XTR105
XTR
105
XTR
105
SBOS061B – FEBRUARY 1997 – REVISED AUGUST 2004
4-20mA CURRENT TRANSMITTER
with Sensor Excitation and Linearization
FEATURES
APPLICATIONS
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DESCRIPTION
The XTR105 is a monolithic 4-20mA, 2-wire current transmitter with two precision current sources. It provides complete
current excitation for platinum RTD temperature sensors and
bridges, instrumentation amplifiers, and current output circuitry on a single integrated circuit.
INDUSTRIAL PROCESS CONTROL
FACTORY AUTOMATION
SCADA REMOTE DATA ACQUISITION
REMOTE TEMPERATURE AND PRESSURE
TRANSDUCERS
Pt100 NONLINEARITY CORRECTION
USING XTR105
5
4
Nonlinearity (%)
LOW UNADJUSTED ERROR
TWO PRECISION CURRENT SOURCES: 800µA 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
Uncorrected
RTD Nonlinearity
2
1
Corrected
Nonlinearity
0
−1
−200°C
Versatile linearization circuitry provides a 2nd-order correction 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 unadjusted error of the complete current transmitter is low
enough to permit use without adjustment in many applications. This includes zero output current drift, span drift, and
nonlinearity. The XTR105 operates on loop power-supply
voltages down to 7.5V.
3
+850°C
Process Temperature (°C)
IR = 0.8mA
IR = 0.8mA
VLIN
VREG
7.5V to 36V
+
VPS
4-20 mA
RTD
The XTR105 is available in DIP-14 and SO-14 surfacemount packages and is specified for the –40°C to +85°C
industrial temperature range.
XTR105
RG
VO
RL
–
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.
Copyright © 1997-2004, Texas Instruments Incorporated
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.
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ABSOLUTE MAXIMUM RATINGS(1)
ELECTROSTATIC
DISCHARGE SENSITIVITY
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
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling
and installation procedures can cause damage.
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.
ESD damage can range from subtle performance degradation 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.
PACKAGE/ORDERING INFORMATION(1)
PACKAGE-LEAD
PACKAGE
DESIGNATOR
SPECIFIED
TEMPERATURE
RANGE
DIP-14
N
–40°C to +85°C
"
"
"
SO-14 Surface-Mount
D
–40°C to +85°C
"
"
"
SO-14 Surface-Mount
D
–40°C to +85°C
"
"
"
PRODUCT
XTR105
"
XTR105
"
XTR105
"
PACKAGE
MARKING
ORDERING
NUMBER
TRANSPORT
MEDIA, QUANTITY
XTR105PA
XTR105P
XTR105UA
XTR105UA
XTR105U
XTR105U
XTR105PA
XTR105P
XTR105UA
XTR105UA/2K5
XTR105U
XTR105U/2K5
Rails, 25
Rails, 25
Rails, 58
Tape and Reel, 2500
Rails, 58
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.
FUNCTIONAL BLOCK DIAGRAM
PIN CONFIGURATION
Top View
DIP and SO
VLIN
IR1
12
IR2
1
14
VREG
V+
800µA
800µA
11
+
VIN
13
5.1V
4
B
RLIN
1kΩ
Q1
9
100µA
RG
3
–
VIN
1
14 IR2
–
VIN
2
13 VIN
RG
3
12 VLIN
RG
4
11 VREG
NC
5
10 V+
IRET
6
9
B (Base)
IO
7
8
E (Emitter)
IR1
10
E
I = 100µA +
2
VIN
8
RG
975Ω
+
25Ω
NC = No Internal Connection
7
IO = 4mA + VIN •
( R40 )
G
6
IRET
2
XTR105
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SBOS061B
ELECTRICAL CHARACTERISTICS
At TA = +25°C, V+ = 24V, and TIP29C external transistor, unless otherwise noted.
