XTR106
XTR
106
X TR
1 06
SBOS092A – JUNE 1998 – REVISED NOVEMBER 2003
4-20mA CURRENT TRANSMITTER
with Bridge Excitation and Linearization
FEATURES
APPLICATIONS
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LOW TOTAL UNADJUSTED ERROR
2.5V, 5V BRIDGE EXCITATION REFERENCE
5.1V REGULATOR OUTPUT
LOW SPAN DRIFT: ±25ppm/°C max
LOW OFFSET DRIFT: 0.25µV/°C
HIGH PSR: 110dB min
HIGH CMR: 86dB min
WIDE SUPPLY RANGE: 7.5V to 36V
14-PIN DIP AND SO-14 SURFACE-MOUNT
PRESSURE BRIDGE TRANSMITTERS
STRAIN GAGE TRANSMITTERS
TEMPERATURE BRIDGE TRANSMITTERS
INDUSTRIAL PROCESS CONTROL
SCADA REMOTE DATA ACQUISITION
REMOTE TRANSDUCERS
WEIGHING SYSTEMS
ACCELEROMETERS
BRIDGE NONLINEARITY CORRECTION
USING XTR106
DESCRIPTION
2.0
1.5
Nonlinearity (%)
The XTR106 is a low cost, monolithic 4-20mA, twowire current transmitter designed for bridge sensors. It
provides complete bridge excitation (2.5V or 5V reference), instrumentation amplifier, sensor linearization,
and current output circuitry. Current for powering additional external input circuitry is available from the
VREG pin.
The instrumentation amplifier can be used over a wide
range of gain, accommodating a variety of input signal
types and sensors. Total unadjusted error of the complete current transmitter, including the linearized bridge,
is low enough to permit use without adjustment in many
applications. The XTR106 operates on loop power supply voltages down to 7.5V.
Linearization circuitry provides second-order correction
to the transfer function by controlling bridge excitation
voltage. It provides up to a 20:1 improvement in
nonlinearity, even with low cost transducers.
The XTR106 is available in 14-pin plastic DIP and
SO-14 surface-mount packages and is specified for the
–40°C to +85°C temperature range. Operation is from
–55°C to +125°C.
Uncorrected
Bridge Output
1.0
0.5
Corrected
0
–0.5
0
5
10
Bridge Output (mV)
VREG (5.1V)
VREF5
VREF 2.5V
RLIN
+
7.5V to 36V
VPS
4-20mA
5V
VO
XTR106
RG
RL
–
Lin
Polarity
IOUT
IRET
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 © 1998-2003, 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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SPECIFICATIONS
At TA = +25°C, V+ = 24V, and TIP29C external transistor, unless otherwise noted.
XTR106P, U
PARAMETER
CONDITIONS
OUTPUT
Output Current Equation
Output Current, Specified Range
Over-Scale Limit
Under-Scale Limit
IO
IOVER
IUNDER
ZERO OUTPUT(1)
Initial Error
vs Temperature
vs Supply Voltage, V+
vs Common-Mode Voltage (CMRR)
vs VREG (IO)
Noise: 0.1Hz to 10Hz
IZERO
IO = VIN
4
24
1
2.9
• (40/RG) + 4mA, VIN in Volts, RG in Ω
20
✻
28
30
✻
✻
1.6
2.2
✻
✻
3.4
4
✻
✻
VIN = 0V, RG = ∞
4
±5
±0.07
0.04
0.02
0.8
0.035
S
VOS
CMRR
VCM
IB
Full Scale (VIN) = 50mV
TA = –40°C to +85°C
Full Scale (VIN) = 50mV
S = 40/RG
±0.05
±3
±0.001
VCM = 2.5V
TA = –40°C to +85°C
V+ = 7.5V to 36V
VCM = 1.1V to 3.5V(5)
±50
±0.25
±0.1
±10
1.1
5
20
±0.2
5
0.1 || 1
5 || 10
0.6
TA = –40°C to +85°C
IOS
TA = –40°C to +85°C
ZIN
Vn
MAX
MIN
✻
✻
✻
✻
✻
✻
✻
±25
±0.9
0.2
✻
✻
✻
✻
±0.2
±25
±0.01
±100
±1.5
±3
±50
3.5
25
TYP
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
✻
±3
MAX
UNITS
✻
✻
✻
✻
A
mA
mA
mA
mA
±50
✻
✻
±0.4
✻
✻
±250
±3
✻
±100
✻
50
±10
mA
µA
µA/°C
µA/V
µA/V
µA/mA
µAp-p
A/V
%
ppm/°C
%
µV
µV/°C
µV/V
µV/V
V
nA
pA/°C
nA
pA/°C
GΩ || pF
GΩ || pF
µVp-p
Lin Polarity Connected
to VREG, RLIN = 0
Initial: 2.5V Reference
5V Reference
Accuracy
vs Temperature
