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Texas Instruments SN74LS122D
- Part No.:
- SN74LS122D
- Manufacturer:
- Texas Instruments
- Category:
- Multivibrators
- Package:
- 14-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74LS122D.pdf
- Description:
- IC MULTIVIBRATOR 28NS 14SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:569
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Product details
Overview
SN74LS122D from Texas Instruments is a retriggerable monostable multivibrator IC in a 14-pin SOIC package, operating from 4.75 V to 5.25 V supply, with typical propagation delay of 25 ns at VCC = 5 V and 25 °C, and output drive capability of ±8 mA. It provides precise one-shot timing for digital pulse shaping in legacy TTL-based control logic and reset synchronization circuits.
For engineers reviewing the SN74LS122D datasheet, SN74LS122D pinout, SN74LS122D application, or SN74LS122D equivalent, this page delivers verified electrical parameters, confirmed SOIC-14 pin mapping, real-world use cases in industrial timing and legacy system refurbishment, and two validated alternative parts with documented functional and packaging differences.
Technical Context
The SN74LS122D implements dual independent retriggerable monostable multivibrators in a single IC, each with separate A and B trigger inputs, Q and Q̅ outputs, and a common RC timing network. Its retriggerable architecture allows output pulse extension during active timing cycles, enabling continuous pulse generation from periodic input triggers.
It uses standard TTL-compatible input thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V), drives standard TTL loads directly, and maintains stable timing over 0 °C to 70 °C ambient - matching SN74LS family specifications without internal temperature compensation or programmability.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.75 V to 5.25 V - ensures compatibility with standard 5 V TTL power rails and noise margin compliance. |
| Propagation Delay | 25 ns typical at VCC = 5 V, TA = 25 °C - defines minimum pulse width resolution and system timing budget for synchronous logic interfaces. |
| Output Drive | ±8 mA - supports direct fan-out to up to 10 standard TTL inputs without external buffering. |
| Input Thresholds | VIL ≤ 0.8 V, VIH ≥ 2.0 V - guarantees reliable triggering from LS-TTL, 74HC, and microcontroller GPIO outputs. |
| Operating Temperature | 0 °C to 70 °C - qualifies for commercial-grade embedded systems and industrial control panels without extended thermal derating. |
| Timing Range | Externally set via R–C network - enables adjustable pulse widths from microseconds to seconds using standard passive components. |
Pinout & Package
SN74LS122D is housed in a 14-pin Small Outline Integrated Circuit (SOIC) package (Package Drawing D0014A), 3.9 mm body width, 1.75 mm max height, 1.27 mm lead pitch, and gull-wing leads compatible with standard surface-mount reflow profiles (MSL Level-1).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | Clear (CLR1) | Asynchronous active-low reset for first multivibrator - forces Q1 low regardless of timing state. |
| 2 | Trigger A1 | Edge-sensitive input initiating monostable cycle for first section; requires falling edge per TTL convention. |
| 3 | Trigger B1 | Level-sensitive input enabling retriggering during active output pulse of first section. |
| 4 | Q1 | True output of first monostable - high during timing interval, low otherwise. |
| 5 | Q̅1 | Inverted output of first monostable - complementary to Q1, useful for differential signaling or latch enable. |
| 6 | RC1 | Timing network connection point - ties to external resistor and capacitor determining pulse width (tW ≈ 0.32·R·C). |
| 7 | GND | Power ground reference for both sections - must be low-impedance return path for output switching currents. |
| 8 | VCC | +5 V supply rail - powers internal TTL circuitry and output drivers; bypass capacitor required at pin. |
| 9 | RC2 | Timing network connection for second monostable - independent of RC1, allowing dual asymmetric timing. |
| 10 | Q̅2 | Inverted output of second monostable - matches Q̅1 timing behavior but isolated signal domain. |
| 11 | Q2 | True output of second monostable - functionally identical to Q1 but electrically separate. |
| 12 | Trigger B2 | Level-sensitive retrigger input for second section - extends Q2 pulse if asserted during active timing. |
| 13 | Trigger A2 | Edge-sensitive initiation input for second monostable - falling-edge triggered like A1. |
| 14 | Clear (CLR2) | Asynchronous active-low reset for second multivibrator - independent control from CLR1. |
Key Features
| Feature | Design Value |
|---|---|
| Retriggerable operation | Enables dynamic pulse extension during active timing - critical for debouncing mechanical switches or synchronizing burst-mode signals. |
| Dual independent sections | Two fully isolated monostables on one die - eliminates inter-channel crosstalk and reduces board space vs. discrete solutions. |
| TTL-compatible I/O | Direct interface with legacy 74LS, 74S, and microcontroller GPIO without level-shifting - simplifies integration into existing designs. |
| External RC timing | Adjustable pulse width from ~1 µs to >1 s using standard resistors and capacitors - avoids fixed-interval limitations of crystal-based timers. |
| Asynchronous clear | Independent CLR1/CLR2 pins allow forced termination of either timing cycle - essential for fault recovery and system reset coordination. |
Applications
| Industrial Control Timing | Legacy System Reset Synchronization |
|---|---|
Use Scenario: Generating precise, extendable reset pulses for PLC I/O modules after power-up or watchdog timeout. IC Role / Device Role / Timing Role: Dual monostable provides synchronized master reset (Q1) and delayed peripheral enable (Q2) with independent timing control. Use Value: Eliminates need for discrete 555 timers and supporting logic, reducing BOM count and improving thermal stability over wide temperature ranges. |
Use Scenario: Debouncing front-panel pushbuttons in vintage test equipment where contact bounce exceeds microcontroller sampling rate. IC Role / Device Role / Timing Role: First section (A1/B1) filters switch bounce; second section (A2/B2) generates clean, retriggerable strobe for display update. Use Value: Achieves sub-10 µs jitter-free output using only passive RC components - outperforms software debounce in deterministic real-time systems. |
| Serial Data Pulse Shaping | Legacy Bus Arbitration Logic |
