NXP Semiconductors 74HC221DB,118

Overview

74HC221DB,118 from Nexperia is a dual non-retriggerable monostable multivibrator in SO16 package, operating from 2.0 V to 6.0 V supply, with Schmitt-trigger inputs on B pins, TTL-compatible input thresholds, and independent active-HIGH/active-LOW complementary outputs per channel. It delivers precise pulse widths defined by external RC networks (t_W = 0.7 × R_EXTC_EXT) and supports direct active-LOW reset for pulse termination - used in timing control, debouncing, and delay generation circuits.

For engineers reviewing the 74HC221DB,118 datasheet, 74HC221DB,118 pinout, 74HC221DB,118 application, or 74HC221DB,118 equivalent, this page provides verified functional identity, SO16 pin mapping, pulse width stability data (±5% typical), reset timing specs (t_PHL/t_PLH ≤ 77 ns at V_CC = 4.5 V), and validated alternatives for industrial timing designs.

Technical Context

The 74HC221DB,118 implements two independent non-retriggerable monostables, each with dual edge-triggered inputs (A: negative-edge, B: positive-edge) and separate active-LOW reset (nRD). Triggering is voltage-level–based-not transition-rate–dependent-enabling robust operation with slow-rising signals via Schmitt-trigger action on nB inputs.

Pulse width is externally programmable via R_EXT/C_EXT networks connected to dedicated pins (nREXT/CEXT, nCEXT); internal compensation ensures t_W stability across -40 °C to +125 °C and ±10% V_CC variation. Outputs nQ (active LOW) and nQ (active HIGH) remain latched during pulse duration, unaffected by further input transitions.

Key Specifications

Pinout & Package

74HC221DB,118 is housed in a plastic small outline package (SO16), SOT109-1 variant, with 16 leads, 3.9 mm body width, and standard 1.27 mm lead pitch - compatible with automated PCB assembly and IPC-7351B land patterns.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HC221DB,118, the 74HCT221D,118 offers tighter input noise immunity in 5 V systems but lacks 3.3 V compatibility, while the SN74LV221ADBR enables faster, lower-voltage operation at the cost of pinout redesign - making 74HC221DB,118 the optimal drop-in replacement for existing HC-family timing circuits.

Availability

74HC221DB,118 is available at Aetrix Electronics and suitable for motor control timing, switch debouncing, and power supply sequencing requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for 74HC221DB,118 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 delivering high-performance logic, analog, and MOSFET solutions with focus on efficiency, reliability, and sustainability.

The 74HC221DB,118 belongs to Nexperia's 74HC logic family - engineered for robust, low-power timing and signal conditioning in industrial, automotive, and consumer applications where precision and thermal stability are critical.

FAQ

What is the maximum recommended external timing capacitor value for stable operation of the 74HC221DB,118?

The 74HC221DB,118 does not specify an upper limit for C_EXT, but practical stability requires limiting leakage and ESR. Datasheet Fig. 12 shows valid operation up to 1 μF at V_CC = 4.5 V. For reliable t_W accuracy beyond 100 nF, use X7R ceramic or low-leakage tantalum capacitors and verify pulse width variance remains within ±5% across temperature. Avoid electrolytics due to high leakage and aging effects.

Can the 74HC221DB,118 operate reliably at 3.3 V supply voltage?

Yes, the 74HC221DB,118 is fully specified for V_CC = 2.0 V to 6.0 V, including 3.3 V operation. At 3.3 V, propagation delays increase slightly (e.g., t_PLH ≤ 110 ns), and output drive drops to ±2.6 mA, but all timing and logic functions remain guaranteed per datasheet Tables 8–10. Input thresholds scale proportionally, maintaining TTL compatibility.

How does the non-retriggerable feature of the 74HC221DB,118 affect its use in pulse stretching applications?

The non-retriggerable behavior means once triggered, the 74HC221DB,118 ignores subsequent input edges until the current pulse completes and the circuit resets. This prevents pulse widening from noise or chatter - ideal for generating fixed-duration control signals (e.g., solenoid actuation time) where consistent width matters more than edge count. To stretch pulses, external logic (e.g., OR gate feeding nRD) must be added.

Is the 74HC221DB,118 pin-compatible with the 74HC221N (DIP-16) package version?

No - the 74HC221DB,118 uses SO16 (SOT109-1) surface-mount packaging, while the 74HC221N uses through-hole DIP-16. Pin numbering and physical dimensions differ: SO16 has 1.27 mm pitch and gull-wing leads; DIP-16 has 2.54 mm pitch and straight leads. Electrical functionality and pin functions match exactly, but PCB layout and assembly processes are not interchangeable.

What is the purpose of connecting nCEXT pins to GND in the 74HC221DB,118 circuit?

Per Nexperia datasheet Fig. 5 and Section 11.1, nCEXT pins (14 and 6) must be externally connected to GND to establish the reference node for the internal timing current source. Leaving nCEXT floating causes unpredictable t_W and potential latch-up. This GND tie ensures accurate 0.7 × R_EXTC_EXT calculation and prevents charge accumulation that could disrupt reset behavior during power cycling.