vs Supply Voltage, V+
vs Load
Noise: 0.1Hz to 10Hz
VREF2.5
VREF5
VREG(5)
Accuracy
vs Temperature
vs Supply Voltage, V+
Output Current
Output Impedance
VREG
TA = –40°C to +85°C
V+ = 7.5V to 36V
IREG
IREG = 0mA to 2.5mA
RLIN
KLIN Linearization Factor
KLIN
Accuracy
vs Temperature
Max Correctable Sensor Nonlinearity
±0.25
±35
±20
✻
✻
✻
✻
✻
✻
✻
5.1
±0.02
±0.1
±0.3
1
See Typical Curves
80
✻
✻
✻
✻
✻
✻
2.5
5
±0.05
±20
±5
60
10
VREF = 2.5V or 5V
TA = –40°C to +85°C
V+ = 7.5V to 36V
IREF = 0mA to 2.5mA
LINEARIZATION(6)
RLIN (external) Equation
TEMPERATURE RANGE
Specification
Operating
Storage
Thermal Resistance
14-Pin DIP
SO-14 Surface Mount
TYP
in
VOLTAGE REFERENCES(5)
POWER SUPPLY
Specified
Voltage Range
MIN
TA = –40°C to +85°C
V+ = 7.5V to 36V
VCM = 1.1V to 3.5V(5)
SPAN
Span Equation (Transconductance)
Untrimmed Error
vs Temperature(2)
Nonlinearity: Ideal Input (3)
INPUT(4)
Offset Voltage
vs Temperature
vs Supply Voltage, V+
vs Common-Mode Voltage, RTI
Common-Mode Range(5)
Input Bias Current
vs Temperature
Input Offset Current
vs Temperature
Impedance: Differential
Common-Mode
Noise: 0.1Hz to 10Hz
IREG = 0, IREF = 0
IREF + IREG = 2.5mA
XTR106PA, UA
B
RLIN = KLIN •
VREF = 5V
VREF = 2.5V
✻
4B
, KLIN in Ω, B is nonlinearity relative to VFS
1 – 2B
6.645
9.905
±1
±50
±5
–2.5, +5
TA = –40°C to +85°C
VREF = 5V
VREF = 2.5V
±0.5
±75
✻
✻
✻
✻
✻
✻
✻
±5
±100
✻
✻
V
V
%
ppm/°C
ppm/V
ppm/mA
µVp-p
V
V
mV/°C
mV/V
mA
Ω
Ω
kΩ
kΩ
%
ppm/°C
% of VFS
% of VFS
V+
✻
+7.5
+24
+36
✻
✻
V
V
–40
–55
–55
+85
+125
+125
✻
✻
✻
✻
✻
✻
°C
°C
°C
θJA
80
100
✻
✻
°C/W
°C/W
✻ Specification same as XTR106P, XTR106U.
NOTES: (1) Describes accuracy of the 4mA low-scale offset current. Does not include input amplifier effects. Can be trimmed to zero. (2) Does not include initial
error or TCR of gain-setting resistor, RG. (3) Increasing the full-scale input range improves nonlinearity. (4) Does not include Zero Output initial error. (5) Voltage
measured with respect to IRET pin. (6) See “Linearization” text for detailed explanation. VFS = full-scale VIN.
2
XTR106
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SBOS092A
ABSOLUTE MAXIMUM RATINGS(1)
PIN CONFIGURATION
Top View
DIP and SOIC
VREG
1
14 VREF5
V–
IN
2
13 VREF2.5
RG
3
12 Lin Polarity
RG
4
11 RLIN
+
VIN
5
10 V+
IRET
6
9
B (Base)
IO
7
8
E (Emitter)
Power Supply, V+ (referenced to IO pin) .......................................... 40V
+
–
Input Voltage, VIN, VIN (referenced to IRET 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
NOTE: (1) Stresses above these ratings may cause permanent damage.
Exposure to absolute maximum conditions for extended periods may degrade
device reliability.
ELECTROSTATIC
DISCHARGE SENSITIVITY
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.
PACKAGE/ORDERING INFORMATION
For the most current package and ordering information, see
the Package Option Addendum at the end of this data sheet.
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.
XTR106
SBOS092A
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3
FUNCTIONAL DIAGRAM
VREG
Lin
Polarity
12
RLIN
V+
11
1
10
VREF5
VREF2.5
14
REF
Amp
Bandgap
VREF
5.1V
13
Lin
Amp
Current
Direction
Switch
+
VIN
5
4
100µA
B
9
RG
975Ω
25Ω
3
–
VIN
2
I = 100µA +
E
VIN
RG
8
7
6
IO = 4mA + VIN • (
40
)
RG
IRET
4
XTR106
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SBOS092A
TYPICAL PERFORMANCE CURVES
At TA = +25°C, V+ = 24V, unless otherwise noted.
