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Home > Products > Integrated Circuits (ICs) > Logic > Multivibrators

Texas Instruments CD74HCT221MT

Name: CD74HCT221MT
Brand: Texas Instruments
SKU: CD74HCT221MT
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: CD74HCT221MT

Manufacturer:: Texas Instruments

Category:: Multivibrators

Package:: 16-SOIC (0.154", 3.90mm Width)

Datasheet:: CD74HCT221MT.pdf

Description:: IC MULTIVIBRATOR 18NS 16SOIC

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Product details

Overview

CD74HCT221MT 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 ambient, delivers pulse widths from ~140 ns to >800 µs via external RX/CX, and is used in precision timing control, edge-triggered event capture, and reset-synchronized waveform generation.

For engineers reviewing the CD74HCT221MT datasheet, CD74HCT221MT pinout, CD74HCT221MT application, or CD74HCT221MT equivalent, key selection criteria include LSTTL-compatible input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V), dual independent mono functionality with overriding reset, wide temperature operation, and SOIC-16 package compatibility with industrial and aerospace timing subsystems.

Technical Context

The CD74HCT221MT implements two independent monostable circuits, each with separate A (edge-triggered), B (Schmitt-triggered), and R (active-low reset) inputs. Triggering is asynchronous: A responds to rising/falling edges; B responds at a fixed voltage threshold, independent of slew rate. Output pulse width t_W = 0.7 × R_X × C_X at V_CC = 4.5 V, with minimum R_X = 500 Ω and C_X = 0 pF.

Each monostable features buffered complementary Q and Q̅ outputs, enabling direct fanout to 10 LSTTL loads over full temperature range. Propagation delays are tightly matched: t_PLH/t_PHL ≤ 63 ns (CL = 50 pF, V_CC = 4.5 V), and pulse width matching between internal monos is ±2% under identical R_X/C_X conditions.

Key Specifications

Parameter	Value and Actual Design Meaning
Supply Voltage	4.5 V to 5.5 V - Ensures direct compatibility with standard 5 V LSTTL logic systems without level translation.
Input Thresholds	V_IL ≤ 0.8 V (max), V_IH ≥ 2.0 V (min) - Guarantees robust noise margin and seamless interface with legacy TTL outputs.
Operating Temp	-55°C to +125°C - Validated for use in extended-temperature industrial, automotive, and military-grade applications.
Pulse Width Range	140 ns to >800 µs - Achieved via external R_X/C_X; enables flexible timing from high-speed glitch suppression to long-duration control pulses.
Propagation Delay	≤63 ns (max, CL = 50 pF) - Supports reliable timing in sub-10 MHz digital control loops with deterministic latency.
Fanout Capability	10 LSTTL loads - Sufficient drive strength to directly control multiple downstream logic gates or small-signal buffers.
Reset Function	Asynchronous active-low R pin - Allows immediate termination of output pulse regardless of ongoing trigger activity on A/B inputs.

Pinout & Package

CD74HCT221MT is housed in a 16-pin SOIC (Small Outline Integrated Circuit) package per JEDEC MS-012, 3.9 mm body width, 1.75 mm height max, with 1.27 mm lead pitch. Pin 1 is located at the top-left corner with notch or dot marking.

Pin/Terminal	Circuit Role	Design Meaning
1A, 9A	Edge-trigger input (Mono 1 & 2)	Rising or falling edge detection; no internal hysteresis - requires clean signal edges.
1B, 10B	Schmitt-trigger input (Mono 1 & 2)	Voltage-level triggered with hysteresis - tolerant of slow or noisy input transitions.
1R, 11R	Active-low reset (Mono 1 & 2)	Forces Q low and Q̅ high immediately; overrides all trigger states and timing cycles.
1Q, 2Q	True output (Mono 1 & 2)	Buffered, non-inverted output; drives LSTTL loads directly; pulse width defined by R_X/C_X.
1Q̅, 2Q̅	Inverted output (Mono 1 & 2)	Complementary buffered output; enables differential timing or logic inversion without external gate.
1CX, 2CX	Timing capacitor connection	Connects external capacitor (CX); sets pulse width with associated RX resistor (pins 2/12).
1CXRX, 2CXRX	Timing resistor connection	Connects external resistor (RX); forms RC network with CX to define t_W = 0.7·R_X·C_X.
V_CC (16)	Positive supply	4.5–5.5 V power rail; decoupling capacitor required near pin for stable timing performance.
GND (8)	Ground reference	Common return path for all signals and power; must be low-impedance to minimize timing jitter.

