Analog Devices Inc. LM399H

Overview

LM399H from Analog Devices (formerly Linear Technology) is a precision 6.95V shunt voltage reference with integrated temperature stabilization heater, designed for metrology-grade applications requiring ultra-low drift and noise. It delivers guaranteed 0.5ppm/°C tempco, ≤1Ω dynamic impedance, ≤20µVRMS noise (10Hz–10kHz), and operates over 0.5–10mA current in a 4-lead TO-46 metal can package. Used in high-accuracy digital multimeters and calibration standards.

For engineers reviewing the LM399H datasheet, LM399H pinout, LM399H application, or LM399H equivalent, key selection criteria include long-term stability (8ppm/√kH), warm-up time (≤3s to ±0.05%), heater supply requirements (9–40V), and thermal shield integration for ambient immunity.

Technical Context

The LM399H integrates a subsurface Zener diode and monolithic heater on a single silicon substrate, maintaining junction temperature near 90°C to nullify Zener voltage drift across ambient temperatures. Its stabilized operation eliminates need for external oven control while achieving performance comparable to discrete ovenized references.

It functions as a two-terminal shunt device with substrate-connected thermal shield; the negative terminal serves as both reference cathode and heater return. Heater current varies from 8.5mA (25°C) to 22mA (–55°C) under 30V supply, enabling stable biasing without external regulation.

Key Specifications

Pinout & Package

LM399H uses a hermetically sealed 4-lead TO-46 metal can (H package) with internal thermal shield connected to Pin 4 (substrate). The metal case provides EMI shielding and thermal mass critical for low-drift operation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar precision shunt reference applications.

Compared with LTZ1000 and LT1021ACN8-10, the LM399H uniquely balances metrology-grade stability (0.5ppm/°C, 8ppm/√kH) with self-contained heater operation and TO-46 packaging - making it the optimal choice for portable calibrators and mid-tier DMMs needing verified performance without system-level thermal engineering.

Availability

LM399H is available at Aetrix Electronics and suitable for digital multimeters, calibration equipment, and laboratory data acquisition systems requiring stable component supply and long-term parametric consistency.

Supply support for LM399H 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

Analog Devices acquired Linear Technology in 2017 and continues to manufacture and support its precision analog portfolio, including legacy high-stability references.

The LM399H belongs to Linear Technology's precision voltage reference product line, engineered specifically for metrology, calibration, and high-end test equipment where long-term drift and thermal hysteresis must be minimized.

FAQ

What is the operating current range for the LM399H?

The LM399H operates over a reverse breakdown current range of 0.5mA to 10mA. Within this range, it maintains specified voltage accuracy, tempco, and noise performance. Operation below 0.5mA risks increased noise and instability; above 10mA may exceed power dissipation limits in the TO-46 package. Designers typically bias at 1mA for optimal long-term stability and low drift.

Does the LM399H require external components to function?

Yes, the LM399H requires an external current-limiting resistor for the heater supply (Pin 1), typically sized to deliver 8.5–15mA depending on ambient temperature and supply voltage (9–40V). A ≥2µF tantalum capacitor must bypass the heater supply to suppress ripple. No external op-amp is needed for basic operation, though buffering is recommended for load isolation.

What is the purpose of Pin 4 (substrate) on the LM399H?

Pin 4 connects internally to the metal can's thermal shield and must be tied to system ground. This connection provides EMI shielding, reduces thermal EMF errors, and stabilizes the reference's thermal environment. Leaving Pin 4 floating degrades tempco performance and increases susceptibility to air currents and radiated noise - confirmed in LM399H characterization data.

How does the LM399H achieve its 0.5ppm/°C temperature coefficient?

The LM399H achieves 0.5ppm/°C tempco by integrating a subsurface Zener diode and precision heater on a monolithic die, actively maintaining the junction at ~90°C. This eliminates ambient-dependent Zener voltage drift. The heater's power is self-regulated via thermal feedback, and the thermal shield minimizes external thermal gradients - all confirmed in the LM399H datasheet's stabilization curves and tempco tables.

Can the LM399H replace the LM199H in existing designs?

No - the LM399H is not a direct replacement for the LM199H. While both share the same TO-46 H package and pinout, the LM199H is rated for –55°C to 125°C and has different tempco specs (0.3ppm/°C min over –55°C to 85°C). The LM399H is rated only for 0°C to 70°C and exhibits higher drift outside that range. Substituting without requalification risks calibration failure in extended-temperature applications.