Rainbow Electronics LM334 User Manual
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, 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. In addition, 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
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
March 2000
±
3˚C and±6˚C, respectively.
LM134/LM234/LM334 3-Terminal Adjustable Current Sources
Connection Diagrams
SO-8
Surface Mount Package
Order Number LM334M or LM334MX
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
00569724
SO-8 Alternative Pinout
Surface Mount Package
00569725
Order Number LM334SM or LM334SMX
See NS Package Number M08A
00569710
Bottom View
Order Number LM334Z, LM234Z-3 or LM234Z-6
See NS Package Number Z03A
© 2004 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.
+
to V−Forward Voltage
V
LM134/LM234/LM334 40V
LM134/LM234/LM334
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
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.
ESD Susceptibility (Note 6) 2000V
Operating Temperature Range (Note
5)
LM134 −55˚C to +125˚C
Electrical Characteristics (Note 2)
Parameter Conditions LM134/LM234 LM334 Units
Set Current Error, V
(Note 3) 1mA
Ratio of Set Current to 100µA ≤ I
Bias Current 1mA ≤ I
Minimum Operating Voltage 2µA ≤ I
Average Change in Set Current 2µA ≤ I
with Input Voltage 1.5 ≤ V
+
=2.5V, 10µA ≤ I
2µA ≤ I
2µA≤I
100µA
1mA
5V ≤ V
1mA
≤ 1mA 3 6 %
SET
<
I
≤ 5mA 5 8 %
SET
<
10µA 8 12 %
SET
≤ 1mA 14 18 23 14 18 26
SET
≤ 5mA 14 14
SET
≤100 µA 18 23 18 26
SET
≤ 100µA 0.8 0.8 V
SET
<
I
≤ 1mA 0.9 0.9 V
SET
<
I
≤ 5mA 1.0 1.0 V
SET
≤ 1mA
SET
+
≤ 5V 0.02 0.05 0.02 0.1 %/V
+
≤ 40V 0.01 0.03 0.01 0.05 %/V
<
I
≤ 5mA
SET
1.5V ≤ V ≤ 5V 0.03 0.03 %/V
5V ≤ V ≤ 40V 0.02 0.02 %/V
Temperature Dependence of 25µA ≤ I
≤ 1mA 0.96T T 1.04T 0.96T T 1.04T
SET
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
Note 3: Set current is the current flowing into the V
determined by the following formula: I
0.336%/˚C
@
Tj= 25˚C (227 µV/˚C).
= 67.7 mV/R
SET
= 25˚C with pulse testing so that junction temperature does not change during test
j
+
pin. For the Basic 2-Terminal Current Source circuit shown on the first page of this data sheet. I
(@25˚C). Set current error is expressed as a percent deviation from this amount. I
SET
Min Typ Max Min Typ Max
SET
SET
increases at
is
www.national.com 2
Electrical Characteristics (Note 2) (Continued)
Note 4: I
(˚K).
Note 5: For elevated temperature operation, T
Note 6: Human body model, 100pF discharged through a 1.5kΩ resistor.
is directly proportional to absolute temperature (˚K). I
SET
max is:
J
Thermal Resistance TO-92 TO-46 SO-8
θ
(Junction to
ja
Ambient)
(Junction to Case) N/A 32˚C/W 80˚C/W
θ
jc
at any temperature can be calculated from: I
SET
SET=Io
LM134 150˚C
LM234 125˚C
LM334 100˚C
180˚C/W (0.4" leads) 440˚C/W 165˚C/W
160˚C/W (0.125"
leads)
(T/To) where Iois I
measured at T
SET
Electrical Characteristics (Note 2)
Parameter Conditions LM234-3 LM234-6 Units
Set Current Error, V
(Note 3) T
+
=2.5V, 100µA ≤ I
= 25˚
J
SET
≤ 1mA
Equivalent Temperature Error
Ratio of Set Current to 100µA ≤ I
≤ 1mA 14 18 26 14 18 26
SET
Bias Current
Minimum Operating Voltage 100µA I
Average Change in Set Current 100µA ≤ I
with Input Voltage 1.5 ≤ V
5V ≤ V
Temperature Dependence of 100µA ≤ I
≤ 1mA 0.9 0.9 V
SET
≤ 1mA
SET
+
≤ 5V 0.02 0.05 0.02 0.01 %/V
+
≤ 30V 0.01 0.03 0.01 0.05 %/V
≤ 1mA 0.98T T 1.02T 0.97T T 1.03T
SET
Set Current (Note 4) and
Equivalent Slope Error
Effective Shunt Capacitance 15 15 pF
Min Typ Max Min Typ Max
±
1
±
3
±
2
±
±
±
2%
6˚C
3%
LM134/LM234/LM334
o
www.national.com3
Typical Performance Characteristics
Output Impedance
LM134/LM234/LM334
00569730 00569731
Start-Up Transient Response
Maximum Slew Rate
Linear Operation
Voltage Across R
00569732
) Current Noise
SET(VR
00569734
00569733
00569735
www.national.com 4
Typical Performance Characteristics (Continued)
LM134/LM234/LM334
Turn-On Voltage Ratio of I
00569729
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
The total current through the LM134 (I
current going through the SET resistor (I
bias current (I
SET
), as shown in Figure 1.
BIAS
) is the sum of the
SET
) and the LM134’s
R
to I
SET
BIAS
00569703
where n is the ratio of I
SET
to I
as specified in the
BIAS
Electrical Characteristics Section and shown in the graph.
Since n is typically 18 for 2µA ≤ I
≤ 1mA, the equation can
SET
be further simplified to
for most set currents.
00569727
FIGURE 1. Basic Current Source
A graph showing the ratio of these two currents is supplied
under Ratio of I
SET
to I
Characteristics section. The current flowing through R
determined by V
, which is approximately 214µV/˚K (64
R
in the Typical Performance
BIAS
SET
mV/298˚K ∼ 214µV/˚K).
Since (for a given set current) I
, the equation can be rewritten
I
SET
is simply a percentage of
BIAS
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
= 10µA, maximum dV/dt is 0.01V/µs; at I
I
SET
SET
.At
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
1V increase across the LM134 at I
greater than 100µA. For example, each
SET
= 1 mA will increase
SET
junction temperature by ≈0.4˚C in still air. Output current
) has a temperature coefficient of ≈0.33%/˚C, so the
(I
SET
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
is
package or the TO-92 leads can reduce this effect by more
exceeds 100µA. Heat sinking of the TO-46
SET
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
www.national.com5
Loading...