SBOS092C June   1998  – January 2026 XTR106

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 Recommended Operating Conditions
    3. 5.3 Thermal Information
    4. 5.4 Electrical Characteristics
    5. 5.5 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Linearization
      2. 6.3.2 Reverse-Voltage Protection
      3. 6.3.3 Overvoltage Surge Protection
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 External Transistor
      2. 7.1.2 Loop Power Supply
      3. 7.1.3 Bridge Balance
      4. 7.1.4 Underscale Current
      5. 7.1.5 Low-Impedance Bridges
      6. 7.1.6 Other Sensor Types
      7. 7.1.7 Radio Frequency Interference
      8. 7.1.8 Error Analysis
    2. 7.2 Typical Applications
    3. 7.3 Layout
    4. 7.4 Layout Guidelines
  9. 8 Device and Documentation Support
    1. 8.1 Device Nomenclature
    2. 8.2 Documentation Support
    3. 8.3 Related Documentation
    4. 8.4 Receiving Notification of Documentation Updates
    5. 8.5 Support Resources
    6. 8.6 Trademarks
    7. 8.7 Electrostatic Discharge Caution
    8. 8.8 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.1 Application Information

Figure 7-1 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, overload conditions, or both can 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, connect pin 14 (VREF5) to the bridge; see also Figure 7-1. For 2.5V excitation, connect pin 13 (VREF2.5) to pin 14; see also Figure 6-3. 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.

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; connect either to IRET or VREG. Connect Lin Polarity to VREG even if linearity correction is not desired. RLIN is chosen according to Equation 7 and depends on KLIN (linearization constant) and the bridge nonlinearity relative to VFS (see Section 6.3.1).

Equation 7. R L I N = K L I N × 4 B 1 - 2 B

where:

  • KLIN is in Ω

Equation 8. R G = V F S 400 μ A × 1 + 2 B 1 - 2 B

where:

  • VFS is in V
  • 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

The transfer function for the complete current transmitter is:

Equation 9. IO=4mA+VIN×40RG

Where:

  • VIN VIN is the differential input voltage in Volts
  • RG is in Ohms

As evident from the transfer function, if no RG is used (RG = ∞), the gain is zero and the output is simply the XTR106 zero current.

A negative input voltage, VIN, causes the output current to be less than 4mA. Increasingly negative VIN causes the output current to limit at approximately 1.6mA. If current is being sourced from the reference and/or VREG, the current limit value can increase. See also Figure 5-9 and Figure 5-10.

Increasingly positive input voltage (greater than the full-scale input, VFS) produces increasing output current according to the transfer function, up to the output current limit of approximately 28mA. See also Figure 5-11.

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 onboard 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.

XTR106 Basic Bridge Measurement Circuit With Linearization
(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 the Linerization section.
(2) Recommended for bridge impedances > 10kΩ.
(3) R1 and R2 form bridge trim circuit to compensate for the initial accuracy of the bridge. See the Bridge Balance text.
Figure 7-1 Basic Bridge Measurement Circuit With Linearization