Key Features

Feature	Design Value
Dual independent monostables	Enables two synchronized or isolated timing functions in one IC - reduces board space and component count vs discrete solutions.
Separate A/B triggering modes	A input supports edge-sensitive triggering; B input provides noise-immune level-sensitive triggering - increases design flexibility across diverse signal sources.
Overriding active-low reset	Allows real-time termination of any active output pulse - critical for safety interlocks, fault recovery, and dynamic timing adjustment.
Wide pulse width range (140 ns – 800+ µs)	Configurable via external R_X/C_X - supports applications from pulse shaping and debouncing to delay generation and periodic control.
CMOS power efficiency with TTL compatibility	Quiescent ICC ≤ 160 µA at 125°C while maintaining LSTTL input thresholds - ideal for low-power, high-reliability embedded systems.

Applications

Industrial Control Timing	Automotive Sensor Signal Conditioning
Use Scenario: Generating precise, reset-controllable timing windows for PLC I/O scan cycles and motor enable/disable sequencing. IC Role / Device Role / Timing Role: Dual monostable provides independent timing for input sampling window and output hold duration, both interruptible via system fault signal. Use Value: Eliminates need for external RC networks and discrete logic; ensures deterministic timing across -55°C to +125°C operating range.	Use Scenario: Debouncing and pulse-stretching signals from crankshaft position sensors before feeding to microcontroller capture units. IC Role / Device Role / Timing Role: B-input Schmitt trigger cleans noisy analog-derived edges; A-input captures transient events; reset synchronizes to engine start sequence. Use Value: Reduces MCU firmware complexity and interrupt load; improves timing accuracy under EMI-prone under-hood conditions.
Test Equipment Pulse Generation	Aerospace Power Sequencing
Use Scenario: Creating calibrated, variable-width stimulus pulses for DUT functional testing in automated test systems. IC Role / Device Role / Timing Role: External R_X/C_X selection enables user-selectable pulse widths; Q/Q̅ outputs drive DUT enable and strobe lines simultaneously. Use Value: Provides hardware-based, jitter-free pulse generation without FPGA resource usage or software timing dependencies.	Use Scenario: Controlling staged power-up of avionics subsystems (e.g., RF front-end before baseband processor) with fail-safe reset coordination. IC Role / Device Role / Timing Role: One monostable generates primary power-on delay; second provides watchdog-resettable hold-off for secondary rail activation. Use Value: Meets DO-254 timing integrity requirements; avoids single-point failure via independent reset paths per channel.

Industrial Control Timing

Automotive Sensor Signal Conditioning

Use Scenario: Generating precise, reset-controllable timing windows for PLC I/O scan cycles and motor enable/disable sequencing.

IC Role / Device Role / Timing Role: Dual monostable provides independent timing for input sampling window and output hold duration, both interruptible via system fault signal.

Use Value: Eliminates need for external RC networks and discrete logic; ensures deterministic timing across -55°C to +125°C operating range.

Use Scenario: Debouncing and pulse-stretching signals from crankshaft position sensors before feeding to microcontroller capture units.

IC Role / Device Role / Timing Role: B-input Schmitt trigger cleans noisy analog-derived edges; A-input captures transient events; reset synchronizes to engine start sequence.

Use Value: Reduces MCU firmware complexity and interrupt load; improves timing accuracy under EMI-prone under-hood conditions.

Test Equipment Pulse Generation

Aerospace Power Sequencing

Use Scenario: Creating calibrated, variable-width stimulus pulses for DUT functional testing in automated test systems.

IC Role / Device Role / Timing Role: External R_X/C_X selection enables user-selectable pulse widths; Q/Q̅ outputs drive DUT enable and strobe lines simultaneously.

Use Value: Provides hardware-based, jitter-free pulse generation without FPGA resource usage or software timing dependencies.

Use Scenario: Controlling staged power-up of avionics subsystems (e.g., RF front-end before baseband processor) with fail-safe reset coordination.

IC Role / Device Role / Timing Role: One monostable generates primary power-on delay; second provides watchdog-resettable hold-off for secondary rail activation.

Use Value: Meets DO-254 timing integrity requirements; avoids single-point failure via independent reset paths per channel.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
CD74HC221M96	HC logic family: 2–6 V supply, VIH/VIL referenced to VCC (not fixed TTL levels); higher noise immunity but not LSTTL-input compatible.	Used where supply voltage varies or mixed-voltage logic domains exist; unsuitable for direct replacement in legacy 5 V TTL systems.	Select when system uses 3.3 V or variable supply and does not require strict TTL input compatibility.
SN74LS221N	Bipolar TTL technology: 4.75–5.25 V only, higher ICC (~30 mA), shorter min pulse width (~25 ns), no Schmitt B input.	Legacy designs requiring LS-series footprint and speed; lacks temperature range (-25°C to +70°C only) and reset override flexibility.	Choose only for drop-in replacement in existing LS-based boards where power and thermal budgets allow.