TRANSCONDUCTANCE vs FREQUENCY
RG = 50Ω
50
STEP RESPONSE
CCOUT
0.01µF
OUT==0.01µF
COUT = 0.033µF
COUT = 0.01µF
RG = 1kΩ
COUT connected
between V+ and IO
40
30
20mA
4mA/div
Transconductance (20 log mA/V)
60
RG = 1kΩ
RG = 50Ω
20
4mA
10
RL = 250Ω
0
100
1k
10k
100k
1M
50µs/div
Frequency (Hz)
POWER SUPPLY REJECTION vs FREQUENCY
160
100
140
Power Supply Rejection (dB)
Common-Mode Rejection (dB)
COMMON-MODE REJECTION vs FREQUENCY
110
90
RG = 50Ω
80
RG = 1kΩ
70
60
50
120
100
RG = 1kΩ
80
60
40
20
40
0
30
10
100
1k
10k
100k
10
1M
100
1k
10k
100k
Frequency (Hz)
Frequency (Hz)
INPUT OFFSET VOLTAGE DRIFT
PRODUCTION DISTRIBUTION
INPUT OFFSET VOLTAGE CHANGE
vs VREG and VREF CURRENTS
Typical production
distribution of
packaged units.
80
70
1M
1.5
90
VOS vs IREG
1.0
0.5
60
∆ VOS (µV)
Percent of Units (%)
COUT = 0
RG = 50Ω
50
40
30
0
–0.5
VOS vs IREF
–1.0
–1.5
20
–2.0
10
–2.5
–1.0
3.0
2.75
2.5
2.25
2.0
1.75
1.5
1.0
1.25
0.75
0.5
0.25
0
0
–0.5
0
0.5
1.0
1.5
2.0
2.5
Current (mA)
Offset Voltage Drift (µV/°C)
XTR106
SBOS092A
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5
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, V+ = 24V, unless otherwise noted.
UNDER-SCALE CURRENT vs TEMPERATURE
UNDER-SCALE CURRENT vs IREF + IREG
4.0
2.5
Under-Scale Current (mA)
Under-Scale Current (mA)
3.5
2.0
1.5
1.0
0.5
2.5
2.0
TA = +25°C
1.5
0.5
0
0
–75
–50
–25
0
25
50
75
100
0
125
0.5
1.0
1.5
2.0
Temperature (°C)
IREF + IREG (mA)
OVER-SCALE CURRENT vs TEMPERATURE
ZERO OUTPUT ERROR
vs VREF and VREG CURRENTS
2.5
3.0
30
With External Transistor
2.5
29
Zero Output Error (µA)
Over-Scale Current (mA)
TA = +125°C
1.0
V+ = 7.5V to 36V
28
V+ = 36V
27
V+ = 7.5V
26
V+ = 24V
25
2.0
IZERO Error vs IREG
1.5
1.0
0.5
IZERO Error vs IREF
0
–0.5
–1.0
24
–75
–50
–25
0
25
50
75
100
–1
125
–0.5
0
0.5
1.0
1.5
Temperature (°C)
Current (mA)
ZERO OUTPUT CURRENT ERROR
vs TEMPERATURE
ZERO OUTPUT DRIFT
PRODUCTION DISTRIBUTION
4
70
2
60
0
Percent of Units (%)
Zero Output Current Error (µA)
TA = –55°C
3.0
–2
–4
–6
–8
2.0
2.5
Typical production
distribution of
packaged units.
50
40
30
20
10
–10
–12
0
–50
–25
0
25
50
75
100
125
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
–75
Temperature (°C)
Zero Output Drift (µA/°C)
6
XTR106
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SBOS092A
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, V+ = 24V, unless otherwise noted.
INPUT BIAS and OFFSET CURRENT
vs TEMPERATURE
INPUT VOLTAGE, INPUT CURRENT, and ZERO
OUTPUT CURRENT NOISE DENSITY vs FREQUENCY
Input Current Noise
100
100
Input Voltage Noise
10
1
10
100
1k
10k
Input Bias and Offset Current (nA)
1k
1k
Input Current Noise (fA/√Hz)
Zero Output Noise
Zero Output Current Noise (pA/√Hz)
Input Voltage Noise (nV/√Hz)
10
10k
10k
8
IB
6
4
2
IOS
0
–2
10
100k
–75
–50
–25
25
50
75
100
125
REFERENCE TRANSIENT RESPONSE
VREF = 5V
VREG OUTPUT VOLTAGE vs VREG OUTPUT CURRENT
50mV/div
5.5
Reference
Output
5.6
5.4
5.3
5.2
TA = +25°C, –55°C
5.1
5.0
4.9
4.8
–1.0
TA = +125°C
–0.5
0
0.5
1mA
500µA/div
VREG Output Current (V)
0
Temperature (°C)
Frequency (Hz)
1.0
1.5
2.0
0
2.5
10µs/div
VREG Output Current (mA)
REFERENCE AC LINE REJECTION vs FREQUENCY
VREF5 vs VREG OUTPUT CURRENT
120
5.008
100
TA = +25°C
Line Rejection (dB)
VREF5 (V)
5.004
5.000
4.996
TA = +125°C
4.992
VREF2.5
80
60
VREF5
40
20
TA = –55°C
4.988
–1.0
0
–0.5
0
0.5
1.0
1.5
2.0
10
2.5
XTR106
SBOS092A
100
1k
10k
100k
1M
Frequency (Hz)
VREG Current (mA)
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7
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, V+ = 24V, unless otherwise noted.
