LM134/LM234/LM334 - National Semiconductor

TL/H/5697

LM134/LM234/LM334 3-Terminal Adjustable Current Sources

March 1995

LM134/LM234/LM334

3-Terminal Adjustable Current Sources

General Description

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

rent sources featuring 10,000:1 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 accu-

racy is g3%. The LM134/LM234/LM334 are true floating

current sources with no separate power supply connections.

In addition, reverse applied voltages of up to 20V will draw

only a few dozen microamperes of current, allowing the de-

vices to act as both a rectifier and current source in AC

applications.

The sense voltage used to establish operating current in the

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

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

connection, then, generates a current with &a0.33%/§C

temperature dependence. Zero drift operation can be ob-

tained 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 LM134-3/

LM234-3 and LM134-6/LM234-6 are specified as true tem-

perature sensors with guaranteed initial accuracy of g3§C

and g6§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

b55§Ctoa

125§C, the LM234 from b25§Ctoa

100§C and

the LM334 from 0§Ctoa

70§C. These devices are available

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

Features

YOperates from 1V to 40V

Y0.02%/V current regulation

YProgrammable from 1 mAto10mA

YTrue 2-terminal operation

YAvailable as fully specified temperature sensor

Yg3% initial accuracy

Connection Diagrams

SO-8

Surface Mount Package

TL/H/5697– 24

Order Number LM334M

See NS Package

Number M08A

Typical Application

Basic 2-Terminal Current Source

TL/H/5697– 1

SO-8 Alternative Pinout

Surface Mount Package

TL/H/5697– 25

Order Number LM334SM

See NS Package

Number M08A

TO-46

Metal Can Package

TL/H/5697– 12

Bottom View

VbPin is electrically

connected to case.

Order Number LM134H,

LM134H-3, LM134H-6,

LM234H or LM334H

See NS Package

Number H03H

TO-92

Plastic Package

TL/H/5697– 10

Bottom View

Order Number LM334Z,

LM234Z-3 or LM234Z-6

See NS Package

Number Z03A

C1995 National Semiconductor Corporation RRD-B30M75/Printed in U. S. A.

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

Vato VbForward Voltage

LM134/LM234/LM334 40V

LM134-3/LM134-6/LM234-3/LM234-6 30V

Vato VbReverse Voltage 20V

R Pin to VbVoltage 5V

Set Current 10 mA

Power Dissipation 400 mW

ESD Susceptibility (Note 5) 2000V

Operating Temperature Range (Note 4)

LM134/LM134-3/LM134-6 b55§Ctoa

125§C

LM234/LM234-3/LM234-6 b25§Ctoa

100§C

LM334 0§Ctoa

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 1)

Parameter Conditions LM134/LM234 LM334 Units

Min Typ Max Min Typ Max

Set Current Error, Vae2.5V, 10 mAsISETs1mA 3 6 %

(Note 2) 1 mAkISETs5mA 5 8 %

2mA

SETk10 mA 8 12 %

Ratio of Set Current to 100 mAsISETs1mA141823 141826

Bias Current 1 mAsISETs5mA 14 14

2mA

SETs100 mA1823 1826

Minimum Operating Voltage 2 mAsISETs100 mA 0.8 0.8 V

100 mAkISETs1 mA 0.9 0.9 V

1mA

SETs5 mA 1.0 1.0 V

Average Change in Set Current 2 mAsISETs1mA

with Input Voltage 1.5sVas5V 0.02 0.05 0.02 0.1 %/V

5VsVas40V 0.01 0.03 0.01 0.05 %/V

1mA

SETs5mA

1.5VsVs5V 0.03 0.03 %/V

5VsVs40V 0.02 0.02 %/V

Temperature Dependence of 25 mAsISETs1 mA 0.96T T 1.04T 0.96T T 1.04T

Set Current (Note 3)

Effective Shunt Capacitance 15 15 pF

Note 1: Unless otherwise specified, tests are performed at Tje25§C with pulse testing so that junction temperature does not change during test.

