Texas Instruments LF398H/NOPB

Overview

LF398H/NOPB from Texas Instruments is a monolithic BI-FET sample-and-hold amplifier operating as a unity-gain follower with 0.004% typical DC gain error, 20 µs acquisition time to 0.1% with 0.01 µF hold capacitor, and 1 mV typical hold step - used in precision data acquisition systems for analog-to-digital conversion timing control.

For engineers reviewing the LF398H/NOPB datasheet, LF398H/NOPB pinout, LF398H/NOPB application, or LF398H/NOPB equivalent, key selection criteria include hold-step sensitivity to logic coupling, droop rate dependence on external capacitor dielectric, input impedance stability during hold mode, and ±5-V to ±18-V dual-supply operation across 0°C to +70°C ambient range.

Technical Context

The LF398H/NOPB implements a bipolar input stage combined with P-channel JFET output devices to achieve low offset voltage (2–7 mV typ), high input impedance (10¹⁰ Ω), and low droop rate (e.g., 5 mV/min with 1 µF capacitor). Its differential logic interface accepts TTL/CMOS-compatible signals with 1.4 V threshold and supports direct connection without level-shifting.

Functional mode switching between sample and hold is controlled by the relative voltage of LOGIC pin to LOGIC REFERENCE pin. During hold, the input is fully isolated from the output path, eliminating feedthrough even at supply-rail input levels; acquisition dynamics are governed by internal 300-Ω series resistance into the external hold capacitor.

Key Specifications

Pinout & Package

LF398H/NOPB is packaged in an 8-pin PDIP (P package) with 9.81 mm × 6.35 mm body size and through-hole mounting. Pin functions are validated per TI SNOSBI3C Rev C datasheet.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LF398H/NOPB, LF398N offers identical electrical behavior with non-RoHS packaging, while AD585SQ delivers lower hold step at the cost of added external components and narrower commercial temperature support.

Availability

LF398H/NOPB is available at Aetrix Electronics and suitable for precision data acquisition, analog front-end calibration, and synchronous signal processing requiring stable component supply across industrial and test equipment lifecycles.

Supply support for LF398H/NOPB 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 company specializing in analog and embedded processing technologies, with leadership in precision signal chain components since the 1960s.

The LFx98x product line was designed specifically for high-fidelity sample-and-hold applications in data converters, instrumentation, and radar signal conditioning - emphasizing DC accuracy, low droop, and logic interface robustness.

FAQ

What is the maximum recommended hold capacitor value for LF398H/NOPB?

The LF398H/NOPB does not specify an absolute maximum hold capacitor value, but practical limits arise from acquisition time and droop trade-offs. With a 1 µF capacitor, acquisition time extends beyond 100 µs and droop drops to ~5 mV/min. For most 12–16-bit systems, 0.001 µF to 0.1 µF is optimal. Larger values require careful layout to minimize stray coupling that increases hold step - always use low-dielectric-absorption types like polypropylene or C0G ceramic.

Does LF398H/NOPB support single-supply operation?

No, LF398H/NOPB requires dual symmetric supplies (±5 V to ±18 V) and is not rated for single-supply use. The internal BI-FET architecture depends on balanced positive and negative rails to bias both bipolar and JFET stages correctly. Attempting single-supply operation risks latch-up, increased offset, or permanent damage due to violation of absolute maximum ratings on input and supply pins.

How does logic signal rise time affect hold step in LF398H/NOPB?

LF398H/NOPB requires a minimum logic signal dV/dt of 1.0 V/µs at the LOGIC pin to limit hold step error. Slower edges cause incomplete switching of the internal JFET sample gate during the critical aperture window, increasing hold step by up to 3×. This is especially critical when using RC-filtered logic or long PCB traces - always verify edge rate at the pin with a scope, not at the driver output.

Can LF398H/NOPB be used inside the feedback loop of a high-speed op-amp?

Yes - the LF398H/NOPB's wide bandwidth (enabled by its bipolar input stage) allows stable inclusion within the feedback loop of op-amps up to 1 MHz, as confirmed in TI's application notes. However, phase margin must be verified per specific op-amp model and gain configuration; avoid placing it in loops with dominant poles below 100 kHz unless compensated. The LF398H/NOPB itself contributes minimal phase lag in sample mode.

What is the role of the OFFSET ADJUST pin on LF398H/NOPB?

The OFFSET ADJUST pin on LF398H/NOPB provides a dedicated connection for nulling input stage DC offset voltage using a 1 kΩ potentiometer tied between V+ and ground. Unlike conventional op-amp offset trims, this method does not degrade input offset drift over temperature. It directly adjusts the bipolar input stage bias, enabling <1 mV residual offset after calibration - critical for DC-coupled precision measurement paths involving LF398H/NOPB.