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Texas Instruments SN74LS423D
- Part No.:
- SN74LS423D
- Manufacturer:
- Texas Instruments
- Category:
- Multivibrators
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74LS423D.pdf
- Description:
- IC MULTIVIBRATOR 28NS 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,844
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Product details
Overview
SN74LS423D from Texas Instruments is a dual monostable multivibrator IC used for precise pulse generation and timing control in digital logic systems. It features two independent retriggerable one-shots with 15 ns typical propagation delay, 30 ns minimum output pulse width, and TTL-compatible inputs/outputs. It operates over 0°C to 70°C and is commonly deployed in debounce circuits, event timing, and clock stretching applications.
For engineers reviewing the SN74LS423D datasheet, SN74LS423D pinout, SN74LS423D application, or SN74LS423D equivalent, key selection criteria include retriggerability, pulse width stability across temperature, input noise immunity, and compatibility with legacy 74LS logic families in industrial control and instrumentation designs.
Technical Context
The SN74LS423D implements two identical, edge-triggered monostable multivibrators with separate A and B inputs per channel, enabling asynchronous triggering. Each section supports both negative-edge (A) and positive-edge (B) trigger modes via external RC networks that set output pulse duration.
It uses bipolar TTL technology with Schmitt-trigger inputs on the B inputs for noise rejection, and internal clamping diodes protect against input overvoltage. The outputs drive standard TTL loads with 8 mA sink and 0.4 mA source capability at VCC = 5 V.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic family | 74LS (Low-power Schottky TTL) - ensures compatibility with legacy 5 V TTL systems and low power consumption vs standard 74 series. |
| Propagation delay | 15 ns typical - enables precise timing in high-speed digital control loops with minimal jitter accumulation. |
| Minimum pulse width | 30 ns - supports short-duration timing events such as switch debouncing or strobe generation without race conditions. |
| Supply voltage | 4.75 V to 5.25 V - tight tolerance ensures stable operation under regulated 5 V rails common in industrial backplanes. |
| Operating temperature | 0°C to 70°C - validated for commercial-grade embedded systems including test equipment and programmable logic interfaces. |
| Output drive | 8 mA sink / 0.4 mA source - sufficient to directly drive multiple 74LS inputs or small LED indicators without buffering. |
Pinout & Package
SN74LS423D is housed in a 16-pin SOIC (Small Outline Integrated Circuit) package with 1.27 mm pitch, 7.5 mm body width, and 2.00 mm max height per TI NS0016A drawing. The package is RoHS-compliant with NiPdAu lead finish and MSL Level-1 rating.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 13 | Channel 1 & 2 Reset (Active-Low) | Asynchronous reset pins; pulling low forces output Q to low regardless of trigger state - critical for system initialization and fault recovery. |
| 2, 12 | Channel 1 & 2 B Input (Schmitt-trigger) | Positive-edge sensitive inputs with hysteresis - reject noise on slow-rising signals like mechanical switch closures. |
| 3, 11 | Channel 1 & 2 A Input (Non-inverting) | Negative-edge sensitive inputs - used with external RC network to define pulse width; direct TTL-level compatibility. |
| 4, 10 | Channel 1 & 2 RC Ext | Connect external resistor and capacitor to set output pulse duration (tW ≈ 0.3 × R × C); enables field-adjustable timing. |
| 5, 9 | Channel 1 & 2 Q Output | Active-high, non-inverted output - drives downstream logic or discrete loads with TTL-compatible voltage levels. |
| 6, 8 | Channel 1 & 2 Q̅ Output | Complementary active-low output - provides inverted timing signal without external inverters, reducing component count. |
| 7 | GND | Ground reference for all internal circuitry and I/O - must be low-impedance connection to minimize switching noise coupling. |
| 14 | VCC | +5 V supply pin - requires local 0.1 µF ceramic decoupling capacitor placed within 5 mm of this pin for stable operation. |
Key Features
| Feature | Design Value |
|---|---|
| Retriggerable operation | Allows new trigger pulses to extend current output pulse - essential for continuous timing windows in data acquisition gating. |
| Independent RC timing per channel | Enables asymmetric pulse widths on each channel - supports dual-function timing such as enable/strobe sequencing in memory controllers. |
| Schmitt-trigger B inputs | Provides >0.8 V hysteresis - eliminates false triggering from EMI or contact bounce in industrial sensor interface applications. |
| TTL-compatible I/O levels | Ensures direct interfacing with 74LS, 74S, and 74F families without level-shifting - simplifies board design in mixed-logic systems. |
Applications
| Switch Debounce Circuit | Digital Event Timing |
|---|---|
Use Scenario: Mechanical pushbutton or rotary encoder interfacing where contact bounce causes multiple unintended logic transitions. IC Role / Device Role / Timing Role: Monostable multivibrator generating clean, fixed-duration pulses per valid button press. Use Value: Eliminates need for software debouncing or RC + Schmitt circuits - reduces firmware overhead and PCB area while ensuring deterministic response time. | Use Scenario: Precise interval measurement between asynchronous digital events such as interrupt requests or sensor triggers. IC Role / Device Role / Timing Role: Pulse stretcher and synchronizer that converts narrow glitches into measurable, aligned logic pulses. Use Value: Enables reliable capture by slower microcontrollers or logic analyzers - improves diagnostic accuracy in test and measurement equipment. |
| Serial Data Strobe Generation | Legacy System Clock Stretching |
Use Scenario: Generating synchronized strobe signals for parallel-to-serial shift register loading in industrial PLC I/O modules. IC Role / Device Role / Timing Role: Dual-channel timing generator producing complementary enable and latch pulses with adjustable width. Use Value: Ensures setup/hold timing compliance for 74LS595-type shift registers - prevents data corruption during high-noise factory floor operation. | Use Scenario: Extending CPU wait states in vintage 8-bit computer bus interfaces or retro computing expansion cards. IC Role / Device Role / Timing Role: Programmable delay element inserted into READY signal path to accommodate slow peripherals. Use Value: Maintains full hardware compatibility with original Z80/6502 bus timing - avoids FPGA-based glue logic redesigns in heritage system upgrades. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar monostable multivibrator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS123N | Non-retriggerable dual monostable; different RC timing configuration (R-C vs R×C); 22 ns typical tPLH. | Lacks retriggerability - unsuitable for continuous pulse extension but offers tighter pulse width tolerance (±10%). | Select SN74LS123N when fixed, non-overlapping timing intervals are required and retriggering is not needed. |
| CD74HC221M | High-speed CMOS; 2 V–6 V supply range; 14 ns tpd; non-retriggerable; Schmitt B inputs retained. | Requires level translation for 5 V TTL systems; superior noise immunity but incompatible with direct 74LS fanout. | Choose CD74HC221M for battery-powered or mixed-voltage designs where power efficiency and wider VCC range outweigh legacy compatibility. |
Compared with SN74LS123N and CD74HC221M, the SN74LS423D uniquely supports retriggerable operation in a 74LS-compatible footprint - making it the only option among the three for applications requiring dynamic pulse extension without external logic.
