RTD XTR105
4-20 mA
V
PS
V
O
R
L
R
G
V
LIN
V
REG
+7.5V to 36V
I
R
= 0.8mA
I
R
= 0.8mA
4-20mA CURRENT TRANSMITTER
with Sensor Excitation and Linearization
FEATURES
LOW UNADJUSTED ERROR
TWO PRECISION CURRENT SOURCES: 800
µ
A each
LINEARIZATION
2- OR 3-WIRE RTD OPERATION
LOW OFFSET DRIFT: 0.4µV/°C
LOW OUTPUT CURRENT NOISE: 30nAPP
HIGH PSR: 110dB minimum
HIGH CMR: 86dB minimum
WIDE SUPPLY RANGE: 7.5V to 36V
DIP-14 AND SO-14 PACKAGES
APPLICATIONS
INDUSTRIAL PROCESS CONTROL
FACTORY AUTOMATION
SCADA REMOTE DATA ACQUISITION
REMOTE TEMPERATURE AND PRESSURE
TRANSDUCERS
200°C
Pt100 NONLINEARITY CORRECTION
USING XTR105
Process Temperature (°C) +850°C
5
4
3
2
1
0
1
Uncorrected
RTD Nonlinearity
Corrected
Nonlinearity
Nonlinearity (%)
DESCRIPTION
The XTR105 is a monolithic 4-20mA, 2-wire current transmit-
ter with two precision current sources. It provides complete
current excitation for platinum RTD temperature sensors and
bridges, instrumentation amplifiers, and current output cir-
cuitry on a single integrated circuit.
Versatile linearization circuitry provides a 2nd-order correc-
tion to the RTD, typically achieving a 40:1 improvement in
linearity.
Instrumentation amplifier gain can be configured for a wide
range of temperature or pressure measurements. Total un-
adjusted error of the complete current transmitter is low
enough to permit use without adjustment in many applica-
tions. This includes zero output current drift, span drift, and
nonlinearity. The XTR105 operates on loop power-supply
voltages down to 7.5V.
The XTR105 is available in DIP-14 and SO-14 surface-
mount packages and is specified for the 40°C to +85°C
industrial temperature range.
XTR105
XTR105
XTR105
SBOS061B FEBRUARY 1997 REVISED AUGUST 2004
www.ti.com
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
Copyright © 1997-2004, Texas Instruments Incorporated
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
2SBOS061B
www.ti.com XTR105
FUNCTIONAL BLOCK DIAGRAM
975
6
I = 100µA +
100µA
800µA 800µA
25
V+
Q
1
9
B
10
11
4
13
2
3
8
E
V
IN
R
G
I
O
= 4mA + V
IN
40
R
G
( )
5.1V
R
G
R
LIN
1k
V
IN
+
V
IN
I
RET
7
V
REG
14
1
12 I
R2
I
R1
V
LIN
SPECIFIED
PACKAGE TEMPERATURE PACKAGE ORDERING TRANSPORT
PRODUCT PACKAGE-LEAD DESIGNATOR RANGE MARKING NUMBER MEDIA, QUANTITY
XTR105 DIP-14 N 40°C to +85°C XTR105PA XTR105PA Rails, 25
" """XTR105P XTR105P Rails, 25
XTR105 SO-14 Surface-Mount D 40°C to +85°C XTR105UA XTR105UA Rails, 58
" """XTR105UA XTR105UA/2K5 Tape and Reel, 2500
XTR105 SO-14 Surface-Mount D 40°C to +85°C XTR105U XTR105U Rails, 58
" """XTR105U XTR105U/2K5 Tape and Reel, 2500
NOTE: (1) For the most current package and ordering information, see the Package Option Addendum located at the end of this data sheet.
PACKAGE/ORDERING INFORMATION(1)
ABSOLUTE MAXIMUM RATINGS(1)
Power Supply, V+ (referenced to the IO pin)...................................... 40V
Input Voltage, VIN+, VIN (referenced to the IO pin) .................... 0V to V+
Storage Temperature Range .........................................55°C to +125°C
Lead Temperature (soldering, 10s)............................................... +300°C
Output Current Limit ................................................................ Continuous
Junction Temperature.................................................................... +165°C
ELECTROSTATIC
DISCHARGE SENSITIVITY
This integrated circuit can be damaged by ESD. Texas Instru-
ments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling
and installation procedures can cause damage.
ESD damage can range from subtle performance degrada-
tion to complete device failure. Precision integrated circuits
may be more susceptible to damage because very small
parametric changes could cause the device not to meet its
published specifications.
NOTE: (1) Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to absolute maximum
conditions for extended periods may affect device reliability.
Top View DIP and SO
PIN CONFIGURATION
I
R1
V
IN
R
G
R
G
NC
I
RET
I
O
I
R2
V
IN
V
LIN
V
REG
V+
B (Base)
E (Emitter)
NC = No Internal Connection
1
2
3
4
5
6
7
14
13
12
11
10
9
8
+
XTR105 3
SBOS061B www.ti.com
Specification same as XTR105P and XTR105U.
NOTES:(1) Describes accuracy of the 4mA low-scale offset current. Does not include input amplifier effects. Can be trimmed to zero.
(2) Voltage measured with respect to IRET pin.
(3) Does not include initial error or TCR of gain-setting resistor, RG.
(4) Increasing the full-scale input range improves nonlinearity.