XTR105P, U
PARAMETER
CONDITIONS
OUTPUT
Output Current Equation
Output Current, Specified Range
Over-Scale Limit
Under-Scale Limit
OUTPUT(1)
ZERO
Initial Error
vs Temperature
vs Supply Voltage, V+
vs Common-Mode Voltage
vs VREG Output Current
Noise, 0.1Hz to 10Hz
SPAN
Span Equation (transconductance)
Initial Error (3)
vs Temperature(3)
Nonlinearity, Ideal Input (4)
INPUT(5)
Offset Voltage
vs Temperature
vs Supply Voltage, V+
vs Common-Mode Voltage,
RTI (CMRR)
Common-Mode Input Range(2)
Input Bias Current
vs Temperature
Input Offset Current
vs Temperature
Impedance, Differential
Common-Mode
Noise, 0.1Hz to 10Hz
CURRENT SOURCES
Current
Accuracy
vs Temperature
vs Power Supply, V+
Matching
vs Temperature
vs Power Supply, V+
Compliance Voltage, Positive
Negative(2)
Output Impedance
Noise, 0.1Hz to 10Hz
IREG = 0V
MIN
TYP
XTR105PA, UA
MAX
MIN
TYP
IO = VIN • (40/RG) + 4mA, VIN in Volts, RG in Ω
4
20
✻
24
27
30
✻
✻
1.8
2.2
2.6
✻
✻
VIN = 0V, RG = ∞
4
±5
±0.07
0.04
0.02
0.3
0.03
V+ = 7.5V to 36V
VCM = 1.25V to 3.5V(2)
Full-Scale (VIN) = 50mV
Full-Scale (VIN) = 50mV
VCM = 2V
V+ = 7.5V to 36V
VCM = 1.25V to 3.5V(2)
✻
✻
✻
✻
✻
✻
✻
±25
±0.5
0.2
MAX
UNITS
✻
✻
✻
A
mA
mA
mA
±50
±0.9
✻
S = 40/RG
±0.05
±3
0.003
±0.2
±25
0.01
✻
✻
✻
✻
±0.4
✻
✻
A/V
%
ppm/°C
%
±50
±0.4
±0.3
±10
±100
±1.5
±3
±50
✻
✻
✻
✻
±250
±3
✻
±100
µV
µV/°C
µV/V
µV/V
✻
50
V
nA
pA/°C
nA
pA/°C
GΩ || pF
GΩ || pF
µVPP
1.25
5
20
±0.2
5
0.1 || 1
5 || 10
0.6
3.5
25
✻
✻
✻
✻
✻
✻
✻
✻
±3
±10
VO = 2V(6)
V+ = 7.5V to 36V
V+ = 7.5V to 36V
(V+) – 3
0
800
±0.05
±15
±10
±0.02
±3
1
(V+) – 2.5
–0.2
150
0.003
VREG(2)
Accuracy
vs Temperature
vs Supply Voltage, V+
Output Current
Output Impedance
5.1
±0.02
±0.2
1
±1
75
LINEARIZATION
RLIN (internal)
Accuracy
vs Temperature
1
±0.2
±25
POWER SUPPLY
Specified
Voltage Range
TEMPERATURE RANGE
Specification, TMIN to TMAX
Operating
Storage
Thermal Resistance, θJA
DIP-14
SO-14 Surface-Mount
mA
µA
µA/°C
µA/V
µA/V
µA/mA
µAPP
±0.2
±35
±25
±0.1
±15
10
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
±0.1
✻
✻
✻
±0.5
±100
±0.4
±75
✻
±0.2
±30
✻
✻
V
V
mV/°C
mV/V
mA
Ω
±1
✻
kΩ
%
ppm/°C
✻
+24
µA
%
ppm/°C
ppm/V
%
ppm/°C
ppm/V
V
V
MΩ
µAPP
+7.5
+36
✻
✻
V
V
–40
–55
–55
+85
+125
+125
✻
✻
✻
✻
✻
✻
°C
°C
°C
80
100
✻
✻
°C/W
°C/W
✻ Specification same as XTR105P and XTR105U.
