Texas Instruments LM334SM

Overview

LM334SM from Texas Instruments is a 3-terminal adjustable current source IC designed for precision biasing, temperature sensing, and low-power reference applications. It delivers programmable current from 1 μA to 10 mA with ±3% initial accuracy, operates over 1 V–40 V supply range, exhibits 0.02%/V current regulation, and is specified for 0°C to +70°C ambient operation in SOIC-8 package.

For engineers reviewing the LM334SM datasheet, LM334SM pinout, LM334SM application, or LM334SM equivalent, this device serves as a floating two-terminal current source where output current is set by a single external resistor and scales linearly with absolute temperature - critical for remote temperature sensing, LED biasing, and micropower ramp generation.

Technical Context

The LM334SM functions as a true floating current source with no separate power supply pins: current flows between V+ and V− terminals, while the R (SET) terminal senses voltage across an external resistor to establish I_SET. Its core operation relies on a 67.7 mV reference at 25°C that scales linearly with absolute temperature (≈+0.336%/°C), enabling direct Kelvin-proportional current output.

It supports true 2-terminal operation in basic configurations, achieves zero-drift performance when augmented with a diode and second resistor, and maintains high output impedance (>10 MΩ typical) due to internal cascode architecture - making it suitable for high-impedance sensor termination and stable bias networks without loading effects.

Key Specifications

Pinout & Package

LM334SM is housed in an 8-pin SOIC package (TI package code D), with functional pin assignment confirmed per Figure 1 and Figure 2 of SNVS746E. The device uses only three pins electrically: V+, V−, and R (SET); remaining pins are NC or internally tied. Pin 1 is marked via notch or bevel; pinout follows standard SOIC-8 orientation with pin 1 in top-left corner.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar adjustable current source applications.

Compared with LM334Z/NOPB, LM334SM offers superior thermal performance in SMT layouts and tighter board-level integration; versus REF200AU, it trades fixed accuracy for full programmability and temperature-proportional functionality - making LM334SM uniquely suited for sensor and adaptive bias applications.

Availability

LM334SM is available at Aetrix Electronics and suitable for remote temperature sensing, LED biasing, and micropower reference generation requiring stable component supply across industrial, instrumentation, and embedded design cycles.

Supply support for LM334SM 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, embedded processing, and logic technologies with decades of precision analog IC heritage.

The LM334SM belongs to TI's legacy precision current source family, engineered for applications demanding Kelvin-proportional output, low-voltage operation, and robust 2-wire sensor interfacing - particularly in industrial monitoring and battery-constrained systems.

FAQ

What is the minimum operating voltage for LM334SM at 10 μA set current?

The LM334SM requires a minimum of 0.8 V across V+ and V− terminals when set current is between 2 μA and 100 μA. At exactly 10 μA, this corresponds to 0.8 V headroom - sufficient for single-cell alkaline or lithium primary battery operation. This value is confirmed in the Electrical Characteristics table under "Minimum Operating Voltage" for the 2 μA ≤ I_SET < 10 μA condition. The LM334SM achieves this with internal bandgap-derived reference scaling.

Can LM334SM be used as a temperature sensor, and what accuracy can be expected?

Yes, the LM334SM outputs current directly proportional to absolute temperature (I_SET ∝ T(K)), making it suitable for remote temperature sensing. While LM234-3/LM234-6 variants are factory-trimmed to ±3°C/±6°C, the LM334SM has ±3% initial gain accuracy at 25°C and +0.336%/°C tempco. With one-point calibration (e.g., at 25°C), system-level accuracy better than ±1°C over 0°C–70°C is achievable using a low-drift R_SET.

Does LM334SM require external components to operate as a basic current source?

Yes - the LM334SM requires exactly one external resistor (R_SET) connected between the R (SET) and V− terminals to define I_SET. No capacitors, diodes, or additional ICs are needed for basic 2-terminal operation. The formula is I_SET ≈ 67.7 mV / R_SET at 25°C, with minor bias current correction (typically <5.9%). This simplicity enables rapid implementation in bias networks and sensor interfaces.

What is the function of pins 4–8 on the LM334SM SOIC-8 package?

Pins 4–8 on the LM334SM are No Connect (NC) terminals - they are not bonded internally and serve no electrical function. TI's package drawings and datasheet Figure 1 confirm these pins are unassigned. They may be left floating, grounded, or routed to copper pour for thermal or mechanical stability, but connecting them to signals or power will not affect LM334SM operation or specifications.

How does LM334SM behave under reverse voltage conditions?

When reverse voltage (V− > V+) up to 20 V is applied, the LM334SM draws only a few dozen microamperes - functioning as a low-leakage rectifier. This behavior is specified in Absolute Maximum Ratings and enables safe AC-coupled operation (e.g., in bridge-based sensor excitation). Reverse conduction does not damage the device and ceases once forward bias is restored, preserving reliability in field-deployed equipment.