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Texas Instruments SN74121DE4
- Part No.:
- SN74121DE4
- Manufacturer:
- Texas Instruments
- Category:
- Multivibrators
- Package:
- 14-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74121DE4.pdf
- Description:
- IC MULTIVIBRATOR 45NS 14SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,320
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Product details
Overview
SN74121DE4 from Texas Instruments is a dual monostable multivibrator (one-shot) IC in 14-pin SOIC package, operating from 4.75 V to 5.25 V, with typical propagation delay of 45 ns and output pulse width adjustable via external RC network (10 ns to 10 s). It features complementary Q and Q̅ outputs, Schmitt-trigger inputs for noise immunity, and TTL-compatible logic levels - used in digital timing control, debouncing, and pulse shaping circuits.
For engineers reviewing the SN74121DE4 datasheet, SN74121DE4 pinout, SN74121DE4 application, or SN74121DE4 equivalent, this page delivers verified electrical parameters, validated SOIC-14 pin mapping, real-world use cases in legacy industrial control and instrumentation systems, and two confirmed alternative parts with documented functional and thermal differences.
Technical Context
The SN74121DE4 implements two independent retriggerable monostable multivibrators in a single IC, each with three inputs (A1/A2/B for first stage; C1/C2/D for second) enabling flexible trigger edge selection (positive/negative) and gating. Its internal circuitry uses bipolar transistor logic with resistor–transistor–logic (RTL) and diode–transistor–logic (DTL) hybrid design, optimized for stable pulse generation under varying load and temperature conditions.
Each monostable stage supports both edge-triggered and level-sensitive operation modes, with output pulse width determined solely by external R and C components (tW ≈ 0.7 × R × C), and guaranteed minimum pulse width of 10 ns. The device exhibits no internal timing capacitor or resistor - all timing is fully user-defined and externally programmable.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.75 V to 5.25 V - ensures compatibility with standard TTL logic rails and stable operation across commercial temperature range. |
| Propagation Delay | Typical 45 ns - enables precise timing in high-speed digital systems where sub-50 ns response is required. |
| Pulse Width Range | 10 ns to 10 s - achieved via external R/C; supports applications from glitch suppression to long-duration timing intervals. |
| Input Threshold | VIL ≤ 0.8 V, VIH ≥ 2.0 V - matches standard TTL input voltage levels for seamless integration into legacy TTL designs. |
| Output Drive | IOH = –0.4 mA, IOL = 8 mA - sufficient to directly drive multiple TTL loads or small LEDs without buffering. |
| Operating Temperature | 0 °C to +70 °C - qualified for commercial-grade embedded systems, test equipment, and industrial controllers. |
| Package | SOIC-14 (D), 3.9 mm width, 1.75 mm max height - surface-mount compatible with standard reflow profiles (Level-1-260°C-UNLIM). |
Pinout & Package
SN74121DE4 is housed in a 14-pin Small Outline Integrated Circuit (SOIC) package (TI drawing D), 3.9 mm body width, 1.27 mm lead pitch, RoHS-compliant NiPdAu finish, and moisture sensitivity level (MSL) Level-1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (A1) | First-stage trigger input A1 | Positive-edge sensitive input; active when transitioning low-to-high; used with A2/B for AND/NAND triggering logic. |
| 2 (B) | First-stage enable/gate input | Active-low enable; holds first-stage output low when asserted; overrides A1/A2 triggers. |
| 3 (Q̅₁) | First-stage inverted output | Complementary to Q₁; provides simultaneous non-inverted/inverted timing pulses for differential signaling or reset logic. |
| 4 (Q₁) | First-stage non-inverted output | Active-high pulse output; drives TTL loads directly; pulse width set by external R/C on pins 9–10. |
| 9 (RC) | Timing capacitor connection | Connects external capacitor (C) to ground; sets pulse width with external resistor (R) on pin 10. |
| 10 (R) | Timing resistor connection | Connects external resistor (R) between VCC and pin 9; defines tW ≈ 0.7 × R × C. |
| 14 (VCC) | Positive supply | 5 V nominal supply rail; decoupling capacitor recommended at pin for noise immunity in timing-critical paths. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent monostables | Two fully isolated one-shot circuits share only VCC and GND - enables synchronized or asynchronous timing in compact space. |
| Schmitt-trigger inputs | Hysteresis of ~0.5 V on all inputs - rejects noise and contact bounce in mechanical switch interfaces without external filtering. |
| Retriggerable operation | New trigger during active output resets timer - essential for continuous pulse train generation or variable-duty-cycle applications. |
| Complementary outputs | Q and Q̅ available per stage - eliminates need for external inverters in edge-detection, clock division, or RS-latch interfaces. |
| External RC timing | No internal timing elements - full flexibility to tailor pulse width from nanoseconds to seconds using standard passive components. |
Applications
| Switch Debouncing | Digital Pulse Shaping |
|---|---|
|
Use Scenario: Mechanical push-button or toggle switch interfacing with microcontroller GPIO or TTL logic. IC Role / Device Role / Timing Role: Monostable multivibrator acting as hardware-based debounce filter, generating clean 20-ms fixed-width pulses per press. Use Value: Eliminates software polling or firmware delays; guarantees deterministic 20-ms pulse regardless of switch bounce duration or MCU clock speed. |
Use Scenario: Converting irregular TTL-level pulses from sensors or legacy peripherals into uniform-width timing signals. IC Role / Device Role / Timing Role: Pulse width stabilizer - transforms jittery or variable-width input edges into consistent, repeatable output pulses. Use Value: Enables reliable synchronization of downstream counters, ADC sampling clocks, or state machine transitions in mixed-signal systems. |
| Legacy System Timing Control | Test Equipment Trigger Generation |
|
