LM134 Series
Constant Current Source
and Temperature Sensor
FEATURES
s
s
s
s
s
s
DESCRIPTIO
1µA to 10mA Operation
0.02%/V Regulation
0.8V to 40V Operating Voltage
Can be Used as Linear Temperature Sensor
Draws No Reverse Current
Supplied in Standard Transistor Packages
The LM134 is a three-terminal current source designed to
operate at current levels from 1µA to 10mA, as set by an
external resistor. The device operates as a true two-
terminal current source, requiring no extra power connec-
tions or input signals. Regulation is typically 0.02%/V and
terminal-to-terminal voltage can range from 800mV to
40V.
Because the operating current is
directly proportional to
absolute temperature
in degrees Kelvin, the device will
also find wide applications as a temperature sensor. The
temperature dependence of the operating current is
0.336%/°C at room temperature. For example, a device
operating at 298µA will have a temperature coefficient of
1µA/°C. The temperature dependence is extremely accu-
rate and repeatable. Devices specified as temperature
sensors in the 100µA to 1mA range are the LM134-3,
LM234-3 and the LM134-6, LM234-6, with the dash
numbers indicating
±3°C
and
±6°C
accuracies, respec-
tively.
If a zero temperature coefficient current source is re-
quired, this is easily achieved by adding a diode and a
resistor.
APPLICATIO S
s
s
s
s
s
s
s
Current Mode Temperature Sensing
Constant Current Source for Shunt References
Cold Junction Compensation
Constant-Gain Bias for Bipolar Differential Stage
Micropower Bias Networks
Buffer for Photoconductive Cell
Current Limiter
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
Remote Temperature Sensor with Voltage Output
500
Operating Current vs Temperature
225
V
IN
≥
5V
400
TEMPERATURE (°K)
V
+
R
R
SET
226Ω
10mV/°K
R1
10k
TA01a
300
LM234-3 V
–
200
100
0
0
100
300
400
200
OPERATING CURRENT (µA)
U
125
R
SET
= 226Ω
25
U
U
TEMPERATURE (°C)
–75
–175
–275
500
TA01b
1
LM134 Series
ABSOLUTE
AXI U RATI GS
(Note 1)
Power Dissipation .............................................. 200mW
Operating Temperature Range
LM134
(OBSOLETE) ...................
–55°C to 125°C
LM234-3/LM234-6 ............................–25°C to 100°C
LM334 ..................................................... 0°C to 70°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
V
+
to V
–
Forward Voltage
LM134 ................................................................. 40V
LM134-3/LM134-6/LM234-3/
LM234-6/LM334 ................................................. 30V
+
to V
–
Reverse Voltage ........................................ 20V
V
R Pin to V
–
Voltage.................................................... 5V
Set Current ........................................................... 10mA
PACKAGE/ORDER I FOR ATIO
BOTTOM VIEW
V
+
V
–
ORDER PART
NUMBER