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

determined by the following formula: ISETe67.7 mV/RSET (@25§C). Set current error is expressed as a percent deviation from this amount. ISET increases at

0.336%/§C@Tje25§C (227 mV/§C).

Note 3: ISET is directly proportional to absolute temperature (§K). ISET at any temperature can be calculated from: ISETeIo(T/To) where Iois ISET measured at To

(§K).

Note 4: For elevated temperature operation, Tjmax is:

LM134 150§C

LM234 125§C

LM334 100§C

Thermal Resistance TO-92 TO-46 SO-8

ija (Junction to Ambient) 180§C/W (0.4×leads) 440§C/W 165§C/W

160§C/W (0.125×leads)

ijc (Junction to Case) N/A 32§C/W 80§C/W

Note 5: Human body model, 100 pF discharged through a 1.5 kXresistor.

Electrical Characteristics (Note 1) (Continued)

Parameter Conditions LM134-3, LM234-3 LM134-6, LM234-6 Units

Min Typ Max Min Typ Max

Set Current Error, Vae2.5V, 100 mAsISETs1mA g

(Note 2) Tje25§

Equivalent Temperature Error g3g6§C

Ratio of Set Current to 100 mAsISETs1mA141826 141826

Bias Current

Minimum Operating Voltage 100 mAI

SETs1 mA 0.9 0.9 V

Average Change in Set Current 100 mAsISETs1mA

with Input Voltage 1.5sVas5V 0.02 0.05 0.02 0.01 %/V

5VsVas30V 0.01 0.03 0.01 0.05 %/V

Temperature Dependence of 100 mAsISETs1 mA 0.98T T 1.02T 0.97T T 1.03T

Set Current (Note 3) and

Equivalent Slope Error g2g3%

Effective Shunt Capacitance 15 15 pF

Typical Performance Characteristics

Output Impedance

Maximum Slew Rate for

Linear Operation Start-Up

Transient Response Voltage Across RSET (VR) Current Noise

TL/H/5697– 2

Typical Performance Characteristics (Continued)

Turn-On Voltage

TL/H/5697– 29

Ratio of ISET to IBIAS

TL/H/5697– 3

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 RSET

The total current through the LM134 (ISET) is the sum of the

current going through the SET resistor (IR) and the LM134’s

bias current (IBIAS), as shown in

Figure 1.

TL/H/5697– 27

FIGURE 1. Basic Current Source

A graph showing the ratio of these two currents is supplied

under Ratio of ISET to IBIAS in the Typical Performance

Characteristics section. The current flowing through RSET is

determined by VR, which is approximately 214 mV/§K

(64 mV/298§KE214 mV/§K).

ISET eIRaIBIAS eVR

RSET

aIBIAS

Since (for a given set current) IBIAS is simply a percentage

of ISET, the equation can be rewritten

ISET e#VR

RSET J#n

nb1J

where n is the ratio of ISET to IBIAS as specified in the Elec-

trical Characteristics Section and shown in the graph. Since

n is typically 18 for 2 mAsISET s1 mA, the equation can

be further simplified to

ISET e#VR

RSET J(1.059) e227 mV/§K

RSET

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 ISET.At

SET e10 mA, maximum dV/dt is 0.01V/ms; at ISET e

1 mA, the limit is 1V/ms. 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 reg-

ulation for ISET greater than 100 mA. For example, each 1V

increase across the LM134 at ISET e1 mA will increase

junction temperature by &0.4§C in still air. Output current

(ISET) has a temperature coefficient of &0.33%/§C, so the

change in current due to temperature rise will be

(0.4) (0.33) e0.132%. This is a 10:1 degradation in regula-

tion compared to true electrical effects. Thermal effects,

therefore, must be taken into account when DC regulation is

critical and ISET exceeds 100 mA. Heat sinking of the TO-46

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

than 3:1.

Application Hints (Continued)

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 buff-

ering 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 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 12 dB. 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 100 mV. 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 0.7X

contact 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:

ISET e(227 mV/§K) (T)

RSET

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 RSET or any initial inaccuracy.