REFERENCE VOLTAGE DEVIATION
vs TEMPERATURE
REFERENCE VOLTAGE DRIFT
PRODUCTION DISTRIBUTION
40
30
25
20
15
10
5
Reference Voltage Deviation (%)
Percent of Units (%)
35
0.1
Typical production
distribution of
packaged units.
0
0
–0.1
VREF = 5V
–0.2
VREF = 2.5V
–0.3
–0.4
–0.5
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
–75
–50
–25
0
25
50
75
100
125
Temperature (°C)
Reference Voltage Drift (ppm/°C)
8
XTR106
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SBOS092A
APPLICATIONS INFORMATION
The transfer function for the complete current transmitter is:
IO = 4mA + VIN • (40/RG)
Figure 1 shows the basic connection diagram for the XTR106.
The loop power supply, VPS, provides power for all circuitry.
Output loop current is measured as a voltage across the series
load resistor, RL. A 0.01µF to 0.03µF supply bypass capacitor
connected between V+ and IO is recommended. For applications where fault and/or overload conditions might saturate
the inputs, a 0.03µF capacitor is recommended.
where VIN is the differential input voltage. As evident from
the transfer function, if no RG is used (RG = ∞), the gain is
zero and the output is simply the XTR106’s zero current.
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 1.6mA. If current is
being sourced from the reference and/or VREG, the current
limit value may increase. Refer to the Typical Performance
Curves, “Under-Scale Current vs IREF + IREG” and “UnderScale Current vs Temperature.”
A 2.5V or 5V reference is available to excite a bridge sensor.
For 5V excitation, pin 14 (VREF5) should be connected to the
bridge as shown in Figure 1. For 2.5V excitation, connect
pin 13 (VREF2.5) to pin 14 as shown in Figure 3b. The output
terminals of the bridge are connected to the instrumentation
amplifier inputs, VIN and VIN. A 0.01µF capacitor is shown
+
–
connected between the inputs and is recommended for high
impedance bridges (> 10kΩ). The resistor RG sets the gain
of the instrumentation amplifier as required by the full-scale
bridge voltage, VFS.
Increasingly positive input voltage (greater than the fullscale input, VFS) will produce increasing output current
according to the transfer function, up to the output current
limit of approximately 28mA. Refer to the Typical Performance Curve, “Over-Scale Current vs Temperature.”
Lin Polarity and RLIN provide second-order linearization
correction to the bridge, achieving up to a 20:1 improvement
in linearity. Connections to Lin Polarity (pin 12) determine
the polarity of nonlinearity correction and should be connected either to IRET or VREG. Lin Polarity should be connected to VREG even if linearity correction is not desired.
RLIN is chosen according to the equation in Figure 1 and is
dependent on KLIN (linearization constant) and the bridge’s
nonlinearity relative to VFS (see “Linearization” section).
The IRET pin is the return path for all current from the
references and VREG. IRET also serves as a local ground and
is the reference point for VREG and the on-board voltage
references. The IRET pin allows any current used in external
circuitry to be sensed by the XTR106 and to be included in
the output current without causing error. The input voltage
range of the XTR106 is referred to this pin.
For 2.5V excitation, connect VREG
pin 13 to pin 14
VREF5
VREF2.5
Possible choices for Q1 (see text).
RLIN(3)
14
13
5
11
RLIN 1
VREG
+
VIN
CIN
0.01µF(2)
5V
(5)
R1(5)
R2
+
RB
4
3
2
PACKAGE
TO-225
TO-220
TO-220
7.5V to 36V
10
V+
IO
4-20 mA
(4)
Bridge
Sensor
TYPE
2N4922
TIP29C
TIP31C
RG
RG
–
(1)
VIN in Volts, RG in Ohms
B
XTR106
E
Lin(1)
Polarity
IRET
Q1
COUT
0.01µF
VO
RG
–
VIN
9
+
8
RL
IO
VPS
–
7
12
6
VREG(1)
IO = 4mA + VIN • ( 40 )
RG
or
NOTES:
(1) Connect Lin Polarity (pin 12) to IRET (pin 6) to correct for positive
bridge nonlinearity or connect to VREG (pin 1) for negative bridge
nonlinearity. The RLIN pin and Lin Polarity pin must be connected to
VREG if linearity correction is not desired. Refer to “Linearization”
section and Figure 3.
(2) Recommended for bridge impedances > 10kΩ
( 3) RLIN = KLIN •
4B
1 – 2B
(4) RG = (VFS/400µA) •
1 + 2B
1 – 2B
(VFS in V)
where KLIN = 9.905kΩ for 2.5V reference
KLIN = 6.645kΩ for 5V reference
B is the bridge nonlinearity relative to VFS
VFS is the full-scale input voltage
(5) R1 and R2 form bridge trim circuit to compensate for the initial
accuracy of the bridge. See “Bridge Balance” text.
(KLIN in Ω)
FIGURE 1. Basic Bridge Measurement Circuit with Linearization.
XTR106
SBOS092A
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9
EXTERNAL TRANSISTOR
External pass 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 XTR106,
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 XTR106 can be operated without an external pass
transistor. Accuracy, however, 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 guarantee the full 20mA full-scale output,
especially with V+ near 7.5V.
