Three terminal adjustable current sources
Features
■■■■
Operates from 1V to 40V0.02%/V current regulationProgrammable from 1µA to 10mA±3% initial accuracy
ZTO-92(Plastic package)Description
The LM134/LM234/LM334 are 3-terminal adjustable current sources characterized by:
■■■
an operating current range of 10000: 1an excellent current regulation
a wide dynamic voltage range of 1V t 10V
DSO-8(Plastic micropackage)The current is determined by an external resistor without requiring other external components.Reverse voltages of up to 20V will only draw a current of several microamperes. This enables the circuit to operate as a rectifier and as a source of current in a.c. applications.
For the LM134/LM234/LM334, the voltage on the control pin is 64mV at +25°C and is directly
proportional to the absolute temperature (°K). The simplest external resistor connection generates a current with approximately 0.33%/°C temperature dependence. Zero drift can be obtained by adding an additional resistor and a diode to the external circuit.
Pin connectionsTO-92(Bottom view)v+2ADJ1v-3SO-8(Top view)NC8NC7V-6NC51ADJ2NC3NC4V+
May 2007 Rev 31/16
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Schematic diagramLM134-LM234-LM334
1 Schematic diagram
Figure 1.
Schematic diagram
2 Absolute maximum ratings
Table 1.
Symbol
Absolute maximum ratings
Parameter
Voltage V+ to V-Forward
Reverse
LM134
4020
510400-65 to +150
-55 to +125
-25 to +100
0 to +70
LM234
LM3343020
UnitVVmAmW°C°C
VADJ-IsetPtotTstgToper
ADJ pin to V- voltageSet currentPower dissipation
Storage temperature range
Operating free-air temperature range
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LM134-LM234-LM334Electrical characteristics
3 Electrical characteristics
Tj = +25°C with pulse testing so that junction temperature does not change during testing
(unless otherwise specified)
Table 2.
Electrical characteristics
LM134 - LM234
Parameter
Min.
Set current error (V+ = +2.5V) -(1)
1mA10µA ≤ Iset ≤
1mA ≤ Iset ≤ 5mA2µA ≤ Iset ≤ 10µA
Ratio of set current to V- current
1mA10µA ≤ Iset ≤ 5mA1mA ≤ Iset ≤
2µA ≤ Iset ≤ 10µAMinimum operating voltage2µA ≤ Iset ≤ 100µA
1mA100µA ≤ Iset ≤
1mA ≤ Iset ≤ 5mA
Average change in set current with input voltage2µA ≤ Iset ≤ 1mA
+5V +1.5V ≤ V+ ≤+
+5V ≤ V≤ +40V
5mA1mA ≤ Iset ≤+
+1.5V ≤ V ≤ +5V
+ ≤ +40V+5V ≤ V
Temperature dependence of set current - (2)
25µA ≤ Iset ≤ 1mA
Effective shunt capacitance
Iset = 67.7mV/Rset (Tj = +25°C)
The set current error is expressed as a percent deviation from this amount.
2.Iset is directly proportional to absolute temperature (°K). Iset at any temperature can be calculated from
Iset = Io (T/To)
where Io is Iset measured at To (°K).
LM334
Unit
Min.
Typ.
Max.6812
14
1814140.80.91
26
Typ.Max.358
%
14
1814140.80.91
23
V
0.020.010.030.02
0.96 T
T15
0.050.030.020.010.030.02
0.10.05
% / V
1.04 T0.96 TT15
1.04 T
pF
1.The set current is the current flowing into the V+ pin. It is determined by the following formula:
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Electrical characteristics
LM134-LM234-LM334
Figure 3.
Maximum slew rate for linear operation
Figure 2.Output impedance
Impedance (Ohm)Frequency (Hz)
Slew rate (V/µs)Iset (µA)
Figure 5.
Transient response
Figure 4.Startup
Time (scale changes at each current level)
Time (scale changes at each current level)Figure 7.
Current noise
Figure 6.
Voltage across Rset
Current (pA/√Hz)Voltage (mV)Temperature (°C)
Frequency (Hz)
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LM134-LM234-LM334Figure 8.
Turn-on voltage
Figure 9.
