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

Texas Instruments CD74HCT221MG4

Name: CD74HCT221MG4
Brand: Texas Instruments
SKU: CD74HCT221MG4
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: CD74HCT221MG4

Manufacturer:: Texas Instruments

Category:: Multivibrators

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

Datasheet:: CD74HCT221MG4.pdf

Description:: IC MULTIVIBRATOR 18NS 16SOIC

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Product details

Overview

CD74HCT221MG4 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 edge-triggering (A = trailing, B = leading), delivers pulse widths from ~140ns to >800µs via external RX/CX, and is rated for -55°C to +125°C operation in industrial and aerospace timing applications.

For engineers reviewing the CD74HCT221MG4 datasheet, CD74HCT221MG4 pinout, CD74HCT221MG4 application, or CD74HCT221MG4 equivalent, this device is selected for precision one-shot generation where LSTTL-compatible input thresholds, wide temperature stability, and reset-controlled pulse termination are required - especially in legacy control logic, instrumentation timing, and fault-clearing circuits.

Technical Context

The CD74HCT221MG4 implements two independent monostable multivibrators, each with separate A (trailing-edge) and B (leading-edge, Schmitt-triggered) trigger inputs and dedicated R (active-low reset) pins. Pulse width is determined solely by external RX and CX components using t_W ≈ 0.7·R_XC_X, with no internal timing elements.

Its HCT logic family ensures direct compatibility with LSTTL inputs (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V at V_CC = 5 V), while maintaining CMOS-level quiescent current (ICC ≤ 160 µA over full temperature range) and noise immunity (NIL/NIH = 30% of V_CC).

Key Specifications

Parameter	Value and Actual Design Meaning
Supply Voltage	4.5 V to 5.5 V - Ensures interoperability with standard 5 V TTL/LSTTL systems without level-shifting.
Input Compatibility	LSTTL-compatible - Accepts V_IL ≤ 0.8 V (max), V_IH ≥ 2.0 V (min); eliminates need for input conditioning in mixed-logic designs.
Pulse Width Range	140 ns to 805 µs - Achieved via external R_X/C_X; enables precise timing from high-speed glitch suppression to long-duration system resets.
Operating Temperature	-55°C to +125°C - Qualified for extended industrial, automotive under-hood, and military-grade environments.
Propagation Delay	34 ns to 63 ns (CL = 50 pF, V_CC = 4.5–5.5 V) - Predictable, low-jitter response critical for synchronous event capture and pulse shaping.
Reset Function	Asynchronous active-low R pin per monostable - Allows immediate pulse termination independent of trigger state, supporting fail-safe timing control.
Output Drive	15 LSTTL loads - Sufficient fanout to drive multiple downstream logic gates or small-signal loads without buffering.

Pinout & Package

CD74HCT221MG4 is supplied in a 16-pin SOIC (D) package with 1.27 mm pitch, 7.4 mm width, and 10.0 mm length. Pin 1 is located in the top-left corner adjacent to the index marking.

Pin/Terminal	Circuit Role	Design Meaning
1A, 9A	Trailing-edge trigger input (Mono 1 & 2)	Accepts falling-edge transitions only; requires minimum pulse width of 14 ns at V_CC = 4.5 V.
1B, 10B	Leading-edge Schmitt-trigger input (Mono 1 & 2)	Hysteresis prevents false triggering on noisy signals; unlimited input rise/fall time tolerance.
1R, 11R	Active-low reset (Mono 1 & 2)	Forces Q low and Q̅ high immediately; overrides ongoing output pulse regardless of trigger state.
1Q, 2Q	True output (Mono 1 & 2)	Buffered, non-inverted output; drives up to 15 LSTTL loads with 34–63 ns propagation delay.
1Q̅, 2Q̅	Inverted output (Mono 1 & 2)	Complementary buffered output; enables differential timing or dual-signal generation without external inverters.
1CX, 2CX	Timing capacitor connection (Mono 1 & 2)	Connects external capacitor (0 pF min) to ground; sets pulse width with associated RX pin.
1CXRX, 2CXRX	Timing resistor connection (Mono 1 & 2)	Connects external resistor (≥500 Ω typical) between CX and V_CC; completes RC timing network.
V_CC, GND	Power supply and ground	Single 4.5–5.5 V supply; decoupling recommended within 1 cm of pins 8 (GND) and 16 (V_CC).

