Datasheet XTR106UA-2K5, XTR106UA, XTR106U, XTR106U-2K5, XTR106PA Datasheet (Burr Brown)

®

XTR106

XTR106

XTR106

4-20mA CURRENT TRANSMITTER

with Bridge Excitation and Linearization

FEATURES

● 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

DESCRIPTION

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
V

pin.

REG

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.

APPLICATIONS

● PRESSURE BRIDGE TRANSMITTER

● STRAIN GAGE TRANSMITTER

● TEMPERATURE BRIDGE TRANSMITTER

● INDUSTRIAL PROCESS CONTROL

● SCADA REMOTE DATA ACQUISITION

● REMOTE TRANSDUCERS

● WEIGHING SYSTEMS

● ACCELEROMETERS

2.0

1.5

1.0

0.5

Nonlinearity (%)

–0.5

5V

0

0mV

BRIDGE NONLINEARITY CORRECTION

V

5

REF

R

V

REF

+

G

USING XTR106

5mV

Bridge Output

(5.1V)

V

REG

2.5V

XTR106

Corrected

R

LIN

7.5V to 36V

Uncorrected
Bridge Output

4-20mA

10mV

V

PS

V

O

R

L

–

I

RET

International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: [phone] • Twx: 910-952-1111

Internet: http://www.burr-brown.com/ • FAXLine: [phone] (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: [phone] • Immediate Product Info: [phone]

©

1998 Burr-Brown Corporation PDS-1449A Printed in U.S.A. June, 1998

Polarity

Lin

I

OUT

SPECIFICATIONS

At TA = +25°C, V+ = 24V, and TIP29C external transistor, unless otherwise noted.

XTR106P, U XTR106PA, UA
PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS
OUTPUT

Output Current Equation I
Output Current, Specified Range 4 20 ✻✻mA
Over-Scale Limit I
Under-Scale Limit I

ZERO OUTPUT

(1)

Initial Error ±5 ±25 ✻ ±50 µA

vs Temperature T
vs Supply Voltage, V+ V+ = 7.5V to 36V 0.04 0.2 ✻✻ µA/V
vs Common-Mode Voltage

(IO) 0.8 ✻ µA/mA

vs V

REG

Noise: 0.1Hz to 10Hz i

(CMRR)

OVER

UNDER

I

ZERO

O

I

= 0, I

I

REF

REG

+ I

= 0 1 1.6 2.2 ✻✻✻ mA

REF

= 2.5mA 2.9 3.4 4 ✻✻✻ mA

REG

VIN = 0V, RG = ∞ 4 ✻ mA

= –40°C to +85°C ±0.07 ±0.9 ✻✻ µA/°C

A

VCM = 1.1V to 3.5V

n

(5)

SPAN

Span Equation (Transconductance) S
Untrimmed Error Full Scale (V
vs Temperature
Nonlinearity: Ideal Input

INPUT

Offset Voltage V

vs Temperature T
vs Supply Voltage, V+ V+ = 7.5V to 36V ±0.1 ±3 ✻✻ µV/V

vs Common-Mode Voltage, RTI CMRR V
Common-Mode Range
Input Bias Current I

vs Temperature T
Input Offset Current I

vs Temperature T
Impedance: Differential Z

Noise: 0.1Hz to 10Hz V

VOLTAGE REFERENCES

(2)

(3)

(4)

(5)

Common-Mode 5 || 10 ✻ GΩ || pF

(5)

TA = –40°C to +85°C ±3 ±25 ✻✻ ppm/°C

Full Scale (VIN) = 50mV ±0.001 ±0.01 ✻✻ %

OS

V

CM

OS

IN

= –40°C to +85°C ±0.25 ±1.5 ✻ ±3 µV/°C

A

CM

B

= –40°C to +85°C20 ✻ pA/°C

A

= –40°C to +85°C5 ✻pA/°C

A

n

Lin Polarity Connected

to V

Initial: 2.5V Reference V

5V Reference V

Accuracy V

vs Temperature T

vs Supply Voltage, V+ V+ = 7.5V to 36V ±5 ±20 ✻✻ ppm/V

vs Load I
Noise: 0.1Hz to 10Hz 10 ✻ µVp-p

(5)

