Texas Instruments CD74HCT4538MT

Overview

CD74HCT4538MT 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 (55 ns typical at 5 V), Schmitt-trigger inputs on A/B pins, buffered Q/Q̅ outputs, and supports output pulse widths from microseconds to milliseconds via external RX/CX components. It operates across -55°C to +125°C and is widely deployed in industrial control sequencers and pulse-width modulation circuits.

For engineers reviewing the CD74HCT4538MT datasheet, CD74HCT4538MT pinout, CD74HCT4538MT application, or CD74HCT4538MT equivalent, key selection criteria include its HCT-level LSTTL input compatibility (VIH ≥ 2 V, VIL ≤ 0.8 V), 16-pin SOIC package, dual-section independent reset capability, and retrigger time independence from CX value - critical for jitter-sensitive edge-triggered timing functions.

Technical Context

The CD74HCT4538MT implements two independent monostable sections, 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 CMOS logic with TTL-compatible input thresholds and Schmitt-trigger hysteresis on A/B inputs to reject noise on slow-rising signals.

Timing is externally controlled by resistor RX and capacitor CX per section, with pulse width τ ≈ 0.7 × RX × CX. Propagation delays from A/B or R to Q/Q̅ are independent of RX and CX values, ensuring stable timing accuracy across wide component tolerances and temperature ranges (-55°C to +125°C).

Key Specifications

Pinout & Package

CD74HCT4538MT is housed in a 16-pin SOIC (D) package, 7.5 mm × 10.3 mm body size, 1.75 mm max height, with 1.27 mm pitch gull-wing leads. Pin 1 is marked by a beveled corner or notch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HCT4538MT, CD74HC4538M96 offers broader voltage operation but requires careful input threshold validation, while SN74LS423N sacrifices retrigger control and noise rejection for raw TTL interoperability - making CD74HCT4538MT optimal for new designs demanding robust edge-triggered timing in industrial 5 V environments.

Availability

CD74HCT4538MT is available at Aetrix Electronics and suitable for industrial motor control sequencers, automotive ignition calibration modules, and medical imaging signal gating systems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HCT4538MT 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 components.

The CD74HCT4538MT belongs to TI's High-Speed CMOS Logic family, designed specifically for precision timing applications requiring TTL-compatible inputs, wide temperature operation, and deterministic retrigger behavior in industrial and automotive control systems.

FAQ

What is the recommended external timing capacitor range for stable operation of CD74HCT4538MT?

The CD74HCT4538MT supports CX values from 0 pF minimum up to practical limits governed by leakage and board parasitics. For stable operation, TI recommends CX ≥ 100 pF when RX ≤ 1 MΩ to minimize susceptibility to noise. At CX = 0.1 µF and RX = 10 kΩ, CD74HCT4538MT delivers a nominal pulse width of 0.63 ms with ±1% match between sections. Always use NP0/C0G dielectric capacitors for best temperature stability.

Can CD74HCT4538MT operate reliably at 125°C ambient temperature?

Yes, CD74HCT4538MT is fully specified and tested for continuous operation from -55°C to +125°C ambient. Its absolute maximum junction temperature is 150°C, and thermal resistance θJA for the SOIC package is 73°C/W. With proper PCB copper pour and ≤10 mA average output current, CD74HCT4538MT maintains timing accuracy and logic integrity across the full military-grade temperature range.

How does the retrigger time specification impact multi-pulse applications using CD74HCT4538MT?

The CD74HCT4538MT has a maximum retrigger time of 175 ns, meaning it can accept new trigger events no sooner than 175 ns after the prior trigger without missing or distorting the output pulse. This enables reliable operation in burst-mode applications such as encoder pulse stretching or PWM edge synchronization, provided input pulse spacing exceeds this limit. For tighter intervals, external synchronization logic may be required.

Is CD74HCT4538MT pin-compatible with CD74HC4538M96?

Yes, CD74HCT4538MT and CD74HC4538M96 share identical 16-pin SOIC (D) packages and pinouts, including matching terminal functions for RXCX, A, B, R, Q, Q̅, VCC, and GND. However, they differ electrically: CD74HCT4538MT requires 4.5–5.5 V and matches LSTTL input thresholds, while CD74HC4538M96 operates from 2–6 V with VCC-referenced thresholds. Direct substitution is possible only if supply and driver compatibility are verified.

What failure modes should be considered when using large timing capacitors (>0.5 µF) with CD74HCT4538MT?

When CX ≥ 0.5 µF, rapid power-down events can cause stored energy to discharge into pins 2 or 14 (RXCX), risking latch-up or oxide damage. TI recommends adding a 1 A protection diode (e.g., 1N5395) between RXCX and ground, or a 51 Ω series current-limiting resistor. Failure to implement protection may result in premature device failure during brown-out or short-circuit conditions - a documented design requirement for CD74HCT4538MT in high-reliability systems.