Texas Instruments CD74HCT221EG4

Overview

CD74HCT221EG4 from Texas Instruments is a dual monostable multivibrator with independent reset, Schmitt-trigger B inputs, and buffered Q/Q̅ outputs. It operates from 4.5V to 5.5V, supports -55°C to +125°C ambient range, delivers pulse widths from ~140 ns to >800 µs via external RX/CX networks, and is used in precision timing control, edge-triggered event capture, and reset-synchronized waveform generation in industrial control systems.

For engineers reviewing the CD74HCT221EG4 datasheet, CD74HCT221EG4 pinout, CD74HCT221EG4 application, or CD74HCT221EG4 equivalent, key selection considerations include its HCT-level LSTTL input compatibility (VIH ≥ 2.0 V, VIL ≤ 0.8 V), dual-edge triggering (A = trailing, B = leading), overriding reset functionality, ±2% pulse width matching between internal monostables, and PDIP-16 package suitability for prototyping and high-reliability legacy designs.

Technical Context

The CD74HCT221EG4 integrates two independent monostable circuits, each with separate A (trailing-edge), B (leading-edge), and R (active-low reset) inputs. Triggering initiates a single-shot output pulse whose width is determined by external RX and CX components using t_W ≈ 0.7·R_XC_X at V_CC = 4.5 V. Once triggered, outputs remain unaffected by further A/B transitions until reset.

Its HCT logic family ensures direct interface with standard TTL outputs while maintaining CMOS power efficiency. The Schmitt-trigger on B inputs enables robust noise immunity for slow-rising signals, and the overriding reset terminates the output pulse immediately regardless of timing state - critical for fault recovery in safety-critical timing paths.

Key Specifications

Pinout & Package

CD74HCT221EG4 is supplied in a 16-pin plastic dual in-line package (PDIP) with 0.3-inch body width and through-hole mounting. Pin spacing is 0.1 inch (2.54 mm), and the package conforms to JEDEC MS-001.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC221E and SN74LS221N, CD74HCT221EG4 uniquely combines LSTTL input compatibility, overriding reset, Schmitt-trigger B inputs, and ±2% inter-monostable pulse matching - making it the optimal choice for new 5 V industrial and automotive timing designs requiring robustness and configurability.

Availability

CD74HCT221EG4 is available at Aetrix Electronics and suitable for industrial automation, aerospace avionics, and automotive engine control applications requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HCT221EG4 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.

The CD74HCT221EG4 belongs to TI's High-Speed CMOS Logic family, engineered for robust timing control in harsh environments - emphasizing precision pulse generation, noise immunity, and seamless integration with legacy TTL systems.

FAQ

What is the minimum external timing resistor value supported by CD74HCT221EG4?

The CD74HCT221EG4 specifies a minimum external timing resistor (RX) value of 500 Ω. Using lower values may cause excessive current draw, timing inaccuracy, or potential damage to the internal timing circuitry. This limit ensures stable operation across the full -55°C to +125°C temperature range and maintains specified pulse width accuracy per the t_W = 0.7·R_XC_X formula.

Does CD74HCT221EG4 support both rising- and falling-edge triggering on the same input pin?

No. CD74HCT221EG4 provides dedicated edge sensitivity per input: pin 1A/9A responds only to falling edges (trailing-edge trigger), while pin 1B/10B responds only to rising edges (leading-edge trigger). This separation prevents ambiguity and ensures deterministic timing behavior - critical for reliable event capture in real-time control systems.

Can CD74HCT221EG4 operate with a 3.3 V supply?

No. CD74HCT221EG4 is an HCT-family device with a specified supply range of 4.5 V to 5.5 V. Operation below 4.5 V violates the absolute minimum VCC rating and will result in undefined logic levels, unreliable triggering, and failure to meet VIH/VIL thresholds for LSTTL compatibility. For 3.3 V systems, consider HC-family alternatives like CD74HC221E with appropriate level translation.

How does the overriding reset function behave during an active output pulse?

When the reset pin (1R or 2R) is driven LOW during an active output pulse, CD74HCT221EG4 immediately forces Q = LOW and Q̅ = HIGH, terminating the pulse regardless of its remaining duration. This overriding behavior occurs with zero propagation delay (t_SU = 0 ns), enabling deterministic fault response - a key requirement in safety-critical timing applications such as motor emergency stop circuits.

Is the CD74HCT221EG4 RoHS compliant?

Yes. CD74HCT221EG4 is RoHS compliant, as confirmed by Texas Instruments' packaging documentation. The device uses NiPdAu (NIPDAU) lead finish and meets EU Directive 2011/65/EU requirements. Its PDIP package is exempt from lead-free reflow profile constraints due to its through-hole construction, but full compliance applies to material content and restricted substances.