V

REG

Accuracy ±0.02 ±0.1 ✻✻ V

vs Temperature T

vs Supply Voltage, V+ V+ = 7.5V to 36V 1 ✻ mV/V
Output Current I
Output Impedance I

LINEARIZATION

R

(external) Equation R

LIN

K

Linearization Factor K

LIN

(6)

2.5 2.5 ✻ V

REF

55✻V

V

REF

REG

REG

LIN

LIN

REF

= –40°C to +85°C ±20 ±35 ✻ ±75 ppm/°C

A

REF

= –40°C to +85°C ±0.3 ✻ mV/°C

A

REG

Accuracy ±1 ±5 ✻✻ %

vs Temperature T
Max Correctable Sensor Nonlinearity B V

= –40°C to +85°C ±50 ±100 ✻✻ ppm/°C

A

) = 50mV ±0.05 ±0.2 ✻ ±0.4 %

IN

VCM = 2.5V ±50 ±100 ✻ ±250 µV

= 1.1V to 3.5V

, R

REG

(5)

= 0

LIN

= 2.5V or 5V ±0.05 ±0.25 ✻ ±0.5 %

= 0mA to 2.5mA 60 ✻ ppm/mA

= 0mA to 2.5mA 80 ✻ Ω

V

= 5V 6.645 ✻ k Ω

REF

= 2.5V 9.905 ✻ k Ω

V

REF

= 5V ±5 ✻ % of V

REF

V

= 2.5V –2.5, +5 ✻ % of V

REF

POWER SUPPLY V+
Specified +24 ✻ V
Voltage Range +7.5 +36 ✻✻V

TEMPERATURE RANGE

Specification –40 +85 ✻✻°C
Operating –55 +125 ✻✻°C
Storage –55 +125 ✻✻°C
Thermal Resistance

14-Pin DIP 80 ✻ °C/W

θ

JA

SO-14 Surface Mount 100 ✻ °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, R
measured with respect to I

®

pin. (6) See “Linearization” text for detailed explanation. VFS = full-scale VIN.

RET

. (3) Increasing the full-scale input range improves nonlinearity. (4) Does not include Zero Output initial error. (5) Voltage

G

XTR106

IO = VIN • (40/RG) + 4mA, VIN in Volts, RG in Ω

A

24 28 30 ✻✻✻ mA

0.02 ✻ µA/V

0.035 ✻ µAp-p

S = 40/R

G

✻ A/V

±10 ±50 ✻ ±100 µV/V

1.1 3.5 ✻✻V
525 ✻50 nA

±0.2 ±3 ✻ ±10 nA

0.1 || 1 ✻ GΩ || pF

0.6 ✻ µVp-p

5.1 ✻ V

See Typical Curves ✻ mA

R

= K

LIN

4B

• , K

LIN

1 – 2B

in Ω, B is nonlinearity relative to V

LIN

FS

Ω

FS
FS

2

PIN CONFIGURATION

Top View DIP and SOIC

1

V

REG

–

2

V

IN

3

R

G

4

R

G

+

5

V

IN

6

I

RET

7

I

O

14
13
12
11
10

9
8

V

5

REF

2.5

V

REF

Lin Polarity
R

LIN

V+
B (Base)
E (Emitter)

ABSOLUTE MAXIMUM RATINGS

Power Supply, V+ (referenced to IO pin) .......................................... 40V

Input Voltage, 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.

+

–

, VIN (referenced to I

IN

(1)

pin) ......................... 0V to V+

RET

ELECTROSTATIC
DISCHARGE SENSITIVITY

This integrated circuit can be damaged by ESD. Burr-Brown
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 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

PACKAGE SPECIFIED

DRAWING TEMPERATURE PACKAGE ORDERING TRANSPORT

PRODUCT PACKAGE NUMBER

XTR106P 14-Pin DIP 010 –40°C to +85°C XTR106P XTR106P Rails
XTR106PA 14-Pin DIP 010 –40°C to +85°C XTR106PA XTR106PA Rails
XTR106U SO-14 Surface Mount 235 –40°C to +85°C XTR106U XTR106U Rails

(1)

RANGE MARKING NUMBER

"""""XTR106U/2K5 Tape and Reel

XTR106UA SO-14 Surface Mount 235 –40°C to +85°C XTR106UA XTR106UA Rails

"""""XTR106UA/2K5 Tape and Reel

NOTES: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. (2) Models with a slash (/ ) are
available only in Tape and Reel in the quantities indicated (e.g., /2K5 indicates 2500 devices per reel). Ordering 2500 pieces of “XTR106U/2K5” will get a single
2500-piece Tape and Reel. For detailed Tape and Reel mechanical information, refer to Appendix B of Burr-Brown IC Data Book.

