Texas Instruments LF198AH

Overview

LF198AH from Texas Instruments is a monolithic BI-FET sample-and-hold IC operating as a unity-gain follower with 0.002% typical DC gain accuracy, ≤10 µs acquisition time to 0.1%, and 0.5 mV typical hold step at 0.01 µF hold capacitance. It functions in precision data acquisition systems where high input impedance (10¹⁰ Ω), low droop rate (5 mV/min with 1 µF), and ±5 V to ±18 V dual-supply operation are required.

For engineers reviewing the LF198AH datasheet, LF198AH pinout, LF198AH application, or LF198AH equivalent, key selection considerations include logic-compatible TTL/CMOS/PMOS control interface, differential logic threshold of 1.4 V, hold capacitor leakage current ≤100 pA, and guaranteed operation over –55°C to +125°C ambient temperature.

Technical Context

The LF198AH uses a bipolar input stage combined with P-channel JFET output devices to achieve low offset voltage (<1 mV typ), wide bandwidth (supports inclusion inside 1-MHz op-amp feedback loops), and minimal feedthrough attenuation (≥86 dB at 1 kHz). Its BI-FET architecture ensures stable input characteristics during hold mode and no degradation of input offset drift when using the dedicated OFFSET ADJUST pin.

Functional modes are controlled differentially via LOGIC and LOGIC REFERENCE pins: sample mode activates when LOGIC is ≥1.4 V above LOGIC REFERENCE; hold mode engages when LOGIC is ≤1.4 V below it. Input-to-output isolation in hold mode remains effective even for input signals equal to supply rails, and output impedance stays ≤1 Ω in hold mode.

Key Specifications

Pinout & Package

LF198AH is supplied in the hermetically sealed TO-99 metal can package (8-pin, 9.08 mm × 9.08 mm body), rated for military-temperature operation (–55°C to +125°C) and space-qualified per JM38510/12501SGA.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar sample-and-hold applications.

Compared with LF198A-N, LF198AH provides identical pinout and core performance but with relaxed gain error and hold step specs-making it suitable for high-reliability commercial applications where full MIL-STD qualification isn't mandated. Compared with LF398-N, LF198AH delivers superior DC accuracy, faster acquisition, and broader temperature support in a hermetic metal-can package.

Availability

LF198AH is available at Aetrix Electronics and suitable for precision data acquisition, military-grade instrumentation, and aerospace signal conditioning requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LF198AH 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 IC design and military/aerospace component qualification.

The LF198AH belongs to TI's LFx98x monolithic sample-and-hold product line, engineered for ultrahigh DC accuracy, fast acquisition, and low droop in demanding measurement and control systems where signal fidelity cannot be compromised.

FAQ

What is the maximum recommended hold capacitor value for LF198AH?

The LF198AH datasheet does not specify an absolute maximum hold capacitor value, but practical limits arise from acquisition time and droop trade-offs. With Ch = 0.01 µF, acquisition time is ≤20 µs; increasing to 1 µF reduces droop to 5 mV/min but extends acquisition time significantly. For most precision applications, 0.001 µF to 0.1 µF is optimal. The LF198AH itself supports Ch values up to several microfarads, provided drive capability and layout parasitics are managed.

Does LF198AH require external components for basic operation?

Yes - the LF198AH requires an external hold capacitor (Ch) connected directly to its Ch pin, plus decoupling capacitors on V+ and V– supplies. An optional 1-kΩ potentiometer is needed on the OFFSET ADJUST pin for DC offset trimming. No external op-amps or buffers are required, as the LF198AH operates as a self-contained unity-gain follower with integrated input and output stages.

Can LF198AH operate with single-supply configurations?

No - the LF198AH is designed exclusively for dual-supply operation from ±5 V to ±18 V. Its internal BI-FET architecture relies on symmetrical positive and negative rails to bias both bipolar and JFET sections. Single-supply use is not supported, and attempting it may cause malfunction or permanent damage due to violation of absolute maximum ratings.

What logic families are compatible with LF198AH's LOGIC input?

The LF198AH LOGIC input is fully differential and compatible with TTL, PMOS, and CMOS logic families. Its 1.4 V differential threshold allows direct interface with standard 5-V TTL outputs, 3.3-V or 5-V CMOS, and older PMOS devices. For CMOS logic with V_DD > 7 V, the threshold becomes 0.6×V_DD ±1.4 V - verified in TI's SNOSBI3C datasheet Section 7.2.

How does LF198AH handle input signals near the supply rails?

The LF198AH maintains functional integrity with input signals ranging from –V_S + 3.5 V to +V_S – 3.5 V, and its hold mode provides complete input-to-output isolation even when inputs reach ±V_S. This rail-to-rail-capable hold behavior is confirmed in the Functional Description (Section 8.4) and ensures no feedthrough occurs during hold, making LF198AH suitable for monitoring unbuffered sensor outputs or power supply monitoring circuits.