STMicroelectronics LM235D

Overview

LM235D 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 +125°C. It operates from 450 µA to 5 mA, exhibits <1 Ω dynamic impedance, and is housed in an SO-8 plastic micropackage for surface-mount thermal sensing in industrial control systems.

For engineers reviewing the LM235D datasheet, LM235D pinout, LM235D application, or LM235D equivalent, key selection criteria include its Kelvin-referenced linearity, low self-heating error, calibration flexibility at +25°C, and compatibility with low-current biasing circuits in embedded temperature monitoring.

Technical Context

The LM235D functions as a programmable Zener diode whose breakdown voltage tracks absolute temperature with nominal 10 mV/°K slope. Its two-terminal architecture eliminates need for external resistors or op-amps in basic configurations, and its low dynamic impedance (<0.6 Ω) ensures stable output under varying load conditions.

Calibration relies on single-point adjustment at +25°C (298.15 K), correcting slope-only nonlinearity across the full operating range. Self-heating effects are minimized by operation within 450 µA–5 mA, and thermal time constant is 10 s in 0.5 m/s air flow per STMicroelectronics characterization.

Key Specifications

Pinout & Package

LM235D is supplied in an SO-8 plastic micropackage (JEDEC MS-012AC), with 8-pin surface-mount footprint and gull-wing leads. Pin 1 is marked via notch or dot; device orientation follows standard top-view labeling.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM335D and TSIC 506, the LM235D uniquely balances analog simplicity, extended high-temperature capability (+125°C), and field-calibration flexibility-making it optimal for ruggedized analog temperature loops where digital interfaces are unavailable or undesirable.

Availability

LM235D is available at Aetrix Electronics and suitable for industrial oven temperature control, automotive cabin climate monitoring, and server rack thermal management requiring stable component supply and long-term lifecycle continuity.

Supply support for LM235D 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 LM235D belongs to ST's precision analog sensor family, engineered specifically for Kelvin-referenced, low-drift temperature measurement in harsh environments where reliability and calibration stability are critical.

FAQ

What is the recommended operating current for optimal accuracy?

The LM235D achieves best linearity and minimal self-heating at 1 mA, as specified in ST's electrical characteristics table. At this current, dynamic impedance is 0.5 Ω, non-linearity is ±0.3°C, and thermal time constant remains stable at 10 s in 0.5 m/s airflow. Operation below 450 µA risks increased noise; above 5 mA raises self-heating beyond 0.5°C.

Can the LM235D be used without calibration?

Yes-the LM235D provides usable output without calibration, with typical uncalibrated error of ±2°C over –40°C to +125°C. However, single-point calibration at +25°C reduces error to ±0.5°C across the full range by correcting slope deviation. The ADJ pin enables precise resistor-based trimming for system-level accuracy alignment.

How does the SO-8 package affect thermal response compared to TO-92?

The SO-8 package offers superior board-level thermal coupling due to larger copper pad area and shorter thermal path to PCB, resulting in faster response (10 s vs. 80 s in still air) and lower effective thermal resistance. However, TO-92 provides better isolation in air-gap mounting; SO-8 requires careful thermal pad design to avoid conduction errors from nearby heat sources.

Is the LM235D compatible with 3.3 V microcontroller ADC inputs?

Yes-when biased at 1 mA, the LM235D outputs 2.982 V at +25°C (298.15 K × 10 mV/°K), well within 3.3 V ADC full-scale range. For extended range (e.g., +125°C = 4.23 V), a resistive divider or rail-to-rail op-amp buffer is required. No level-shifting is needed for 0°C to +70°C operation (2.73 V to 3.43 V).