(2)

MEDIA

The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.

3

XTR106

®

FUNCTIONAL DIAGRAM

Lin

Polarity

V

REG

12

R

LIN

11

1

V+

10

14

V

5

REF

13

2.5

V

REF

5

+

V

IN

4

REF

Amp

Bandgap

V

REF

100µA

Lin

Amp

Current

Direction

Switch

5.1V

B
9

R

G

975

3

V

2

–

V

IN

I = 100µA +

IN

R

G

25

Ω

Ω

E
8

®

XTR106

6

I

RET

7

= 4mA + V

I

O

• ( )

IN

40

R

G

4

TYPICAL PERFORMANCE CURVES

10 1k100 10k 100k 1M

Frequency (Hz)

POWER SUPPLY REJECTION vs FREQUENCY

160
140
120
100

80
60
40
20

0

Power Supply Rejection (dB)

RG = 1kΩ

C

OUT

= 0

RG = 50Ω

At TA = +25°C, V+ = 24V, unless otherwise noted.

60

RG = 50Ω

50

40

30

RG = 1kΩ

C

C

OUT

C

OUT

connected

C

OUT

between V+ and I

20

TRANSCONDUCTANCE vs FREQUENCY

10

Transconductance (20 log mA/V)

R

= 250Ω

L

0

100 1k 10k 100k 1M

Frequency (Hz)

COMMON-MODE REJECTION vs FREQUENCY

110
100

90
80
70

RG = 1kΩ

RG = 50Ω

60
50

Common-Mode Rejection (dB)

40
30

10 1k100 10k 100k 1M

Frequency (Hz)

= 0.01µF

= 0.01µF

OUT

= 0.033µF

STEP RESPONSE

C

= 0.01µF

RG = 1kΩ

OUT

20mA

O

RG = 50Ω

4mA/div

4mA

50µs/div

INPUT OFFSET VOLTAGE DRIFT

90

PRODUCTION DISTRIBUTION

80
70
60
50
40
30

Percent of Units (%)

20
10

0

0

0.25

0.5

0.75

1.0

Offset Voltage Drift (µV/°C)

INPUT OFFSET VOLTAGE CHANGE

Typical production
distribution of
packaged units.

1.5

1.0

0.5

vs V

REG

VOS vs I

and V

CURRENTS

REF

REG

0

(µV)

–0.5

OS

∆ V

–1.0
–1.5

VOS vs I

REF

–2.0
–2.5

–1.0 –0.5 0 0.5 1.0 1.5 2.0 2.5

1.25

1.5

1.75

2.0

2.25

2.5

2.75

3.0

5

Current (mA)

®

XTR106

TYPICAL PERFORMANCE CURVES (CONT)

At TA = +25°C, V+ = 24V, unless otherwise noted.

2.5

UNDER-SCALE CURRENT vs TEMPERATURE

2.0

1.5

1.0

Under-Scale Current (mA)

0.5
V+ = 7.5V to 36V

0

–75 –50 –25 0 25 50 75 100

Temperature (°C)

OVER-SCALE CURRENT vs TEMPERATURE

30

With External Transistor

29

28

V+ = 36V

27

26

Over-Scale Current (mA)

25

V+ = 24V

V+ = 7.5V

24

–75 –50 –25 0 25 50 75 100

Temperature (°C)

125

125

4.0

UNDER-SCALE CURRENT vs I

REF

3.5
T

3.0

= –55°C

A

2.5

2.0

TA = +25°C

1.5

1.0

Under-Scale Current (mA)

TA = +125°C

0.5

0

0 0.5 1.0 1.5 2.0 2.5

+ I

REG

(mA)