CURRENT
SOURCE
LM134H
LM334H
TEMP
SENSOR
LM134H-3
LM234H-3
LM134H-6
LM234H-6
R
H PACKAGE
3-LEAD TO-46 METAL CAN
T
JMAX
= 150°C,
θ
JA
= 440°C/W,
θ
JA
= 80°C/W
OBSOLETE PACKAGE
Consider the S8 or Z Packages for Alternate Source
V
–
1
R
2
V
+
3
NC 4
8 NC
7 NC
6 NC
5 NC
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 100°C,
θ
JA
= 180°C/W
Consult LTC Marketing for availability of LM234Z-3 and LM234Z-6
2
U
U
W
W W
U
W
BOTTOM VIEW
V
+
R
V
–
ORDER PART
NUMBER
CURRENT
SOURCE
LM334Z
TEMP
SENSOR
LM234Z-3
LM234Z-6
Z PACKAGE
3-LEAD PLASTIC TO-92
T
JMAX
= 100°C,
θ
JA
= 160°C/W
ORDER PART
NUMBER
LM334S8
S8 PART
MARKING
334
LM134 Series
ELECTRICAL CHARACTERISTICS
CURRENT SOURCE (Note 2)
SYMBOL
∆I
SET
PARAMETER
Set Current Error, V
+
= 2.5V
(Note 3)
Ratio of Set Current to
V
–
Current
V
MIN
Minimum Operating Voltage
CONDITIONS
10µA
≤
I
SET
≤
1mA
1mA < I
SET
≤
5mA
2µA
≤
I
SET
< 10µA
10µA
≤
I
SET
≤
1mA
1mA
≤
I
SET
≤
5mA
2µA
≤
I
SET
≤
10µA
2µA
≤
I
SET
≤
100µA
100µA < I
SET
≤
1mA
1mA < I
SET
≤
5mA
1.5V
≤
V
+
≤
5V
2µA
≤
I
SET
≤
1mA
5V
≤
V
+
≤
V
MAX
(Note 5)
1.5V
≤
V
≤
5V
1mA < I
SET
≤
5mA
5V
≤
V
≤
V
MAX
(Note 5)
Temperature Dependence of
Set Current (Note 4)
C
S
Effective Shunt Capacitance
25µA
≤
I
SET
≤
1mA
0.96
15
14
18
14
18
0.8
0.9
1.0
0.02
0.01
0.03
0.02
1.04
0.96
15
0.05
0.03
MIN
LM134
TYP
MAX
3
5
8
23
23
14
18
14
18
0.8
0.9
1.0
0.02
0.01
0.03
0.02
1.04
pF
0.1
0.05
MIN
LM334
TYP
MAX
6
8
12
26
26
V
V
V
%/V
%/V
%/V
%/V
UNITS
%
%
%
∆I
SET
∆V
IN
Average Change in Set Current
with Input Voltage
TEMPERATURE SENSOR (Note 2)
SYMBOL
∆I
SET
PARAMETER
Set Current Error, V
+
= 2.5V
(Note 3)
Equivalent Temperature Error
Ratio of Set Current to
V
–
Current
V
MIN
∆I
SET
∆V
IN
Minimum Operating Voltage
Average Change in Set Current
with Input Voltage
Temperature Dependence of
Set Current (Note 4)
Equivalent Slope Error
C
S
Effective Shunt Capacitance
100µA
≤
I
SET
≤
1mA
100µA
≤
I
SET
≤
1mA
1.5V
≤
V
+
≤
5V
100µA
≤
I
SET
≤
1mA
5V
≤
V
+
≤
30V
100µA
≤
I
SET
≤
1mA
0.98
±2
15
14
18
0.9
0.02
0.01
0.05
0.03
1.02
0.97
±3
15
CONDITIONS
100µA
≤
I
SET
≤
1mA
T
j
= 25°C
LM134-3,LM234-3
MIN
TYP
MAX
±1
±3
26
14
18
0.9
0.02
0.01
0.1
0.05
1.03
%
pF
LM134-6, LM234-6
MIN
TYP
MAX
±2
±6
26
V
%/V
%/V
UNITS
%
°C
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Unless otherwise specified, tests are performed at T
j
= 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. It is determined
by the following formula: I
SET
= 67.7mV/R
SET
(at 25°C). Set current error
is expressed as a percent deviation from this amount. I
SET
increases at
0.336%/°C at T
j
= 25°C.
Note 4:
I
SET
is nominally directly proportional to absolute temperature
(°K). I
SET
at any temperature can be calculated from: I
SET
= I
O
(T/T
O
)
where I
O
is I
SET
measured at T
O
(°K).
Note 5:
V
MAX
= 40V for LM134 and 30V for other grades.