TL/H/5697– 4

FIGURE 2. Gain Adjustment

This property of the LM134 is illustrated in the accompany-

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

Line aÊbÊcÊis the desired output. A gain trim done at T2 will

move the output from b to bÊand will simultaneously correct

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

This gain trim can be done on RSET or on the load resistor

used to terminate the LM134. Slope error after trim will nor-

mally be less than g1%. To maintain this accuracy, howev-

er, a low temperature coefficient resistor must be used for

RSET.

A 33 ppm/§C drift of RSET will give a 1% slope error be-

cause the resistor will normally see about the same temper-

ature variations as the LM134. Separating RSET 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 config-

uration can cancel the temperature-dependent characteris-

tic of the LM134. The circuit shown in

Figure 3

balances the

positive tempco of the LM134 (about a0.23 mV/§C) with

the negative tempco of a forward-biased silicon diode

(about b2.5 mV/§C).

TL/H/5697– 28

FIGURE 3. Zero Tempco Current Source

The set current (ISET) is the sum of I1and I2, each contribut-

ing approximately 50% of the set current, and IBIAS.I

BIAS is

usually included in the I1term by increasing the VRvalue

used for calculations by 5.9%. (See CALCULATING RSET.)

ISET eI1aI2aIBIAS, where

I1eVR

and I2eVRaVD

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

the following equations. An example is given using a value

of a227 mV/§C as the tempco of the LM134 (which in-

cludes the IBIAS component), and b2.5 mV/§C as the temp-

co of the diode (for best results, this value should be directly

measured or obtained from the manufacturer of the diode).

ISET eI1aI2

dISET

dT edI1

dT adI2

&227 mV/§C

a227 mV/§Cb2.5 mV/§C

e0 (solve for tempco e0)

Application Hints (Continued)

&2.5 mV/§Cb227 mV/§C

227 mV/§C&10.0

With the R1to R2ratio determined, values for R1and R2

should be determined to give the desired set current. The

formula for calculating the set current at T e25§C is shown

below, followed by an example that assumes the forward

voltage drop across the diode (VD) is 0.6V, the voltage

across R1is 67.7 mV (64 mV a5.9% to account for IBIAS),

and R2/R1e10 (from the previous calculations).

ISET eI1aI2aIBIAS

eVR

aVRaVD

&67.7 mV

a67.7 mV a0.6V

10.0 R1

ISET &0.134V

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 ISET, however, the circuit should be built and

tested over temperature. If the measured tempco of ISET is

positive, R2should be reduced. If the resulting tempco is

negative, R2should 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 R2

e10 R1. You can also use this circuit to create a current

source with non-zero tempcos by setting the tempco com-

ponent of the tempco equation to the desired value instead

of 0.

EXAMPLE: A 1 mA, Zero-Tempco Current Source

First, solve for R1and R2:

ISET &1mAe0.134V

R1e134Xe10 R2

R2e1340X

The values of R1and R2can be changed to standard 1%

resistor values (R1e133Xand R2e1.33 kX) 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 cur-

rent will be

ISET e67.7 mV

a67.7 mV a0.65V

e67.7 mV

133 a67.7 mV a0.65V

1330

e1.049 mA

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 ef-

fective. Assume the tempco of the diode is 2.6 mV/§C in-

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

circuit is now:

dISET

dT edI1

dT adI2

e227 mV/§C

133X

a227 mV/§Cb2.6 mV/§C

1330X

77 nA/§C

A 1 mA LM134 current source with no temperature compen-

sation would have a set resistor of 68Xand a resulting

tempco of

227 mV/§C

68X

e3.3 mA/§C

So even if the diode’s tempco varies as much as g4% from

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

LM134’s inherent tempco.