Key Features

Feature	Design Value
Dual independent monostables	Enables two synchronized or isolated one-shot functions in one IC - reduces board space and interconnect complexity vs. discrete solutions.
Separate A/B trigger inputs per channel	Supports flexible edge selection: A for falling-edge detection (e.g., clock stop), B for rising-edge with noise immunity (e.g., sensor wake-up).
Overriding active-low reset	Guarantees deterministic pulse termination - essential for safety-critical timeout monitoring and emergency shutdown circuits.
Wide pulse width adjustability	External R_X/C_X tuning allows design-specific timing from nanoseconds to milliseconds without changing IC or firmware.
High noise immunity	NIL/NIH = 30% of V_CC ensures reliable operation in electrically noisy environments such as motor controls and power supplies.

Applications

Industrial Control Timing	Instrumentation Pulse Shaping
Use Scenario: Generating fixed-duration enable pulses for solenoid drivers in PLC I/O modules. IC Role / Device Role / Timing Role: Monostable #1 provides clean, jitter-free 50 ms activation window; Mono #2 generates complementary reset strobe. Use Value: Eliminates microcontroller timing overhead and ensures deterministic actuation even during CPU interrupts or brownouts.	Use Scenario: Converting irregular analog comparator outputs into standardized digital pulses for data acquisition sampling clocks. IC Role / Device Role / Timing Role: Schmitt-trigger B input cleans noisy threshold crossings; adjustable pulse width matches ADC conversion latency. Use Value: Prevents multiple false triggers from signal bounce or EMI, improving measurement repeatability in lab-grade equipment.
Fault Detection & Recovery	Legacy System Interfacing
Use Scenario: Monitoring watchdog timer timeouts in avionics subsystems to initiate controlled reboot sequences. IC Role / Device Role / Timing Role: Reset input tied to MCU WDT output; Q pulse triggers power-cycle logic upon timeout detection. Use Value: Provides hardware-enforced recovery window independent of software execution state - meets DO-254 functional safety requirements.	Use Scenario: Bridging TTL-based legacy test equipment with modern 3.3 V FPGA controllers requiring 5 V–compatible timing signals. IC Role / Device Role / Timing Role: Acts as level-tolerant one-shot translator: accepts 0.8 V/2.0 V TTL inputs and drives 5 V CMOS loads. Use Value: Avoids external level shifters or voltage translators, simplifying redesign of aging test fixtures and calibration rigs.

Industrial Control Timing

Instrumentation Pulse Shaping

Use Scenario: Generating fixed-duration enable pulses for solenoid drivers in PLC I/O modules.

IC Role / Device Role / Timing Role: Monostable #1 provides clean, jitter-free 50 ms activation window; Mono #2 generates complementary reset strobe.

Use Value: Eliminates microcontroller timing overhead and ensures deterministic actuation even during CPU interrupts or brownouts.

Use Scenario: Converting irregular analog comparator outputs into standardized digital pulses for data acquisition sampling clocks.

IC Role / Device Role / Timing Role: Schmitt-trigger B input cleans noisy threshold crossings; adjustable pulse width matches ADC conversion latency.

Use Value: Prevents multiple false triggers from signal bounce or EMI, improving measurement repeatability in lab-grade equipment.

Fault Detection & Recovery

Legacy System Interfacing

Use Scenario: Monitoring watchdog timer timeouts in avionics subsystems to initiate controlled reboot sequences.

IC Role / Device Role / Timing Role: Reset input tied to MCU WDT output; Q pulse triggers power-cycle logic upon timeout detection.

Use Value: Provides hardware-enforced recovery window independent of software execution state - meets DO-254 functional safety requirements.

Use Scenario: Bridging TTL-based legacy test equipment with modern 3.3 V FPGA controllers requiring 5 V–compatible timing signals.

IC Role / Device Role / Timing Role: Acts as level-tolerant one-shot translator: accepts 0.8 V/2.0 V TTL inputs and drives 5 V CMOS loads.

Use Value: Avoids external level shifters or voltage translators, simplifying redesign of aging test fixtures and calibration rigs.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74LS221N	Bipolar LSTTL technology; higher ICC (40 mA typ), narrower V_CC range (4.75–5.25 V), no Schmitt B input.	Lower noise immunity, higher power draw, less tolerant of slow-rising or noisy triggers.	Choose only if strict LSTTL loading or legacy board compatibility is mandatory; not suitable for wide-temp or low-power use.
CD74HC221M96	Same pinout and function but HC logic: 2–6 V operation, CMOS input thresholds (V_IL ≤ 0.5 V, V_IH ≥ 1.5 V at 2 V).	Requires level-shifting when interfacing with LSTTL sources; unsuitable for direct replacement in existing 5 V TTL systems.	Select when supply voltage flexibility or lower static power is prioritized over LSTTL input compatibility.

