Texas Instruments CD74HC221PW

Overview

CD74HC221PW 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, delivers pulse widths from ~140 ns to >770 µs (via external RX/CX), and is used in precision timing, edge-triggered event capture, and digital pulse shaping circuits.

For engineers reviewing the CD74HC221PW datasheet, CD74HC221PW pinout, CD74HC221PW application, or CD74HC221PW equivalent, key selection criteria include its dual independent monostable architecture, TSSOP-16 package thermal profile (θJA = 108°C/W), wide VCC range, edge-selectable triggering (A = trailing, B = leading), and overriding reset functionality.

Technical Context

The CD74HC221PW implements two fully independent monostable multivibrators, each with separate A (trailing-edge), B (leading-edge), and R (active-low reset) inputs. Timing is externally set via resistor RX and capacitor CX, with pulse width tW ≈ 0.7·RX·CX at VCC = 4.5V. Each mono features Schmitt-trigger input on B, enabling robust noise immunity for slow or noisy trigger signals.

Outputs Q and Q̅ are buffered, providing fanout of 10 LSTTL loads over temperature. Propagation delays are specified down to 14 ns (tPLH/tPHL, CL = 15 pF, VCC = 5 V), and output transition times are as low as 13 ns (CL = 50 pF, VCC = 6 V), supporting reliable high-speed digital timing in industrial control and instrumentation.

Key Specifications

Pinout & Package

TSSOP-16 package (16-pin Thin Shrink Small Outline Package), 4.4 mm × 5.0 mm body, 0.65 mm pitch, 1.2 mm max height, JEDEC MO-153 compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC221PW, CD74HC221PWR offers identical functionality with guaranteed supply-chain continuity, while CD74HCT221PWR trades VCC flexibility for native TTL input compatibility-making it suitable only in pure 5 V environments.

Availability

CD74HC221PW is available at Aetrix Electronics and suitable for industrial control timing, test equipment pulse generation, and power supply sequencing requiring stable component supply across extreme temperature ranges (-55°C to +125°C).

Supply support for CD74HC221PW 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 CD74HC221PW belongs to TI's High-Speed CMOS Logic family, designed specifically for robust, low-power, wide-temperature digital timing applications where reliability and parameter stability are critical.

FAQ

What is the minimum external timing capacitor value supported by the CD74HC221PW?

The CD74HC221PW supports CX = 0 pF as the minimum external timing capacitor value. This allows ultra-short pulse widths (down to ~140 ns with RX = 2 kΩ), making it suitable for high-speed glitch suppression and narrow-pulse generation. The device's internal timing circuitry remains stable even with no external capacitor, relying solely on RX for basic timing control.

Can the CD74HC221PW operate reliably at 3.3 V supply voltage?

Yes, the CD74HC221PW is fully specified for operation from 2 V to 6 V, including 3.3 V nominal systems. At VCC = 3.3 V, its VIH is 2.31 V (min), VIL is 0.99 V (max), and propagation delays remain within datasheet limits (e.g., tPLH ≤ 53 ns, CL = 50 pF). This makes CD74HC221PW ideal for mixed-voltage 3.3 V/5 V designs without level-shifting circuitry.

How does the Schmitt-trigger input on the B pin improve noise immunity in the CD74HC221PW?

The Schmitt-trigger on the B input of CD74HC221PW provides hysteresis (typically ~0.6 V at VCC = 5 V), ensuring clean, bounce-free triggering on slow-rising or noisy signals such as mechanical switch closures or sensor outputs. Unlike standard CMOS inputs, it prevents multiple false triggers during signal transitions, which is essential in industrial environments where EMI or contact bounce would otherwise corrupt timing accuracy.

Is the CD74HC221PW pin-compatible with the CD74HCT221PWR variant?

Yes, the CD74HC221PW and CD74HCT221PWR share identical TSSOP-16 pinouts, footprint, and mechanical dimensions. However, they differ electrically: CD74HC221PW accepts 2–6 V and has CMOS-input thresholds, while CD74HCT221PWR requires 4.5–5.5 V and accepts TTL-level inputs. Swapping them requires verifying VCC and driver compatibility-no PCB changes are needed, but system-level logic levels must match.

What is the maximum recommended timing resistor value for stable operation of the CD74HC221PW?

The datasheet does not specify an absolute maximum RX value, but practical stability limits arise from leakage current and noise sensitivity. For reliable operation across -55°C to +125°C, TI recommends keeping RX ≤ 1 MΩ when using standard film or metal-film resistors. Higher values increase susceptibility to stray capacitance and input leakage, potentially causing pulse width drift or failure to trigger-especially at temperature extremes or low VCC.