NXP Semiconductors 74HCT221N,112

Overview

74HCT221N,112 from Nexperia is a dual non-retriggerable monostable multivibrator in SO16 package, operating from 4.5 V to 5.5 V supply, delivering ±5% pulse width stability across -40 °C to +125 °C, with Schmitt-trigger nB inputs for jitter-free triggering in noise-prone timing circuits such as debounce and pulse shaping.

For engineers reviewing the 74HCT221N,112 datasheet, 74HCT221N,112 pinout, 74HCT221N,112 application, or 74HCT221N,112 equivalent, key selection criteria include TTL-level input compatibility, external R/C programmable pulse width (t_W = 0.7 × C_EXTR_EXT), active LOW direct reset (nRD), non-retriggerable behavior, and SO16 thermal performance up to 125 °C ambient.

Technical Context

The 74HCT221N,112 implements two independent non-retriggerable monostables, each with edge-triggered inputs (nA: negative-edge, nB: positive-edge) and separate reset (nRD). Triggering is voltage-level–based-not transition-rate–dependent-enabling reliable operation with slow-rising signals via Schmitt-trigger nB inputs.

Output pulse width is externally set by R_EXT/C_EXT network connected to pins nREXT/CEXT and nCEXT; internal compensation ensures t_W stability over V_CC (4.5–5.5 V) and temperature (-40 to +125 °C), with typical variance < ±5%. Reset terminates output pulses asynchronously and independently per channel.

Key Specifications

Pinout & Package

74HCT221N,112 uses the SOT109-1 (SO16) plastic small outline package: 16-pin, 3.9 mm body width, 1.27 mm pitch, surface-mount, rated for 500 mW total power dissipation with linear derating above 110 °C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HC221D and SN74LS221N, the 74HCT221N,112 uniquely combines TTL-level input compatibility, Schmitt-trigger noise immunity on nB, and ±5% pulse width stability across -40 to +125 °C-making it optimal for robust industrial timing where signal integrity and thermal margin are critical.

Availability

74HCT221N,112 is available at Aetrix Electronics and suitable for industrial control panels, telecom infrastructure timing modules, and automotive body electronics requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for 74HCT221N,112 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

Nexperia is a global semiconductor expert focused on essential efficiency technologies, delivering high-performance, reliable standard products including logic, discretes, MOSFETs, and ESD protection devices.

The 74HCT221N,112 belongs to Nexperia's 74HCT logic family-designed specifically for TTL-compatible 5 V systems requiring low power, high noise immunity, and guaranteed operation across industrial temperature extremes.

FAQ

What is the maximum recommended external timing resistor value for 74HCT221N,112?

The datasheet specifies R_EXT up to 1000 kΩ for stable operation. Using values beyond this may cause timing inaccuracies due to leakage currents and reduced noise margin. For pulse widths >1 ms, verify C_EXT stability and consider power-down protection per Figure 16. The 74HCT221N,112 achieves best accuracy with R_EXT between 2 kΩ and 100 kΩ and C_EXT ≥ 100 pF.

Can 74HCT221N,112 operate reliably at 4.5 V supply?

Yes-the 74HCT221N,112 is fully specified from 4.5 V to 5.5 V. At V_CC = 4.5 V, all parameters-including propagation delay (max 77 ns), output drive (V_OH ≥ 3.7 V, V_OL ≤ 0.4 V), and pulse width stability (±5%)-remain guaranteed across -40 °C to +125 °C. The 74HCT221N,112 maintains TTL-level input compatibility even at minimum V_CC.

Is the 74HCT221N,112 pinout compatible with 74HC221N?

Yes-both share identical SO16 pin configuration (SOT109-1) and functional pin mapping per Table 2. However, the 74HCT221N,112 has Schmitt-trigger nB inputs and TTL-level thresholds, while 74HC221N uses standard CMOS thresholds and lacks Schmitt action. Electrical substitution requires verification of input signal slew rate and noise environment before using 74HCT221N,112 as a drop-in replacement.

How does the non-retriggerable feature of 74HCT221N,112 affect its use in switch debounce?

The non-retriggerable behavior ensures that once triggered, subsequent input transitions during the output pulse have no effect-preventing extended or repeated pulses from contact bounce. This guarantees exactly one clean output pulse per switch press, eliminating race conditions in downstream logic. In 74HCT221N,112, this is implemented per-channel and enforced independently for nA/nB inputs and nRD reset.

What is the purpose of connecting nCEXT to GND in 74HCT221N,112?

Per Figure 5 and Section 11.1, nCEXT must be externally connected to GND to complete the timing capacitor path and ensure correct RC network operation. Leaving nCEXT floating causes undefined timing behavior and potential latch-up. This requirement applies to both channels (pins 6 and 14) and is mandatory for stable pulse width generation in the 74HCT221N,112.