NOTES: (1)
(2)
(3)
(4)
(5)
(6)
Describes accuracy of the 4mA low-scale offset current. Does not include input amplifier effects. Can be trimmed to zero.
Voltage measured with respect to IRET pin.
Does not include initial error or TCR of gain-setting resistor, RG.
Increasing the full-scale input range improves nonlinearity.
Does not include Zero Output initial error.
Current source output voltage with respect to IRET pin.
XTR105
SBOS061B
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3
TYPICAL CHARACTERISTICS
At TA = +25°C and V+ = 24V, unless otherwise noted.
TRANSCONDUCTANCE vs FREQUENCY
STEP RESPONSE
RG = 125Ω
RG = 500Ω
RG = 2kΩ
40
20mA
30
4mA/div
Transconductance (20 Log mA/V)
50
20
RG = 125Ω
RG = 2kΩ
4mA
10
0
100
1k
10k
100k
25µs/div
1M
Frequency (Hz)
COMMON-MODE REJECTION vs FREQUENCY
POWER-SUPPLY REJECTION vs FREQUENCY
140
Full-Scale Input = 50mV
100
Power Supply Rejection (dB)
Common-Mode Rejection (dB)
110
90
80
RG = 125Ω
70
60
RG = 2kΩ
50
40
30
20
120
RG = 125Ω
100
80
RG = 2kΩ
60
40
20
0
10
100
1k
10k
100k
1M
10
100
Frequency (Hz)
1k
10k
100k
1M
Frequency (Hz)
UNDER-SCALE CURRENT vs TEMPERATURE
OVER-SCALE CURRENT vs TEMPERATURE
2.40
29
Under-Scale Current (mA)
Over-Scale Current (mA)
With External Transistor
28
27
V+ = 36V
26
V+ = 7.5V
25
V+ = 24V
24
2.30
2.25
2.20
V+ = 7.5V to 36V
23
2.15
–75
–50
–25
0
25
50
75
100
–75
125
–50
–25
0
25
50
75
100
125
Temperature (°C)
Temperature (°C)
4
2.35
XTR105
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SBOS061B
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C and V+ = 24V, unless otherwise noted.
ZERO OUTPUT AND REFERENCE
CURRENT NOISE vs FREQUENCY
INPUT VOLTAGE AND CURRENT
NOISE DENSITY vs FREQUENCY
10k
10k
1k
Current Noise
100
100
Voltage Noise
10
1
10
100
1k
Zero Output Current
Noise (pA/√Hz)
1k
Input Current Noise (fA/√Hz)
Input Voltage Noise (nV/√Hz)
10k
1k
100
Reference Current
10
10
100k
10k
1
1k
10k
INPUT BIAS AND OFFSET CURRENT
vs TEMPERATURE
ZERO OUTPUT CURRENT ERROR
vs TEMPERATURE
100k
4
20
15
+IB
10
–IB
5
IOS
Zero Output Current Error (µA)
Input Bias and Offset Current (nA)
100
Frequency (Hz)
25
2
0
–2
–4
–6
–8
–10
–12
0
–75
–50
–25
0
25
50
75
100
–75
125
–50
–25
0
25
50
75
Temperature (°C)
Temperature (°C)
INPUT OFFSET VOLTAGE DRIFT
PRODUCTION DISTRIBUTION
ZERO OUTPUT DRIFT
PRODUCTION DISTRIBUTION
50
100
125
40
Typical Production Distribution
of Packaged Units.
45
35
Percent of Units (%)
40
Percent of Units (%)
10
Frequency (Hz)
35
30
25
20
15
10
0.02%
0.1%
5
Typical Production Distribution
of Packaged Units.
30
25
20
15
10
5
0
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
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
Input Offset Voltage Drift (µV/°C)
Zero Output Drift (µA/°C)
XTR105
SBOS061B
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5
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C and V+ = 24V, unless otherwise noted.
