Texas Instruments CD74HC221MG4

Overview

CD74HC221MG4 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 ambient, delivers pulse widths from ~140ns to >770µs via external RX/CX networks, and is used in precision timing control for industrial sensor interfaces and power sequencing circuits.

For engineers reviewing the CD74HC221MG4 datasheet, CD74HC221MG4 pinout, CD74HC221MG4 application, or CD74HC221MG4 equivalent, key selection considerations include its dual independent monoshots with edge-selectable triggering (A = trailing, B = leading), overriding reset capability, wide temperature range, and SOIC-16 packaging compatible with high-reliability embedded timing designs.

Technical Context

The CD74HC221MG4 implements two fully independent CMOS monostable multivibrators, each with separate A (trailing-edge), B (leading-edge), and R (active-low reset) inputs. Timing is externally set by resistor RX and capacitor CX, with pulse width t_W ≈ 0.7·R_XC_X at V_CC = 4.5V.

Each monostable features Schmitt-trigger input on B, enabling robust noise immunity on trigger signals, and provides complementary buffered Q and Q̅ outputs capable of driving up to 10 LSTTL loads over full temperature range. Power-up reset ensures deterministic initial state.

Key Specifications

Pinout & Package

CD74HC221MG4 is packaged in a 16-pin SOIC (Small Outline Integrated Circuit) with 1.27mm pitch, 7.5mm body width, and 1.75mm max height per TI PW0016A outline. Pin 1 is located in Quadrant Q1 per tape-and-reel orientation standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HCT221M96 and SN74LV221AD, the CD74HC221MG4 uniquely combines wide 2–6V operation, built-in Schmitt B inputs, and extended -55°C to +125°C qualification-making it optimal for ruggedized, mixed-voltage industrial timing where noise immunity and temperature resilience are non-negotiable.

Availability

CD74HC221MG4 is available at Aetrix Electronics and suitable for industrial automation, aerospace avionics, and automotive powertrain control requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC221MG4 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 delivering analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The CD74HC221MG4 belongs to TI's High-Speed CMOS Logic family, designed specifically for reliable, low-power timing functions in harsh-environment applications where precision, noise immunity, and wide operating margins are essential.

FAQ

What is the minimum external timing capacitor value supported by the CD74HC221MG4?

The CD74HC221MG4 supports a minimum external timing capacitor (CX) value of 0pF, enabling very short pulse widths down to approximately 140ns when paired with minimum RX (500Ω). This capability is confirmed in the Absolute Maximum Ratings and Prerequisite For Switching Function sections of the TI datasheet SCHS166F, where CX = 28pF and RX = 2kΩ yields t_W = 140ns at V_CC = 4.5V. The CD74HC221MG4 does not require a minimum capacitance for stable oscillation or timing function.

Does the CD74HC221MG4 support both rising- and falling-edge triggering on the same input pin?

No, the CD74HC221MG4 does not support both edge types on a single input. It provides dedicated pins: A inputs (pins 1 and 9) respond exclusively to trailing (falling) edges, while B inputs (pins 2 and 10) respond exclusively to leading (rising) edges. Each B input includes an internal Schmitt trigger for noise rejection. This separation ensures deterministic, glitch-free triggering without ambiguity-confirmed in the Functional Diagram and Truth Table of the CD74HC221MG4 datasheet SCHS166F.

Can the CD74HC221MG4 operate reliably at 2.5V supply voltage?

Yes, the CD74HC221MG4 is fully specified to operate at 2.5V supply voltage. As an HC-type device, its guaranteed operating range is 2V to 6V, and electrical parameters-including propagation delay (t_PLH/t_PHL = 210ns max), output drive (10 LSTTL loads), and input thresholds (VIH = 1.5V min, VIL = 0.5V max)-are characterized down to 2V per the DC Electrical Specifications table in SCHS166F. At 2.5V, performance remains within published limits across -55°C to +125°C.

How does the overriding reset function work on the CD74HC221MG4?

The overriding reset function on the CD74HC221MG4 is active-low and asynchronous: asserting R (pin 3 or 11) to logic LOW immediately forces Q to LOW and Q̅ to HIGH, terminating any ongoing output pulse regardless of trigger input state or timing network conditions. This behavior is explicitly documented in the Description section ("Once triggered, the outputs are independent of further trigger inputs… The output pulse can be terminated by a LOW level on the Reset (R) pin") and verified in the Truth Table of the CD74HC221MG4 datasheet SCHS166F.

Is the CD74HC221MG4 pin-compatible with the CD74HCT221 series?

Yes, the CD74HC221MG4 is pin-compatible with CD74HCT221 variants (e.g., CD74HCT221M96) in the same SOIC-16 package. Both share identical pin assignments, timing network connections (CX/CXRX), and functional block layout. However, they differ in supply range (HC: 2–6V; HCT: 4.5–5.5V) and input threshold compatibility (HCT matches LSTTL levels). This pin compatibility is confirmed in TI's Ordering Information table and Package Option Addendum for CD74HC221MG4 and CD74HCT221M96.