Texas Instruments CD74HC221PWT

Overview

CD74HC221PWT 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 nanoseconds to microseconds via external RX/CX networks, and is used in precision timing control for industrial logic systems and instrumentation.

For engineers reviewing the CD74HC221PWT datasheet, CD74HC221PWT pinout, CD74HC221PWT application, or CD74HC221PWT equivalent, key selection criteria include dual independent monostable operation, edge-selective triggering (A = trailing, B = leading), overriding reset capability, wide temperature range, and TSSOP-16 packaging for high-density PCB layouts.

Technical Context

The CD74HC221PWT implements two independent monostable circuits, each with separate A (trailing-edge), B (leading-edge), and R (active-low reset) inputs. Triggering is decoupled from input rise/fall time on B due to integrated Schmitt triggers, while A requires defined pulse width per voltage level.

Output pulse width t_W = 0.7 × R_X × C_X at V_CC = 4.5V, with minimum R_X = 500Ω and C_X = 0pF. Propagation delays are 36–63ns (V_CC = 6V–4.5V, CL = 50pF), and pulse width matching between internal monostables is ±2% under matched RX/CX conditions.

Key Specifications

Pinout & Package

TSSOP-16 package (PW), 4.4mm × 5.0mm body, 0.65mm pitch, 1.2mm max height, exposed pad not present.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC221PWT, CD74HCT221PWR offers tighter input threshold compatibility with legacy TTL but sacrifices wide-voltage flexibility, while SN74LV221APWR delivers superior speed and ultra-low ICC but lacks the -55°C lower limit and requires careful layout for ESD-sensitive LV operation.

Availability

CD74HC221PWT is available at Aetrix Electronics and suitable for industrial automation, aerospace avionics, and test equipment requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC221PWT 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 for industrial, automotive, and communications markets.

The CD74HC221PWT belongs to TI's High-Speed CMOS Logic family, designed specifically for robust, wide-temperature timing functions in mission-critical systems where reliability and parameter stability outweigh raw speed.

FAQ

What is the minimum external timing capacitor value supported by the CD74HC221PWT?

The CD74HC221PWT supports C_X = 0pF as the minimum external timing capacitor value. This enables shortest achievable pulse widths (e.g., 140ns with 28pF/2kΩ configuration). For stable operation below 100pF, use NP0/C0G ceramic capacitors with tight tolerances to minimize drift across temperature and voltage.

Can both monostable sections of the CD74HC221PWT be triggered simultaneously without interference?

Yes, both monostable sections of the CD74HC221PWT operate fully independently. Triggering Mono 1 via its A/B inputs has no effect on Mono 2 timing or output state, and vice versa. Each section features dedicated R, Q, Q̅, CX, and CXRX terminals - enabling true parallel timing generation in a single TSSOP-16 footprint.

Does the CD74HC221PWT require pull-up or pull-down resistors on unused inputs?

Yes, unused inputs on the CD74HC221PWT must be terminated either high or low. Floating A, B, or R pins can cause unintended triggering or increased ICC due to CMOS input stage instability. TI recommends tying unused A/B inputs to VCC or GND via ≤10kΩ resistors, and unused R inputs to VCC (inactive state) to prevent spurious resets.

What is the maximum recommended external timing resistor value for the CD74HC221PWT?

The datasheet does not specify an absolute maximum R_X, but practical limits arise from leakage current and noise sensitivity. For reliable operation across -55°C to +125°C, R_X should not exceed 100kΩ. Higher values increase susceptibility to noise-induced false triggering and reduce pulse width accuracy due to input bias current effects on the internal timing comparator.

Is the CD74HC221PWT pin-compatible with the CD74HCT221PWR?

Yes, the CD74HC221PWT and CD74HCT221PWR share identical TSSOP-16 pinouts, terminal functions, and package dimensions. They differ only in electrical specifications: HC supports 2–6V operation with CMOS input thresholds, while HCT is 4.5–5.5V only with TTL-compatible inputs. No PCB changes are required for substitution within 5V systems.