Texas Instruments LM135H

Overview

LM135H from Texas Instruments is a precision 2-terminal Kelvin-referenced temperature sensor operating as a zener-like device with linear 10 mV/°K output voltage, ±1°C initial accuracy at 25°C, −55°C to +150°C operating range, and <1 Ω dynamic impedance. It enables high-stability thermal monitoring in industrial power supplies and battery management systems where absolute temperature accuracy and low self-heating are critical.

For engineers reviewing the LM135H datasheet, LM135H pinout, LM135H application, or LM135H equivalent, key selection considerations include its TO-46 hermetic package, calibration-adjustable slope via ADJ pin, 400 μA–5 mA bias current range, and compatibility with simple resistor-based readout circuits without signal conditioning ICs.

Technical Context

The LM135H functions as a 2-terminal temperature-dependent zener with output voltage V_OUT = (10 mV/°K) × T_K, where T_K is absolute temperature. Its internal architecture includes a bandgap-derived reference and trimming circuitry enabling single-point calibration via the ADJ pin to correct scale-factor errors across the full temperature range.

It operates in two functional modes - uncalibrated (typical ±2.7°C error over −55°C to +150°C) and calibrated (±1°C max over same range). Thermal time constant is 1 sec in stirred oil, 10 sec in 100 ft/min air, and 80 sec in still air - confirming direct thermal coupling to ambient or surface is essential for response fidelity.

Key Specifications

Pinout & Package

LM135H is housed in a hermetic TO-46 metal can package (body size 4.699 mm × 4.699 mm) with three terminals. Pin configuration is defined per bottom view: Pin 1 (ADJ), Pin 2 (−), Pin 3 (+). The ADJ pin enables external slope calibration; Pins 2 and 3 form the main 2-terminal sensing path.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM135AH/NOPB, LM135H offers legacy Pb-based termination and slightly relaxed initial accuracy but identical thermal performance and calibration flexibility; versus LM235H, it provides 30°C wider operational range and tighter uncalibrated error spec - making it the only choice for −55°C cold-start or 150°C high-temp industrial use cases.

Availability

LM135H is available at Aetrix Electronics and suitable for industrial power supplies, battery thermal management, and HVAC control systems requiring stable component supply with long-term obsolescence planning and consistent parametric performance.

Supply support for LM135H 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 heritage in precision analog sensors and industrial-grade ICs.

The LM135H belongs to TI's LMx35 precision temperature sensor family, designed specifically for applications demanding absolute Kelvin-referenced accuracy, low-drift operation, and robustness in demanding thermal environments.

FAQ

What is the operating temperature range of the LM135H?

The LM135H operates continuously from −55°C to +150°C, with intermittent capability up to +200°C. This extended range is enabled by its hermetic TO-46 metal package and internal thermal design. The LM135H datasheet specifies that operation beyond +150°C is limited to short-duration intermittent use to preserve long-term reliability - critical for engine bay or industrial furnace monitoring where peak transients occur.

How does the ADJ pin on the LM135H enable calibration?

The ADJ pin on the LM135H provides access to an internal trimming node that adjusts the device's output voltage slope (10 mV/°K). By connecting a potentiometer between Pins 3 (+) and 2 (−) with its wiper to ADJ, users perform a single-point calibration at 25°C to correct scale-factor errors across the entire −55°C to +150°C range. This works because LM135H errors are predominantly linear slope deviations, not offset shifts - so correcting at one temperature corrects all.

What is the minimum and maximum bias current required for stable operation of the LM135H?

The LM135H requires a reverse bias current between 400 μA and 5 mA for stable operation and specified accuracy. Below 400 μA, dynamic impedance rises and output becomes unstable; above 5 mA, self-heating increases measurement error. At 1 mA bias - the typical design point - the LM135H achieves optimal balance of low self-heating (≈0.3°C rise), low noise, and minimal voltage drop across series resistors in standard configurations.

Can the LM135H be used in a 3-wire configuration for improved accuracy?

No - the LM135H is strictly a 2-terminal device: Pins 2 (−) and 3 (+) form the primary sensing path, while Pin 1 (ADJ) is a calibration auxiliary and not a third sensing terminal. Unlike 3-wire RTDs or digital sensors, the LM135H does not support remote sensing or lead-wire compensation. For long-cable applications, designers must calculate wire resistance-induced voltage drop (e.g., 1°C error ≈ 10 mV = 10 Ω @ 1 mA) and either oversize conductors or use local signal conditioning.

What package type is used for the LM135H and why is it significant?

The LM135H uses a hermetic TO-46 metal can package (3-pin, 4.699 mm × 4.699 mm body). This package provides superior long-term stability, moisture resistance, and thermal conductivity compared to plastic alternatives like TO-92. Its hermetic seal prevents parameter drift due to humidity ingress - essential for aerospace, medical, and outdoor industrial deployments where 10+ year field life and repeatability are mandated. The metal case also serves as a thermal mass that dampens rapid ambient fluctuations.