(5) Does not include Zero Output initial error.
(6) Current source output voltage with respect to IRET pin.
ELECTRICAL CHARACTERISTICS
At TA = +25°C, V+ = 24V, and TIP29C external transistor, unless otherwise noted.
XTR105P, U XTR105PA, UA
PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS
OUTPUT
Output Current Equation A
Output Current, Specified Range 4 20 ✻✻mA
Over-Scale Limit 24 27 30 ✻✻ mA
Under-Scale Limit IREG = 0V 1.8 2.2 2.6 ✻✻ mA
ZERO OUTPUT(1) VIN = 0V, RG = 4mA
Initial Error ±5±25 ±50 µA
vs Temperature ±0.07 ±0.5 ±0.9 µA/°C
vs Supply Voltage, V+ V+ = 7.5V to 36V 0.04 0.2 ✻✻ µA/V
vs Common-Mode Voltage
VCM = 1.25V to 3.5V(2) 0.02 µA/V
vs VREG Output Current 0.3 µA/mA
Noise, 0.1Hz to 10Hz 0.03 µAPP
SPAN
Span Equation (transconductance)
S = 40/R
G
A/V
Initial Error(3) Full-Scale (VIN) = 50mV ±0.05 ±0.2 ±0.4 %
vs Temperature(3) ±3±25 ✻✻ ppm/°C
Nonlinearity, Ideal Input(4) Full-Scale (VIN) = 50mV 0.003 0.01 ✻✻ %
INPUT(5)
Offset Voltage VCM = 2V ±50 ±100 ±250 µV
vs Temperature ±0.4 ±1.5 ±3µV/°C
vs Supply Voltage, V+ V+ = 7.5V to 36V ±0.3 ±3✻✻ µV/V
vs Common-Mode Voltage, VCM = 1.25V to 3.5V(2) ±10 ±50 ±100 µV/V
RTI (CMRR)
Common-Mode Input Range(2) 1.25 3.5 ✻✻V
Input Bias Current 525 50 nA
vs Temperature 20 pA/°C
Input Offset Current ±0.2 ±3±10 nA
vs Temperature 5pA/°C
Impedance, Differential 0.1 || 1 G|| pF
Common-Mode 5 || 10 G|| pF
Noise, 0.1Hz to 10Hz 0.6 µVPP
CURRENT SOURCES VO = 2V(6)
Current 800 µA
Accuracy ±0.05 ±0.2 ±0.4 %
vs Temperature ±15 ±35 ±75 ppm/°C
vs Power Supply, V+ V+ = 7.5V to 36V ±10 ±25 ✻✻ ppm/V
Matching ±0.02 ±0.1 ±0.2 %
vs Temperature ±3±15 ±30 ppm/°C
vs Power Supply, V+ V+ = 7.5V to 36V 1 10 ✻✻ ppm/V
Compliance Voltage, Positive (V+) 3
(V+) 2.5
✻✻ V
Negative(2) 00.2 ✻✻ V
Output Impedance 150 M
Noise, 0.1Hz to 10Hz 0.003 µAPP
VREG(2) 5.1 V
Accuracy ±0.02 ±0.1 ✻✻ V
vs Temperature ±0.2 mV/°C
vs Supply Voltage, V+ 1 mV/V
Output Current ±1mA
Output Impedance 75
LINEARIZATION
RLIN (internal) 1k
Accuracy ±0.2 ±0.5 ±1%
vs Temperature ±25 ±100 ✻✻ ppm/°C
POWER SUPPLY
Specified +24 V
Voltage Range +7.5 +36 ✻✻V
TEMPERATURE RANGE
Specification, TMIN to TMAX 40 +85 ✻✻°C
Operating 55 +125 ✻✻°C
Storage 55 +125 ✻✻°C
Thermal Resistance,
θ
JA
DIP-14 80 °C/W
SO-14 Surface-Mount 100 °C/W
IO = V IN (40/RG) + 4mA, VIN in Volts, RG in
4SBOS061B
www.ti.com XTR105
TYPICAL CHARACTERISTICS
At TA = +25°C and V+ = 24V, unless otherwise noted.
20mA
STEP RESPONSE
25µs/div
4mA/div
RG = 125
RG = 2k
4mA
100 1k 10k 100k
Frequency (Hz)
TRANSCONDUCTANCE vs FREQUENCY
1M
50
40
30
20
10
0
Transconductance (20 Log mA/V)
R
G
= 125
R
G
= 500
R
G
= 2k
10 100 1k 10k 100k
Frequency (Hz) 1M
110
100
90
80
70
60
50
40
30
20
Common-Mode Rejection (dB)
COMMON-MODE REJECTION vs FREQUENCY
R
G
= 2k
R
G
= 125
Full-Scale Input = 50mV
10 100 1k 10k 100k
Frequency (Hz)
POWER-SUPPLY REJECTION vs FREQUENCY
1M
140
120
100
80
60
40
20
0
Power Supply Rejection (dB)
R
G
= 2k
R
G
= 125
75 50 25 0 25 50 75 100
Temperature (°C)
OVER-SCALE CURRENT vs TEMPERATURE
125
29
28
27
26
25
24
23
Over-Scale Current (mA)
V+ = 7.5V
V+ = 36V
V+ = 24V
With External Transistor
75 50 25 0 25 50 75 100
Temperature (°C)
UNDER-SCALE CURRENT vs TEMPERATURE
125
2.40
2.35
2.30
2.25
2.20
2.15
Under-Scale Current (mA)
V+ = 7.5V to 36V
XTR105 5
SBOS061B www.ti.com
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C and V+ = 24V, unless otherwise noted.
