Texas Instruments CD74HC221E

Overview

CD74HC221E from Texas Instruments is a dual monostable multivibrator with independent reset, Schmitt-trigger B inputs, and buffered Q/Q̅ outputs. It operates from 2V to 6V, supports -55°C to +125°C temperature range, and delivers pulse widths from nanoseconds to microseconds via external RX/CX timing components. It is used in precision timing control, debouncing, and edge-triggered event generation in industrial control and test equipment.

For engineers reviewing the CD74HC221E datasheet, CD74HC221E pinout, CD74HC221E application, or CD74HC221E equivalent, key selection considerations include its dual independent monostable architecture, leading/trailing-edge triggering flexibility, overriding reset functionality, wide VCC range, and guaranteed operation across extended temperature extremes.

Technical Context

The CD74HC221E implements two fully independent monostable circuits, each with separate A (edge-trigger), B (Schmitt-trigger level-sensitive), and R (asynchronous active-low reset) inputs. Triggering is decoupled: once triggered, outputs remain stable regardless of further A/B transitions.

Timing is externally set by resistor RX and capacitor CX per channel, with pulse width t_W = 0.7·R_XC_X at V_CC = 4.5V. Propagation delays are specified down to 12 ns (t_PLH/t_PHL, V_CC = 6V, C_L = 50 pF), and input rise/fall times on B inputs are unrestricted - enabling compatibility with slow or noisy signals.

Key Specifications

Pinout & Package

CD74HC221E is supplied in a 16-lead plastic dual in-line package (PDIP), with 0.3-inch body width and standard through-hole footprint. Pin 1 is located at the top-left corner adjacent to the notch or dot marking.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HCT221E and SN74LV221A, CD74HC221E uniquely combines wide-voltage operation (2–6V), Schmitt-trigger B inputs for noise immunity, and full extended-temperature qualification - making it the only option for ruggedized, mixed-voltage, or mechanically noisy timing applications.

Availability

CD74HC221E is available at Aetrix Electronics and suitable for industrial control systems, aerospace avionics, and automotive test equipment requiring stable component supply across extreme temperature ranges and long production lifecycles.

Supply support for CD74HC221E 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 for industrial, automotive, and communications markets.

CD74HC221E belongs to TI's High-Speed CMOS Logic family, designed specifically for robust, low-power timing functions in mission-critical systems where reliability across wide temperature and voltage ranges is mandatory.

FAQ

What is the minimum external timing resistor value supported by CD74HC221E?

The CD74HC221E specifies a minimum external timing resistor (RX) of 500 Ω. Using lower values may cause excessive current draw, timing inaccuracies, or potential damage due to increased power dissipation in the internal timing circuitry. This value is confirmed in the Functional Description section of the official datasheet (SCHS166F).

Can CD74HC221E operate reliably at 3.3V supply voltage?

Yes, CD74HC221E is fully specified for operation from 2V to 6V, including 3.3V. At V_CC = 3.3V, it maintains guaranteed propagation delays (t_PLH/t_PHL ≤ 63 ns), noise immunity (NIL/NIH ≈ 30%), and output drive capability - making it suitable for mixed-voltage 3.3V/5V system designs without level-shifting.

Does CD74HC221E require external pull-up or pull-down resistors on unused inputs?

Yes. Per the datasheet, if either monostable circuit is unused, all associated inputs (A, B, R) must be terminated either high or low - floating inputs can cause unpredictable triggering or increased ICC. For example, tie unused 1A and 1B to V_CC and 1R to GND to ensure stable quiescent state for Mono 1.

How does the Schmitt-trigger input on B pins improve noise immunity in CD74HC221E?

The Schmitt-trigger on each B input provides hysteresis - typically ~0.8V at V_CC = 4.5V - meaning the rising and falling thresholds differ. This prevents multiple false triggers from slowly varying or noisy signals (e.g., mechanical switch bounce), ensuring only one clean output pulse per valid level transition, which is essential for reliable debouncing and signal conditioning.

What is the maximum recommended timing capacitor value for CD74HC221E?

The datasheet does not specify an absolute maximum CX value, but practical limits arise from leakage current and timing accuracy. For stable operation across -55°C to +125°C, ceramic or film capacitors up to 1 µF are routinely used. Larger values (e.g., >10 µF) risk significant timing drift due to dielectric absorption and leakage, especially at temperature extremes - verified in Figure 7 and Figure 8 of SCHS166F.