Texas Instruments CD74HCT4538M

Overview

CD74HCT4538M from Texas Instruments is a dual retriggerable/resettable monostable multivibrator IC used for precision timing in fixed-voltage digital systems. It delivers independent trigger/reset propagation delays (≤83 ns at 4.5 V), Schmitt-trigger inputs on A/B pins, buffered Q/Q̅ outputs, and operates across -55°C to +125°C with 4.5–5.5 V supply. It enables wide-range pulse width generation (e.g., 0.595–0.805 ms with RX = 10 kΩ, CX = 0.1 µF) in industrial control timing circuits.

For engineers reviewing the CD74HCT4538M datasheet, CD74HCT4538M pinout, CD74HCT4538M application, or CD74HCT4538M equivalent, this page provides verified functional identity, SOIC-16 package mapping, timing parameter validation, reset/trigger edge behavior, and direct LSTTL-compatible input thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V) critical for legacy interface integration and high-reliability timing design.

Technical Context

The CD74HCT4538M implements two independent monostable sections, each with separate A (leading-edge) and B (trailing-edge) trigger inputs, dedicated R reset terminals, and external RC timing networks (RX/CX). Propagation delays from A/B or R to Q/Q̅ are fully independent of RX and CX values, ensuring stable timing accuracy across pulse-width adjustments.

Each section supports retriggerable operation (pulse width extends on successive triggers) or non-retriggerable mode via internal feedback (Q→B for A-triggered, Q→A for B-triggered). Schmitt-trigger inputs provide noise immunity, while buffered complementary outputs drive up to 10 LSTTL loads over full temperature range.

Key Specifications

Pinout & Package

CD74HCT4538M is housed in a 16-pin SOIC (D) package (7.4 mm × 10.3 mm, 1.75 mm height), RoHS-compliant with NIPDAU lead finish and moisture sensitivity level (MSL) 1 (260°C peak reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC4538M and SN74LS221N, the CD74HCT4538M uniquely combines LSTTL input compatibility, -55°C to +125°C operation, Schmitt-trigger noise immunity, and retriggerable precision timing - making it the sole choice for new ruggedized digital timing designs requiring legacy interface support.

Availability

CD74HCT4538M is available at Aetrix Electronics and suitable for industrial motor control, automotive powertrain timing, test equipment pulse generation, and avionics watchdog circuits requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HCT4538M 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 over 90 years of innovation in high-reliability IC design and manufacturing.

The CD74HCT4538M belongs to TI's HCT logic family, engineered specifically for seamless integration into legacy 5 V TTL-based systems while delivering CMOS power efficiency and extended temperature performance.

FAQ

What is the minimum external timing resistor value supported by the CD74HCT4538M?

The CD74HCT4538M specifies a minimum external timing resistor (RX) of 5 kΩ. Using lower values risks exceeding the maximum allowable current (30 mA) into pins 2 or 14, potentially causing timing inaccuracy or device stress. This limit ensures stable operation across -55°C to +125°C and maintains specified pulse width accuracy per the τ = 0.7·RX·CX formula. Always verify current compliance when selecting RX for CD74HCT4538M designs.

Can the CD74HCT4538M operate with zero external timing capacitance (CX = 0 pF)?

Yes, the CD74HCT4538M supports CX = 0 pF as specified in its datasheet. In this configuration, timing relies solely on internal device characteristics and RX value, enabling minimal-component timing solutions. However, pulse width becomes more sensitive to supply voltage and temperature variations compared to RC-based configurations. For CD74HCT4538M designs requiring high stability, use CX ≥ 100 pF with appropriate RX scaling per the K-factor curves in Figure 10.

How does the retriggerable mode function differ from non-retriggerable mode in the CD74HCT4538M?

In retriggerable mode, each new trigger pulse (on A or B) extends the output pulse width by a full τ period - ideal for detecting ongoing activity like encoder rotation. In non-retriggerable mode, the output pulse starts at the first trigger and ignores subsequent triggers until completion - used for fixed-duration events like ADC conversion windows. The CD74HCT4538M achieves non-retriggerable behavior by feeding Q to B (for A-triggered) or Q to A (for B-triggered), a hardware-configured function requiring no external logic.

Is the CD74HCT4538M pin-compatible with the CD74HC4538M?

Yes, the CD74HCT4538M and CD74HC4538M share identical SOIC-16 pinouts, terminal functions, and package dimensions. However, they are not functionally interchangeable without circuit review: CD74HCT4538M has LSTTL-compatible inputs (VIH ≥ 2.0 V), while CD74HC4538M requires VIH ≥ 3.15 V at 4.5 V. Swapping them may cause logic misreads in 5 V TTL systems. Always validate input threshold compatibility before substituting CD74HCT4538M with CD74HC4538M.

What thermal considerations apply to the CD74HCT4538M in SOIC package?

The CD74HCT4538M in SOIC (D) package has a thermal impedance θJA of 73°C/W. At maximum ambient temperature (+125°C) and worst-case active current (1 mA), junction temperature rise remains within safe limits (<150°C) with standard PCB copper area. However, for sustained high-frequency operation (>1 MHz trigger rates), add thermal relief traces and local ground plane beneath the package. Avoid placing heat-generating components adjacent to CD74HCT4538M to prevent derating of its -55°C to +125°C specification.