Texas Instruments LF398 MDC

Overview

LF398 MDC from Texas Instruments is a monolithic BI-FET sample-and-hold IC operating as a unity-gain follower with 0.004% typical DC gain accuracy, 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 LF398 MDC datasheet, LF398 MDC pinout, LF398 MDC application, or LF398 MDC equivalent, key selection considerations include ±5-V to ±18-V dual-supply operation, TTL/CMOS-compatible logic interface, 10 GΩ input impedance, low droop rate (5 mV/min with 1 µF capacitor), and hold-mode feedthrough rejection of 80–90 dB at 1 kHz.

Technical Context

The LF398 MDC implements a bipolar-input/JFET-output BI-FET architecture enabling simultaneous high DC accuracy and fast signal acquisition. Its differential logic interface uses a 1.4 V threshold referenced to LOGIC REFERENCE, supporting direct TTL, PMOS, and CMOS drive without level-shifting.

In sample mode, the output tracks the input via internal charge transfer to the external hold capacitor (Ch); in hold mode, the input is isolated and the output maintains the last sampled voltage with leakage-limited droop. Input offset adjustment is performed externally via a single dedicated pin without degrading drift performance.

Key Specifications

Pinout & Package

LF398 MDC is packaged in an 8-pin PDIP (P package) with 9.81 mm × 6.35 mm body size. 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 applications.

Compared with LF398N, LF398 MDC offers identical performance and mechanical fit, while AD585JN delivers superior speed and hold fidelity at the cost of non-interchangeability and stricter supply requirements.

Availability

LF398 MDC is available at Aetrix Electronics and suitable for precision data acquisition, automated test equipment, and industrial process monitoring requiring stable component supply across extended production lifecycles.

Supply support for LF398 MDC 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 U.S.-based semiconductor company specializing in analog and embedded processing technologies, with over 90 years of innovation in precision signal conditioning.

The LF398 MDC belongs to TI's legacy LFx98x monolithic sample-and-hold product line, designed specifically for high-accuracy analog capture in data converters, instrumentation, and control systems operating from 0°C to 70°C ambient.

FAQ

What is the maximum recommended hold capacitor value for LF398 MDC?

The LF398 MDC datasheet 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, droop drops to ~5 mV/min, yet acquisition time increases significantly. For most applications, 0.001 µF to 0.1 µF balances speed and stability. The LF398 MDC's output driver can safely charge/discharge up to 1 µF, though thermal rise must be monitored at high repetition rates. Always verify settling behavior with actual board layout and parasitics.

Does LF398 MDC support single-supply operation?

No, LF398 MDC requires dual-symmetric supplies (±5 V to ±18 V) and is not rated for single-supply use. Its internal BI-FET architecture relies on balanced positive and negative rails to maintain input common-mode range (–VS + 3.5 V to +VS – 3.5 V) and output swing. Attempting single-supply operation violates absolute maximum ratings and causes undefined behavior, including latch-up risk and degraded hold-step performance. The LF398 MDC must be powered from true dual rails for guaranteed specification compliance.

How does logic input slew rate affect hold step in LF398 MDC?

LF398 MDC requires a minimum logic input dV/dt of 1.0 V/µs to minimize hold step error. Slower edges cause increased charge injection during the transition, raising hold step beyond the typical 1–2.5 mV spec. This is confirmed in Section 9.1.3 of the TI datasheet. For reliable operation, ensure the driving source (e.g., microcontroller GPIO or logic gate) meets this slew rate at the LF398 MDC's LOGIC pin - not just at its output. Layout-induced RC filtering must also be minimized. The LF398 MDC's performance degrades measurably below this threshold, especially with larger hold capacitors.

Can LF398 MDC be used inside the feedback loop of an op-amp?

Yes - the LF398 MDC'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, as explicitly stated in the TI datasheet overview. This enables applications like switched-capacitor filters and precision gain-switching circuits. However, the external hold capacitor and PCB parasitics must be carefully controlled to preserve phase margin. The LF398 MDC's 10 GΩ input impedance prevents loading of high-Z nodes in such configurations, making it uniquely suited among sample-and-hold devices for this demanding topology.

What is the operating temperature range for LF398 MDC?

The LF398 MDC is specified for an operating ambient temperature range of 0°C to 70°C, consistent with the commercial-grade LF398-N variant per TI SNOSBI3C Rev C. This range is defined in Section 6.2 (Recommended Operating Conditions) and applies across all electrical parameters unless otherwise noted. Junction temperature must remain ≤100°C, and thermal derating per RθJA = 48.9°C/W (PDIP package) must be observed at elevated ambient. The LF398 MDC is not rated for extended or military temperature ranges; for –25°C to 85°C operation, LF298 is the appropriate variant.