1 10 100 1k 10k
Frequency (Hz)
INPUT VOLTAGE AND CURRENT
NOISE DENSITY vs FREQUENCY
100k
10k
1k
100
10
Input Voltage Noise (nV/Hz)
10k
1k
100
10
Input Current Noise (fA/Hz)
Current Noise
Voltage Noise
1 10 100 1k 10k
Frequency (Hz)
ZERO OUTPUT AND REFERENCE
CURRENT NOISE vs FREQUENCY
100k
10k
1k
100
10
Noise (pA/Hz)
Zero Output Current
Reference Current
75 50 25 0 25 50 75 100
Temperature (°C)
INPUT BIAS AND OFFSET CURRENT
vs TEMPERATURE
125
25
20
15
10
5
0
Input Bias and Offset Current (nA)
+I
B
I
OS
I
B
75 50 25 0 25 50 75 100
Temperature (°C)
ZERO OUTPUT CURRENT ERROR
vs TEMPERATURE
125
4
2
0
2
4
6
8
10
12
Zero Output Current Error (µA)
Input Offset Voltage Drift (µV/°C)
INPUT OFFSET VOLTAGE DRIFT
PRODUCTION DISTRIBUTION
50
45
40
35
30
25
20
15
10
5
0
Percent of Units (%)
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
0.1% 0.02%
Typical Production Distribution
of Packaged Units.
Zero Output Drift (µA/°C)
ZERO OUTPUT DRIFT
PRODUCTION DISTRIBUTION
40
35
30
25
20
15
10
5
0
Percent of Units (%)
0.025
0.050
0.075
0.100
0.125
0.150
0.175
0.200
0.225
0.250
0.275
0.300
0.325
0.350
0.375
0.400
0.425
0.450
0.475
0.500
Typical Production Distribution
of Packaged Units.
6SBOS061B
www.ti.com XTR105
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C and V+ = 24V, unless otherwise noted.
Current Source Drift (ppm/°C)
CURRENT SOURCE DRIFT
PRODUCTION DISTRIBUTION
40
35
30
25
20
15
10
5
0
Percent of Units (%)
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
0.04% 0.01%
Typical Production Distribution
of Packaged Units.
IR1 AND IR2 Included.
Current Source Matching Drift (ppm/°C)
CURRENT SOURCE MATCHING
DRIFT PRODUCTION DISTRIBUTION
80
70
60
50
40
30
20
10
0
Percent of Units (%)
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
0.07% 0.02%
Typical Production Distribution
of Packaged Units.
1.0 0.5 0 0.5 1.0 1.5
VREG Output Current (mA)
VREG OUTPUT VOLTAGE vs VREG OUTPUT CURRENT
2.0
5.35
5.30
5.25
5.20
5.15
5.10
5.05
5.00
VREG Output Voltage (V)
125°C
NOTE: Above 1mA,
Zero Output Degrades
55°C
25°C
Temperature (°C)
REFERENCE CURRENT ERROR
vs TEMPERATURE
+0.05
0
0.05
0.10
0.15
0.20
Reference Current Error (%)
75 50 25 0 25 50 75 100 125
XTR105 7
SBOS061B www.ti.com
14 11
12
13
4
3
2
R
G
XTR105
R
CM
= 1k
7
1
0.01µF
I = 4mA + V
IN
( )
O
40
R
G
R
Z
RTD 6
(2)
NOTES: (1) R
Z
= RTD resistance at minimum measured temperature.
R
G
R
G
V
IN
V
IN
+
V
LIN
I
R1
I
R2
V
REG
V+
I
RET
I
O
E
B
(1)
R
G
= 2R
1
(R
2
+R
Z
) 4(R
2
R
Z
)
R
2
R
1
(2)
R
LIN1
=
where R
1
= RTD Resistance at (T
MIN
+ T
MAX
)/2
R
2
= RTD Resistance at T
MAX
R
LIN
= 1k (Internal)
R
LIN
(R
2
R
1
)
2(2R
1
R
2
R
Z
)
(3)
V
PS
8
4-20 mA
I
O
0.01µF
I
R
= 0.8mA
I
R
= 0.8mA
7.5V to 36V
+
9
10
R
LIN1(3)
R
L
V
O
Q
1
TYPE
2N4922
TIP29C
TIP31C
PACKAGE
TO-225
TO-220
TO-220
Possible choices for Q
1
(see text).
APPLICATION INFORMATION
Figure 1 shows the basic connection diagram for the XTR105.
The loop power supply, VPS, provides power for all circuitry.
Output loop current is measured as a voltage across the
series load resistor, RL.
Two matched 0.8mA current sources drive the RTD and
zero-setting resistor, RZ. The instrumentation amplifier input
of the XTR105 measures the voltage difference between the
RTD and RZ. The value of RZ is chosen to be equal to the
resistance of the RTD at the low-scale (minimum) measure-
ment temperature. RZ can be adjusted to achieve 4mA output
at the minimum measurement temperature to correct for
input offset voltage and reference current mismatch of the
XTR105.