Compared with CD74HC221M96 and SN74LS221N, the CD74HCT221MT uniquely combines LSTTL input compatibility, extended temperature operation, Schmitt-trigger B inputs, and overriding reset - making it optimal for new industrial and aerospace timing designs requiring robustness and interoperability.

Availability

CD74HCT221MT is available at Aetrix Electronics and suitable for industrial control timing, automotive sensor conditioning, test equipment pulse generation, and aerospace power sequencing requiring stable component supply across extended temperature ranges.

Supply support for CD74HCT221MT 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 heritage in high-reliability logic families.

The CD74HCT221MT belongs to TI's HCT logic series, designed specifically for seamless integration into legacy 5 V TTL systems while delivering CMOS power efficiency and extended temperature capability.

FAQ

What is the minimum external timing capacitor value supported by the CD74HCT221MT?

The CD74HCT221MT supports an external timing capacitor (C_X) down to 0 pF, enabling minimal pulse widths. With R_X = 2 kΩ and C_X = 28 pF, typical output pulse width is 140 ns at V_CC = 4.5 V. For stable operation, TI recommends using ≥100 pF in production designs to mitigate parasitic effects. The CD74HCT221MT datasheet confirms C_X = 0 pF is electrically valid but may reduce repeatability in high-noise environments.

Does the CD74HCT221MT support both rising- and falling-edge triggering on the same input pin?

No - the CD74HCT221MT assigns distinct triggering behaviors per input: pin 1A (and 9A) responds to *either* rising or falling edges (user-selectable via external circuitry), while pins 1B and 10B are Schmitt-trigger inputs that respond only at a fixed voltage threshold, independent of edge direction. The CD74HCT221MT truth table and functional diagram confirm this dual-mode architecture, allowing designers to choose edge-sensitive or level-sensitive triggering per channel.

Can the CD74HCT221MT operate reliably at 125°C ambient temperature?

Yes - the CD74HCT221MT is fully specified for continuous operation from -55°C to +125°C ambient, with all electrical parameters (propagation delay, pulse width, input thresholds, fanout) guaranteed across this range. Absolute maximum ratings permit junction temperatures up to 150°C. The CD74HCT221MT's SOIC package has θ_JA = 73°C/W, so proper PCB copper area and airflow ensure safe operation at max ambient.

Is the CD74HCT221MT pin-compatible with the CD74HC221 series?

Yes - the CD74HCT221MT shares identical pinout, package (SOIC-16), and terminal functions with CD74HC221M, CD74HC221M96, and other members of the '221 family. However, the CD74HCT221MT differs electrically: it uses HCT input thresholds (TTL-compatible) versus HC's VCC-referenced thresholds. This means the CD74HCT221MT can replace HC variants in 5 V TTL systems without redesign, but not vice versa in mixed-voltage or low-VCC applications.

What is the maximum recommended external timing resistor value for the CD74HCT221MT?

The CD74HCT221MT datasheet does not specify a maximum R_X, but practical limits arise from leakage current and noise sensitivity. TI application notes recommend R_X ≤ 10 MΩ for stable operation at 125°C. At R_X = 10 MΩ and C_X = 1000 pF, t_W ≈ 7 ms - well within specification. Higher values increase susceptibility to stray capacitance and input bias current errors. The CD74HCT221MT's minimum R_X is 500 Ω, confirmed in the "Description" section of the datasheet.

CD74HCT221MT Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74HCT

Package/Case:: 16-SOIC (0.154", 3.90mm Width)

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Logic Type:: Monostable

Independent Circuits:: 2

Schmitt Trigger Input:: Yes

Propagation Delay:: 18 ns

Current - Output High, Low:: 4mA, 4mA

Voltage - Supply:: 4.5 V ~ 5.5 V

Operating Temperature:: -55°C ~ 125°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 16-SOIC

CD74HCT221MT FAQ

1.How can I place an order for CD74HCT221MT through Aetrix?

Please submit a Request for Quotation (RFQ) for CD74HCT221MT on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for CD74HCT221MT reliable?

The price and inventory of CD74HCT221MT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for CD74HCT221MT is usually 5 days.

3.What payment methods are accepted for CD74HCT221MT?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for CD74HCT221MT transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for CD74HCT221MT?

CD74HCT221MT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your CD74HCT221MT order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for CD74HCT221MT?

For technical support, including CD74HCT221MT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your CD74HCT221MT requirements.

6.How does Aetrix verify that CD74HCT221MT is sourced from the original manufacturer or authorized distributors?

All CD74HCT221MT products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that CD74HCT221MT meets industry standards.

7.What is the process for return or replacement of CD74HCT221MT?

All CD74HCT221MT units undergo pre-shipment inspection (PSI). If there is an issue with CD74HCT221MT, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The CD74HCT221MT part is unused and in its original packaging.

Return procedure for CD74HCT221MT:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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