Compared with SN74LS221N and CD74HC221M96, the CD74HCT221MG4 uniquely balances LSTTL input compatibility, wide temperature operation, and low quiescent power - making it optimal for upgrading legacy 5 V systems without redesigning interface logic or thermal management.

Availability

CD74HCT221MG4 is available at Aetrix Electronics and suitable for industrial control timing, instrumentation pulse shaping, fault detection & recovery, and legacy system interfacing requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HCT221MG4 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 over 90 years of innovation in high-reliability components.

The CD74HCT221MG4 belongs to TI's High-Speed CMOS Logic (HCT) product line, engineered specifically for seamless integration into 5 V TTL-based systems requiring robust timing, wide temperature resilience, and low-power consumption.

FAQ

What is the minimum external timing resistor value supported by the CD74HCT221MG4?

The CD74HCT221MG4 specifies a typical minimum external timing resistor (R_X) of 500 Ω. Using values below this may cause timing inaccuracies or failure to trigger reliably due to internal circuit loading effects. For stable operation across -55°C to +125°C, TI recommends R_X ≥ 1 kΩ in production designs. The CD74HCT221MG4 datasheet confirms this limit in the "Description" section and absolute maximum ratings table.

Can the CD74HCT221MG4 operate with a 3.3 V supply?

No, the CD74HCT221MG4 is an HCT-family device specified only for 4.5 V to 5.5 V operation. At 3.3 V, input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) become invalid, and output drive capability degrades significantly. For 3.3 V systems, consider the pin-compatible CD74HC221M96 instead. The CD74HCT221MG4 datasheet explicitly defines its V_CC range in the "Operating Conditions" table.

Does the CD74HCT221MG4 require external pull-up or pull-down resistors on unused inputs?

Yes - per the CD74HCT221MG4 datasheet, all unused inputs (A, B, R) must be terminated either high or low to prevent floating states that could cause excessive current draw or erratic triggering. Leaving inputs unconnected risks increased ICC, noise susceptibility, and unintended monostable activation. This requirement applies to both active and unused channels on the CD74HCT221MG4.

How does the Schmitt-trigger input on the B pin improve noise immunity for the CD74HCT221MG4?

The Schmitt-trigger on the CD74HCT221MG4's B input provides hysteresis (~0.8 V typical at V_CC = 5 V), meaning the rising and falling thresholds differ. This prevents multiple false triggers caused by slow-rising edges or noise-induced oscillations near the switching point. Unlike standard CMOS inputs, the B pin tolerates unlimited input rise/fall times - a key advantage confirmed in the "Prerequisite For Switching Function" table of the CD74HCT221MG4 datasheet.

Is the CD74HCT221MG4 RoHS compliant and lead-free?

Yes, the CD74HCT221MG4 is RoHS compliant and features a NiPdAu (NIPDAU) lead finish, as documented in TI's Packaging Information Addendum. It meets JEDEC J-STD-020 moisture sensitivity Level-1 (unlimited floor life at <30°C/60% RH) and is qualified for Pb-free reflow soldering up to 260°C peak. This compliance is verified for the SOIC (D) package variant used in the CD74HCT221MG4.

CD74HCT221MG4 Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74HCT

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

Packaging:: Tube

Product Status:: Discontinued at Digi-Key

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

CD74HCT221MG4 FAQ

1.How can I place an order for CD74HCT221MG4 through Aetrix?

Please submit a Request for Quotation (RFQ) for CD74HCT221MG4 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 CD74HCT221MG4 reliable?

The price and inventory of CD74HCT221MG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for CD74HCT221MG4 is usually 5 days.

3.What payment methods are accepted for CD74HCT221MG4?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for CD74HCT221MG4 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for CD74HCT221MG4?

CD74HCT221MG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your CD74HCT221MG4 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 CD74HCT221MG4?

For technical support, including CD74HCT221MG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your CD74HCT221MG4 requirements.

6.How does Aetrix verify that CD74HCT221MG4 is sourced from the original manufacturer or authorized distributors?

All CD74HCT221MG4 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 CD74HCT221MG4 meets industry standards.

7.What is the process for return or replacement of CD74HCT221MG4?

All CD74HCT221MG4 units undergo pre-shipment inspection (PSI). If there is an issue with CD74HCT221MG4, 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 CD74HCT221MG4 part is unused and in its original packaging.

Return procedure for CD74HCT221MG4:

1.Submit a request within 90 days.

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

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