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Texas Instruments SN74121NSR
- Part No.:
- SN74121NSR
- Manufacturer:
- Texas Instruments
- Category:
- Multivibrators
- Package:
- 14-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74121NSR.pdf
- Description:
- IC MULTIVIBRATOR 45NS 14SOP
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
SN74121NSR from Texas Instruments is a dual monostable multivibrator (one-shot) IC in SO-14 package, featuring complementary Schmitt-trigger inputs (A1, B1, A2, B2), active-low clear (CLR), and open-collector outputs (Q, Q̅). It delivers programmable pulse widths from 30 ns to 10 s via external RC networks, operates over 0°C to 70°C, and supports TTL-level compatibility for legacy digital timing control in industrial logic systems.
For engineers reviewing the SN74121NSR datasheet, SN74121NSR pinout, SN74121NSR application, or SN74121NSR equivalent, key selection criteria include its dual independent one-shot architecture, non-retriggerable operation mode, TTL input thresholds, open-collector output drive capability, and RoHS-compliant SOIC-14 packaging with MSL Level-2 moisture sensitivity rating.
Technical Context
The SN74121NSR implements two identical, electrically isolated monostable multivibrators on a single die. Each section uses internal Schmitt-trigger inputs to reject noise and ensure clean edge detection, and generates a single, precise output pulse upon triggering - with no retriggering allowed during the output pulse duration. Pulse width is externally set by REXT and CEXT, with timing governed by τ ≈ 0.7 × REXT × CEXT.
It features active-low asynchronous clear (CLR) that forces both Q outputs low regardless of input state or timing cycle, and open-collector outputs capable of sinking up to 16 mA per channel while supporting wired-AND configurations and level translation to higher supply rails (e.g., 12 V or 15 V) when used with external pull-up resistors.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Dual non-retriggerable monostable multivibrator (one-shot) |
| Supply Voltage | 4.75 V to 5.25 V - ensures stable TTL-compatible operation without marginal rail conditions |
| Pulse Width Range | 30 ns to 10 s - selectable via external R/C network; enables use from high-speed glitch suppression to long-delay timing |
| Input Thresholds | VIL = 0.8 V max, VIH = 2.0 V min - compatible with standard TTL logic families |
| Output Type | Open-collector - allows wired-AND logic, level shifting, and interface to loads beyond 5 V |
| Output Sink Current | 16 mA per output - sufficient to directly drive LEDs, small relays, or TTL inputs without buffering |
| Operating Temperature | 0°C to +70°C - suitable for commercial-grade embedded control and instrumentation applications |
Pinout & Package
SN74121NSR is housed in a 14-pin Small Outline Integrated Circuit (SOIC) package (package drawing NS), 3.9 mm wide, 8.65 mm long, and 1.75 mm maximum height, with gull-wing leads and RoHS-compliant NiPdAu finish.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (A1) | Schmitt-trigger input | Active-high trigger input for first multivibrator; requires ≥2.0 V for logic high |
| 2 (B1) | Schmitt-trigger input | Alternative active-high trigger input for first multivibrator; ORed with A1 internally |
| 3 (CLR1) | Asynchronous clear | Active-low reset for first multivibrator; overrides timing and forces Q1 low |
| 4 (Q1) | Open-collector output | Inverted output of first multivibrator; sinks current when active |
| 5 (Q̅1) | Open-collector output | True output of first multivibrator; sinks current when active |
| 6 (GND) | Ground reference | Primary return path for all internal circuitry and output sinks |
| 7 (VCC) | Power supply | +5 V nominal supply; must be decoupled locally for noise immunity |
| 8 (Q̅2) | Open-collector output | True output of second multivibrator; sinks current when active |
| 9 (Q2) | Open-collector output | Inverted output of second multivibrator; sinks current when active |
| 10 (CLR2) | Asynchronous clear | Active-low reset for second multivibrator; independent of CLR1 |
| 11 (B2) | Schmitt-trigger input | Alternative active-high trigger input for second multivibrator; ORed with A2 |
| 12 (A2) | Schmitt-trigger input | Active-high trigger input for second multivibrator |