CURRENT SOURCE DRIFT
PRODUCTION DISTRIBUTION
CURRENT SOURCE MATCHING
DRIFT PRODUCTION DISTRIBUTION
40
80
30
Current Source Drift (ppm/°C)
Current Source Matching Drift (ppm/°C)
VREG OUTPUT VOLTAGE vs VREG OUTPUT CURRENT
REFERENCE CURRENT ERROR
vs TEMPERATURE
30
0.02%
28
0.07%
26
12
8
10
6
4
2
75
70
60
55
50
45
40
35
30
25
20
15
0
5
0
10
10
24
20
0.01%
5
22
10
40
20
15
50
18
20
60
14
25
0.04%
Typical Production Distribution
of Packaged Units.
70
Percent of Units (%)
30
65
Percent of Units (%)
35
16
Typical Production Distribution
of Packaged Units.
IR1 AND IR2 Included.
+0.05
5.35
125°C
5.25
Reference Current Error (%)
VREG Output Voltage (V)
5.30
25°C
5.20
5.15
–55°C
NOTE: Above 1mA,
Zero Output Degrades
5.10
5.05
5.00
–1.0
–0.05
–0.10
–0.15
–0.20
–0.5
0
0.5
1.0
1.5
–75
2.0
–50
–25
0
25
50
75
100
125
Temperature (°C)
VREG Output Current (mA)
6
0
XTR105
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SBOS061B
APPLICATION INFORMATION
The transfer function through the complete instrumentation
amplifier and voltage-to-current converter is:
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.
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 XTR105’s zero
current. The value of RG varies slightly for 2-wire RTD and 3wire RTD connections with linearization. RG can be calculated from the equations given in Figure 1 (2-wire RTD
connection) and Table I (3-wire RTD connection).
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) measurement 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.
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.
RCM provides an additional voltage drop to bias the inputs of
the XTR105 within their common-mode input range. RCM
should be bypassed with a 0.01µF capacitor to minimize
common-mode noise. Resistor RG sets the gain of the instrumentation amplifier according to the desired temperature
range. RLIN1 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 VREG pin provides an on-chip voltage source of approximately 5.1V and is suitable for powering external input
circuitry (refer to Figure 6). It is a moderately accurate
voltage reference—it 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.
IR = 0.8mA
Possible choices for Q1 (see text).
IR = 0.8mA
12
13
4
VLIN
+
VIN
1
IR1
TO-225
TO-220
TO-220
IO
RG
RG
RLIN1(3)
PACKAGE
7.5V to 36V
14
11
IR2
10
VREG
V+
4-20 mA
(2)
XTR105
3
TYPE
2N4922
TIP29C
TIP31C
RG
B
9
Q1
0.01µF
VO
E
8
RL
IO
2
–
VIN
+
VPS
–
7
IRET
RTD
(1)
RZ
6
IO = 4mA + VIN • ( 40 )
RG
NOTES: (1) RZ = RTD resistance at minimum measured temperature.
RCM = 1kΩ
(2) RG =
(3) RLIN1 =
0.01µF
2R1(R2 +RZ) – 4(R2RZ)
R2 – R1
RLIN(R2 – R1)
2(2R1 – R2 – RZ)
where R1 = RTD Resistance at (TMIN + TMAX)/2
R2 = RTD Resistance at TMAX
RLIN = 1kΩ (Internal)
FIGURE 1. Basic 2-Wire RTD Temperature Measurement Circuit with Linearization.
