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PDF LM134 Data sheet ( Hoja de datos )
| Número de pieza | LM134 | |
| Descripción | 3-Terminal Adjustable Current Sources | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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March 2000
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
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
SO-8 Alternative Pinout
Surface Mount Package
TO-46
Metal Can Package
DS005697-24
Order Number LM334M or
LM334MX
See NS Package Number M08A
DS005697-25
Order Number LM334SM or
LM334SMX
See NS Package Number M08A
TO-92 Plastic Package
DS005697-12
V− Pin is electrically connected to case.
Bottom View
Order Number LM134H,
LM234H or LM334H
See NS Package
Number H03H
DS005697-10
Bottom View
Order Number LM334Z, LM234Z-3 or LM234Z-6
See NS Package Number Z03A
© 2000 National Semiconductor Corporation DS005697
www.national.com
1 page  
Typical Performance Characteristics (Continued)
Turn-On Voltage
Ratio of ISET to IBIAS
DS005697-29
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.
DS005697-27
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 214µV/˚K (64 mV/
298˚K ∼ 214µV/˚K).
Since (for a given set current) IBIAS is simply a percentage of
ISET, the equation can be rewritten
DS005697-3
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 2µA ≤ ISET ≤ 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 ISET. At
ISET = 10µA, maximum dV/dt is 0.01V/µs; at ISET = 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 ISET greater than 100µA. For example, each 1V in-
crease across the LM134 at ISET = 1 mA will increase junc-
tion 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) = 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 ISET 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 regu-
lation by at least an order of magnitude. DC characteristics
(with the exception of minimum input voltage), are not af-
fected.
5 www.national.com
5 Page 
Typical Applications (Continued)
Generating Negative Output Impedance
In-Line Current Limiter
DS005697-23
*ZOUT ≈ −16 • R1 (R1/VIN must not exceed ISET)
Schematic Diagram
DS005697-9
*Use minimum value required to ensure stability of protected device. This
minimizes inrush current to a direct short.
DS005697-11
11 www.national.com
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet LM134.PDF ] | |
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