Availability
SN74LS423D is available at Aetrix Electronics and suitable for industrial control panels, test instrumentation, and legacy system upgrades requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS423D 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 solutions for industrial, automotive, and communications markets.
The SN74LS423D belongs to TI's legacy 74LS logic family, designed specifically for robust, low-power timing and signal conditioning in commercial-grade digital systems operating at 5 V.
FAQ
What is the function of the SN74LS423D in digital timing circuits?
The SN74LS423D functions as a dual retriggerable monostable multivibrator, generating precise, user-defined output pulses in response to input triggers. Each channel accepts independent A (negative-edge) and B (positive-edge with hysteresis) inputs and produces complementary Q and Q̅ outputs. Its retriggerable nature allows extending an active output pulse upon receiving subsequent triggers - a key capability for applications like switch debouncing and event gating. The SN74LS423D remains fully functional in legacy 74LS-based systems due to its TTL-compatible electrical characteristics and timing behavior.
How do I calculate the output pulse width for the SN74LS423D?
The output pulse width tW of the SN74LS423D is determined by an external resistor (R) and capacitor (C) connected to the RC Ext pin (pins 4 and 10), using the formula tW ≈ 0.3 × R × C. For example, a 10 kΩ resistor and 1000 pF capacitor yield ~3 µs pulse width. Component tolerances and temperature drift affect accuracy - typical variation is ±20% over 0°C to 70°C. The SN74LS423D does not support internal timing; all pulse durations must be set externally via this RC network.
Is the SN74LS423D pin-compatible with other 74LS monostable devices?
No, the SN74LS423D is not pin-compatible with other 74LS monostables such as the SN74LS122 or SN74LS123. Its 16-pin SOIC layout assigns dedicated A/B inputs, RC Ext, Q/Q̅, and Reset pins per channel in a unique arrangement. Substituting another part requires PCB redesign. The SN74LS423D pinout is standardized per TI's NS0016A package drawing and must be verified against schematic symbols before integration. Always consult the official SN74LS423D datasheet for exact terminal mapping.
What are the recommended decoupling practices for the SN74LS423D?
Each SN74LS423D requires a 0.1 µF ceramic capacitor placed as close as possible (≤5 mm) between VCC (pin 14) and GND (pin 7), with short, low-inductance traces. For boards with multiple SN74LS423D units, add a bulk 4.7 µF–10 µF electrolytic capacitor near the power entry point. Avoid shared vias between decoupling caps and other signals. These practices suppress high-frequency switching noise generated during output transitions and prevent supply rail droop that could cause metastability in adjacent logic. This applies identically to every SN74LS423D instance on the board.
Can the SN74LS423D operate outside the 0°C to 70°C range?
No - the SN74LS423D is specified and tested only for operation from 0°C to 70°C. TI does not guarantee performance or reliability beyond this commercial temperature range. Attempting to use the SN74LS423D in extended or industrial temperature environments (e.g., –40°C to +85°C) may result in increased propagation delay, reduced noise margin, or failure to trigger reliably. For wider temperature operation, consider modern alternatives like the CD74HC221, but note that those require voltage and logic-level adaptation. The SN74LS423D must be applied strictly within its rated thermal envelope.
SN74LS423D Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- Monostable
- Independent Circuits:
- 2
- 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:
- 16-SOIC
SN74LS423D FAQ
1.How can I place an order for SN74LS423D through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS423D 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 SN74LS423D reliable?
The price and inventory of SN74LS423D are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS423D is usually 5 days.
3.What payment methods are accepted for SN74LS423D?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS423D transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS423D?
SN74LS423D orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS423D 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 SN74LS423D?
For technical support, including SN74LS423D datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS423D requirements.
6.How does Aetrix verify that SN74LS423D is sourced from the original manufacturer or authorized distributors?
All SN74LS423D 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 SN74LS423D meets industry standards.
7.What is the process for return or replacement of SN74LS423D?
All SN74LS423D units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS423D, 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 SN74LS423D part is unused and in its original packaging.
Return procedure for SN74LS423D:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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