I

REF

ZERO OUTPUT ERROR

3.0

REF

and V

CURRENTS

REG

vs V

2.5

2.0

I

ZERO

Error vs I

1.5

1.0

0.5

0

Zero Output Error (µA)

I

ZERO

Error vs I

–0.5
–1.0

–1 –0.5 0 0.5 1.0 1.5 2.0

Current (mA)

+ I

REG

REG

REF

2.5

ZERO OUTPUT CURRENT ERROR

vs TEMPERATURE

4
2

0
–2
–4
–6
–8

Zero Output Current Error (µA)

–10
–12

–75 –50 –25 0 25 50 75 100

Temperature (°C)

®

XTR106

125

ZERO OUTPUT DRIFT

70

60

PRODUCTION DISTRIBUTION

Typical production
distribution of
packaged units.

50

40

30

20

Percent of Units (%)

10

0

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.05

0.15

0.25

0.35

0.45

0.55

0.65

0.75

0.85

0.9

Zero Output Drift (µA/°C)

6

TYPICAL PERFORMANCE CURVES (CONT)

10 100 1k 10k 100k 1M

Frequency (Hz)

REFERENCE AC LINE REJECTION vs FREQUENCY

120

100

80

60

40

20

0

Line Rejection (dB)

V

REF

2.5

V

REF

5

At TA = +25°C, V+ = 24V, unless otherwise noted.

INPUT VOLTAGE, INPUT CURRENT, and ZERO

OUTPUT CURRENT NOISE DENSITY vs FREQUENCY

10k

Zero Output Noise

1k

Input Current Noise

100

Input Voltage Noise (nV/√Hz)

10

Input Voltage Noise

1 10 100 1k 10k

Frequency (Hz)

V

5.6

OUTPUT VOLTAGE vs V

REG

OUTPUT CURRENT

REG

5.5

5.4

5.3

5.2

5.1

Output Current (V)

REG

5.0

V

4.9

TA = +125°C

TA = +25°C, –55°C

4.8
–1.0 –0.5 0 0.5 1.0 1.5 2.0 2.5

Output Current (mA)

V

REG

100k

10k

1k

100

10

Input Current Noise (fA/√Hz)

10

8

6

4

2

0

Input Bias and Offset Current (nA)

Zero Output Current Noise (pA/√Hz)

–2

–75 –50 –25 0 25 50 75 100 125

REFERENCE TRANSIENT RESPONSE

50mV/div

500µA/div

INPUT BIAS and OFFSET CURRENT

vs TEMPERATURE

I

B

I

OS

Temperature (°C)

= 5V

V

REF

10µs/div

Output

Reference

1mA

0

V

5 vs V

REF

5.008

5.004

5.000

5 (V)

REF

V

4.996

4.992

4.988
–1.0 –0.5 0 0.5 1.0 1.5 2.0 2.5

V

OUTPUT CURRENT

REG

T

= +25°C

A

T

= +125°C

A

T

= –55°C

A

Current (mA)

REG

®

7

XTR106

TYPICAL PERFORMANCE CURVES (CONT)

–75 –50 –25 0 25 50 75 100 125

Temperature (°C)

REFERENCE VOLTAGE DEVIATION

vs TEMPERATURE

0.1

0

–0.1

–0.2

–0.3

–0.4

–0.5

Reference Voltage Deviation (%)

V

REF

= 5V

V

REF

= 2.5V

At TA = +25°C, V+ = 24V, unless otherwise noted.

REFERENCE VOLTAGE DRIFT
40
35
30
25
20
15

Percent of Units (%)

10

5
0

02468

PRODUCTION DISTRIBUTION

Typical production
distribution of
packaged units.

101214161820222426283032343638

Reference Voltage Drift (ppm/°C)

40

®

XTR106

8

APPLICATIONS INFORMATION

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.

A 2.5V or 5V reference is available to excite a bridge sensor.
For 5V excitation, pin 14 (V
bridge as shown in Figure 1. For 2.5V excitation, connect
pin 13 (V
terminals of the bridge are connected to the instrumentation
amplifier inputs, VIN and VIN. A 0.01µF capacitor is shown

2.5) to pin 14 as shown in Figure 3b. The output

REF

+–

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.

