Texas Instruments CD74HCT221M96

Overview

CD74HCT221M96 from Texas Instruments is a dual monostable multivibrator with independent reset, Schmitt-trigger B inputs, and buffered Q/Q̅ outputs. It operates from 4.5V to 5.5V, supports -55°C to +125°C operation, delivers pulse widths from ~140 ns to >770 µs (depending on RX/CX), and is used in precision timing, edge-triggered event capture, and reset-synchronized waveform generation in industrial control and test equipment.

For engineers reviewing the CD74HCT221M96 datasheet, CD74HCT221M96 pinout, CD74HCT221M96 application, or CD74HCT221M96 equivalent, key selection criteria include LSTTL-compatible input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V), dual-edge triggering capability (A = trailing, B = leading), overriding reset functionality, pulse width adjustability via external RX/CX, and SOIC-16 packaging for high-reliability embedded timing.

Technical Context

The CD74HCT221M96 implements two independent monostable circuits, each with separate A (trailing-edge) and B (leading-edge) trigger inputs, individual reset (R) pins, and complementary Q/Q̅ outputs. Timing is externally set by resistor RX and capacitor CX, with pulse width t_W ≈ 0.7·R_XC_X at V_CC = 4.5 V.

Its HCT logic family ensures direct compatibility with LSTTL inputs while maintaining CMOS power efficiency; propagation delays are 34–63 ns (t_PLH/t_PHL, CL = 50 pF, V_CC = 4.5 V), and output transition times are ≤22 ns. The Schmitt-trigger on B inputs enables robust noise immunity for slow-rising signals.

Key Specifications

Pinout & Package

CD74HCT221M96 is housed in a 16-pin SOIC (D) package (7.5 mm × 10.3 mm, 1.27 mm pitch), RoHS-compliant, with moisture sensitivity level 1 (MSL-1, unlimited floor life at ≤30°C/60% RH).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS221N and CD74HC221M96, CD74HCT221M96 uniquely balances LSTTL input compatibility, wide temperature range, low power, and Schmitt-trigger noise immunity - making it optimal for new industrial and automotive timing designs where robustness and interoperability are prioritized.

Availability

CD74HCT221M96 is available at Aetrix Electronics and suitable for industrial control, avionics power sequencing, and automotive sensor signal conditioning requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HCT221M96 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 technologies with over 50 years of innovation in high-reliability IC design.

The CD74HCT221M96 belongs to TI's High-Speed CMOS Logic family, engineered for precision timing applications demanding LSTTL compatibility, wide temperature operation, and predictable pulse generation in mission-critical systems.

FAQ

What is the minimum external timing resistor value supported by CD74HCT221M96?

The CD74HCT221M96 specifies a typical minimum external timing resistor (RX) value of 500 Ω. Using resistors below this threshold may cause timing inaccuracies, increased power dissipation in the internal timing circuit, or failure to meet specified pulse width tolerances. Always verify stability and pulse width error against the datasheet's t_W vs. R_X/C_X curves when operating near minimum values.

Can CD74HCT221M96 operate reliably at 4.5 V supply voltage?

Yes, CD74HCT221M96 is fully specified and guaranteed to operate across its entire rated supply range of 4.5 V to 5.5 V. At 4.5 V, key parameters including propagation delay (34–63 ns), output drive (3.7–3.98 V VOH into TTL loads), and input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) remain within datasheet limits, ensuring robust performance in nominal 5 V systems with rail tolerance.

Does CD74HCT221M96 require external pull-up or pull-down resistors on unused inputs?

Yes - per the datasheet, any unused A, B, or R inputs on CD74HCT221M96 must be terminated either high (to VCC) or low (to GND). Floating inputs can cause excessive ICC, unpredictable triggering, or oscillation due to internal node coupling. For unused monostables, tie A and B to VCC and R to GND to force inactive, stable states.

How does the Schmitt trigger on the B input improve noise immunity in CD74HCT221M96?

The Schmitt trigger on each B input of CD74HCT221M96 provides hysteresis (~0.8 V typical), meaning the rising-edge threshold (V_IH) and falling-edge threshold (V_IL) differ significantly. This prevents multiple false triggers from slowly rising or noisy signals - a critical advantage when interfacing with inductive sensors, long traces, or microcontroller GPIOs lacking slew-rate control.

Is CD74HCT221M96 pin-compatible with CD74HC221M96?

Yes, CD74HCT221M96 and CD74HC221M96 share identical SOIC-16 pinouts, terminal functions, and package dimensions. However, they differ electrically: CD74HCT221M96 uses TTL-compatible input thresholds (fixed VIH/VIL), while CD74HC221M96 uses VCC-referenced thresholds. Interchangeability requires verifying host system logic levels match the selected variant's input specification.