Electrical characteristics
Ratio of Iset to V- current
Iset (mA)V+ to V- voltage (V)
RatioIset (mA)
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Application informationLM134-LM234-LM334
4 Application information
4.1 Slew rate
At slew rates above a threshold (see Figure4 and Figure5), the LM134, LM234, LM334 can
have a non-linear current characteristic. The slew rate at which this takes place is directly proportional to Iset. At Iset = 10µA, dv/dt max. = 0.01V/µs ; at Iset = 1mA, dv/dt max. = 1V/µs. Slew rates of more than 1V/µs do not damage the circuit nor do they produce high currents.
4.2 Thermal effects
Internal heating can have a significant effect on current regulation for an Iset above 100µA.
For example, each increase of 1V in the voltage across the LM134 at Iset = 1mA will increase the junction temperature by ≈ 0.4°C (in still air). The output current (Iset) has a temperature coefficient of about 0.33%/°C. Thus the change in current due to the increase in temperature will be (0.4) (0.33) = 0.132%. This is a degradation of 10 : 1 in regulation versus the true electrical effects. Thermal effects should be taken into account when d.c. regulation is critical and Iset is higher than 100µA.
4.3 Shunt capacitance
In certain applications, the 15pF value for the shunt capacitance should be reduced:
●●
because of loading problems,
because of limitation of output impedance of the current source in a.c. applications.
You can easily reduce the capacitance by adding a FET as shown in Typical applications on
page8.
The value of this capacitance can be reduced by at least 3pF and regulation can be improved by an order of magnitude without any modifications of the d.c. characteristics (except for the minimum input voltage).
4.4 Noise
The current noise produced by LM134, LM234, and LM334 is about 4 times that of a
transistor. If the LM134, LM234, LM334 is used as an active load for a transistor amplifier, the noise at the input will increase by about 12dB. In most cases this is acceptable, and a single amplifier can be built with a voltage gain higher than 2000.
4.5 Lead resistance
The sense voltage which determines the current of the LM134, LM234, LM334 is less than
100mV. At this level, the thermocouple effects and the connection resistance should be reduced by locating the current setting resistor close to the device. Do not use sockets for the ICs. A contact resistance of 0.7Ω is sufficient to decrease the output current by 1% at the 1mA level.
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LM134-LM234-LM334Application information
4.6 Sensing temperature
The LM134, LM234, LM334 are excellent remote controlled temperature sensors because
their operation as current sources preserves their accuracy even in the case of long
connecting wires. The output current is directly proportional to the absolute temperature in Kelvin degrees according to the following equation.
(227µV/°K) (T)Iset = ----------------------------------------Rset
The calibration of the LM134, LM234, LM334 is simplified by the fact that most of the initial accuracy is due to gain limitation (slope error) and not an offset. Gain adjustment is a one point trim because the output of the device extrapolates to zero at 0°K.Figure 10.Device calibration
This particularity of the LM134, LM234, LM334 is illustrated in the above diagram. Line abc represents the sensor current before adjustment and line a’b’c’ represents the desired output. A gain adjustment provided at T2 will move the output from b to b’ and will correct the slope at the same time so that the output at T1 and T3 will be correct. This gain
adjustment can be carried out by means of Rset or the load resistor used in the circuit. After adjustment, the slope error should be less than 1%. A low temperature coefficient for Rset is necessary to keep this accuracy. A 33ppm/°C temperature drift of Rset will give an error of 1% on the slope because the resistance follows the same temperature variations as the LM134, LM234, LM334.
Three wires are required to isolate Rset from the LM134, LM234, LM334. Since this solution is not recommended, metal-film resistors with a drift of less than 20ppm/°C are now available. Wirewound resistors can be used when very high stability is required.
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Application informationLM134-LM234-LM334
Typical applications
Figure 11.Basic 2-terminal current sourceFigure 12.Alternate trimming technique
Figure 13.Terminating remote sensor for
voltage outputFigure 14.Zero temperature coefficient
current source
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LM134-LM234-LM334
Application information
Figure 16.Low output impedance
thermometer
Figure 15.Low output impedance
thermometer
Figure 17.Micropower biasFigure 18.Low input voltage reference driver
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Application information
LM134-LM234-LM334
Figure 20.Fet cascading for low capacitance
Figure 19.In-line current limiter
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分销商库存信息:
STM
LM334DTLM334Z
LM234DTLM234Z
LM334D
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