3
LM134 Series
TYPICAL PERFOR A CE CHARACTERISTICS
10
9
Output Impedance
10
I = 10µA
IMPEDANCE (Ω)
10
8
SLEW RATE (V/µs)
0.1
I
SET
I = 100µA
10
7
I = 1mA
10
6
10
100
1k
FREQUENCY (Hz)
Transient Response
2
1
0
–1
2µs
I
SET
= 1mA
∆V
= 0.4V
t
r
,
f
= 500ns
10µs
V
+
TO V
–
= 5V
CURRENT (pA/√Hz)
VOLTAGE (mV)
∆I
SET
(%)
5
0
–5
10
0
–10
–20
50µs
I
SET
= 100µA
I
SET
= 10µA
TIME
(*NOTE SCALE CHANGES FOR EACH CURRENT LEVEL)
134 G04
Turn-On Voltage
10mA
T
j
= 25°C
R
SET
= 14Ω
1mA
R
SET
= 68Ω
RATIO
18
17
16
15
TEMPERATURE (°K)
I
SET
100µA
R
SET
= 680Ω
10µA
R
SET
= 6.8k
1µA
0.4
0.6
0.8
1.0
V
+
TO V
–
VOLTAGE
4
U W
134 G01
Maximum Slew Rate for
Linear Operation
10µA
Start-Up
200µs
1.0
0µA
100µA
0µA
50µs
0.01
1mA
0mA
5V
5µs
0.001
10k
INPUT
1
10
100
I
SET
(µA)
1000
10000
134 G02
0V
TIME
(*NOTE SCALE CHANGES FOR EACH CURRENT LEVEL)
134 G03
Voltage Across R
SET
86
82
78
74
70
66
62
58
54
50
46
–50
1
1k
10k
Current Noise
I
SET
= 5mA
100
I
SET
= 1mA
I
SET
= 100µA
10
I
SET
= 10µA
–25
50
25
0
75
TEMPERATURE (°C)
100
125
10
100
1k
10k
FREQUENCY (Hz)
100k
134 G06
1314/15 G01
Ratio of I
SET
to
21
20
19
V
–
Current
500
Operating Current vs
Temperature
225
R
SET
= 226Ω
400
125
TEMPERATURE (°C)
300
25
200
–75
14
13
12
1.2
1.4
134 G02
100
–175
11
10µA
0
100µA
I
SET
134 G08
1mA
10mA
0
100
300
400
200
OPERATING CURRENT (µA)
–275
500
134 G09
LM134 Series
APPLICATIO S I FOR ATIO
Basic Theory of Operation
The equivalent circuit of the LM134 is shown in Figure 1.
A reference voltage of 64mV is applied to the minus input
of A1 with respect to the V
–
pin. A1 serves the drive to Q2
to keep the R pin at 64mV, independent of the value of
R
SET
. Transistor Q1 is matched to Q2 at a 17:1 ratio so that
the current flowing out of the V
–
pin is always 1/18 of the
total current into the V
+
pin. This total current is called I
SET
and is equal to:
64mV
18
67.7mV
=
R
SET
17
R
SET
V
+
I
SET
Q1
Q2
+
A1
R
–
+
64mV
R
SET
–
V
–
134 F01
Figure 1.
The 67.7mV equivalent reference voltage is directly pro-
portional to absolute temperature in degrees Kelvin (see
curve, “Operating Current vs Temperature”). This means
that the reference voltage can be plotted as a straight line
going from 0mV at absolute zero temperature to 67.7mV
at 298°K (25°C). The slope of this line is 67.7mV/298 =
227µV/°C.
The accuracy of the device is specified as a percent error
at room temperature, or in the case of the -3 and -6
devices, as both a percent error and an equivalent tem-
perature error. The LM134 operating current changes at a
percent rate equal to (100)(227µV/°C)/(67.7mV) = 0.336%/
°C
at 25°C, so each 1% operating current error is equiva-
lent to
≈3°C
temperature error when the device is used as
a temperature sensor. The slope accuracy (temperature
coefficient) of the LM134 is expressed as a ratio com-
pared to unity. The LM134-3, for instance, is specified at
0.98 to 1.02, indicating that the maximum slope error of
U
the device is
±2%
when the room temperature current is
set to the exact desired value.
Supply Voltage Slew Rate
At slew rates above a given threshold (see curve), the
LM134 may exhibit nonlinear 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 limits 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
SET
greater than 100µA. For example, each
1V increase across the LM134 at I
SET
= 1mA will increase
junction 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 com-
pared 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 pack-
age or the TO-92 leads can reduce this effect by more than
3:1.
Shunt Capacitance
In certain applications, the 15pF 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 a FET, as shown in the applica-
tions. This can reduce capacitance to less than 3pF and
improve regulation by at least an order of magnitude. DC
characteristics (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 12dB. In many cases, this
is acceptable and a single stage amplifier can be built with
a voltage gain exceeding 2000.
W
U
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