R
CM
provides an additional voltage drop to bias the inputs of
the XTR105 within their common-mode input range. R
CM
should be bypassed with a 0.01µF capacitor to minimize
common-mode noise. Resistor R
G
sets the gain of the instru-
mentation amplifier according to the desired temperature
range. R
LIN1
provides 2nd-order linearization correction to the
RTD, typically achieving a 40:1 improvement in linearity. An
additional resistor is required for 3-wire RTD connections
(see Figure 3).
The transfer function through the complete instrumentation
amplifier and voltage-to-current converter is:
IO = 4mA + VIN (40/RG)
(VIN in volts, RG in ohms)
where VIN is the differential input voltage.
As evident from the transfer function, if no RG is used the
gain is zero and the output is simply the XTR105s zero
current. The value of RG varies slightly for 2-wire RTD and 3-
wire RTD connections with linearization. RG can be calcu-
lated from the equations given in Figure 1 (2-wire RTD
connection) and Table I (3-wire RTD connection).
The IRET pin is the return path for all current from the current
sources and VREG. The IRET pin allows any current used in
external circuitry to be sensed by the XTR105 and to be
included in the output current without causing an error.
The VREG pin provides an on-chip voltage source of approxi-
mately 5.1V and is suitable for powering external input
circuitry (refer to Figure 6). It is a moderately accurate
voltage referenceit is not the same reference used to set
the 800µA current references. VREG is capable of sourcing
approximately 1mA of current. Exceeding 1mA may affect
the 4mA zero output.
FIGURE 1. Basic 2-Wire RTD Temperature Measurement Circuit with Linearization.
8SBOS061B
www.ti.com XTR105
TMIN 100°C 200°C 300°C 400°C 500°C 600°C 700°C 800°C 900°C1000°C
200°C 18.7/86.6 18.7/169 18.7/255 18.7/340 18.7/422 18.7/511 18.7/590 18.7/665 18.7/750 18.7/845
15000 9760 8060 6650 5620 4750 4020 3480 3090 2740
16500 11500 10000 8870 7870 7150 6420 5900 5360 4990
100°C 60.4/80.6 60.4/162 60.4/243 60.4/324 60.4/402 60.4/487 60.4/562 60.4/649 60.4/732
27400 15400 10500 7870 6040 4990 4220 3570 3090
29400 17800 13000 10200 8660 7500 6490 5900 5360
0°C 100/78.7 100/158 100/237 100/316 100/392 100/475 100/549 100/634
33200 16200 10500 7680 6040 4870 4020 3480
35700 18700 13000 10000 8250 7150 6340 5620
100°C 137/75 137/150 137/226 137/301 137/383 137/453 137/536
31600 15400 10200 7500 5760 4750 3920
34000 17800 12400 9760 8060 6810 6040
200°C 174/73.2 174/147 174/221 174/294 174/365 174/442
30900 15000 9760 7150 5620 4530
33200 17400 12100 9310 7680 6490
300°C 210/71.5 210/143 210/215 210/287 210/357
30100 14700 9530 6980 5360
32400 16500 11500 8870 7320
400°C 249/68.1 249/137 249/205 249/274
28700 14000 9090 6650
30900 16200 11000 8450
500°C 280/66.5 280/133 280/200
28000 13700 8870
30100 15400 10500
600°C 316/64.9 313/130
26700 13000
28700 14700
700°C 348/61.9
26100
27400
800°C 374/60.4
24900
26700
MEASUREMENT TEMPERATURE SPAN T (°C)
RZ/RG
RLIN1
RLIN2
RG=2(R2RZ)(R1RZ)
(R2R1)
R
LIN1
=R
LIN
(R
2
R
1
)
2(2R
1
R
2
R
Z
)
RLIN2 =(RLIN +RG)(R2R1)
2(2R1R2RZ)
R2 = RTD resistance at TMAX
where: R1 = RTD resistance at (TMIN + TMAX)/2
RLIN = 1k (Internal)
EXAMPLE:
The measurement range is 100°C to +200°C for a 3-wire Pt100 RTD connection. Determine the values for RS, RG, RLIN1, and RLIN2. Look up the values
from the chart or calculate the values according to the equations provided.
METHOD 1: TABLE LOOK UP
For TMIN = 100°C and T = 300°C, the 1% values are:
RZ = 60.4RLIN1 = 10.5k
RG = 243RLIN2 = 13k
METHOD 2: CALCULATION
Step 1: Determine RZ, R1, and R2.
RZ is the RTD resistance at the minimum measured temperature,TMIN = 100°C.
Using Equation 1 at right gives RZ = 60.25 (1% value is 60.4).
R2 is the RTD resistance at the maximum measured temperature, TMAX = 200°C.
Using Equation 2 at right gives R2 = 175.84.
R1 is the RTD resistance at the midpoint measured temperature,
TMID = (TMIN + TMAX)/2 = 50°C. R1 is NOT the average of RZ and R2.
Using Equation 2 at right gives R1 = 119.40.
Step 2: Calculate RG, RLIN1, and RLIN2 using equations above.
RG = 242.3 (1% value is 243)
RLIN1 = 10.413k (1% value is 10.5k)
RLIN2 = 12.936k (1% value is 13k)
Calculation of Pt100 Resistance Values
(according to DIN IEC 751)
(Equation 1) Temperature range from 200°C to 0°C:
R(T) = 100 [1 + 3.90802 103 T 0.5802 106
T2 4.27350 1012 (T 100) T3]
(Equation 2) Temperature range from 0°C to +850°C:
R(T) = 100 (1 + 3.90802 103 T 0.5802 106 T2)
where: R(T) is the resistance in at temperature T.
