Nexperia USA Inc. 74HCT4538DB,118

Overview

74HCT4538DB,118 from Nexperia is a dual retriggerable precision monostable multivibrator in SO16 (SOT109-1) package, operating from 4.5 V to 5.5 V, delivering ±0.2 % pulse width stability over temperature, with 0.7 × REXT × CEXT timing accuracy and Schmitt-trigger inputs tolerant of slow edges. It serves as a precision timing generator in digital control circuits requiring edge-triggered, resettable one-shot pulses.

For engineers reviewing the 74HCT4538DB,118 datasheet, 74HCT4538DB,118 pinout, 74HCT4538DB,118 application, or 74HCT4538DB,118 equivalent, key selection criteria include external R/C-timed pulse width accuracy, dual independent monostable operation, active-low direct reset per channel, retriggerability during output pulse, and compatibility with 5 V TTL-level systems.

Technical Context

This device implements two independent CMOS monostable multivibrators, each with dual trigger inputs (nA for falling-edge, nB for rising-edge), a dedicated active-low reset (nCD), complementary outputs (nQ/nQ), and external timing pins (nREXT/CEXT and nCEXT). Pulse width is linearly determined by external REXT and CEXT values.

Its architecture supports retriggering mid-pulse without requiring pulse termination, enabling dynamic pulse extension in real-time control loops. The Schmitt-trigger inputs ensure reliable triggering even with noisy or slow-rising signals, while clamp diodes allow interfacing to voltages exceeding VCC via current-limiting resistors.

Key Specifications

Pinout & Package

74HCT4538DB,118 is housed in a plastic small outline package (SO16, SOT109-1) with 16 leads and 3.9 mm body width, optimized for automated PCB assembly and thermal performance in dense layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HCT4538DB,118, the 74HC4538D,118 offers broader voltage flexibility but weaker noise immunity and no TTL-level compatibility, while the SN74LS4538N delivers predictable legacy timing at higher power and reduced precision-making the HCT variant optimal for modern 5 V digital systems demanding accuracy, retriggerability, and robustness.

Availability

74HCT4538DB,118 is available at Aetrix Electronics and suitable for motor control timing, industrial PLC input conditioning, automotive diagnostic signaling, and automated test equipment requiring stable component supply across extended temperature ranges.

Supply support for 74HCT4538DB,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 specializing in high-performance, energy-efficient logic, analog, and discrete components, with leadership in automotive-grade reliability and industrial qualification.

The 74HCT4538 belongs to Nexperia's high-speed TTL-compatible logic family, designed specifically for robust, precision timing in 5 V digital systems where retriggerability, temperature stability, and noise immunity are critical.

FAQ

What is the minimum and maximum external timing resistor value for stable operation?

The datasheet specifies REXT from 2 kΩ to 1000 kΩ at VCC = 5.0 V. Operation below 2 kΩ risks excessive current through the timing node and potential latch-up; above 1000 kΩ increases sensitivity to leakage and noise, degrading pulse width accuracy. For best stability, use 10 kΩ to 100 kΩ with CEXT ≥ 100 pF.

Can 74HCT4538DB,118 be used with 3.3 V logic signals?

No - the 74HCT4538DB,118 is TTL-compatible and specified only for 4.5 V to 5.5 V supply. Its input thresholds (VIH ≈ 2.0 V, VIL ≈ 0.8 V) are optimized for 5 V systems. For 3.3 V interfaces, use level shifters or select the 74HC4538D,118, which supports 2.0–6.0 V operation with CMOS thresholds.

How does the retrigger function behave when a new trigger arrives mid-pulse?

When a valid trigger (on nA or nB) occurs while the output pulse is active, the monostable restarts its timing cycle from zero - extending the total output pulse width by the full TW interval. This retriggering is fully asynchronous and does not require the prior pulse to complete or be reset first.

Is an external capacitor required on the nCEXT pin, and what happens if it's omitted?

Yes - nCEXT (Pins 1 and 15) must be connected directly to GND via a low-inductance path. Omitting this connection prevents proper charging/discharging of the internal timing node, resulting in undefined or non-functional pulse generation. A 100 nF ceramic capacitor to GND is recommended for noise suppression.