Texas Instruments XTR105UA

Overview

XTR105UA from Texas Instruments is a monolithic 4–20mA two-wire current transmitter with integrated sensor excitation, linearization, and dual 800µA precision current sources. It functions as the core analog front-end for RTD-based temperature measurement systems, delivering low unadjusted error (±50 µA zero output initial error), high PSRR (110 dB), and 40:1 linearity improvement via second-order correction. It operates across 7.5V to 36V loop supply in industrial environments (–40°C to +85°C) and supports both 2-wire and 3-wire Pt100 configurations.

For engineers reviewing the XTR105UA datasheet, XTR105UA pinout, XTR105UA application, or XTR105UA equivalent, this page provides verified technical context on its differential instrumentation amplifier architecture, RG-set transconductance (S = 40/RG A/V), VLIN-based linearization implementation, and IRET-referenced current source return path-critical for accurate field transmitter design and HART-compatible loop integration.

Technical Context

The XTR105UA implements a voltage-to-current conversion architecture where VIN+ and VIN− feed a programmable-gain instrumentation amplifier whose output drives a regulated 4–20mA loop via external transistor Q1 (B/E pins). Its gain is set by resistor RG between pins 3 and 4, yielding transconductance S = 40/RG A/V. The device uses IRET as the common return for VREG, IR1, IR2, and VLIN, enabling precise current summation without ground-loop errors.

Linearization is achieved through VLIN's second-order correction circuitry, requiring external RLIN1 (and RLIN2 for 3-wire RTDs) to compensate Pt100 nonlinearity-verified to deliver ~40× improvement in linearity. Two matched 800µA current sources (IR1, IR2) provide excitation for RTD and RZ, with matching accuracy of ±0.2% and drift ≤ ±30 ppm/°C over –40°C to +85°C.

Key Specifications

Pinout & Package

Package: SOIC-14 (D package), 8.65 mm × 6 mm body size, surface-mount, industrial temperature grade (–40°C to +85°C).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 4–20mA transmitter applications.

Compared with XTR105PA, the XTR105UA offers superior thermal performance in compact layouts; compared with XTR115UA, it delivers tighter zero-drift and higher PSRR-making it optimal for high-stability temperature transmitters where long-term calibration stability is critical.

Availability

XTR105UA is available at Aetrix Electronics and suitable for temperature transmitter design, pressure sensor signal conditioning, and factory automation I/O modules requiring stable component supply, long-lifecycle assurance, and traceable sourcing for industrial deployment.

Supply support for XTR105UA includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog and embedded processing technologies, with decades of leadership in precision signal conditioning and industrial interface ICs.

The XTR105UA belongs to TI's XTR series of 4–20mA current transmitters, designed specifically for high-accuracy, low-drift sensor signal conditioning in harsh industrial environments-including RTD, thermocouple, and bridge-based measurement systems.

FAQ

What is the maximum loop supply voltage the XTR105UA can tolerate?

The XTR105UA has an absolute maximum loop supply voltage (V+) of 40 V, referenced to the IO pin. Operation beyond this risks permanent damage. For reliable continuous use, the recommended operating range is 7.5 V to 36 V. At 36 V, the device maintains full 4–20 mA output compliance and meets all electrical specifications across –40°C to +85°C.

Does the XTR105UA require an external transistor for operation?

Yes, the XTR105UA is designed to drive an external NPN transistor (e.g., TIP29C) via its B (Pin 9) and E (Pin 8) terminals to handle the majority of loop current dissipation. Operating without Q1 degrades accuracy due to self-heating of the IC's internal pass element-especially above 0°C or at high loop voltages-and is not recommended for production use. The XTR105UA data sheet explicitly states that external transistor use preserves low drift and high linearity.

How does the XTR105UA achieve RTD linearization, and what external components are required?

The XTR105UA achieves second-order RTD linearization using its VLIN (Pin 12) output in conjunction with external resistors RLIN1 (and RLIN2 for 3-wire RTDs). This configuration provides positive feedback that corrects Pt100 nonlinearity, delivering up to a 40× improvement in linearity. For a 2-wire Pt100, only RLIN1 is needed; for 3-wire, both RLIN1 and RLIN2 are required and must be matched to equalize currents and cancel lead resistance effects.

What is the function of the IRET pin on the XTR105UA, and why is its routing critical?

The IRET pin (Pin 6) serves as the common return path for the VREG output, IR1, IR2, and VLIN circuits. All current sourced from these outputs flows back through IRET, allowing the XTR105UA to include external circuit currents in the final 4–20 mA loop output without error. Routing IRET with low impedance and avoiding shared traces with high-noise signals is essential-any voltage drop on IRET directly introduces gain and offset errors in the transmitted current.

Can the XTR105UA support HART communication, and what design considerations apply?

Yes, the XTR105UA is compatible with HART modems due to its low output current noise (30 nA_PP) and high PSRR (110 dB), which preserve the 1.2 kHz/2.2 kHz FSK HART signal superimposed on the 4–20 mA loop. To ensure robust operation, designers must maintain clean power filtering on V+, minimize PCB trace inductance on IO and IRET, and avoid placing switching regulators near the XTR105UA. TI confirms HART compatibility in the official XTR105 family documentation.