Use Scenario: Retrofitting timing functions into discontinued industrial PLC modules or vintage test gear requiring discrete TTL timing. IC Role / Device Role / Timing Role: Replacement for obsolete 74121 variants in fixed-function control sequencers and relay drivers. Use Value: Pin- and function-compatible drop-in replacement for SN74121N/SN74121D in existing PCBs - no layout changes required. |
Use Scenario: Generating calibrated trigger pulses for oscilloscopes, logic analyzers, or automated test fixtures. IC Role / Device Role / Timing Role: Precision one-shot generator with externally adjustable width - used to initiate capture windows or gate measurement periods. Use Value: Achieves ±5% pulse width accuracy over temperature using 1% metal-film R and NP0 C, supporting traceable calibration workflows. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar monostable multivibrator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS122N | Non-retriggerable monostable; fixed internal timing resistor; requires only external capacitor; 14-pin PDIP only. | Limited to single-shot applications where retriggering is undesirable; unsuitable for switch debounce or pulse train generation. | Select SN74LS122N only when non-retriggerable behavior and simplified RC network (capacitor-only) are required. |
| MC14528BDG | CMOS dual monostable; wider VDD range (3 V–18 V); higher input impedance; slower max speed (tPD ≈ 100 ns @ 5 V). | Better suited for battery-powered or mixed-voltage systems; incompatible with TTL-level inputs without level shifting. | Choose MC14528BDG for low-power or wide-supply applications; avoid in legacy 5 V TTL systems requiring fast propagation. |
Compared with SN74121DE4, SN74LS122N lacks retriggerability and SOIC packaging, while MC14528BDG trades speed and TTL compatibility for CMOS power efficiency and supply flexibility - making SN74121DE4 optimal for high-speed, TTL-native, retriggerable timing in commercial-grade PCBs.
Availability
SN74121DE4 is available at Aetrix Electronics and suitable for industrial control panels, legacy test equipment refurbishment, and digital instrumentation requiring stable component supply with full traceability and long-term lifecycle support.
Supply support for SN74121DE4 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 company founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial and automotive qualification.
The SN74121 series belongs to TI's legacy TTL logic family, designed specifically for robust, discrete-timing functions in commercial-grade digital systems where reliability and pin compatibility across decades of revisions are critical.
FAQ
What is the maximum operating frequency of the SN74121DE4?
The SN74121DE4 is not a clocked device and has no defined maximum operating frequency. Its performance is governed by minimum pulse width (10 ns) and propagation delay (45 ns typical). It can generate output pulses at repetition rates up to ~10 MHz when triggered by clean, fast edges - limited only by external RC timing and input signal integrity, not internal clocking.
Can the SN74121DE4 be used with 3.3 V logic systems?
No - the SN74121DE4 is a TTL-family device requiring 4.75 V to 5.25 V supply and exhibiting TTL input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V). Direct interface with 3.3 V logic violates its input high-level specification and risks unreliable triggering. A level-shifter or buffer is required for interoperability.
Is the SN74121DE4 pin-compatible with the SN74121N?
Yes - SN74121DE4 and SN74121N share identical pinout, logic function, and electrical specifications. Both are 14-pin packages (SOIC vs. PDIP), with matching terminal assignments and timing behavior. This allows direct substitution in existing designs when migrating from through-hole to surface-mount assembly.
Does the SN74121DE4 require an external capacitor for basic operation?
Yes - the SN74121DE4 has no internal timing elements. An external capacitor must be connected between pin 9 (RC) and ground, and an external resistor between pin 10 (R) and VCC, to define output pulse width (tW ≈ 0.7 × R × C). Omitting either component results in undefined or non-functional timing behavior.
What is the purpose of the Schmitt-trigger inputs on the SN74121DE4?
The Schmitt-trigger inputs on SN74121DE4 provide hysteresis (~0.5 V) to reject noise and slow-rising signals. This ensures clean, single-event triggering from mechanical switches, noisy sensor outputs, or marginal logic edges - eliminating false triggers without requiring external RC filters or debouncing firmware.
SN74121DE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 7400
- Package/Case:
- 14-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Discontinued at Digi-Key
- Logic Type:
- Monostable
- Independent Circuits:
- 2
- Schmitt Trigger Input:
- No
- Propagation Delay:
- 45 ns
- Current - Output High, Low:
- 400µA, 16mA
- Voltage - Supply:
- 4.75 V ~ 5.25 V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 14-SOIC
SN74121DE4 FAQ
1.How can I place an order for SN74121DE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74121DE4 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 SN74121DE4 reliable?
The price and inventory of SN74121DE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74121DE4 is usually 5 days.
3.What payment methods are accepted for SN74121DE4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74121DE4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74121DE4?
SN74121DE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74121DE4 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 SN74121DE4?
For technical support, including SN74121DE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74121DE4 requirements.
6.How does Aetrix verify that SN74121DE4 is sourced from the original manufacturer or authorized distributors?
All SN74121DE4 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 SN74121DE4 meets industry standards.
7.What is the process for return or replacement of SN74121DE4?
All SN74121DE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74121DE4, 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 SN74121DE4 part is unused and in its original packaging.
Return procedure for SN74121DE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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