STMicroelectronics LM335AD

Overview

LM335AD from STMicroelectronics is a precision 2-terminal Zener-based temperature sensor calibrated in Kelvin, delivering 10 mV/°K linear output with ±1°C initial accuracy over –40°C to +100°C. It operates from 450 µA to 5 mA, exhibits <0.6 Ω dynamic impedance, and is housed in a TO-92 plastic package. Used in environmental monitoring systems for HVAC control, battery thermal management, and industrial process sensing.

For engineers reviewing the LM335AD datasheet, LM335AD pinout, LM335AD application, or LM335AD equivalent, key selection factors include its Kelvin-referenced linearity, low self-heating error at 1 mA bias, calibration flexibility via single-point slope adjustment, and compatibility with simple op-amp conditioning circuits in cost-sensitive analog temperature measurement designs.

Technical Context

The LM335AD functions as a temperature-dependent Zener diode whose breakdown voltage rises linearly at 10 mV per Kelvin - enabling direct absolute temperature readout without signal conditioning. Its internal circuitry maintains stable operation across 450 µA–5 mA supply current, with negligible voltage shift (<14 mV) over that range at constant temperature.

Calibration is performed at +25°C (298.15 K), yielding a nominal output of 2.98 V. Uncalibrated error is ≤±3°C over full range; after 25°C calibration, typical error reduces to ±1°C. Non-linearity remains ≤±1.5°C, and thermal time constant in still air is 80 s - critical for slow-response ambient sensing applications.

Key Specifications

Pinout & Package

LM335AD is supplied in a TO-92 plastic package (bottom view), with three leads: Pin 1 = ADJ (adjust terminal for calibration), Pin 2 = V+ (anode/cathode depending on bias direction), Pin 3 = V− (cathode/anode). The device operates as a 2-terminal device; ADJ is unused in basic configurations but enables precision slope calibration.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar temperature sensing applications.

Compared with LM335AZ and TSIC 506, the LM335AD uniquely balances analog simplicity, Kelvin linearity, and reel-compatible packaging - making it optimal for cost-sensitive, low-complexity analog temperature loops where calibration flexibility and PCB space efficiency are prioritized.

Availability

LM335AD is available at Aetrix Electronics and suitable for HVAC control systems, battery thermal monitoring, and industrial process sensing requiring stable component supply and consistent TO-92 mechanical fit.

Supply support for LM335AD 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, mixed-signal, power, and microcontroller solutions for industrial, automotive, and consumer markets.

The LM335AD belongs to ST's precision analog sensor family, engineered specifically for high-accuracy, low-cost, and low-power analog temperature measurement in non-automotive industrial and commercial equipment.

FAQ

What is the correct biasing method for LM335AD in a 5 V system?

Apply a series resistor between 5 V and the V+ pin, sized to deliver 1 mA (e.g., 2 kΩ for ~2.98 V drop), with V− tied to ground. This ensures optimal dynamic impedance and minimizes self-heating. Avoid exceeding 5 mA to prevent thermal stress.

Can LM335AD be used for Celsius-only output without Kelvin conversion?

Yes - subtract 2.7315 V from the output voltage to obtain volts proportional to °C (since 0 K = –273.15°C → 2.7315 V offset). This requires a precision reference or op-amp subtractor stage; the IC itself outputs strictly Kelvin-referenced voltage.

How does self-heating affect LM335AD accuracy in enclosed spaces?

At 1 mA bias, self-heating raises junction temperature by ~0.2°C in still air. In sealed enclosures, this error increases proportionally with thermal resistance. Use lower bias current (e.g., 450 µA) or add external calibration to compensate for predictable offset.

Is the ADJ pin required for basic operation?

No - LM335AD functions as a 2-terminal device with only V+ and V− connected. ADJ is optional and used only when fine-tuning the 10 mV/°K slope via external potentiometer; leaving it unconnected or grounded has no effect on standard operation.