T is the temperature in °C.
TABLE I. RZ, RG, RLIN1, and RLIN2 Standard 1% Resistor Values for 3-Wire Pt100 RTD Connection with Linearization.
NOTE: The values listed in this table are 1% resistors (in ).
Exact values may be calculated from the following equa-
tions:
RZ = RTD resistance at minimum measured temperature.
NOTE: Most RTD manufacturers provide reference tables for
resistance values at various temperatures.
A negative input voltage, VIN, will cause the output current to
be less than 4mA. Increasingly negative VIN will cause the
output current to limit at approximately 2.2mA. Refer to the
typical characteristic Under-Scale Current vs Temperature.
Increasingly positive input voltage (greater than the full-scale
input) will produce increasing output current according to the
transfer function, up to the output current limit of approxi-
mately 27mA. Refer to the typical characteristic Over-Scale
Current vs Temperature.
XTR105 9
SBOS061B www.ti.com
It is recommended to design for V+ equal or greater than
7.5V with loop currents up to 30mA to allow for out-of-range
input conditions.
The low operating voltage (7.5V) of the XTR105 allows
operation directly from personal computer power supplies
(12V ±5%). When used with the RCV420 current loop re-
ceiver (see Figure 7), the load resistor voltage drop is limited
to 3V.
ADJUSTING INITIAL ERRORS
Many applications require adjustment of initial errors. Input
offset and reference current mismatch errors can be cor-
rected by adjustment of the zero resistor, RZ. Adjusting the
gain-setting resistor, RG, corrects any errors associated with
gain.
2- AND 3-WIRE RTD CONNECTIONS
In Figure 1, the RTD can be located remotely simply by
extending the two connections to the RTD. With this remote
2-wire connection to the RTD, line resistance will introduce
error. This error can be partially corrected by adjusting the
values of RZ, RG, and RLIN1.
A better method for remotely located RTDs is the 3-wire RTD
connection (see Figure 3). This circuit offers improved accu-
racy. RZs current is routed through a third wire to the RTD.
Assuming line resistance is equal in RTD lines 1 and 2, this
produces a small common-mode voltage that is rejected by
the XTR105. A second resistor, RLIN2, is required for linear-
ization.
Note that although the 2-wire and 3-wire RTD connection
circuits are very similar, the gain-setting resistor, RG, has
slightly different equations:
2-wire:
RRR R RR
RR
GZZ
=+24
12 2
21
()()
3-wire:
RRRRR
RR
GZZ
=221
21
()( )
where: RZ = RTD resistance at TMIN
R1 = RTD resistance at (TMIN + TMAX)/2
R2 = RTD resistance at TMAX
To maintain good accuracy, at least 1% (or better) resistors
should be used for RG. Table I provides standard 1% RG
resistor values for a 3-wire Pt100 RTD connection with
linearization.
LINEARIZATION
RTD temperature sensors are inherently (but predictably)
nonlinear. With the addition of one or two external resistors,
RLIN1 and RLIN2, it is possible to compensate for most of this
nonlinearity resulting in 40:1 improvement in linearity over
the uncompensated output.
See Figure 1 for a typical 2-wire RTD application with
linearization. Resistor RLIN1 provides positive feedback and
controls linearity correction. RLIN1 is chosen according to the
desired temperature range. An equation is given in Figure 1.
EXTERNAL TRANSISTOR
Transistor Q1 conducts the majority of the signal-dependent
4-20mA loop current. Using an external transistor isolates
the majority of the power dissipation from the precision input
and reference circuitry of the XTR105, maintaining excellent
accuracy.
Since the external transistor is inside a feedback loop, its
characteristics are not critical. Requirements are: VCEO = 45V
min,
β
= 40 min, and PD = 800mW. Power dissipation
requirements may be lower if the loop power-supply voltage
is less than 36V. Some possible choices for Q1 are listed in
Figure 1.
The XTR105 can be operated without this external transis-
tor, however, accuracy will be somewhat degraded due to
the internal power dissipation. Operation without Q1 is not
recommended for extended temperature ranges. A resistor
(R = 3.3k) connected between the IRET pin and the E
(emitter) pin may be needed for operation below 0°C with-
out Q1 to ensure the full 20mA full-scale output, especially
with V+ near 7.5V.
FIGURE 2. Operation Without an External Transistor.
8
XTR105 0.01µF
E
IO
IRET
V+
10
7
6
RQ = 3.3k
For operation without an external
transistor, connect a 3.3k
resistor between pin 6 and pin 8.
See text for discussion
of performance.
LOOP POWER SUPPLY
The voltage applied to the XTR105, V+, is measured with
respect to the IO connection, pin 7. V+ can range from 7.5V
to 36V. The loop-supply voltage, VPS, will differ from the
voltage applied to the XTR105 according to the voltage drop
on the current sensing resistor, RL (plus any other voltage
drop in the line).