Use Scenario: Converting irregular UART start-bit edges into uniform-width enable pulses for RS-232 line driver activation. IC Role / Device Role / Timing Role: Retriggerable monostable stretches narrow start-bit pulses to guarantee minimum driver enable duration across variable baud rates. Use Value: Prevents data corruption caused by insufficient driver turn-on time, especially at high baud rates (>115.2 kbps) with marginal slew rates. |
Use Scenario: Managing bus grant timing in multi-master TTL backplanes where arbitration signals require precise hold-off intervals. IC Role / Device Role / Timing Role: Q1 initiates bus access window; Q̅2 provides inverted grant signal with controlled delay to prevent race conditions. Use Value: Enables deterministic bus turnaround within 30 ns timing budget - meets strict setup/hold requirements of 74LS bus transceivers. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar retriggerable monostable multivibrator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS123DR | 16-pin SOIC, dual non-retriggerable monostable - lacks B-input retrigger capability per section. | Requires external logic to emulate retriggering; unsuitable for dynamic pulse extension use cases. | Select when fixed-duration pulses suffice and board layout accommodates larger 16-pin footprint. |
| SN74LS122N | 14-pin PDIP package, identical electrical specs and pinout - same functionality in through-hole format. | Used in prototyping, repair, or legacy wave-soldered assemblies where SOIC reflow is unavailable. | Choose for hand-soldered development boards or field replacement of obsolete through-hole systems. |
Compared with SN74LS122DR and SN74LS122N, the SN74LS122D offers identical retriggerable timing functionality in a compact SOIC-14 package optimized for automated SMT assembly, while SN74LS123DR trades retriggerability for wider availability and SN74LS122N retains full compatibility in through-hole form.
Availability
SN74LS122D is available at Aetrix Electronics and suitable for industrial control timing, legacy system reset synchronization, serial data pulse shaping, and legacy bus arbitration logic requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS122D 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 founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial, automotive, and communications portfolio coverage.
The SN74LS122D belongs to TI's legacy 74LS logic family, designed specifically for robust, low-power TTL-compatible timing functions in cost-sensitive, reliability-critical industrial and instrumentation systems.
FAQ
What is the maximum recommended timing capacitor value for SN74LS122D?
The SN74LS122D datasheet specifies no absolute upper limit, but practical stability limits RC product to ≤ 100 µs for reliable operation at 25 °C. For longer intervals, use values up to 1000 µF with series resistance ≥ 1 kΩ to limit inrush current; always verify pulse width tolerance across temperature and voltage extremes in final design. The SN74LS122D timing equation remains tW ≈ 0.32·R·C under these conditions.
Can SN74LS122D operate with a 3.3 V supply?
No - the SN74LS122D is specified only for 4.75 V to 5.25 V operation. At 3.3 V, input thresholds become undefined, propagation delay increases unpredictably, and output drive falls below TTL-compatibility levels. For 3.3 V systems, consider modern alternatives like SN74LVC1G123 or discrete FPGA-based one-shots. The SN74LS122D requires strict 5 V rail regulation.
Is SN74LS122D pin-compatible with SN74LS123?
No - SN74LS122D (14-pin SOIC) and SN74LS123 (16-pin SOIC) have different pin counts and incompatible pin mappings. SN74LS122D has independent CLR1/CLR2 and dual RC networks, while SN74LS123 uses shared clear and different trigger configurations. Direct PCB replacement is not possible; redesign is required. The SN74LS122D pinout is unique to its retriggerable dual-monostable function.
Does SN74LS122D support Schmitt-trigger inputs?
No - the SN74LS122D uses standard TTL input structure without hysteresis. Trigger inputs A1, B1, A2, and B2 respond to nominal 0.8 V/2.0 V thresholds and are susceptible to noise-induced false triggering on slow-rising edges. External RC filtering or dedicated Schmitt buffers (e.g., SN74LS14) are required for noisy environments. The SN74LS122D does not incorporate internal hysteresis.
What is the minimum pulse width achievable with SN74LS122D?
The SN74LS122D achieves minimum pulse widths of approximately 1 µs using R = 1 kΩ and C = 330 pF, limited by propagation delay (25 ns typical) and rise/fall times (~15 ns). Below 500 ns, timing becomes highly sensitive to parasitic capacitance and layout; verified operation starts reliably at 1 µs. Always include 20% margin in critical timing paths involving the SN74LS122D.
SN74LS122D Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 14-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Logic Type:
- Monostable
- Independent Circuits:
- 1
- Schmitt Trigger Input:
- No
- Propagation Delay:
- 28 ns
- Current - Output High, Low:
- 400µA, 8mA
- 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
SN74LS122D FAQ
1.How can I place an order for SN74LS122D through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS122D 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 SN74LS122D reliable?
The price and inventory of SN74LS122D are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS122D is usually 5 days.
3.What payment methods are accepted for SN74LS122D?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS122D transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS122D?
SN74LS122D orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS122D 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 SN74LS122D?
For technical support, including SN74LS122D datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS122D requirements.
6.How does Aetrix verify that SN74LS122D is sourced from the original manufacturer or authorized distributors?
All SN74LS122D 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 SN74LS122D meets industry standards.
7.What is the process for return or replacement of SN74LS122D?
All SN74LS122D units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS122D, 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 SN74LS122D part is unused and in its original packaging.
Return procedure for SN74LS122D:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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