The low operating voltage (7.5V) of the XTR106 allows
operation directly from personal computer power supplies
(12V ±5%). When used with the RCV420 Current Loop
Receiver (Figure 8), load resistor voltage drop is limited to 3V.
BRIDGE BALANCE
Figure 1 shows a bridge trim circuit (R1, R2). This adjustment can be used to compensate for the initial accuracy of
the bridge and/or to trim the offset voltage of the XTR106.
The values of R1 and R2 depend on the impedance of the
bridge, and the trim range required. This trim circuit places
an additional load on the VREF output. Be sure the additional
load on VREF does not affect zero output. See the Typical
Performance Curve, “Under-Scale Current vs IREF + IREG.”
The effective load of the trim circuit is nearly equal to R2.
An approximate value for R1 can be calculated:
R1 ≈
(3)
5V • R B
4 • V TRIM
where, RB is the resistance of the bridge.
VTRIM is the desired ±voltage trim range (in V).
Make R2 equal or lower in value to R1.
LINEARIZATION
Many bridge sensors are inherently nonlinear. With the
addition of one external resistor, it is possible to compensate
for parabolic nonlinearity resulting in up to 20:1 improvement over an uncompensated bridge output.
10
V+
E
8
XTR106
0.01µF
IO
7
IRET
6
RQ = 3.3kΩ
For operation without external
transistor, connect a 3.3kΩ
resistor between pin 6 and
pin 8. See text for discussion
of performance.
FIGURE 2. Operation without External Transistor.
LOOP POWER SUPPLY
The voltage applied to the XTR106, 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 XTR106 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:
R L max =
(V+) – 7. 5V
– R WIRING
20mA
(2)
It is recommended to design for V+ equal or greater than
7.5V with loop currents up to 30mA to allow for out-ofrange input conditions. V+ must be at least 8V if 5V sensor
excitation is used and if correcting for bridge nonlinearity
greater than +3%.
10
Linearity correction is accomplished by varying the bridge
excitation voltage. Signal-dependent variation of the bridge
excitation voltage adds a second-order term to the overall
transfer function (including the bridge). This can be tailored
to correct for bridge sensor nonlinearity.
Either positive or negative bridge non-linearity errors can be
compensated by proper connection of the Lin Polarity pin.
To correct for positive bridge nonlinearity (upward bowing),
Lin Polarity (pin 12) should be connected to IRET (pin 6) as
shown in Figure 3a. This causes VREF to increase with bridge
output which compensates for a positive bow in the bridge
response. To correct negative nonlinearity (downward bowing), connect Lin Polarity to VREG (pin 1) as shown in Figure
3b. This causes VREF to decrease with bridge output. The Lin
Polarity pin is a high impedance node.
If no linearity correction is desired, both the RLIN and Lin
Polarity pins should be connected to VREG (Figure 3c). This
results in a constant reference voltage independent of input
signal. RLIN or Lin Polarity pins should not be left open
or connected to another potential.
RLIN is the external linearization resistor and is connected
between pin 11 and pin 1 (VREG) as shown in Figures 3a and
3b. To determine the value of RLIN, the nonlinearity of the
bridge sensor with constant excitation voltage must be
known. The XTR106’s linearity circuitry can only compensate for the parabolic-shaped portions of a sensor’s
nonlinearity. Optimum correction occurs when maximum
deviation from linear output occurs at mid-scale (see Figure
4). Sensors with nonlinearity curves similar to that shown in
XTR106
www.ti.com
SBOS092A
Figure 4, but not peaking exactly at mid-scale can be
substantially improved. A sensor with a “S-shaped”
nonlinearity curve (equal positive and negative nonlinearity)
cannot be improved with the XTR106’s correction circuitry.
The value of RLIN is chosen according to Equation 4 shown
in Figure 3. RLIN is dependent on a linearization factor,
KLIN, which differs for the 2.5V reference and 5V reference.
The sensor’s nonlinearity term, B (relative to full scale), is
positive or negative depending on the direction of the bow.
A maximum ±5% non-linearity can be corrected when the
5V reference is used. Sensor nonlinearity of +5%/–2.5% can
be corrected with 2.5V excitation. The trim circuit shown in
Figure 3d can be used for bridges with unknown bridge
nonlinearity polarity.
Gain is affected by the varying excitation voltage used to
correct bridge nonlinearity. The corrected value of the gain
resistor is calculated from Equation 5 given in Figure 3.