If a low loop-supply voltage is used, RL (including the loop
wiring resistance) must be made a relatively low value to
assure that V+ remains 7.5V or greater for the maximum loop
current of 20mA:
RVV
mA R
LWIRING
max ().=+
75
20
10 SBOS061B
www.ti.com XTR105
In 3-wire RTD connections, an additional resistor, RLIN2, is
required. As with the 2-wire RTD application, RLIN1 provides
positive feedback for linearization. RLIN2 provides an offset
canceling current to compensate for wiring resistance en-
countered in remotely located RTDs. RLIN1 and RLIN2 are
chosen such that their currents are equal. This makes the
voltage drop in the wiring resistance to the RTD a common-
mode signal that is rejected by the XTR105. The nearest
standard 1% resistor values for RLIN1 and RLIN2 should be
adequate for most applications. Table I provides the 1%
resistor values for a 3-wire Pt100 RTD connection.
If no linearity correction is desired, the VLIN pin should be left
open. With no linearization, RG = 2500 V
FS, where
VFS = full-scale input range.
RTDs
The text and figures thus far have assumed a Pt100 RTD. With
higher resistance RTDs, the temperature range and input
voltage variation should be evaluated to ensure proper com-
mon-mode biasing of the inputs. As mentioned earlier, R
CM
can
be adjusted to provide an additional voltage drop to bias the
inputs of the XTR105 within their common-mode input range.
ERROR ANALYSIS
See Table II for how to calculate the effect various error
sources have on circuit accuracy. A sample error calculation
for a typical RTD measurement circuit (Pt100 RTD, 200°C
measurement span) is provided. The results reveal the
XTR105s excellent accuracy, in this case 1.1% unadjusted.
Adjusting resistors RG and RZ for gain and offset errors
improves circuit accuracy to 0.32%. Note that these are
worst-case errors; ensured maximum values were used in
the calculations and all errors were assumed to be positive
(additive). The XTR105 achieves performance that is difficult
to obtain with discrete circuitry and requires less space.
OPEN-CIRCUIT PROTECTION
The optional transistor Q2 in Figure 3 provides predictable
behavior with open-circuit RTD connections. It assures that
if any one of the three RTD connections is broken, the
XTR105s output current will go to either its high current limit
( 27mA) or low current limit ( 2.2mA). This is easily
detected as an out-of-range condition.
FIGURE 3. Remotely Located RTDs with 3-Wire Connection.
Resistance in this line causes
a small common-mode voltage
which is rejected by the XTR105.
OPEN RTD
TERMINAL I
O
1
2
3
2.2mA
27mA
2.2mA
RTD
(R
LINE2
)(R
LINE1
)
R
Z(1)
R
LIN2(1)
R
LIN1(1)
(R
LINE3
)
21
3
0.01µF
R
CM
= 10000.01µF
Q
2(2)
2N2222
NOTES: (1) See Table I for resistor equations and
1% values. (2) Q
2
optional. Provides predictable
output current if any one RTD connection is
broken:
13
4
3
2
R
G
XTR105
7
6
(1)
R
G
R
G
V
IN
V
IN
+
V
LIN
I
R1
I
R2
V
REG
V+
I
RET
I
O
E
B
8
9Q
1
I
O
I
O
14 11
12 1
10
EQUAL line resistances here
creates a small common-mode
voltage which is rejected by
the XTR105.
XTR105 11
SBOS061B www.ti.com
TABLE II. Error Calculation.
SAMPLE ERROR CALCULATION
RTD value at 4mA Output (RRTD MIN): 100
RTD Measurement Range: 200°C
Ambient Temperature Range (TA): 20°C
Supply Voltage Change (V+): 5V
Common-Mode Voltage Change (CM): 0.1V
SAMPLE
ERROR SOURCE ERROR EQUATION ERROR CALCULATION
(1)
UNADJ. ADJUST.
INPUT
Input Offset Voltage V
OS
/(V
IN MAX
) 10
6
100µV/(800µA 0.38/°C 200°C) 10
6
1645 0
vs Common-Mode CMRR CM/(V
IN MAX
) 10
6
50µV/V 0.1V/(800µA 0.38/°C 200°C) 10
6
82 82
Input Bias Current I
B
/I
REF
10
6
0.025µA/800µA 10
6
31 0
Input Offset Current I
OS
R
RTD MIN
/(V
IN MAX
) 10
6
3nA 100/(800µA 0.38/°C 200°C) 10
6
50
Total Input Error: 1763 82
EXCITATION
Current Reference Accuracy I
REF
Accuracy (%)/100% 10
6
0.2%/100% 10
6
2000 0
vs Supply (I
REF
vs V+) V+ 25ppm/V 5V 125 125
Current Reference Matching I
REF
Matching (%)/100% 800µA 0.1%/100% 800µA 100/(800µA 0.38/°C 200°C) 10
6
1316 0
R
RTD MIN
/(V
IN MAX
) 10
6
vs Supply (I
REF
Matching vs V+) V+ 10ppm/V 5V 800µA 100/(800µA 0.38/°C 200°C) 66 66
R
RTD MIN
/(V
IN MAX
)Total Excitation Error: 3507 191
GAIN
Span Span Error (%)/100% 10
6
0.2%/100% 10
6
2000 0
Nonlinearity Nonlinearity (%)/100% 10
6
0.01%/100% 10
6
100 100
Total Gain Error: 2100 100
OUTPUT
Zero Output (I
ZERO
4mA) /16000µA 10
6
25µA/16000µA 10
6
1563 0
vs Supply (I
ZERO
vs V+) V+/16000µA 10
6
0.2µA/V 5V/16000µA 10
6
63 63
Total Output Error: 1626 63
DRIFT (T
A
= 20
°
C)
Input Offset Voltage Drift T
A
/(V
IN MAX
) 10
6