| 13 (CEXT) | Timing capacitor connection | External capacitor node for setting pulse width of both sections |
| 14 (REXT/CEXT) | Timing resistor/capacitor node | Shared external R/C connection point; defines τ = 0.7 × R × C for both one-shots |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent one-shot sections | Enables synchronized or staggered timing generation without cross-talk; each section has dedicated clear and outputs |
| Non-retriggerable operation | Prevents pulse extension during ongoing output; guarantees fixed-width pulses even under noisy or repeated triggers |
| Complementary Schmitt-trigger inputs | Provides hysteresis (typ. 0.5 V) to suppress contact bounce, EMI, and slow-edge noise in mechanical or sensor interfaces |
| Open-collector outputs with 16 mA sink | Supports direct interfacing to higher-voltage logic, discrete loads, and bus-oriented designs without level-shifter ICs |
| Single external R/C network | Reduces component count and board space by sharing timing components between both monostables |
Applications
| Debounced Switch Interface | Pulse Width Modulation Preconditioning |
|---|---|
Use Scenario: Mechanical pushbutton or toggle switch connected to industrial HMI panel where contact bounce causes spurious interrupts. IC Role / Device Role / Timing Role: SN74121NSR acts as hardware debouncer - each switch feeds A1/B1, and Q̅1 delivers a clean, fixed-duration logic pulse to a microcontroller GPIO. Use Value: Eliminates need for firmware debounce routines or external RC+Schmitt circuits; provides deterministic 10–100 ms pulse width aligned to switch release. | Use Scenario: Legacy analog PWM signal conditioning prior to ADC sampling in test equipment with fixed sample clock. IC Role / Device Role / Timing Role: SN74121NSR converts variable-duty-cycle PWM edges into uniform-width pulses synchronized to system clock domain. Use Value: Enables accurate duty-cycle measurement using counter-based capture; removes jitter introduced by inconsistent rising/falling edge timing. |
| Glitch Suppression in Control Logic | Legacy Bus Arbitration Timing |
Use Scenario: Spurious transients on enable lines of power MOSFET drivers in motor control PCBs cause unintended turn-on events. IC Role / Device Role / Timing Role: SN74121NSR filters sub-30 ns noise spikes using Schmitt inputs and generates minimum 50 ns valid enable pulse only after stable high input. Use Value: Prevents false triggering of gate drivers; improves system reliability without adding FPGA logic or complex filtering. | Use Scenario: Synchronizing legacy parallel bus handshaking (e.g., STB, ACK) between mismatched speed peripherals in retro-computing or avionics maintenance tools. IC Role / Device Role / Timing Role: SN74121NSR generates standardized strobe delay and acknowledge window timing from asynchronous bus signals. Use Value: Resolves timing violations between TTL and LSTTL devices; replaces discrete 74LS123 implementations with reduced footprint and improved consistency. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar monostable multivibrator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS123DR | Retriggerable dual one-shot; different timing equation (τ ≈ 0.45 × R × C); TTL-input thresholds differ slightly | Requires redesign if non-retriggerable behavior is essential; better suited for event-counting or gated oscillator applications | Select SN74LS123DR only when retriggerability is required and timing recalibration is acceptable |
| MC14528BDG | CMOS dual monostable; wider VDD range (3–18 V); higher input impedance; slower max speed (~2 MHz vs. ~30 MHz for SN74121) | Enables single-supply mixed-voltage systems but lacks Schmitt inputs - requires external hysteresis for noisy environments | Choose MC14528BDG for battery-powered or multi-rail designs where power efficiency and voltage flexibility outweigh noise immunity needs |
Compared with SN74LS123DR and MC14528BDG, the SN74121NSR uniquely combines non-retriggerable operation, integrated Schmitt inputs, and open-collector outputs in a single SOIC-14 package - making it optimal for robust, noise-immune timing in legacy TTL-based control systems where pulse fidelity and simplicity are critical.