VREG
VREF5
XTR106
VREF2.5
14
5
5V
R2
Lin
Polarity
RLIN
13
1
+
IRET
11
R1
+
–
RG
2
RY
RX
100kΩ
15kΩ
Open RX for negative bridge nonlinearity
Open RY for positive bridge nonlinearity
XTR106
–
3d. On-Board Resistor Circuit for Unknown Bridge Nonlinearity Polarity
12
6
Lin
Polarity
IRET
EQUATIONS
Linearization Resistor:
3a. Connection for Positive Bridge Nonlinearity, VREF = 5V
VREG
RLIN = KLIN •
VREF2.5
VREF5
RLIN
13
5
2.5V
1
+
11
4
–
RG
RG =
VFS
400µA
1 + 2B
1 – 2B
(in Ω)
(5)
1 + 2B
1 – 2B
(in V)
(6)
KLIN = 9905Ω for the 2.5V reference
–
12
KLIN = 6645Ω for the 5V reference
Lin
Polarity
B is the sensor nonlinearity relative to VFS
(for –2.5% nonlinearity, B = –0.025)
IRET
VFS is the full-scale bridge output without
linearization (in V)
3b. Connection for Negative Bridge Nonlinearity, VREF = 2.5V
Example:
VREG
VREF5
Calculate RLIN and the resulting RG for a bridge sensor with
2.5% downward bow nonlinearity relative to VFS and determine
if the input common-mode range is valid.
VREF2.5
14
RLIN
13
5V
(4)
where, KLIN is the linearization factor (in Ω)
6
5
•
VREF (Adj) = VREF (Initial) •
XTR106
3
2
(in Ω)
Adjusted Excitation Voltage at Full-Scale Output:
R1
+
4B
1– 2B
Gain-Set Resistor:
14
R2
1
12
6
4
3
R2
VREG
1
+
VREF = 2.5V and VFS = 50mV
11
For a 2.5% downward bow, B = –0.025
(Lin Polarity pin connected to VREG)
4
For VREF = 2.5V, KLIN = 9905Ω
R1
+
–
RG
XTR106
RLIN =
3
2
RG =
–
12
6
Lin
Polarity
VCM =
IRET
3c. Connection if no linearity correction is desired, VREF = 5V
(9905Ω) (4) ( –0.025)
= 943Ω
1 – (2) ( –0.025)
0.05V 1 + (2) ( –0.025)
•
= 113Ω
400µA 1 – (2) ( –0.025)
VREF (Adj)
2
=
1
1 + (2) ( –0.025)
• 2.5V •
= 1.13V
2
1 – (2) ( –0.025)
which falls within the 1.1V to 3.5V input common-mode range.
FIGURE 3. Connections and Equations to Correct Positive and Negative Bridge Nonlinearity.
XTR106
SBOS092A
www.ti.com
11
UNDER-SCALE CURRENT
When using linearity correction, care should be taken to
insure that the sensor’s output common-mode voltage remains within the XTR106’s allowable input range of 1.1V to
3.5V. Equation 6 in Figure 3 can be used to calculate the
XTR106’s new excitation voltage. The common-mode voltage of the bridge output is simply half this value if no
common-mode resistor is used (refer to the example in
Figure 3). Exceeding the common-mode range may yield
unpredicatable results.
The total current being drawn from the VREF and VREG
voltage sources, as well as temperature, affect the XTR106’s
under-scale current value (see the Typical Performance
Curve, “Under-Scale Current vs IREF + IREG). This should be
considered when choosing the bridge resistance and excitation voltage, especially for transducers operating over a
wide temperature range (see the Typical Performance Curve,
“Under-Scale Current vs Temperature”).
For high precision applications (errors < 1%), a two-step
calibration process can be employed. First, the nonlinearity
of the sensor bridge is measured with the initial gain resistor
and RLIN = 0 (RLIN pin connected directly to VREG). Using
the resulting sensor nonlinearity, B, values for RG and RLIN
are calculated using Equations 4 and 5 from Figure 3. A
second calibration measurement is then taken to adjust RG to
account for the offsets and mismatches in the linearization.
LOW IMPEDANCE BRIDGES
The XTR106’s two available excitation voltages (2.5V and
5V) allow the use of a wide variety of bridge values. Bridge
impedances as low as 1kΩ can be used without any additional circuitry. Lower impedance bridges can be used with
the XTR106 by adding a series resistance to limit excitation
current to ≤ 2.5mA (Figure 5). Resistance should be added
BRIDGE TRANSDUCER TRANSFER FUNCTION
WITH PARABOLIC NONLINEARITY
NONLINEARITY vs STIMULUS
10
3
Nonlinearity (% of Full Scale)
9
Bridge Output (mV)
8
Positive Nonlinearity
B = +0.025
7
6
5
4
B = –0.019
Negative Nonlinearity
3
2
Linear Response
2
Positive Nonlinearity
B = +0.025
1
0
–1
–2
Negative Nonlinearity
B = –0.019
1
0
–3
0
0.1
0.2
0.3
0.4 0.5 0.6 0.7
Normalized Stimulus
0.8
0.9
1
0
0.1
0.2
0.3
0.4 0.5 0.6 0.7
Normalized Stimulus
0.8
0.9
1
FIGURE 4. Parabolic Nonlinearity.
