Texas Instruments LF198H

Overview

LF198H 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 Ch = 0.01 µF. It supports ±5-V to ±18-V dual supplies and is used in precision data acquisition systems requiring low droop, high input impedance (10¹⁰ Ω), and TTL/CMOS-compatible logic control.

For engineers reviewing the LF198H datasheet, LF198H pinout, LF198H application, or LF198H equivalent, this page delivers verified technical context, real-world design meaning for key specs, validated pin functions, confirmed alternative parts with functional differences, and supply support for aerospace-grade analog signal conditioning in test equipment, instrumentation, and radar subsystems.

Technical Context

The LF198H uses a bipolar input stage combined with P-channel JFET output devices to achieve low offset voltage (<3 mV typ), wide bandwidth (>1 MHz usable in op-amp feedback loops), and ultra-low hold capacitor leakage (30–100 pA). Its differential logic interface has a 1.4-V threshold and accepts TTL, PMOS, and CMOS signals without level-shifting.

In sample mode, the output tracks the input via internal charge/discharge of the external hold capacitor; in hold mode, the input is isolated and output retains the last sampled value with <5 mV/min droop (with 1-µF capacitor). Input offset is trimmed via a dedicated pin without degrading drift performance.

Key Specifications

Pinout & Package

LF198H is housed in a hermetically sealed TO-99 metal can package (9.08 mm × 9.08 mm), rated for –55°C to +125°C operation and qualified to MIL-STD-38510 (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, the LF198H offers broader temperature range and military qualification at relaxed DC specs; versus AD585SD, it trades speed for ruggedness, supply flexibility, and long-term stability in harsh environments.

Availability

LF198H is available at Aetrix Electronics and suitable for radar subsystems, aerospace instrumentation, and high-reliability test equipment requiring stable component supply, extended temperature operation, and long-lifecycle continuity.

Supply support for LF198H 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 linear ICs and military-grade components.

The LFx98x product line was designed specifically for high-fidelity analog signal conditioning in safety-critical and defense applications, emphasizing DC accuracy, thermal stability, and radiation-tolerant construction.

FAQ

What is the maximum recommended hold capacitor value for LF198H to maintain stability?

The LF198H datasheet does not specify an upper limit for the hold capacitor, but practical design guidance indicates that values above 1 µF increase acquisition time significantly and may cause thermal stress due to higher charging currents. For optimal trade-off between droop rate (<5 mV/min) and acquisition speed, 0.01 µF to 1 µF is recommended. Larger capacitors require verification of board layout and thermal dissipation per TI Application Report SBAA223.

Does LF198H support single-supply operation?

No, LF198H requires dual symmetric supplies (e.g., ±15 V) to operate correctly. Its internal architecture relies on bipolar input stages and JFET output devices that need both positive and negative rails for rail-to-rail input voltage swing and proper logic threshold referencing. Attempting single-supply use will result in undefined behavior, loss of hold mode isolation, and potential damage.

How does the OFFSET ADJUST pin function in LF198H?

The OFFSET ADJUST pin on LF198H connects to the wiper of a 1-kΩ potentiometer with one end tied to V+ and the other through a current-setting resistor to ground. This configuration injects a trimming current into the input stage to nullify input offset voltage without degrading temperature drift performance - a key advantage over resistor-divider-based offset compensation methods.

Can LF198H be used inside the feedback loop of a high-speed op-amp?

Yes, LF198H's wide bandwidth and stable phase response allow it to be placed inside the feedback loop of operational amplifiers up to 1 MHz without causing instability. This capability is explicitly validated in the TI datasheet (Section 8.1) and enables precision integrator and correlated double-sampling topologies where the S&H must respond dynamically within the loop.

What logic families are compatible with LF198H's LOGIC input?

LF198H's differential logic interface is fully compatible with TTL, PMOS, and CMOS families. The 1.4-V threshold and low input current (<10 µA) permit direct connection without level shifters. For CMOS with V_LOGIC(HI) >7 V, the threshold shifts to 0.6×V+ ±1.4 V - details are provided in Section 7.2 of the SNOSBI3C datasheet.