XTR105
SBOS061B
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7
MEASUREMENT TEMPERATURE SPAN ∆T (°C)
TMIN
100°C
200°C
300°C
400°C
500°C
600°C
700°C
800°C
900°C
1000°C
–200°C
18.7/86.6
15000
16500
18.7/169
9760
11500
18.7/255
8060
10000
18.7/340
6650
8870
18.7/422
5620
7870
18.7/511
4750
7150
18.7/590
4020
6420
18.7/665
3480
5900
18.7/750
3090
5360
18.7/845
2740
4990
–100°C
60.4/80.6
27400
29400
60.4/162
15400
17800
60.4/243
10500
13000
60.4/324
7870
10200
60.4/402
6040
8660
60.4/487
4990
7500
60.4/562
4220
6490
60.4/649
3570
5900
60.4/732
3090
5360
0°C
100/78.7
33200
35700
100/158
16200
18700
100/237
10500
13000
100/316
7680
10000
100/392
6040
8250
100/475
4870
7150
100/549
4020
6340
100/634
3480
5620
100°C
137/75
31600
34000
137/150
15400
17800
137/226
10200
12400
137/301
7500
9760
137/383
5760
8060
137/453
4750
6810
137/536
3920
6040
200°C
174/73.2
30900
33200
174/147
15000
17400
174/221
9760
12100
174/294
7150
9310
174/365
5620
7680
174/442
4530
6490
300°C
210/71.5
30100
32400
210/143
14700
16500
210/215
9530
11500
210/287
6980
8870
210/357
5360
7320
400°C
249/68.1
28700
30900
249/137
14000
16200
249/205
9090
11000
249/274
6650
8450
500°C
280/66.5
28000
30100
280/133
13700
15400
280/200
8870
10500
316/64.9
26700
28700
313/130
13000
14700
600°C
700°C
800°C
RZ /RG
RLIN1
RLIN2
NOTE: The values listed in this table are 1% resistors (in Ω).
Exact values may be calculated from the following equations:
RZ = RTD resistance at minimum measured temperature.
RG =
348/61.9
26100
27400
374/60.4
24900
26700
2(R2 – RZ )(R1 – RZ )
(R2 – R1)
RLIN1 =
RLIN (R2 – R1)
2(2R1 – R2 – RZ )
RLIN2 =
(RLIN + RG )(R2 – R1)
2(2R1 – R2 – RZ )
where: R1 = RTD resistance at (TMIN + TMAX)/2
R2 = RTD resistance at TMAX
RLIN = 1kΩ (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 = 60.4Ω
RLIN1 = 10.5kΩ
RG = 243Ω
RLIN2 = 13kΩ
METHOD 2: CALCULATION
Calculation of Pt100 Resistance Values
Step 1: Determine RZ, R1, and R2.
(according to DIN IEC 751)
RZ is the RTD resistance at the minimum measured temperature,TMIN = –100°C.
Using Equation 1 at right gives RZ = 60.25Ω (1% value is 60.4Ω).
R2 is the RTD resistance at the maximum measured temperature, TMAX = 200°C.
Using Equation 2 at right gives R2 = 175.84Ω.
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 = 119.40Ω.
(Equation 1) Temperature range from –200°C to 0°C:
R(T) = 100 [1 + 3.90802 • 10–3 • T – 0.5802 • 10–6 •
T2 – 4.27350 • 10–12 (T – 100) T3]
(Equation 2) Temperature range from 0°C to +850°C:
R(T) = 100 (1 + 3.90802 • 10–3 • T – 0.5802 • 10–6 • T2)
where: R(T) is the resistance in Ω at temperature T.
T is the temperature in °C.
Step 2: Calculate RG, RLIN1, and RLIN2 using equations above.
NOTE: Most RTD manufacturers provide reference tables for
resistance values at various temperatures.
RG = 242.3Ω (1% value is 243Ω)
RLIN1 = 10.413kΩ (1% value is 10.5kΩ)
RLIN2 = 12.936kΩ (1% value is 13kΩ)
TABLE I. RZ, RG, RLIN1, and RLIN2 Standard 1% Resistor Values for 3-Wire Pt100 RTD Connection with Linearization.
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.
8
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 approximately 27mA. Refer to the typical characteristic Over-Scale
Current vs Temperature.
XTR105
www.ti.com
SBOS061B
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 transistor, 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 = 3.3kΩ) connected between the IRET pin and the E
(emitter) pin may be needed for operation below 0°C without Q1 to ensure the full 20mA full-scale output, especially
with V+ near 7.5V.
10
8
XTR105
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 receiver (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 corrected 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 accuracy. RZ’s 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 linearization.