700µA at 5V
VREF5
ITOTAL = 0.7mA + 1.6mA ≤ 2.5mA
IREG ≈ 1.6mA
VREF2.5
VREG
3.4kΩ
14
13
5V
1/2
OPA2277
1kΩ
5
1
RLIN
1N4148
11
V+IN
10
V+
4
RG
10kΩ
350Ω
RG
125Ω
412Ω
10kΩ
3.4kΩ
1/2
OPA2277
3
2
B 9
XTR106
E
RG
V
Lin I
O
Polarity
–
IN
0.01µF
IRET
8
7
12
6
IO = 4-20mA
Bridge excitation
voltage = 0.245V
Shown connected to correct positive
bridge nonlinearity. For negative bridge
nonlinearity, see Figure 3b.
Approx. x50
amplifier
FIGURE 5. 350Ω Bridge with x50 Preamplifier.
12
XTR106
www.ti.com
SBOS092A
to the upper and lower sides of the bridge to keep the bridge
output within the 1.1V to 3.5V common-mode input range.
Bridge output is reduced so a preamplifier as shown may be
needed to reduce offset voltage and drift.
OTHER SENSOR TYPES
The XTR106 can be used with a wide variety of inputs. Its
high input impedance instrumentation amplifier is versatile
and can be configured for differential input voltages from
millivolts to a maximum of 2.4V full scale. The linear range
of the inputs is from 1.1V to 3.5V, referenced to the IRET
terminal, pin 6. The linearization feature of the XTR106 can
be used with any sensor whose output is ratiometric with an
excitation voltage.
ERROR ANALYSIS
Table I shows how to calculate the effect various error
sources have on circuit accuracy. A sample error calculation
for a typical bridge sensor measurement circuit is shown
(5kΩ bridge, VREF = 5V, VFS = 50mV) is provided. The
results reveal the XTR106’s excellent accuracy, in this case
1.2% unadjusted. Adjusting gain and offset errors improves
circuit accuracy to 0.33%. Note that these are worst-case
errors; guaranteed maximum values were used in the calculations and all errors were assumed to be positive (additive).
The XTR106 achieves performance which is difficult to
obtain with discrete circuitry and requires less board space.
SAMPLE ERROR CALCULATION
Bridge Impedance (RB)
Ambient Temperature Range (∆TA)
Supply Voltage Change (∆V+)
Full Scale Input (VFS)
Excitation Voltage (VREF)
Common-Mode Voltage Change (∆CM)
INPUT
Input Offset Voltage
vs Common-Mode
vs Power Supply
Input Bias Current
Input Offset Current
ERROR CALCULATION
VOS /VFS • 106
CMRR • ∆CM/VFS • 106
(VOS vs V+) • (∆V+)/VFS • 106
CMRR • IB • (RB /2)/ VFS • 106
IOS • RB /VFS • 106
EXCITATION
Voltage Reference Accuracy
vs Supply
VREF Accuracy (%)/100% • 106
(VREF vs V+) • (∆V+) • (VFS/VREF)
GAIN
Span
Nonlinearity
Span Error (%)/100% • 106
Nonlinearity (%)/100% • 106
OUTPUT
Zero Output
vs Supply
UNADJ
ADJUST
200µV/50mV • 106
50µV/V • 0.025V/50mV • 106
3µV/V • 5V/50mV • 106
50µV/V • 25nA • 2.5kΩ/50mV • 106
3nA • 5kΩ/50mV • 106
Total Input Error
2000
25
300
0.1
300
2625
0
25
300
0
0
325
0.25%/100% • 106
20ppm/V • 5V (50mV/5V)
Total Excitation Error
2500
1
2501
0
1
1
Total Gain Error
2000
100
2100
0
100
100
25µA/16000µA • 106
0.2µA/V • 5V/16000µA • 106
Total Output Error
1563
62.5
1626
0
62.5
63
1.5µV / °C • 20°C / (50mV) • 106
5pA / °C • 20°C • 5kΩ/ (50mV) • 106
35ppm/°C • 20°C
225ppm/°C • 20°C
0.9µA /°C • 20°C / 16000µA • 106
Total Drift Error
600
10
700
500
1125
2936
600
10
700
500
1125
2936
12
2.2
0.6
0.6
15
12
2.2
0.6
0.6
15
0.2%/100% • 106
0.01%/100% • 106
| IZERO – 4mA | /16000µA • 106
(IZERO vs V+) • (∆V+)/16000µA • 106
DRIFT (∆TA = 20°C)
Input Offset Voltage
Input Offset Current (typical)
Voltage Refrence Accuracy
Span
Zero Output
50mV
5V
25mV (= VFS/2)
ERROR
(ppm of Full Scale)
SAMPLE
ERROR EQUATION
ERROR SOURCE
NOISE (0.1Hz to 10Hz, typ)
Input Offset Voltage
Zero Output
Thermal RB Noise
Input Current Noise
5kΩ
20°C
5V
Drift • ∆TA / (VFS) • 106
Drift • ∆TA • RB / (VFS) • 106
Drift • ∆TA / 16000µA • 106
Vn(p-p)/ VFS • 106
IZERO Noise / 16000µA • 106
[√ 2 • √ (RB / 2 ) / 1kΩ • 4nV / √ Hz • √ 10Hz ] / VFS • 106
(in • 40.8 • √2 • RB / 2)/ VFS • 106
0.6µV / 50mV • 106
0.035µA / 16000µA • 106
[√ 2 • √ 2.5kΩ / 1kΩ • 4nV/ √ Hz • √ 10Hz ] / 50mV • 106
(200fA/√Hz • 40.8 • √2 • 2.5kΩ)/50mV• 106
Total Noise Error
NOTE (1): All errors are min/max and referred to input, unless otherwise stated.
