Texas Instruments CD74HC4538MT

Overview

CD74HC4538MT from Texas Instruments is a dual retriggerable/resettable monostable multivibrator IC used for precision timing in digital systems. It delivers independent trigger/reset propagation delays (e.g., 50 ns at VCC = 4.5 V), supports leading- and trailing-edge triggering on separate A/B inputs, provides buffered Q/Q outputs, and operates across -55°C to +125°C with 2V–6V supply. It enables adjustable pulse widths via external RX/CX networks in industrial control sequencers and pulse-width modulation circuits.

For engineers reviewing the CD74HC4538MT datasheet, CD74HC4538MT pinout, CD74HC4538MT application, or CD74HC4538MT equivalent, key selection criteria include retriggerable timing behavior, Schmitt-trigger input hysteresis (30% noise immunity), SOIC-16 package thermal resistance (73°C/W), and compatibility with HC logic families requiring low-power CMOS-level interfacing.

Technical Context

The CD74HC4538MT 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/Q outputs. Timing is set externally via RX (≥5 kΩ) and CX (≥0 pF), with pulse width τ ≈ 0.7·RX·CX - propagation delays from A/B or R to Q/Q are independent of RX/CX values.

Each section features Schmitt-trigger inputs for noise immunity, fanout capability of 10 LSTTL loads, and balanced transition times. The device enters power-up reset state and requires proper termination of unused A/B/R pins: A tied to GND, B to VCC, and R to GND when inactive.

Key Specifications

Pinout & Package

CD74HC4538MT is housed in a 16-pin SOIC (Small Outline Integrated Circuit) package with 1.27 mm pitch, 10.4 mm × 7.4 mm body size, and 2.00 mm max height per TI SOP drawing NS0016A.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC4538MT, CD74HC4538M96 offers identical functionality with scalable packaging for volume manufacturing, while SN74LV4538A trades Schmitt-trigger robustness for lower-voltage operation and faster propagation - making it appropriate for modern low-power digital systems but unsuitable for high-noise legacy environments.

Availability

CD74HC4538MT is available at Aetrix Electronics and suitable for industrial control sequencers, PLC watchdog timers, edge-selective sensor interfaces, and power sequencing controllers requiring stable component supply across extended temperature ranges.

Supply support for CD74HC4538MT 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 50 years of innovation in high-reliability timing and interface ICs.

The CD74HC4538MT belongs to TI's HC-series high-speed CMOS logic family, designed specifically for precision timing applications demanding wide temperature operation, low power, and noise-immune triggering in industrial and defense systems.

FAQ

What is the recommended external timing capacitor range for CD74HC4538MT?

The CD74HC4538MT supports CX ≥ 0 pF, with practical lower limit defined by leakage and board parasitics. For reliable operation, TI recommends CX ≥ 100 pF when RX ≤ 1 MΩ. At CX = 0.1 µF and RX = 10 kΩ, measured pulse width is 0.63–0.81 ms across -55°C to +125°C. Larger CX values extend timing but increase susceptibility to leakage-induced drift.

Can CD74HC4538MT operate with a 3.3 V supply?

Yes, CD74HC4538MT operates across 2V–6V, including 3.3 V nominal supplies. At VCC = 3.3 V, VIH = 2.31 V (min), VIL = 0.99 V (max), and propagation delay increases to ~75 ns (max) versus 50 ns at 4.5 V. All timing parameters remain fully specified and guaranteed over temperature.

How should unused trigger inputs be terminated on CD74HC4538MT?

Unused A inputs must be tied to GND; unused B inputs must be tied to VCC. Leaving them floating violates the absolute maximum rating for input current and may cause erratic triggering or increased ICC. Unused R inputs must also be tied to GND to prevent unintended reset assertion.

Is CD74HC4538MT pin-compatible with CD74HCT4538MT?

No - CD74HC4538MT and CD74HCT4538MT share identical pinout and package (SOIC-16), but differ in input logic thresholds and supply range. HC types accept 2V–6V with CMOS-compatible inputs; HCT types require 4.5V–5.5V and feature TTL-compatible inputs (VIH = 2.0 V min). Interchange requires verification of system VCC and input driver compatibility.

Does CD74HC4538MT support non-retriggerable mode?

Yes, CD74HC4538MT can be configured for non-retriggerable operation: connect Q to B when using A (leading-edge) triggering, or connect Q to A when using B (trailing-edge) triggering. This feedback forces the monostable to ignore subsequent triggers until the initial pulse completes - verified in Figure 5 of the datasheet.