Nexperia USA Inc. 74HCT4538D,118

Overview

74HCT4538D,118 from Nexperia is a dual retriggerable-resettable precision monostable multivibrator in SO16 package, delivering ±0.2 % pulse width stability over temperature, edge-triggered operation (rising or falling), and 0.7 × REXT × CEXT output timing with independent reset per channel. It serves in digital timing control, pulse shaping, and debounce circuits for industrial PLCs and instrumentation.

For engineers reviewing the 74HCT4538D,118 datasheet, 74HCT4538D,118 pinout, 74HCT4538D,118 application, or 74HCT4538D,118 equivalent, key selection factors include external timing component dependency, Schmitt-trigger input tolerance, TTL-compatible logic levels, -40 °C to +125 °C operating range, and dual-channel independent reset capability.

Technical Context

This device implements two independent monostable circuits, each with dual trigger inputs (nA active-low, nB active-high), direct active-low reset (nCD), complementary outputs (nQ/nQ), and external REXT/CEXT timing network. Pulse width is strictly determined by analog RC values-not internal oscillators-enabling programmable delays from microseconds to seconds.

Each channel features Schmitt-trigger inputs for noise immunity against slow edges, clamp diodes enabling overvoltage-tolerant interfacing, and power-down protection guidance for CEXT discharge management. The circuit operates only within 4.5 V to 5.5 V supply range and is not internally compensated for voltage or temperature drift-accuracy relies on external component selection and layout.

Key Specifications

Pinout & Package

74HCT4538D,118 uses SO16 (SOT109-1) plastic small outline package: 16-pin, 3.9 mm body width, 1.27 mm pitch, surface-mount, JEDEC MS-012 compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HCT4538PW, the 74HCT4538D,118 offers superior mechanical robustness and thermal derating margin for high-temperature industrial use; versus SN74LS4538N, it delivers 90% lower quiescent current, Schmitt-trigger noise immunity, and tighter pulse accuracy-critical for modern embedded timing.

Availability

74HCT4538D,118 is available at Aetrix Electronics and suitable for industrial automation, test instrumentation, and safety-critical timing applications requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for 74HCT4538D,118 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

Nexperia is a global semiconductor expert focused on essential efficiency technologies, delivering high-performance logic, analog, and MOSFET solutions for automotive, industrial, and consumer markets.

The 74HCT4538 belongs to Nexperia's HCT logic family-designed specifically for TTL-compatible 5 V systems requiring CMOS power efficiency, robust noise immunity, and extended temperature operation without performance compromise.

FAQ

What is the minimum and maximum external timing resistor value supported?

The datasheet specifies REXT from 2 kΩ to 1 MΩ at VCC = 5.0 V. Below 2 kΩ, timing accuracy degrades due to internal node loading; above 1 MΩ, leakage current and noise sensitivity increase pulse width uncertainty. For sub-microsecond pulses, use REXT ≤10 kΩ with CEXT ≤100 pF.

Can both trigger inputs (nA and nB) be used simultaneously on one channel?

Yes-nA (active-low) and nB (active-high) are logically OR'd internally. A valid edge on either input initiates or retriggers the monostable. This allows flexible edge detection without external gates, but simultaneous assertion has no additional effect beyond a single trigger event.

Is the 74HCT4538D,118 qualified for automotive applications?

No. The device is specified for -40 °C to +125 °C industrial operation but is not AEC-Q100 qualified, lacks automotive-specific reliability testing, and carries no automotive warranty. Nexperia explicitly states non-automotive qualification in its legal disclaimers.

How does power-down affect the external timing capacitor (CEXT)?

During rapid VCC collapse, stored energy in CEXT can discharge through input clamp diodes, risking latch-up or damage. Nexperia recommends adding a Schottky damping diode (DEXT) between nREXT/CEXT and GND, as shown in Figure 10, to safely bleed charge and protect internal junctions.