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Texas Instruments SN74LS221NE4
- Part No.:
- SN74LS221NE4
- Manufacturer:
- Texas Instruments
- Category:
- Multivibrators
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS221NE4.pdf
- Description:
- DUAL MONOSTABLE MULTIVIBRATORS W
- Quantity:
- Payment:
- Shipping:
Inventory:1,484
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Product details
Overview
SN74LS221NE4 from Texas Instruments is a dual monostable multivibrator (one-shot) IC with TTL-compatible inputs and outputs, designed for precise pulse generation in digital timing circuits. It features two independent channels, each with negative- and positive-transition-triggered inputs, overriding clear functionality, and external Rext/Cext-controlled pulse width up to 70 ms. Used in debounce circuits, clock stretching, and delay generation in industrial control and test equipment.
For engineers reviewing the SN74LS221NE4 datasheet, SN74LS221NE4 pinout, SN74LS221NE4 application, or SN74LS221NE4 equivalent, key selection considerations include its 16-pin PDIP package, 0°C to 70°C operating range, 70 ms maximum output pulse length, Schmitt-trigger B-input for jitter-free triggering down to 1 V/s, and compatibility with legacy SN74LS123-based designs via R/C value adjustment.
Technical Context
The SN74LS221NE4 implements two independent TTL-compatible monostable multivibrators sharing a common VCC and GND. Each channel uses internal latching circuitry and Schmitt-trigger input on the B pin (1.0–2.0 V threshold) to ensure noise immunity of 1.2 V and VCC noise rejection up to 1.5 V. Pulse width is defined by tw ≈ 0.7 × Rext × Cext, with Rext ranging 1.4 kΩ to 100 kΩ and Cext spanning 0 to 1000 µF.
Triggering is edge-sensitive: A input responds to positive transitions, B input to negative transitions - either may serve as inhibit. The overriding clear (CLR) terminates output pulses asynchronously, with minimum pulse duration of 40 ns and setup time of 15 ns. Output rise/fall times are TTL-compatible and independent of pulse length.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Max output pulse length | 70 ms - enables long-duration timing without external counters or microcontrollers |
| Timing resistance range | 1.4 kΩ to 100 kΩ - supports wide pulse-width tuning while maintaining jitter-free operation |
| Timing capacitance range | 0 to 1000 µF - allows dc-triggered reset (Cext = 0) or multi-second delays |
| B-input hysteresis | Typical 1.2 V - provides robust noise immunity against slow-rising or noisy signals |
| Supply voltage range | 4.75 V to 5.25 V - ensures stable operation within standard TTL rail tolerances |
| Output drive capability | IOL = 8 mA, IOH = −400 µA - directly drives TTL loads and small LEDs without buffering |
| Pulse width stability | ±0.5% unit-to-unit variation - reduces calibration burden in production systems |
Pinout & Package
SN74LS221NE4 is housed in a 16-pin plastic dual in-line package (PDIP-N), with 0.3-inch body width and through-hole mounting. Pin 1 is located at the top-left corner when the notch faces upward.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 3, 4, 5, 6, 13, 14, 15, 16 | Input/Output terminals | Includes A/B trigger inputs, CLR, Q/Q̅ outputs, and Rext/Cext connections per channel - no internal connection on pins 7, 8, 9, 10, 11, 12 |
| 7, 8, 9, 10, 11, 12 | No internal connection | Unused pins - must be left unconnected; not tied to VCC or GND |
| 16 | VCC | Positive supply (4.75–5.25 V); decoupling capacitor required near pin |
| 8 | GND | Ground reference for all logic and timing functions |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent monostables | Enables two synchronized or isolated timing functions on one IC - reduces board space vs. discrete solutions |
| Overriding asynchronous clear | Allows immediate termination of active output pulses - critical for safety interlocks and emergency stop logic |
| Schmitt-trigger B input | Supports clean triggering from slow or noisy waveforms (as low as 1 V/s slew rate) - eliminates need for external conditioning |
| DC-triggered reset mode | With Cext = 0 and Rext = 2 kΩ, delivers ~30 ns pulse - suitable for synchronous system resets |
| Pinout compatibility | Matches SN74LS123 and SN74123 - enables drop-in replacement in existing designs with only R/C value updates |
Applications
| Debounce Circuit | Programmable Delay Generator |
|---|---|
Use Scenario: Mechanical switch closure in industrial HMI panels introduces contact bounce lasting 1–10 ms. IC Role / Device Role / Timing Role: SN74LS221NE4 acts as a hardware debouncer, generating a clean, fixed-duration output pulse after first valid edge. Use Value: Eliminates firmware polling or RC+Schmitt filters; achieves sub-millisecond response with ±0.5% pulse width consistency across temperature. | Use Scenario: Test equipment requires adjustable delay between stimulus and measurement sampling. IC Role / Device Role / Timing Role: SN74LS221NE4 serves as a programmable one-shot, where Rext/Cext values set delay from 35 ns to 70 ms. Use Value: Enables analog-grade precision without microcontroller overhead; jitter-free over full 0–70°C range and 10 pF–1000 µF Cext. |
| Asynchronous Reset Sequencer | Edge-Detector Pulse Extender |
Use Scenario: FPGA or microprocessor startup requires staggered reset assertion across multiple subsystems. IC Role / Device Role / Timing Role: SN74LS221NE4 generates cascaded reset pulses using Q output to trigger second channel. Use Value: Provides deterministic, temperature-stable delays (e.g., 100 µs, 1 ms, 10 ms) without software intervention or crystal oscillators. | Use Scenario: A short logic-level pulse (e.g., from sensor interrupt) must be extended to meet minimum enable duration of downstream logic. IC Role / Device Role / Timing Role: SN74LS221NE4 extends narrow input edges into configurable-width output pulses. Use Value: Converts 50 ns input spikes into 1–100 µs clean TTL outputs - immune to noise-induced false triggers due to Schmitt B input. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar monostable multivibrator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS123N | Single monostable, identical pinout and timing equation; max pulse width 55 ms (Rext = 40 kΩ, Cext = 1000 µF) | Requires two devices for dual-channel operation; lacks independent B-input hysteresis spec | Select when only one timing channel is needed and board space permits duplication |
| SN74HC123N | CMOS version; wider VCC range (2–6 V), lower ICC (4 µA quiescent), but no Schmitt B input - susceptible to slow-edge noise | Not suitable for noisy industrial environments without external filtering; incompatible with 5 V TTL fanout requirements | Choose for battery-powered or mixed-voltage systems where power efficiency outweighs noise immunity needs |
Compared with SN74LS123N and SN74HC123N, the SN74LS221NE4 uniquely delivers dual-channel operation in one PDIP package with guaranteed Schmitt-trigger noise immunity on B inputs - making it optimal for space-constrained, noise-prone industrial timing applications requiring deterministic pulse widths.