Availability
SN74121NSR is available at Aetrix Electronics and suitable for industrial control panels, test instrumentation, legacy system upgrades, and aerospace ground-support equipment requiring stable component supply across extended production lifecycles.
Supply support for SN74121NSR 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial, automotive, and consumer reach.
The SN74121NSR belongs to TI's legacy 74xx TTL logic family, designed specifically for reliable, low-cost, noise-tolerant digital timing functions in fixed-function control systems where programmability is unnecessary and deterministic pulse generation is paramount.
FAQ
What is the primary function of the SN74121NSR?
The SN74121NSR is a dual non-retriggerable monostable multivibrator (one-shot) IC. Its core function is to generate a single, precisely timed output pulse of programmable width in response to a clean input trigger. Each of its two independent sections accepts Schmitt-trigger inputs and produces complementary open-collector outputs (Q and Q̅), enabling robust timing control in legacy TTL systems. The SN74121NSR does not oscillate or latch - it strictly performs edge-to-pulse conversion with guaranteed minimum pulse integrity.
Can the SN74121NSR operate with a 3.3 V supply?
No, the SN74121NSR is a bipolar TTL device specified only for 4.75 V to 5.25 V operation. Its internal transistor thresholds, input hysteresis, and output saturation characteristics are optimized for 5 V logic levels. Applying 3.3 V will result in undefined behavior - including failure to recognize logic highs, insufficient output drive, or complete functional failure. For 3.3 V systems, consider CMOS alternatives like the MC14528 or 74LVC123, not the SN74121NSR.
Does the SN74121NSR support retriggering during an active output pulse?
No, the SN74121NSR is explicitly non-retriggerable. Once triggered, its output pulse width is fixed and immune to additional input transitions until the pulse completes and the circuit resets. This behavior is hardwired in its TTL architecture and confirmed in the official TI datasheet SDLS042A. If retriggerable operation is required, the SN74LS123 or SN74LV123 should be evaluated instead - but those are not functionally equivalent replacements for the SN74121NSR.
What is the purpose of the shared REXT/CEXT pins on the SN74121NSR?
The SN74121NSR uses a single external resistor and capacitor (connected between pins 13 and 14) to set the pulse width for both monostable sections simultaneously. This shared timing network reduces component count and layout complexity versus dual-independent one-shots. The timing relationship follows τ ≈ 0.7 × REXT × CEXT, and both sections produce identical pulse widths. This architecture makes the SN74121NSR ideal for applications requiring matched delays - such as dual-channel synchronization or redundant timing paths - without trimming or calibration.
Is the SN74121NSR pin-compatible with other 74121 variants like SN74121N or SN74121D?
Yes, the SN74121NSR is pin-compatible with all standard 14-pin 74121 variants including SN74121N (PDIP), SN74121D (SOIC), and SN74121DR. All share identical pinout, electrical specifications, and functional behavior - differing only in package type (SO-14 vs. PDIP vs. SOIC), moisture sensitivity level, and tape-and-reel configuration. The "NSR" suffix denotes the SOIC package with 2000-unit reel packaging and RoHS compliance, but the SN74121NSR maintains full functional and pin-for-pin equivalence with other 74121 versions in the same logic family.
SN74121NSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 7400
- Package/Case:
- 14-SOIC (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- 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-SO
SN74121NSR FAQ
1.How can I place an order for SN74121NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74121NSR 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 SN74121NSR reliable?
The price and inventory of SN74121NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74121NSR is usually 5 days.
3.What payment methods are accepted for SN74121NSR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74121NSR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74121NSR?
SN74121NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74121NSR 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 SN74121NSR?
For technical support, including SN74121NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74121NSR requirements.
6.How does Aetrix verify that SN74121NSR is sourced from the original manufacturer or authorized distributors?
All SN74121NSR 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 SN74121NSR meets industry standards.
7.What is the process for return or replacement of SN74121NSR?
All SN74121NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74121NSR, 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 SN74121NSR part is unused and in its original packaging.
Return procedure for SN74121NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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