Lin Polarity and R

provide second-order linearization

LIN

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 I
nected to V
R

is chosen according to the equation in Figure 1 and is

LIN

REG

dependent on K

or V

RET

even if linearity correction is not desired.

(linearization constant) and the bridge’s

LIN

nonlinearity relative to VFS (see “Linearization” section).

5) should be connected to the

REF

. Lin Polarity should be con-

REG

The transfer function for the complete current transmitter is:

IO = 4mA + VIN • (40/RG) (1)

VIN in Volts, RG in Ohms

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 V

, the current

REG

limit value may increase. Refer to the Typical Performance
Curves, “Under-Scale Current vs I

REF

+ I

REG

” and “Under-

Scale Current vs Temperature.”
Increasingly positive input voltage (greater than the full-

scale 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.”

The I
references and V
is the reference point for V
references. The I

pin is the return path for all current from the

RET

. I

REG

RET

also serves as a local ground and

RET

and the on-board voltage

REG

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.

5V

(5)

R

(5)

R

2

NOTES:
(1) Connect Lin Polarity (pin 12) to I
bridge nonlinearity or connect to V
nonlinearity. The R
V
section and Figure 3.

(2) Recommended for bridge impedances > 10kΩ

( 3)

1

Bridge

Sensor

if linearity correction is not desired. Refer to “Linearization”

REG

= K

LIN

•

R

LIN

R

+–

B

RET

pin and Lin Polarity pin must be connected to

LIN

4B

1 – 2B

REG

(K

For 2.5V excitation, connect

pin 13 to pin 14

V

5

REF

5

V

C

IN

(2)

0.01µF

(pin 6) to correct for positive

(pin 1) for negative bridge

in Ω)

LIN

4

R

(4)

R

G

3

R

V

2

PACKAGE

4-20 mA

R

L

(see text).

1

TO-225
TO-220
TO-220

I

O

V

FS

O

+

V

PS

–

V

REG

V

2.5

REF

14

13

XTR106

6

11

R

LIN

V

(1)

Lin

Polarity

12

or

(4)

(5) R
accuracy of the bridge. See “Bridge Balance” text.

+

IN

G

G

–
IN

I

RET

(3)

R

LIN

7.5V to 36V

10

V+

9

B

Q

1

E

8

I

O

7

I = 4mA + V

O

(1)

= (VFS/400µA) •

G

where K

and R2 form bridge trim circuit to compensate for the initial

1

IN

= 9.905kΩ for 2.5V reference

LIN

= 6.645kΩ for 5V reference

K

LIN

B is the bridge nonlinearity relative to V
VFS is the full-scale input voltage

REG

V

1

REG

R

Possible choices for Q

C

OUT

0.01µF

40

• ( )
R

G

1 + 2B
1 – 2B

TYPE

2N4922
TIP29C
TIP31C

(V

FS

in V)

FIGURE 1. Basic Bridge Measurement Circuit with Linearization.

9

®

XTR106

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: V

CEO

= 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 Q
is not recommended for extended temperature ranges. A
resistor (R = 3.3kΩ) connected between the I

pin and the

RET

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 V
load on V
Performance Curve, “Under-Scale Current vs I

1

The effective load of the trim circuit is nearly equal to R2.

does not affect zero output. See the Typical

REF

output. Be sure the additional

REF

An approximate value for R1 can be calculated:

5V • R

R1≈

4 • V

B

TRIM

where, RB is the resistance of the bridge.

V

is the desired ±voltage trim range (in V).

TRIM

Make R2 equal or lower in value to R1.

REF

+ I

REG

.”

(3)

10

V+

8

E

I

RET

XTR106

6

R

= 3.3kΩ

Q

I

O

7

0.01µF

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:

RLmax =

(V+)–7.5V




20mA




–R

WIRING

(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%.

®

XTR106

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.

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 I
shown in Figure 3a. This causes V

to increase with bridge

REF

(pin 6) as

RET

output which compensates for a positive bow in the bridge
response. To correct negative nonlinearity (downward bow­ing), connect Lin Polarity to V
3b. This causes V

to decrease with bridge output. The Lin

REF

(pin 1) as shown in Figure

REG

Polarity pin is a high impedance node.
If no linearity correction is desired, both the R

Polarity pins should be connected to V

REG

LIN

(Figure 3c). This

results in a constant reference voltage independent of input
signal. R

or Lin Polarity pins should not be left open

LIN

or connected to another potential.

