Texas Instruments CD54HC4538F

Overview

CD54HC4538F from Texas Instruments is a dual retriggerable/resettable monostable multivibrator in the HC logic family, designed for precision timing applications requiring stable pulse generation across extreme temperatures. It delivers independent trigger/reset propagation delays (e.g., 50 ns at 4.5 V), Schmitt-trigger inputs on A/B pins, buffered Q/Q̅ outputs, and operates from 2 V to 6 V over –55 °C to +125 °C - used in aerospace power sequencing and military radar pulse shaping.

For engineers reviewing the CD54HC4538F datasheet, CD54HC4538F pinout, CD54HC4538F application, or CD54HC4538F equivalent, key selection criteria include its CERDIP-16 package, retrigger time independence from CX, wide output pulse width range (calculated as τ ≈ 0.7·RX·CX), and compatibility with external timing networks for deterministic delay control in high-reliability systems.

Technical Context

The CD54HC4538F implements two independent monostable circuits, each with separate A (leading-edge) and B (trailing-edge) trigger inputs, dedicated R reset terminals, and dual buffered Q/Q̅ outputs. Its internal architecture uses Schmitt-trigger input stages and CMOS-compatible output drivers, enabling noise-immune edge detection and fanout of 10 LSTTL loads.

Timing is externally controlled via RX and CX components per section, with propagation delays from A/B or R to Q/Q̅ fully independent of RX/CX values - ensuring consistent timing accuracy regardless of external component tolerances. Retrigger capability allows pulse extension on successive triggers, while non-retriggerable mode is enabled by feedback wiring (Q→B or Q→A).

Key Specifications

Pinout & Package

CD54HC4538F is housed in a 16-lead CERDIP (Ceramic Dual In-line Package) with hermetic sealing and SNPB lead finish, rated for military-grade reliability and long-term storage stability.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC4538E and CD54HCT4538F3A, the CD54HC4538F uniquely combines military-grade temperature operation, wide 2–6 V supply flexibility, and HC-family noise immunity - making it the sole option for high-reliability mixed-voltage timing in aerospace and defense platforms.

Availability

CD54HC4538F is available at Aetrix Electronics and suitable for avionics timing control, military radar pulse shaping, and spacecraft power sequencing requiring stable component supply under extended temperature stress and long-life deployment.

Supply support for CD54HC4538F 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, embedded processing, and logic solutions with decades of heritage in high-reliability military and aerospace components.

The CD54HC4538F belongs to TI's military-grade HC logic family, engineered specifically for precision timing in mission-critical systems where deterministic pulse generation, thermal resilience, and long-term parametric stability are non-negotiable.

FAQ

What is the maximum allowable external timing capacitor value for CD54HC4538F?

The CD54HC4538F datasheet does not specify an absolute maximum CX value, but notes that leakage currents in CX, the device, and PCB layout affect timing accuracy. For reliable operation, CX should be selected so that current into pin 2 or 14 remains below 30 mA. Practical designs typically limit CX to ≤10 µF to maintain stability and avoid excessive retrigger time degradation above 100 pF.

Can CD54HC4538F operate reliably at 3.3 V supply voltage?

Yes, CD54HC4538F supports 2 V to 6 V operation per its HC-family specification. At 3.3 V, it delivers guaranteed propagation delays (e.g., 63 ns max A→Q), Schmitt-trigger input thresholds (~1.0 V and ~2.3 V), and full fanout capability - making it suitable for mixed-voltage systems interfacing with 3.3 V microcontrollers or FPGAs without level translation.

How is retrigger time defined for CD54HC4538F, and what factors influence it?

Retrigger time (trT) for CD54HC4538F is the minimum interval between successive trigger pulses that ensures full pulse width regeneration - specified as 175 ns typical at 5 V. It is independent of CX value and determined solely by internal logic propagation; external RX/CX affect only output pulse width, not retrigger timing. This enables robust operation in high-frequency pulse trains.

What is the recommended protection method for CD54HC4538F when using CX ≥ 0.5 µF?

When CX ≥ 0.5 µF, TI recommends adding a 1 A-rated protection diode (e.g., 1N5395) between pin 2/14 and ground to prevent reverse-current damage during rapid power-down events. Alternatively, a 51 Ω series current-limiting resistor may be used, though this reduces pulse width slightly and requires RX adjustment to compensate - verified in Figure 13 of the CD54HC4538F datasheet.

Does CD54HC4538F support non-retriggerable one-shot operation, and how is it configured?

Yes, CD54HC4538F supports non-retriggerable mode. To configure Monostable 1 for non-retriggerable operation with leading-edge trigger (A), connect Q1 output to B1 input. For trailing-edge trigger (B), connect Q1 to A1. This feedback forces the monostable to ignore subsequent triggers until the initial pulse completes - useful for fixed-interval timing in watchdog or timeout circuits.