1.5µV/°C 20°C/(800µA 0.38/°C 200°C) 10
6
493 493
Input Bias Current (typical) Drift T
A
/800µA 10
6
20pA/°C 20°C/800µA 10
6
0.5 0.5
Input Offset Current (typical) Drift T
A
R
RTD MIN
/(V
IN MAX
) 10
6
5pA/°C 20°C 100W/(800µA 0.38/°C 200°C) 10
6
0.2 0.2
Current Reference Accuracy Drift T
A
35ppm/°C 20°C 700 700
Current Reference Matching Drift T
A
800µA R
RTD MIN
/(V
IN MAX
) 15ppm/°C 20°C 800µA 100/(800µA 0.38/°C 200°C) 395 395
Span Drift T
A
25ppm/°C 20°C 500 500
Zero Output Drift T
A
/16000µA 10
6
0.5µA/°C 20°C/16000µA 10
6
626 626
Total Drift Error: 2715 2715
NOISE (0.1Hz to 10Hz, typ)
Input Offset Voltage v
n
/(V
IN MAX
) 10
6
0.6µV/(800µA 0.38/°C 200°C) 10
6
10 10
Current Reference I
REF
Noise R
RTD MIN
/(V
IN MAX
) 10
6
3nA 100/(800µA 0.38/°C 200°C) 10
6
55
Zero Output I
ZERO
Noise/16000µA 10
6
0.03µA/16000µA 10
6
22
Total Noise Error: 17 17
TOTAL ERROR: 11728 3168
(1.17%) (0.32%)
ERROR
(ppm of Full Scale)
NOTE (1): All errors are min/max and referred to input unless otherwise stated.
12 SBOS061B
www.ti.com XTR105
REVERSE-VOLTAGE PROTECTION
The XTR105s low compliance rating (7.5V) permits the use
of various voltage protection methods without compromising
operating range. Figure 4 shows a diode bridge circuit that
allows normal operation even when the voltage connection
lines are reversed. The bridge causes a two diode drop
(approximately 1.4V) loss in loop-supply voltage. This results
in a compliance voltage of approximately 9Vsatisfactory
for most applications. If a 1.4V drop in loop supply is too
much, a diode can be inserted in series with the loop-supply
voltage and the V+ pin. This protects against reverse output
connection lines with only a 0.7V loss in loop-supply voltage.
SURGE PROTECTION
Remote connections to current transmitters can sometimes be
subjected to voltage surges. It is prudent to limit the maximum
surge voltage applied to the XTR105 to as low as practical.
Various zener diodes and surge clamping diodes are specially
designed for this purpose. Select a clamp diode with as low a
voltage rating as possible for best protection. For example, a
36V protection diode will assure proper transmitter operation
at normal loop voltages, yet will provide an appropriate level
of protection against voltage surges. Characterization tests on
three production lots showed no damage to the XTR105 within
loop-supply voltages up to 65V.
Most surge protection zener diodes have a diode character-
istic in the forward direction that will conduct excessive
current, possibly damaging receiving-side circuitry if the loop
connections are reversed. If a surge protection diode is used,
a series diode or diode bridge should be used for protection
against reversed connections.
RADIO FREQUENCY INTERFERENCE
The long wire lengths of current loops invite radio frequency
(RF) interference. RF can be rectified by the sensitive input
circuitry of the XTR105 causing errors. This generally ap-
pears as an unstable output current that varies with the
position of loop supply or input wiring.
If the RTD sensor is remotely located, the interference may
enter at the input terminals. For integrated transmitter as-
semblies with short connections to the sensor, the interfer-
ence more likely comes from the current loop connections.
Bypass capacitors on the input reduce or eliminate this input
interference. Connect these bypass capacitors to the IRET
terminal (see Figure 5). Although the dc voltage at the IRET
terminal is not equal to 0V (at the loop supply, VPS), this
circuit point can be considered the transmitters ground.
The 0.01µF capacitor connected between V+ and IO may
help minimize output interference.
XTR105
7
V+
I
O
E
B
V
PS
10
0.01µF
R
L
D
1(1)
9
8
NOTE: (1) Zener Diode 36V: 1N4753A or General
Semiconductor Transorb
TM
1N6286A. Use lower
voltage zener diodes with loop-power supply
voltages less than 30V for increased protection.
See the Surge Protection section.
Maximum V
PS
must be
less than minimum
voltage rating of zener
diode.
The diode bridge causes
a 1.4V loss in loop-supply
voltage.
1N4148
Diodes
6
I
RET
FIGURE 4. Reverse Voltage Operation and Over-Voltage Surge Protection.
XTR105 13
SBOS061B www.ti.com
FIGURE 6. Thermocouple Low Offset, Low Drift Loop Measurement with Diode Cold Junction Compensation.
14
1
12
5V
11
13
I
REG
< 1mA
4
3
2
6
R
G
1250XTR105
1/2
OPA2335 7
R
G
R
G
V
IN
V
IN
+
V
REG
I
R2
V+
I
RET
I
O
E
B
8
I
O
= 4mA + (V
IN
V
IN
)
+
40
R
G
9
10
R
F
10k
R
412
1/2
OPA2335
V+
V
Type J
25
(G = 1 + = 50)
2R
F
R
50
1k
R
F
10k
I
R1
V
LIN
R
CM
= 1250
FIGURE 5. Input Bypassing Technique with Linearization.