TOTAL ERROR:
11803
1.18%
3340
0.33%
TABLE I. Error Calculation.
XTR106
SBOS092A
www.ti.com
13
REVERSE-VOLTAGE PROTECTION
The XTR106’s low compliance rating (7.5V) permits the
use of various voltage protection methods without compromising operating range. Figure 6 shows a diode bridge
circuit which 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. A diode can be
inserted in series with the loop supply voltage and the V+
pin as shown in Figure 8 to protect against reverse output
connection lines with only a 0.7V loss in loop supply
voltage.
OVER-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 XTR106 to as low as practical.
Various zener diode 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 XTR106 with
loop supply voltages up to 65V.
VREF5
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 interference. RF can be rectified by the sensitive
input circuitry of the XTR106 causing errors. This generally
appears as an unstable output current that varies with the
position of loop supply or input wiring.
If the bridge sensor is remotely located, the interference may
enter at the input terminals. For integrated transmitter assemblies with short connection 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 as shown in Figure 6. 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.
VREF2.5
14
13
5
+
VIN
4
5V
+
RB
–
RG
RG
XTR106
3
Bridge
Sensor
Maximum VPS must be
less than minimum
voltage rating of zener
diode.
10
V+
B
E
RG
9
Q1
0.01µF
D1(1)
1N4148
Diodes
RL
8
VPS
IO
2
–
VIN
The diode bridge causes
a 1.4V loss in loop supply
voltage.
7
IRET
6
0.01µF
0.01µF
NOTE: (1) Zener Diode 36V: 1N4753A or Motorola
P6KE39A. Use lower voltage zener diodes with loop
power supply voltages less than 30V for increased
protection. See “Over-Voltage Surge Protection.”
FIGURE 6. Reverse Voltage Operation and Over-Voltage Surge Protection.
14
XTR106
www.ti.com
SBOS092A
VREF5
0.01µF
See ISO124 data sheet
if isolation is needed.
1MΩ
VREF2.5
4.8kΩ
6kΩ
Isothermal
Block
14
20kΩ
OPA277
5
+
13
11
RLIN
VIN
7.5V to 36V
1
VREG
4
Type K
1N4148
IO
4-20 mA
XTR106
3
V+
RG
RG
1kΩ
1MΩ(1)
10
E
RG
Lin
Polarity
–
2 VIN
IRET
9
COUT
0.01µF
Q1
VO
8
+
VPS
–
RL
IO
7
12
IO = 4mA + VIN • ( 40 )
RG
6
5.2kΩ
50Ω
B
VREG (pin 1)
100Ω
2kΩ
NOTE: (1) For burn-out indication.
0.01µF
FIGURE 7. Thermocouple Low Offset, Low Drift Loop Measurement with Diode Cold-Junction Compensation.
VREF2.5
Bridge
Sensor
VREG
VREF5
2.5V
14
RLIN
13
1
RB
5 VIN
+
4
+12V
10
V+
B
XTR106
2
1µF
RG
RG
3
1N4148
11
+
–
See ISO124 data sheet
if isolation is needed.
RG
E
Lin
Polarity
–
VIN
IRET
9
0.01µF
16
10
3
8
11
12
15
IO
RCV420
2
7
VO = 0V to 5V
13
5
12
6
14
4
1µF
IO = 4-20mA
NOTE: Lin Polarity shown connected to correct positive bridge
nonlinearity. See Figure 3b to correct negative bridge nonlinearity.
–12V
FIGURE 8. ±12V-Powered Transmitter/Receiver Loop.
XTR106
SBOS092A
www.ti.com
15
PACKAGE OPTION ADDENDUM
www.ti.com
14-Oct-2022
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)
Samples
(4/5)
(6)
XTR106P
ACTIVE
PDIP
N
14
25
RoHS & Green
Call TI
N / A for Pkg Type
XTR106PA
ACTIVE
PDIP
N
14
25
RoHS & Green
Call TI
N / A for Pkg Type
XTR106U
ACTIVE
SOIC
D
14
50
RoHS & Green
Call TI
Level-3-260C-168 HR
XTR106U/2K5
ACTIVE
SOIC
D
14
2500
RoHS & Green
Call TI
XTR106UA
ACTIVE
SOIC
D
14
50
RoHS & Green
XTR106UA/2K5
ACTIVE
SOIC
D
14
2500
RoHS & Green
-40 to 85
XTR106P
A
Samples
XTR106P
A
Samples
-40 to 85
XTR106U
Samples
Level-3-260C-168 HR
-40 to 85
XTR106U
Samples
Call TI
Level-3-260C-168 HR
-40 to 85
XTR106U
A
Samples
Call TI
Level-3-260C-168 HR
-40 to 85
XTR106U
A
Samples
(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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