Typical Applications

Ground Referred Fahrenheit Thermometer

TL/H/5697– 15

*Select R3 eVREF/583 mA. VREF may be any stable positive voltage t2V

Trim R3 to calibrate

Terminating Remote Sensor for Voltage Output

TL/H/5697– 14

Typical Applications (Continued)

Low Output Impedance Thermometer

*Output impedance of the LM134 at the ‘‘R’’ pin is

approximately bR2

16 where R2is the equivalent

external resistance connected from the Vbpin to

ground. This negative resistance can be reduced

by a factor of 5 or more by inserting an equivalent

resistor R3e(R2/16) in series with the output.

TL/H/5697– 6

Low Output Impedance Thermometer

TL/H/5697– 16

Higher Output Current

TL/H/5697– 5

*Select R1 and C1 for optimum stability

Micropower Bias

TL/H/5697– 17

Low Input Voltage Reference Driver

TL/H/5697– 18

Typical Applications (Continued)

Ramp Generator

TL/H/5697– 19

1.2V Reference Operates on 10 mA and 2V

TL/H/5697– 20

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

1.2V Regulator with 1.8V Minimum Input

TL/H/5697– 7

*Select ratio of R1 to R2 for zero temperature drift

Zener Biasing Alternate Trimming Technique Buffer for Photoconductive Cell

TL/H/5697– 8

*For g10% adjustment, select RSET

10% high, and make R1 &3R

SET

Typical Applications (Continued)

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

TL/H/5697– 21

TL/H/5697– 22

*Select Q1 or Q2 to ensure at least 1V across the LM134. Vp(1 bISET/IDSS)t1.2V.

Generating Negative Output Impedance

TL/H/5697– 23

*ZOUT &b16 #R1 (R1/VIN must not exceed ISET)

In-Line Current Limiter

TL/H/5697– 9

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

minimizes inrush current to a direct short.

Schematic Diagram

TL/H/5697– 11

Physical Dimensions inches (millimeters)

Order Number LM134H, LM134H-3,

LM134H-6, LM234H or LM334H

NS Package Number H03H

Physical Dimensions inches (millimeters) (Continued)

SO Package (M)

Order Number LM334M or LM334SM

NS Package Number M08A

LM134/LM234/LM334 3-Terminal Adjustable Current Sources

Physical Dimensions inches (millimeters) (Continued)

Order Number LM334Z, LM234Z-3 or LM234Z-6

NS Package Number Z03A

LIFE SUPPORT POLICY

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 OF NATIONAL

SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or 2. A critical component is any component of a life

systems which, (a) are intended for surgical implant support device or system whose failure to perform can

into the body, or (b) support or sustain life, and whose be reasonably expected to cause the failure of the life

failure to perform, when properly used in accordance support device or system, or to affect its safety or

with instructions for use provided in the labeling, can effectiveness.

be reasonably expected to result in a significant injury

to the user.

National Semiconductor National Semiconductor National Semiconductor National Semiconductor National Semiconductores National Semiconductor

Corporation GmbH Japan Ltd. Hong Kong Ltd. Do Brazil Ltda. (Australia) Pty, Ltd.

2900 Semiconductor Drive Livry-Gargan-Str. 10 Sumitomo Chemical 13th Floor, Straight Block, Rue Deputado Lacorda Franco Building 16

P.O. Box 58090 D-82256 F4urstenfeldbruck Engineering Center Ocean Centre, 5 Canton Rd. 120-3A Business Park Drive

Santa Clara, CA 95052-8090 Germany Bldg. 7F Tsimshatsui, Kowloon Sao Paulo-SP Monash Business Park

Tel: 1(800) 272-9959 Tel: (81-41) 35-0 1-7-1, Nakase, Mihama-Ku Hong Kong Brazil 05418-000 Nottinghill, Melbourne

TWX: (910) 339-9240 Telex: 527649 Chiba-City, Tel: (852) 2737-1600 Tel: (55-11) 212-5066 Victoria 3168 Australia

Fax: (81-41) 35-1 Ciba Prefecture 261 Fax: (852) 2736-9960 Telex: 391-1131931 NSBR BR Tel: (3) 558-9999

Tel: (043) 299-2300 Fax: (55-11) 212-1181 Fax: (3) 558-9998

Fax: (043) 299-2500

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.