuit is
now:

A 1mA LM134 current source with no temperature compen­sation would have a set resistor of 68Ω and 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

DS005697-15

*

Select R3 = V

REF

/583µA. V

REF

may be any stable positive voltage ≥ 2V

Trim R3 to calibrate

LM134/LM234/LM334

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Typical Applications (Continued)

Terminating Remote Sensor for Voltage Output

DS005697-14

Low Output Impedance Thermometer

DS005697-6

*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 R

3

=(R2/16) in series with the

output.

Low Output Impedance Thermometer

DS005697-16

Higher Output Current

DS005697-5

*Select R1 and C1 for optimum stability

Basic 2-Terminal Current Source

DS005697-1

LM134/LM234/LM334

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Typical Applications (Continued)

Micropower Bias

DS005697-17

Low Input Voltage Reference Driver

DS005697-18

Ramp Generator

DS005697-19

LM134/LM234/LM334

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Typical Applications (Continued)

1.2V Reference Operates on 10 µA and 2V

DS005697-20

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

1.2V Regulator with 1.8V Minimum Input

DS005697-7

*Select ratio of R1 to R2 for zero temperature drift

Zener Biasing

DS005697-49

Alternate Trimming Technique

DS005697-50

*For±10% adjustment, select R

SET

10% high, and make R1 ≈ 3R

SET

Buffer for Photoconductive Cell

DS005697-51

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

DS005697-21

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

SET/IDSS

) ≥ 1.2V.

DS005697-22

LM134/LM234/LM334

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Typical Applications (Continued)

Schematic Diagram

Generating Negative Output Impedance

DS005697-23

*Z

OUT

≈ −16•R1 (R1/VINmust not exceed I

SET

)

In-Line Current Limiter

DS005697-9

*Use minimum value required to ensure stability of protected device. This
minimizes inrush current to a direct short.

DS005697-11

LM134/LM234/LM334

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Physical Dimensions inches (millimeters) unless otherwise noted

Order Number LM134H, LM234H or LM334H

NS Package Number H03H

LM134/LM234/LM334

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

SO Package (M)

Order Number LM334M, LM334MX,

LM334SM or LM334SMX

NS Package Number M08A

Order Number LM334Z, LM234Z-3 or LM234Z-6

NS Package Number Z03A

LM134/LM234/LM334

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Notes

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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.

2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.

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LM134/LM234/LM334 3-Terminal Adjustable Current Sources

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.