V+
E
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.
0.01µF
Note that although the 2-wire and 3-wire RTD connection
circuits are very similar, the gain-setting resistor, RG, has
slightly different equations:
IO
7
IRET
2-wire:
6
RQ = 3.3kΩ
For operation without an external
transistor, connect a 3.3kΩ
resistor between pin 6 and pin 8.
See text for discussion
of performance.
3-wire:
RG =
2R1(R2 + RZ ) – 4(R2RZ )
R2 – R1
RG =
2(R2 – RZ )(R1 – RZ )
R2 – R1
where: RZ = RTD resistance at TMIN
R1 = RTD resistance at (TMIN + TMAX)/2
FIGURE 2. Operation Without an External Transistor.
R2 = RTD resistance at TMAX
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:
(V + ) – 7.5V
RL max =
– RWIRING
20mA
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.
XTR105
SBOS061B
www.ti.com
9
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 encountered 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 commonmode 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 • VFS, 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 common-mode biasing of the inputs. As mentioned earlier, RCM can
be adjusted to provide an additional voltage drop to bias the
inputs of the XTR105 within their common-mode input range.
RLIN1(1)
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
XTR105’s 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
XTR105’s 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.
13
RLIN2(1)
4
12
1
VLIN
IR1
+
VIN
IO
14
IR2
11
10
VREG
V+
RG
(1)
RG
XTR105
3
2
B 9
E
RG
Q1
0.01µF
8
IO
–
VIN
7
IRET
EQUAL line resistances here
creates a small common-mode
voltage which is rejected by
the XTR105.
RZ(1)
IO
6
1
2
RCM = 1000Ω
(RLINE2)
RTD
(RLINE1)
NOTES: (1) See Table I for resistor equations and
1% values. (2) Q2 optional. Provides predictable
output current if any one RTD connection is
broken:
Q2(2)
2N2222
(RLINE3)
Resistance in this line causes
a small common-mode voltage
which is rejected by the XTR105.
0.01µF
3
OPEN RTD
TERMINAL
IO
1
2
3
≈ 2.2mA
≈27mA
≈2.2mA
FIGURE 3. Remotely Located RTDs with 3-Wire Connection.
10
XTR105
www.ti.com
SBOS061B
SAMPLE ERROR CALCULATION
RTD value at 4mA Output (RRTD MIN):
RTD Measurement Range:
Ambient Temperature Range (∆TA):
Supply Voltage Change (∆V+):
Common-Mode Voltage Change (∆CM):
ERROR SOURCE
INPUT
Input Offset Voltage
vs Common-Mode
Input Bias Current
Input Offset Current
EXCITATION
Current Reference Accuracy
vs Supply
Current Reference Matching
vs Supply
100Ω
200°C
20°C
5V
0.1V
ERROR EQUATION
VOS/(VIN MAX) • 106
CMRR • ∆CM/(VIN MAX) • 106
IB/IREF • 106
IOS • RRTD MIN/(VIN MAX) • 106
IREF Accuracy (%)/100% • 106
(IREF vs V+) • ∆V+
IREF Matching (%)/100% • 800µA •
RRTD MIN/(VIN MAX) • 106
(IREF Matching vs V+) • ∆V+ •
RRTD MIN/(VIN MAX)
ERROR
(ppm of Full Scale)
SAMPLE
ERROR CALCULATION(1)
UNADJ.
ADJUST.
