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 addi-
tion, 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 ac-
curacy. 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
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 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).
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
θja (Junction to Ambient) 180˚C/W (0.4" leads) 440˚C/W 165˚C/W
160˚C/W (0.125" leads)
θjc (Junction to Case) N/A 32˚C/W 80˚C/W
Note 6: Human body model, 100pF discharged through a 1.5kΩresistor.
LM134/LM234/LM334
www.national.com 2
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
www.national.com3
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
(V
R
)
DS005697-34
Current Noise
DS005697-35
LM134/LM234/LM334
www.national.com 4
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 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
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 Elec-
trical 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 effect on current regu-
lation 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, 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, 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 limits theAC 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 regu-
lation by at least an order of magnitude. DC characteristics
(with the exception of minimum input voltage), are not af-
fected.
Turn-On Voltage
DS005697-29
Ratio of I
SET
to I
BIAS
DS005697-3
DS005697-27
FIGURE 1. Basic Current Source
LM134/LM234/LM334
www.national.com5
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 ac-
ceptable and a single stage amplifier can be built with a volt-
age 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 fol-
lowing 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).
The set current (I
SET
) is the sum of I
1
and I
2
, each contribut-
ing approximately 50% of the set current, and I
BIAS
.I
BIAS
is
usually included in the I
1
term by increasing the V
R
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
I
BIAS
component), and −2.5 mV/˚C as the tempco of the di-
ode (for best results, this value should be directly measured
or obtained from the manufacturer of the diode).
With the R
1
to R
2
ratio determined, values for R
1
and 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
/R
1
= 10 (from the previous calculations).
DS005697-4
FIGURE 2. Gain Adjustment
DS005697-28
FIGURE 3. Zero Tempco Current Source
LM134/LM234/LM334
www.national.com 6
Application Hints (Continued)
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 ex-
ample 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 this circuit is the 1N457 because its tempco is cen-
tered 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 R
2
:
The values of R
1
and R
2
can be changed to standard 1% re-
sistor values (R
1
= 133Ωand R
2
= 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 ef-
fective.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 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
DS005697-15
*Select R3 = VREF/583µA. VREF may be any stable positive voltage ≥2V
Trim R3 to calibrate
LM134/LM234/LM334
www.national.com7
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 R3=(R
2
/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
www.national.com 8
Typical Applications (Continued)
Micropower Bias
DS005697-17
Low Input Voltage Reference Driver
DS005697-18
Ramp Generator
DS005697-19
LM134/LM234/LM334
www.national.com9
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 RSET
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 −
ISET/IDSS)≥1.2V. DS005697-22
LM134/LM234/LM334
www.national.com 10
Typical Applications (Continued)
Schematic Diagram
Generating Negative Output Impedance
DS005697-23
*ZOUT ≈−16 •R1 (R1/VIN must not exceed ISET)
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
www.national.com11
Physical Dimensions inches (millimeters) unless otherwise noted
Order Number LM134H, LM234H or LM334H
NS Package Number H03H
LM134/LM234/LM334
www.national.com 12
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
www.national.com13
Notes
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 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.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
National Semiconductor
Europe Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: ap.support@nsc.com
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
www.national.com
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.
