XTR111AIDGQRG4: Precision Voltage-to-Current Conversion for Industrial Current Loops

The Texas Instruments XTR111AIDGQRG4 is a precision voltage-to-current converter designed for industrial sensor transmitters, programmable logic controllers (PLCs), and distributed I/O systems. The device accurately converts standard 0–5 V or 0–10 V voltage signals into 0–20 mA or 4–20 mA current signals, and through an external N-channel MOSFET, it can withstand loop voltages up to several tens of volts, enabling reliable long-distance transmission.

I. Core Features and Parameter Table
The XTR111 integrates a high-precision operational amplifier, a 2.5 V voltage reference, and fault detection circuitry. A complete current loop can be built with only a few external components.

Parameter	Typical Value / Specification	Unit
Supply Voltage (VSP)	8 to 40	V
Internal Reference Voltage	2.5 ±0.05%	V
Input Voltage Range	0 to 12	V
Output Current Range	0 to 20	mA
Total Unadjusted Error	±0.3%	% FSR
Nonlinearity	±0.01%	% FSR
Quiescent Current	550	µA
Operating Temperature Range	-40 to +125	℃
Package	MSOP-10 (DGQ)	–

II. Design Q&A
Q1: How is the full-scale output current set?
The output current is determined by the input voltage VIN and the RSET resistor, according to the formula IOUT = (VIN / RSET) × 10. The internal current gain is fixed at 10, and RSET is connected between the ISET pin and ground. For example, for a 0–5 V input corresponding to 0–20 mA output, RSET = (5 V / 20 mA) × 10 = 2.5 kΩ. If a 4–20 mA output is required, an input offset voltage can be introduced, or an MCU can provide a DAC output with a DC offset.

Q2: How should the external MOSFET be selected?
The XTR111 drives the gate of an external N-channel MOSFET, with the drain connected to the loop supply VLOOP. When selecting a MOSFET, the VDS breakdown voltage must exceed the maximum VLOOP, the RDS(on) should be as low as possible to reduce power dissipation, and the package should offer good thermal dissipation. TI recommends devices such as the CSD18534KCS. A 10–100 Ω resistor in series with the gate can prevent parasitic oscillations.

Q3: What protection features does the chip provide?
The device incorporates output current limiting, thermal shutdown, and undervoltage lockout. The output automatically shuts down when the junction temperature exceeds approximately 160°C. The EF pin (open-drain) is pulled low during an over-temperature or loop-open condition, and can be connected to an MCU for system diagnostics.

III. Applications and Layout Essentials
The XTR111 is widely used in two-wire transmitters, PLC analog output modules, and current calibrators. For example, in a pressure transmitter, the sensor signal is conditioned and then fed into the XTR111 to directly drive a 4–20 mA loop. Key PCB layout considerations include: placing the RSET resistor close to the ISET pin to minimize parasitic capacitance; decoupling the VSP pin with a 10 µF tantalum capacitor in parallel with a 0.1 µF ceramic capacitor; and routing the MOSFET source feedback path directly to VSP to ensure current accuracy. The thermal pad of the MSOP-10 PowerPAD package must be soldered to a large copper ground plane to enhance heat dissipation.

IV. Summary
With its 0.01% nonlinearity, 40 V wide supply voltage, and integrated fault protection, the XTR111AIDGQRG4 provides a compact and highly reliable solution for industrial current-loop designs. Designers can quickly implement a high-precision voltage-to-current conversion by simply selecting an appropriate RSET and MOSFET, meeting the stringent requirements of harsh industrial environments.

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