R

is the external linearization resistor and is connected

LIN

between pin 11 and pin 1 (V
3b. To determine the value of R

) as shown in Figures 3a and

REG

, the nonlinearity of the

LIN

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

10

and Lin

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 R
in Figure 3. R
K

, which differs for the 2.5V reference and 5V reference.

LIN

is chosen according to Equation 4 shown

LIN

is dependent on a linearization factor,

LIN

The sensor’s nonlinearity term, B (relative to full scale), is
positive or negative depending on the direction of the bow.

V

REG

V

5

REF

5V

R

R

2

1

+–

3a. Connection for Positive Bridge Nonlinearity, V

V

2.5

REF

2.5V

R

R

2

1

+–

3b. Connection for Negative Bridge Nonlinearity, V

V

5

REF

5V

R

R

2

1

+–

3c. Connection if no linearity correction is desired, V

5

4

R

G

3

2

V

REF

5

4

R

G

3

2

I

RET

5

4

R

G

3

2

I

RET

V

2.5

REF

14

13

+

XTR106

–

6

I

RET

= 5V

REF

V

5

14

13

+

XTR106

–

6

= 2.5V

REF

V

V

2.5

REF

14

13

+

XTR106

–

6

= 5V

REF

1

Lin

12

Polarity

REG

1

Lin

12

Polarity

REG

1

Lin

12

Polarity

R

LIN

11

R

LIN

11

R

LIN

11

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.

XTR106

V

Lin

Polarity

I

RET

6

R

X

100kΩ

Open RX for negative bridge nonlinearity

for positive bridge nonlinearity

Open R

Y

3d. On-Board Resistor Circuit for Unknown Bridge Nonlinearity Polarity

EQUATIONS

Linearization Resistor:

R

= K

LIN

4B

•

LIN

1– 2B

Gain-Set Resistor:

V

1 + 2B

FS

RG=

400µA

•

1– 2B

Adjusted Excitation Voltage at Full-Scale Output:

V

where, K

= V

REF ( Adj)

REF (Initial)

is the linearization factor (in Ω)

LIN

K

= 9905Ω for the 2.5V reference

LIN

K

= 6645Ω for the 5V reference

LIN

B is the sensor nonlinearity relative to V

(for –2.5% nonlinearity, B = –0.025)

V

is the full-scale bridge output without

FS

linearization (in V)

•

1 + 2B
1– 2B

Example:

Calculate R

2.5% downward bow nonlinearity relative to V
if the input common-mode range is valid.

V

REF

For a 2.5% downward bow, B = –0.025

(Lin Polarity pin connected to V

For V

R

LIN

RG=

VCM=

which falls within the 1.1V to 3.5V input common-mode range.

and the resulting RG for a bridge sensor with

LIN

= 2.5V and VFS = 50mV

= 2.5V, K

REF

(9905Ω) (4)(–0.025)

=

1– (2) (–0.025)

0.05 V
400µA

V

REF ( Adj)

2

= 9905Ω

LIN

1 + ( 2) ( –0. 025)

•

1 – ( 2 ) ( –0. 025 )

1

=

• 2. 5 V •

2

REG

1

12

R

Y

15kΩ

(in Ω)

(in Ω)

(in V)

)

REG

= 943Ω

= 113 Ω

1 + (2 ) ( –0 . 025)
1 – ( 2 ) ( –0. 025 )

FS

and determine

FS

= 1.13V

(4)

(5)

(6)

FIGURE 3. Connections and Equations to Correct Positive and Negative Bridge Nonlinearity.

11

®

XTR106

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.

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 R
the resulting sensor nonlinearity, B, values for RG and R

LIN

= 0 (R

pin connected directly to V

LIN

REG

). Using

LIN

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.

UNDER-SCALE CURRENT

The total current being drawn from the V

REF

and V

REG

voltage sources, as well as temperature, affect the XTR106’s
under-scale current value (see the Typical Performance
Curve, “Under-Scale Current vs I

REF

+ I

). This should be

REG

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”).