Availability
SN74LS221NE4 is available at Aetrix Electronics and suitable for industrial control panels, test instrumentation, and legacy TTL system upgrades requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS221NE4 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 ICs, with decades of heritage in TTL and LS-family components.
The SN74LS221NE4 belongs to TI's legacy 74LS logic product line, engineered for high-noise-immunity, temperature-stable monostable timing in industrial, aerospace, and test equipment where reliability and pin compatibility with earlier 74-series devices are critical.
FAQ
What is the maximum output pulse width achievable with SN74LS221NE4?
The SN74LS221NE4 supports a maximum output pulse width of 70 ms when configured with Rext = 100 kΩ and Cext = 1000 µF. This value is derived from the timing equation tw ≈ 0.7 × Rext × Cext. At VCC = 5 V and TA = 25°C, the device maintains jitter-free operation across this full range. The SN74LS221NE4 datasheet confirms this limit under recommended operating conditions.
Can SN74LS221NE4 replace SN74LS123N in an existing design?
Yes, the SN74LS221NE4 can replace SN74LS123N in many cases due to identical pin assignments and shared timing architecture. However, SN74LS221NE4 is dual-channel while SN74LS123N is single-channel, so one SN74LS221NE4 replaces two SN74LS123N units. Rext/Cext values may require adjustment, and polarity of timing capacitors must be reversed per channel per the SN74LS221NE4 datasheet.
Does SN74LS221NE4 support DC-triggered reset operation?
Yes, the SN74LS221NE4 supports DC-triggered reset: with Cext = 0 and Rext = 2 kΩ, it delivers a typical 30 ns output pulse. This mode is explicitly validated in the SN74LS221NE4 datasheet and is used for synchronous system resets where minimal pulse width is required. The output remains TTL-compatible regardless of Cext value.
What is the input hysteresis specification for the B input of SN74LS221NE4?
The B input of SN74LS221NE4 features Schmitt-trigger hysteresis with a typical value of 1.2 V, defined by VT+ = 1.0–2.0 V and VT− = 0.7–0.9 V at VCC = 4.75 V. This hysteresis enables jitter-free triggering from slowly rising signals (down to 1 V/s) and provides strong immunity to noise on the B input line - a key differentiator from non-Schmitt monostables like the HC123.
Is SN74LS221NE4 RoHS compliant?
Yes, SN74LS221NE4 is RoHS compliant, with lead finish specified as NIPDAU (Nickel/Palladium/Gold) and packaging meeting JEDEC standards. The device carries "Yes" in the RoHS column of TI's official packaging addendum, and its PDIP-N package (16-pin) is rated for 0°C to 70°C operation with full traceability and lifecycle support through Aetrix Electronics.
SN74LS221NE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Active
- Logic Type:
- Monostable
- Independent Circuits:
- 2
- Schmitt Trigger Input:
- Yes
- Propagation Delay:
- 50 ns
- Current - Output High, Low:
- 8mA, 400µA
- Voltage - Supply:
- 4.75 V ~ 5.25 V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 16-PDIP
SN74LS221NE4 FAQ
1.How can I place an order for SN74LS221NE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS221NE4 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 SN74LS221NE4 reliable?
The price and inventory of SN74LS221NE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS221NE4 is usually 5 days.
3.What payment methods are accepted for SN74LS221NE4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS221NE4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS221NE4?
SN74LS221NE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS221NE4 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 SN74LS221NE4?
For technical support, including SN74LS221NE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS221NE4 requirements.
6.How does Aetrix verify that SN74LS221NE4 is sourced from the original manufacturer or authorized distributors?
All SN74LS221NE4 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 SN74LS221NE4 meets industry standards.
7.What is the process for return or replacement of SN74LS221NE4?
All SN74LS221NE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS221NE4, 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 SN74LS221NE4 part is unused and in its original packaging.
Return procedure for SN74LS221NE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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