NXP Semiconductors HEF4938BT,112

Overview

HEF4938BT,112 from NXP Semiconductors is a dual retriggerable-resettable monostable multivibrator in SO16 package, operating from 3 V to 15 V supply, delivering precise pulse widths from 10 μs to infinity via external R_EXT/C_EXT, with ±0.2 % temperature stability and Schmitt-trigger inputs tolerant of slow edges. It serves as a timing control element in digital logic systems requiring accurate, edge-triggered one-shot pulses.

For engineers reviewing the HEF4938BT,112 datasheet, HEF4938BT,112 pinout, HEF4938BT,112 application, or HEF4938BT,112 equivalent, this device supports dual independent monostable operation with active-low reset, leading/trailing-edge triggering, and LOCMOS-based precision timing for industrial control, instrumentation, and legacy logic interfacing where stable, externally programmable pulse generation is required.

Technical Context

The HEF4938BT,112 implements two independent monostable circuits using LOCMOS linear design techniques to ensure tight output pulse width accuracy (±0.2 % over −40 °C to +85 °C) and low sensitivity to supply voltage variation (±1.5 % across 5–15 V). Each channel features separate active-low direct reset (nCD), dual-edge trigger inputs (nA for falling-edge, nB for rising-edge), and complementary outputs (nQ/nQ).

Timing is fully determined by external components: t_W = R_EXT × C_EXT, with C_EXT ≥ 2000 pF and R_EXT ≥ 5 kΩ. Propagation delays range from 40 ns (15 V, CL = 0 pF) to 440 ns (5 V, CL = 50 pF), and recovery time after reset is as low as 5 ns at 15 V.

Key Specifications

Pinout & Package

HEF4938BT,112 is housed in a plastic small outline package (SO16), 16-lead, 3.9 mm body width (SOT109-1), with gull-wing leads and standard JEDEC-compliant footprint.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar monostable multivibrator applications.

Compared with 74HC4538D,653 and CD4098BE, the HEF4938BT,112 delivers superior pulse width stability (±0.2 % vs. ±5–10 %), integrated Schmitt triggers, and guaranteed minimum pulse width (12 ns at 15 V), making it optimal for industrial instrumentation and deterministic control where timing repeatability is critical.

Availability

HEF4938BT,112 is available at Aetrix Electronics and suitable for industrial timing control, legacy logic interface, instrumentation signal conditioning, and power sequencing supervisor applications requiring stable component supply across extended temperature ranges and multi-voltage environments.

Supply support for HEF4938BT,112 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

NXP Semiconductors is a global semiconductor company specializing in secure connectivity solutions for automotive, industrial, and IoT applications, with leadership in high-reliability logic, RF, and interface ICs.

The HEF4938BT,112 belongs to NXP's legacy LOCMOS logic family, designed specifically for precision timing applications demanding high accuracy, wide supply range, and robust noise immunity in industrial and instrumentation systems.

FAQ

What is the minimum external timing capacitor value supported by the HEF4938BT,112?

The HEF4938BT,112 requires a minimum external timing capacitor (C_EXT) of 2000 pF, as specified in the datasheet. Using smaller values may compromise pulse width accuracy and stability due to leakage and parasitic effects. The HEF4938BT,112 does not impose an upper limit on C_EXT, allowing flexibility for long-duration timing applications.

Can the HEF4938BT,112 generate pulses shorter than 10 μs?

Yes-the HEF4938BT,112 can produce pulses as short as 12 ns (at 15 V) for the nB-triggered path and 24 ns (at 15 V) for the nA-triggered path, per dynamic characteristics tables. The "10 μs to infinity" range refers to typical programmable widths using R_EXT/C_EXT; minimum intrinsic pulse width is governed by propagation delay and internal timing limits.

Does the HEF4938BT,112 require external pull-up or pull-down resistors on unused inputs?

Yes-unused inputs on the HEF4938BT,112 must be connected to VDD, VSS, or another driven input to prevent floating states that could cause excessive supply current or erratic behavior. This requirement is explicitly stated in the General Description section of the datasheet and applies to all inputs including nA, nB, and nCD.

How does the HEF4938BT,112 handle simultaneous trigger and reset events?

The HEF4938BT,112 gives priority to the active-low reset input (nCD): a LOW on nCD immediately terminates the output pulse regardless of concurrent trigger activity on nA or nB. This asynchronous reset behavior is confirmed in the Functional Description and Timing Diagram sections of the datasheet.

Is the HEF4938BT,112 pin-compatible with the HEF4938BP (DIP16) variant?

Yes-the HEF4938BT,112 (SO16) and HEF4938BP (DIP16) share identical pin numbering, pin functions, and electrical specifications. Both variants implement the same dual monostable functionality and timing architecture; only the package type differs. PCB layout must accommodate SO16 footprint dimensions, but no signal routing changes are needed.