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

10

9
8
7
6
5
4
3

Bridge Output (mV)

2
1
0

0

WITH PARABOLIC NONLINEARITY

Positive Nonlinearity

B = +0.025

Linear Response

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Normalized Stimulus

FIGURE 4. Parabolic Nonlinearity.

700µA at 5V

3.4kΩ

5V

350Ω

3.4kΩ

B = –0.019

Negative Nonlinearity

I

≈ 1.6mA

REG

1/2

OPA2277

10kΩ

412Ω

10kΩ

1/2

OPA2277

1kΩ

V

R

125Ω

3

2

1

0

–1

–2

Nonlinearity (% of Full Scale)

–3

0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

5

REF

V

2.5

V

REF

REG

14

13

5

+

V

IN

4

R

G

G

XTR106

3

R

G

–

V

IN

2

I

RET

1

Polarity

6

Lin

R

11

V+

I

12

NONLINEARITY vs STIMULUS

Positive Nonlinearity

Normalized Stimulus

= 0.7mA + 1.6mA ≤ 2.5mA

I

TOTAL

LIN

10

9

B

E

8

O

7

1N4148

0.01µF

IO = 4-20mA

B = +0.025

Negative Nonlinearity

B = –0.019

Bridge excitation
voltage = 0.245V

Approx. x50

amplifier

FIGURE 5. 350Ω Bridge with x50 Preamplifier.

®

XTR106

Shown connected to correct positive
bridge nonlinearity. For negative bridge
nonlinearity, see Figure 3b.

12

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 I

RET

terminal, pin 6. The linearization feature of the XTR106 can
be used with any sensor whose output is ratiometric with an
excitation voltage.

SAMPLE ERROR CALCULATION

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, V

= 5V, VFS = 50mV) is provided. The

REF

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.

Bridge Impedance (RB)5kΩFull Scale Input (VFS) 50mV
Ambient Temperature Range (∆T
Supply Voltage Change (∆V+) 5V Common-Mode Voltage Change (∆CM) 25mV (= V

)20°C Excitation Voltage (V

A

)5V

REF

/2)

FS

ERROR

SAMPLE

(ppm of Full Scale)

ERROR SOURCE ERROR EQUATION ERROR CALCULATION UNADJ ADJUST
INPUT

Input Offset Voltage V

vs Common-Mode CMRR • ∆CM/VFS • 10
vs Power Supply (V

vs V+) • (∆V+)/VFS • 10

OS

Input Bias Current CMRR • IB • (RB/2)/ VFS • 10
Input Offset Current IOS • RB/VFS • 10

OS/VFS

• 10

6

6

6

200µV/50mV • 10

6
6

50µV/V • 0.025V/50mV • 10

3µV/V • 5V/50mV • 10

50µV/V • 25nA • 2.5kΩ/50mV • 10

3nA • 5kΩ/50mV • 10

6

6

6

6

6

2000 0

25 25

300 300

0.1 0

300 0

Total Input Error 2625 325

EXCITATION

Voltage Reference Accuracy V

vs Supply (V

Accuracy (%)/100% • 10

REF

vs V+) • (∆V+) • (VFS/V

REF

6

) 20ppm/V • 5V (50mV/5V) 1 1

REF

0.25%/100% • 10

6

2500 0

Total Excitation Error 2501 1

GAIN

Span Span Error (%)/100% • 10
Nonlinearity Nonlinearity (%)/100% • 10

6

6

0.2%/100% • 10

0.01%/100% • 10

6

6

2000 0

100 100

Total Gain Error 2100 100

OUTPUT

Zero Output | I

vs Supply (I

ZERO

– 4mA |/16000µA • 10

ZERO

vs V+) • (∆V+)/16000µA • 10

6

6

25µA/16000 µA • 10

0.2µA/V • 5V/16000µA • 10

6

6

1563 0

62.5 62.5

Total Output Error 1626 63

DRIFT (∆T

Input Offset Voltage Drift • ∆TA/(VFS) • 10
Input Offset Current (typical) Drift • ∆TA• RB/(VFS) • 10

= 20°C)

