Texas Instruments LF398M/NOPB

Overview

LF398M/NOPB from Texas Instruments is a monolithic BI-FET sample-and-hold IC 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 requiring stable analog signal capture before ADC conversion.

For engineers reviewing the LF398M/NOPB datasheet, LF398M/NOPB pinout, LF398M/NOPB application, or LF398M/NOPB equivalent, this page delivers verified electrical specs, PDIP-8 package mapping, TTL/CMOS-compatible logic interface details, and real-world trade-offs for hold capacitor selection, droop rate, and dynamic sampling error.

Technical Context

The LF398M/NOPB uses 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 (5 mV/min with 1 µF capacitor). Its fully differential logic interface has 1.4 V threshold and supports direct TTL/PMOS/CMOS drive without level-shifting.

In sample mode, the output tracks the input via internal amplifier charging/discharging of the external hold capacitor; in hold mode, the input is isolated and output retains the last sampled value. Logic control is referenced to LOGIC REFERENCE pin, enabling robust operation across ±5 V to ±18 V supplies with supply rejection ratio up to 110 dB.

Key Specifications

Pinout & Package

LF398M/NOPB is supplied in an 8-pin PDIP (Plastic Dual In-line Package) with body size 9.81 mm × 6.35 mm, suitable for through-hole prototyping and legacy industrial PCBs. Thermal resistance R_θJA = 48.9°C/W enables operation up to 70°C ambient without forced airflow.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LF398M/NOPB, LF398N offers identical performance with non-RoHS packaging for legacy repair, while AD585JN trades supply range and logic interface flexibility for faster acquisition and lower hold error - making it suitable only in speed-critical, fixed-supply designs.

Availability

LF398M/NOPB is available at Aetrix Electronics and suitable for precision data acquisition, test instrumentation, and industrial process control requiring stable component supply across extended product lifecycles.

Supply support for LF398M/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 leader specializing in analog and embedded processing technologies, with decades of heritage in precision analog IC design.

The LFx98x family - including LF398M/NOPB - was engineered for high-accuracy sample-and-hold functions in automated test equipment, aerospace telemetry, and calibration-grade instrumentation where DC fidelity and hold stability are non-negotiable.

FAQ

What is the maximum recommended hold capacitor value for LF398M/NOPB?

The LF398M/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 applications, 0.001–0.1 µF is optimal - balancing speed, droop, and PCB area. Larger values require careful layout to avoid stray capacitance-induced hold step.

Can LF398M/NOPB operate from a single +15 V supply?

No - the LF398M/NOPB requires dual symmetric supplies (e.g., ±5 V to ±18 V) and cannot function on a single-ended rail. Its internal BI-FET architecture relies on balanced positive and negative supply paths for input stage biasing and output swing. Attempting single-supply operation results in undefined behavior, loss of input common-mode range, and failure to enter hold mode reliably.

How does logic rise time affect hold step in LF398M/NOPB?

LF398M/NOPB requires a minimum logic dV/dt of 1.0 V/µs at the LOGIC pin to minimize hold step. Slower edges cause increased charge injection during switching, raising hold step beyond the specified 1–2.5 mV. This is especially critical when using RC-filtered logic signals - the slope at the 1.4 V threshold must exceed 1.0 V/µs, or hold step may double due to timing skew between logic transition and internal switch closure.

Is LF398M/NOPB pin-compatible with LF398N?

Yes - LF398M/NOPB and LF398N share identical PDIP-8 pinout, electrical specifications, and functional behavior. The sole difference is RoHS compliance: LF398M/NOPB uses lead-free finish per JEDEC J-STD-609, while LF398N is non-RoHS. Both are drop-in replacements in existing designs, provided soldering profiles match the respective finish requirements.

What capacitor dielectric types are recommended for Ch in LF398M/NOPB?

For LF398M/NOPB, polypropylene and polystyrene capacitors are strongly recommended due to ultra-low dielectric absorption (<0.01%), minimizing hysteresis-induced sag after hold. Teflon and NP0/C0G ceramics are acceptable for high-temperature or space-constrained layouts. Avoid mylar, polyester, and X7R ceramics - their >0.1% absorption causes measurable hold voltage decay within milliseconds, degrading DC accuracy in precision systems.