Texas Instruments SN74LV221ADR

Overview

SN74LV221ADR from Texas Instruments is a dual monostable multivibrator IC with Schmitt-trigger inputs, designed for precise pulse generation in 2V–5.5V systems. It features independent A (falling-edge) and B (rising-edge) trigger inputs per channel, overriding clear functionality, programmable output pulse duration via external R/C networks, and glitch-free power-up reset. It is used in timing control, debouncing, and delay generation circuits in industrial logic interfaces.

For engineers reviewing the SN74LV221ADR datasheet, SN74LV221ADR pinout, SN74LV221ADR application, or SN74LV221ADR equivalent, key selection considerations include its dual-channel monostable operation, Schmitt-trigger input hysteresis for noise immunity, 11ns max propagation delay at 5V, Ioff support for partial-power-down mode, and compatibility with mixed-voltage signal environments.

Technical Context

The SN74LV221ADR implements two independent edge-triggered monostable multivibrators, each supporting three triggering modes: A-low/B-high transition, B-high/A-low transition, or CLR-high with A-low/B-high pre-conditioning. Pulse width is externally set by Rext and Cext connected to dedicated pins (1Rext/Cext, 1Cext, 2Rext/Cext, 2Cext), with typical tw = K × R × C where K ≈ 1.0 for C ≥ 1000 pF.

Each channel includes Schmitt-trigger inputs on A, B, and CLR for robust handling of slow or noisy edges; an overriding clear input terminates output pulses early; and outputs are guaranteed glitch-free at power-up (Q low, Q high). The device supports Ioff, preventing backflow current during partial power-down.

Key Specifications

Pinout & Package

SN74LV221ADR uses a 16-pin SOIC (D) package measuring 9.9 mm × 6.0 mm (body: 9.9 mm × 3.9 mm), RoHS-compliant with NiPdAu lead finish and MSL Level-1 rating.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AHC123DR and MC74LV221ADR2G, the SN74LV221ADR uniquely combines Schmitt-trigger inputs, Ioff, and guaranteed power-up state - making it optimal for noisy, multi-rail, or hot-swap-sensitive designs where reliability trumps marginal speed gain.

Availability

SN74LV221ADR is available at Aetrix Electronics and suitable for industrial automation, test equipment, and embedded control systems requiring stable component supply, long-term lifecycle support, and verified RoHS compliance.

Supply support for SN74LV221ADR 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 decades of experience in high-reliability industrial and automotive-grade components.

The SN74LV221ADR belongs to TI's LV family of low-voltage logic devices, engineered for robust operation across wide supply ranges (2V–5.5V) and demanding industrial environments - emphasizing noise immunity, power-down safety, and timing precision.

FAQ

What is the minimum external timing capacitance supported by the SN74LV221ADR?

The SN74LV221ADR imposes no lower limit on external timing capacitance (Cext); datasheet Table 4.3 lists "No restriction" for Cext. Practical minimum values start around 28 pF (as tested in switching characteristics), but smaller values (e.g., 5–10 pF) are usable with appropriate Rext scaling to maintain stable oscillation and avoid parasitic sensitivity. Always verify pulse width accuracy and jitter in final layout.

Does the SN74LV221ADR support retriggering during an active output pulse?

Yes, the SN74LV221ADR supports retriggering: a new valid trigger (A↓ or B↑) applied during an active output pulse will restart the timing cycle from zero, extending total output duration. This behavior is confirmed in the functional description (Section 6.1) and function table (Table 6-1), where "Outputs enabled" entries allow repeated triggering without requiring CLR deassertion.

Can the SN74LV221ADR operate with VCC = 2.0 V while accepting 3.3 V inputs?

Yes, the SN74LV221ADR supports mixed-mode voltage operation: inputs may swing up to 5.5 V regardless of VCC (per Absolute Maximum Ratings and Recommended Operating Conditions), and VIH/VIL thresholds scale with VCC (e.g., VIH = 0.7×VCC at 3V–3.6V). At VCC = 2.0 V, VIH = 1.5 V - so a 3.3 V input exceeds this and registers as logic high, enabling safe 3.3 V → 2 V level translation.

How does the overriding clear function interact with the external timing components on the SN74LV221ADR?

The overriding clear input (1CLR/2CLR) forces immediate output transition (Q = L, Q = H) independent of Rext/Cext values - it does not discharge or reset the external capacitor. After clear release, the multivibrator remains in reset until next valid trigger. This allows pulse shortening without affecting timing component integrity or requiring capacitor bleed paths.

Is the SN74LV221ADR pin-compatible with older 74LS or 74HC monostables?

No, the SN74LV221ADR is not pin-compatible with standard 74LS221 or 74HC221. Its pinout (e.g., dedicated Cext/Rext/Cext pins) differs fundamentally. However, TI states it matches 'AHC123A/'AHCT123A pin assignments - meaning SN74LV221ADR can substitute for those parts *only* in non-retriggering applications, as noted in Section 6.1 of the datasheet.