A

6

6

1.5µV/°C • 20°C / (50mV) • 10

5pA/ °C • 20°C • 5kΩ/ (50mV) • 10

6

6

600 600

10 10
Voltage Refrence Accuracy 35ppm/°C • 20°C 700 700
Span 225ppm/°C • 20°C 500 500
Zero Output Drift • ∆T

/ 16000 µA • 10

A

6

0.9µA/°C • 20°C / 16000µA • 10

6

1125 1125

Total Drift Error 2936 2936

NOISE (0.1Hz to 10Hz, typ)

Input Offset Voltage V
Zero Output I
Thermal RB Noise

[√ 2 • √ (RB/2)/1kΩ • 4nV/ √ Hz • √10Hz ] / VFS • 10

(p-p)/VFS • 10

n

Noise / 16000µA • 10

ZERO

Input Current Noise (in • 40.8 • √2 • RB/2)/VFS •

6

6

6

6

10

[√ 2 • √2.5kΩ/1kΩ • 4nV/√Hz • √ 10Hz ] /50mV • 10

0.6µV /50mV • 10

0.035µA/ 16000µA • 10

(200fA/√Hz • 40.8 • √2 • 2.5kΩ)/50mV• 10

6

6

6

6

12 12

2.2 2.2

0.6 0.6

0.6 0.6

Total Noise Error 15 15

NOTE (1): All errors are min/max and referred to input, unless otherwise stated.

TOTAL ERROR: 11803 3340

1.18% 0.33%

TABLE I. Error Calculation.

13

®

XTR106

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.

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 I

RET

terminal as shown in Figure 6. Although the dc voltage at
the I

terminal is not equal to 0V (at the loop supply, VPS)

RET

this circuit point can be considered the transmitter’s “ground.”
The 0.01µF capacitor connected between V+ and IO may
help minimize output interference.

V

5

5V

R

+–

B

Bridge
Sensor

REF

R

G

0.01µF0.01µF

V

2.5

REF

14

5

4

3

2

13

+

V

IN

R

G

XTR106

R

G

–

V

IN

I

RET

6

10

V+

9

B

E

8

I

O

7

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.”

0.01µF

Q

1

FIGURE 6. Reverse Voltage Operation and Over-Voltage Surge Protection.

R

L

must be

PS

V

PS

Maximum V
less than minimum
voltage rating of zener
diode.

(1)

D

1

1N4148

Diodes

The diode bridge causes
a 1.4V loss in loop supply
voltage.

®

XTR106

14

Type K

Isothermal

Block

1N4148

6kΩ

50Ω

4.8kΩ

5.2kΩ

100Ω

1MΩ

V

5

REF

0.01µF
See ISO124 data sheet

if isolation is needed.

1MΩ

20kΩ

OPA277

(1)

R

1kΩ

V

2.5

REF

14

13

I

RET

11

R

LIN

XTR106

Lin

Polarity

12

1

V

REG

5

+

V

IN

4

R

G

G

3

R

G

–

V

2

IN

6

V

REG

7.5V to 36V

10

V+

9

Q

B

E

I

O

1

8

7

IO = 4mA + VIN • ( )

(pin 1)

C

OUT

0.01µF

40

R

G

4-20 mA

R

L

I

O

V

O

+

V

PS

–

2kΩ

NOTE: (1) For burn-out indication.

0.01µF

FIGURE 7. Thermocouple Low Offset, Low Drift Loop Measurement with Diode Cold-Junction Compensation.

V

2.5

2.5V

Bridge

Sensor

–+

REF

5

V

REF

14

+

V

5

R

B

IN

4

R

G

R

G

3

R

G

–

2

V

IN

I

RET

6

13

XTR106

Lin

Polarity

V

REG

R

LIN

1

11

10

1N4148

+12V

See ISO124 data sheet
if isolation is needed.

1µF

V+

9

B

8

E

I

O

0.01µF

7

12

IO = 4-20mA

16

10

3

RCV420

2

4

11

1µF

12

13

5

15

V

14

O

= 0V to 5V

NOTE: Lin Polarity shown connected to correct positive bridge
nonlinearity. See Figure 3b to correct negative bridge nonlinearity.

FIGURE 8. ±12V-Powered Transmitter/Receiver Loop.

15

–12V

®

XTR106