1645
82
31
5
1763
0
82
0
0
82
0.2%/100% • 106
25ppm/V • 5V
0.1%/100% • 800µA • 100Ω/(800µA • 0.38Ω/°C • 200°C) • 106
2000
125
1316
0
125
0
10ppm/V • 5V • 800µA • 100Ω/(800µA • 0.38Ω/°C • 200°C)
66
66
3507
191
Total Gain Error:
2000
100
2100
0
100
100
25µA/16000µA • 106
0.2µA/V • 5V/16000µA • 106
Total Output Error:
1563
63
1626
0
63
63
1.5µV/°C • 20°C/(800µA • 0.38Ω/°C • 200°C) • 106
20pA/°C • 20°C/800µA • 106
5pA/°C • 20°C • 100W/(800µA • 0.38Ω/°C • 200°C) • 106
35ppm/°C • 20°C
15ppm/°C • 20°C • 800µA • 100Ω/(800µA • 0.38Ω/°C • 200°C)
25ppm/°C • 20°C
0.5µA/°C • 20°C/16000µA • 106
Total Drift Error:
493
0.5
0.2
700
395
500
626
2715
493
0.5
0.2
700
395
500
626
2715
10
5
2
17
10
5
2
17
11728
(1.17%)
3168
(0.32%)
100µV/(800µA • 0.38Ω/°C • 200°C) • 106
50µV/V • 0.1V/(800µA • 0.38Ω/°C • 200°C) • 106
0.025µA/800µA • 106
3nA • 100Ω/(800µA • 0.38Ω/°C • 200°C) • 106
Total Input Error:
Total Excitation Error:
GAIN
Span
Nonlinearity
OUTPUT
Zero Output
vs Supply
Span Error (%)/100% • 106
Nonlinearity (%)/100% • 106
(IZERO – 4mA) /16000µA • 106
(IZERO vs V+) • ∆V+/16000µA • 106
DRIFT (∆TA = 20°C)
Input Offset Voltage
Drift • ∆TA/(VIN MAX) • 106
Input Bias Current (typical)
Drift • ∆TA/800µA • 106
Input Offset Current (typical) Drift • ∆TA • RRTD MIN/(VIN MAX) • 106
Current Reference Accuracy
Drift • ∆TA
Current Reference Matching Drift • ∆TA • 800µA • RRTD MIN/(VIN MAX)
Span
Drift • ∆TA
Zero Output
Drift • ∆TA/16000µA • 106
NOISE (0.1Hz to 10Hz, typ)
Input Offset Voltage
Current Reference
Zero Output
0.2%/100% • 106
0.01%/100% • 106
vn/(VIN MAX) • 106
IREF Noise • RRTD MIN/(VIN MAX) • 106
IZERO Noise/16000µA • 106
0.6µV/(800µA • 0.38Ω/°C • 200°C) • 106
3nA • 100Ω/(800µA • 0.38Ω/°C • 200°C) • 106
0.03µA/16000µA • 106
Total Noise Error:
NOTE (1): All errors are min/max and referred to input unless otherwise stated.
TOTAL ERROR:
TABLE II. Error Calculation.
XTR105
SBOS061B
www.ti.com
11
REVERSE-VOLTAGE PROTECTION
The XTR105’s 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 9V—satisfactory
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 characteristic 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 appears 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 assemblies with short connections to the sensor, the interference 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 transmitter’s “ground.”
The 0.01µF capacitor connected between V+ and IO may
help minimize output interference.
NOTE: (1) Zener Diode 36V: 1N4753A or General
Semiconductor TransorbTM 1N6286A. Use lower
voltage zener diodes with loop-power supply
voltages less than 30V for increased protection.
See the Surge Protection section.
10
V+
0.01µF
XTR105
B
E
9
D1(1)
1N4148
Diodes
RL
8
IO
7
IRET
6
VPS
Maximum VPS must be
less than minimum
voltage rating of zener
diode.
The diode bridge causes
a 1.4V loss in loop-supply
voltage.
FIGURE 4. Reverse Voltage Operation and Over-Voltage Surge Protection.
12
XTR105
www.ti.com
SBOS061B
12
1kΩ
13
4
RLIN1
VLIN
+
VIN
1
IR1
14
11
IR2
VREG
10
V+
RG
RLIN2
RG
B
XTR105
3
E
RG
9
0.01µF
8
IO
1kΩ
2
–
VIN
7
IRET
RZ
0.01µF
6
0.01µF
RTD
(1)
RCM
NOTE: (1) Bypass capacitors can be connected
to either the IRET pin or the IO pin.