14 11
12
13
4
3
2
RGXTR105
RCM
7
1
0.01µF
0.01µF 0.01µF
RZ
(1)
RTD
6
NOTE: (1) Bypass capacitors can be connected
to either the IRET pin or the IO pin.
RG
RG
VIN
VIN
+
VLIN IR1 IR2 V
REG
V+
IRET
IO
E
B
8
0.01µF
9
10
1k
RLIN1 RLIN2
1k
14 SBOS061B
www.ti.com XTR105
FIGURE 7. ±12V Powered Transmitter/Receiver Loop.
0.01µFQ1
1N4148
12V
1µF
5
4
2
3
15
13 14
11
10 12
1µF
VO = 0 to 5V
RCV420
16
+12V
8
7
9
E
B
14 11
12
13
4
3
2
XTR105
RCM = 1k
1
0.01µF
RZ
137
RLIN1
5760RG
402
RTD
Pt100
100°C to
600°C6
RG
RG
VIN
VIN
+
VLIN IR1 IR2 V
REG
V+
IRET
IO
10
IO = 4mA 20mA
NOTE: A 2-wire RTD connection is shown. For remotely
located RTDs, a 3-wire RTD conection is recommended.
RG becomes 383, RLIN2 is 8060. See Figure 3 and
Table I.
FIGURE 8. Isolated Transmitter/Receiver Loop.
5
4
2
3
15
13 14
11
10 12
RCV420
16
16 2
15
10 87
9
V
VO
V+
0 5V
ISO122
1
+15V
0
15V
1µF
1µF
Isolated Power
from PWS740
0.01µFQ1
1N4148
8
7
9
E
B
14 11
12
13
4
3
2
XTR105
RCM = 1k
1
0.01µF
RLIN1
RG
RLIN2
RTD
6
RG
RG
VLIN IR1 IR2 V
REG
V+
IRET
IO
10
IO = 4mA 20mA
VIN
VIN
+
RZ
NOTE: A 3-wire RTD connection is shown.
For a 2-wire RTD connection eliminate RLIN2.
XTR105 15
SBOS061B www.ti.com
FIGURE 9. Bridge Input, Current Excitation.
4
3
2
RGXTR105
7
6
RG
RG
V+10
13
B
E
9
8
VIN
VIN
+
IRET
RCM = 1k(1)
1.6mA
NOTE: (1) Use RCM to adjust the
common-mode voltage to within
1.25V to 3.5V.
14
1
12
11
V
REG
I
R2
I
R1
V
LIN
PACKAGING INFORMATION
Orderable Device Status (1) Package
Type Package
Drawing Pins Package
Qty Eco Plan (2) Lead/Ball Finish MSL Peak Temp (3)
XTR105P ACTIVE PDIP N 14 25 Green (RoHS &
no Sb/Br) CU NIPDAU N / A for Pkg Type
XTR105PA ACTIVE PDIP N 14 25 Green (RoHS &
no Sb/Br) CU NIPDAU N / A for Pkg Type
XTR105PAG4 ACTIVE PDIP N 14 25 Green (RoHS &
no Sb/Br) CU NIPDAU N / A for Pkg Type
XTR105PG4 ACTIVE PDIP N 14 25 Green (RoHS &
no Sb/Br) CU NIPDAU N / A for Pkg Type
XTR105U ACTIVE SOIC D 14 50 Green (RoHS &
no Sb/Br) CU NIPDAU Level-3-260C-168 HR
XTR105UA ACTIVE SOIC D 14 50 Green (RoHS &
no Sb/Br) CU NIPDAU Level-3-260C-168 HR
XTR105UA/2K5 ACTIVE SOIC D 14 2500 Green (RoHS &
no Sb/Br) CU NIPDAU Level-3-260C-168 HR
XTR105UA/2K5E4 ACTIVE SOIC D 14 2500 Green (RoHS &
no Sb/Br) CU NIPDAU Level-3-260C-168 HR
XTR105UAG4 ACTIVE SOIC D 14 50 Green (RoHS &
no Sb/Br) CU NIPDAU Level-3-260C-168 HR
XTR105UG4 ACTIVE SOIC D 14 50 Green (RoHS &
no Sb/Br) CU NIPDAU Level-3-260C-168 HR
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in
a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check
http://www.ti.com/productcontent for the latest availability information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements
for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered
at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and
package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS
compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame
retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder
temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is
provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the
accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take
reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on
incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited
information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI
to Customer on an annual basis.
PACKAGE OPTION ADDENDUM
www.ti.com 16-Feb-2009
Addendum-Page 1
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0 (mm) B0 (mm) K0 (mm) P1
(mm) W
(mm) Pin1
Quadrant
XTR105UA/2K5 SOIC D 14 2500 330.0 16.4 6.5 9.0 2.1 8.0 16.0 Q1
PACKAGE MATERIALS INFORMATION
www.ti.com 23-May-2008
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
XTR105UA/2K5 SOIC D 14 2500 346.0 346.0 33.0
PACKAGE MATERIALS INFORMATION
www.ti.com 23-May-2008
Pack Materials-Page 2