0.01µF
FIGURE 5. Input Bypassing Technique with Linearization.
IREG < 1mA
5V
12
V+
Type J
VLIN
1/2
OPA2335
13
RF
10kΩ
4
R
412Ω
+
VIN
1
IR1
11
VREG
XTR105
3
10
V+
RG
RG
1250Ω
RF
10kΩ
14
IR2
B
E
RG
9
8
IO
1/2
OPA2335
1kΩ
2
25Ω
7
IRET
V–
50Ω
–
VIN
6
+
–
IO = 4mA + (VIN – VIN) 40
RG
RCM = 1250Ω
(G = 1 +
2RF
= 50)
R
FIGURE 6. Thermocouple Low Offset, Low Drift Loop Measurement with Diode Cold Junction Compensation.
XTR105
SBOS061B
www.ti.com
13
12
13
4
1
IR1
VLIN
+
VIN
3
IR2
+12V
11
VREG
10
V+
1µF
RG
B 9
RG
402Ω
RLIN1
5760Ω
1N4148
14
XTR105
Q1
0.01µF
16
RG
–
VIN
RTD
RZ
137Ω
2
7
VO = 0 to 5V
14
13
5
4
IO = 4mA – 20mA
6
12
RCV420
IRET
Pt100
100°C to
600°C
11
15
IO
2
10
3
E 8
1µF
–12V
RCM = 1kΩ
NOTE: A 2-wire RTD connection is shown. For remotely
located RTDs, a 3-wire RTD conection is recommended.
RG becomes 383Ω, RLIN2 is 8060Ω. See Figure 3 and
Table I.
0.01µF
FIGURE 7. ±12V Powered Transmitter/Receiver Loop.
12
RLIN1
RLIN2
13
4
VLIN
+
VIN
1
IR1
1N4148
14
11
IR2
10
VREG
V+
0
RG
RG
1µF
XTR105
3
+15V
1µF
B
E
RG
9
Q1
–15V
0.01µF
16
11
12
–
2 VIN
IRET
2
7
IO = 4mA – 20mA
6
14
13
4
V+
1
15
RCV420
IO
RZ
10
3
8
Isolated Power
from PWS740
9
15
ISO122
5
10
7
8
VO
0 – 5V
2
16
RTD
NOTE: A 3-wire RTD connection is shown.
For a 2-wire RTD connection eliminate RLIN2.
V–
RCM = 1kΩ
0.01µF
FIGURE 8. Isolated Transmitter/Receiver Loop.
14
XTR105
www.ti.com
SBOS061B
1.6mA
12
VLIN
+
13 VIN
4
1
IR1
14
IR2
11
VREG 10
V+
RG
RG
XTR105
3
2
B
E
RG
–
VIN
9
8
7
IRET
6
RCM = 1kΩ(1)
NOTE: (1) Use RCM to adjust the
common-mode voltage to within
1.25V to 3.5V.
FIGURE 9. Bridge Input, Current Excitation.
XTR105
SBOS061B
www.ti.com
15
PACKAGE OPTION ADDENDUM
www.ti.com
7-Oct-2021
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
XTR105P
ACTIVE
PDIP
N
14
25
RoHS & Green
Call TI
N / A for Pkg Type
-40 to 85
XTR105P
A
XTR105PA
ACTIVE
PDIP
N
14
25
RoHS & Green
Call TI
N / A for Pkg Type
-40 to 85
XTR105P
A
XTR105U
ACTIVE
SOIC
D
14
50
RoHS & Green
Call TI
Level-3-260C-168 HR
-40 to 85
XTR105U
XTR105UA
ACTIVE
SOIC
D
14
50
RoHS & Green
Call TI
Level-3-260C-168 HR
-40 to 85
XTR105U
A
XTR105UA/2K5
ACTIVE
SOIC
D
14
2500
RoHS & Green
NIPDAU
Level-3-260C-168 HR
-40 to 85
XTR105U
A
(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)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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