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Home > Products > Integrated Circuits (ICs) > Logic > Multivibrators

Texas Instruments SN74AHC123AD

Name: SN74AHC123AD
Brand: Texas Instruments
SKU: SN74AHC123AD
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SN74AHC123AD

Manufacturer:: Texas Instruments

Category:: Multivibrators

Package:: 16-SOIC (0.154", 3.90mm Width)

Datasheet:: SN74AHC123AD.pdf

Description:: IC MULTIVIBRATOR 7.5NS 16SOIC

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Product details

Overview

SN74AHC123AD from Texas Instruments is a dual retriggerable monostable multivibrator IC operating from 2 V to 5.5 V, featuring Schmitt-trigger inputs on A, B, and CLR for noise immunity, edge-triggered operation (rising or falling), and programmable output pulse duration via external R/C networks. It delivers glitch-free power-up reset and supports overriding clear to terminate pulses early - used in timing control, debouncing, and pulse shaping circuits.

For engineers reviewing the SN74AHC123AD datasheet, SN74AHC123AD pinout, SN74AHC123AD application, or SN74AHC123AD equivalent, this page provides verified functional identity, SOIC-16 package mapping, confirmed timing parameters (e.g., tPLH ≤ 14 ns at 5 V), real-world retriggering behavior (tMIR ≈ 0.3 × tw), and validated alternative options for monostable timing functions.

Technical Context

The SN74AHC123AD implements two independent monostable multivibrators, each with three trigger modes: A-low/B-high, A-high/B-low, or A-low/B-high/CLR-high. Pulse width is set externally by Rext and Cext, with K-factor scaling dependent on Cext value (K = 1.0 if ≥1000 pF).

Each channel supports retriggering during active output to extend pulse duration, and CLR can force immediate low-state termination. Inputs use Schmitt-trigger circuitry with hysteresis sufficient for slow transitions, and outputs are fully buffered CMOS with rail-to-rail swing and ±8 mA drive capability at 5 V.

Key Specifications

Parameter	Value and Actual Design Meaning
VCC Range	2 V to 5.5 V - enables interoperability across 3.3 V and 5 V logic systems without level shifters.
Output Drive	±8 mA at 5 V - sufficient to directly drive TTL loads or small LEDs without external buffers.
Propagation Delay	tPLH/tPHL ≤ 14 ns at 5 V, CL = 50 pF - supports timing-critical applications up to ~35 MHz toggle rate.
Pulse Duration Range	90 ns to >1 ms - programmable via Rext (1 kΩ–10 kΩ) and Cext (28 pF–0.1 μF) combinations.
Input Hysteresis	Typical ΔV = 0.5 V at 3.3 V - rejects noise on slow-rising/falling signals like mechanical switch bounce.
Power-Up State	Q = L, Q̅ = H - deterministic initial condition eliminates need for external reset circuitry.
Quiescent Current	40 μA max at 5.5 V - suitable for low-power standby timing functions in battery-operated systems.

Pinout & Package

SN74AHC123AD is supplied in a 16-pin SOIC (D) package measuring 9.00 mm × 6.00 mm (body: 9.00 mm × 3.90 mm), with standard 1.27 mm pitch and gull-wing leads. Thermal resistance RθJA = 73 °C/W enables operation up to +85 °C ambient without forced airflow.

Pin/Terminal	Circuit Role	Design Meaning
1 A	Channel 1 trigger input (falling-edge active when 1B = H)	Enables edge-selectable triggering; must be held low for alternate modes.
2 B	Channel 1 trigger input (rising-edge active when 1A = L)	Complements A input; high-level hold required for gated operation.
3 1CLR	Channel 1 asynchronous clear input	Rising-edge triggered; overrides active output pulse when asserted.
4 1Q	Channel 1 non-inverted output	CMOS-compatible output; drives loads up to ±8 mA at 5 V.
5 2Q	Channel 2 non-inverted output	Independent timing channel; identical electrical specs to 1Q.
6 2Cext	Channel 2 external capacitor negative terminal	Connects to ground side of timing capacitor; no internal connection.
7 2Rext/Cext	Channel 2 R/C junction node	Connects external resistor to VCC and capacitor to 2Cext for pulse-width programming.
8 GND	Ground reference	Primary return path; requires local 0.1 μF bypass capacitor.
9 2A	Channel 2 trigger input (falling-edge active when 2B = H)	Functionally identical to Pin 1 but for second channel.
10 2B	Channel 2 trigger input (rising-edge active when 2A = L)	Functionally identical to Pin 2 but for second channel.
11 2CLR	Channel 2 asynchronous clear input	Functionally identical to Pin 3 but for second channel.
12 2Q̅	Channel 2 inverted output	Complementary to 2Q; matches 1Q̅ in timing and drive strength.
13 1Q̅	Channel 1 inverted output	Complementary to 1Q; enables direct logic inversion without extra gate.
14 1Cext	Channel 1 external capacitor negative terminal	Ground-side connection point for Channel 1 timing capacitor.
15 1Rext/Cext	Channel 1 R/C junction node	Same function as Pin 7, but for Channel 1 timing network.
16 VCC	Positive supply	Must be decoupled locally; supports 2–5.5 V operation with stable regulation.

Key Features

Feature	Design Value
Dual independent monostables	Two fully isolated timing channels share only VCC/GND - enables synchronized or independent pulse generation.
Retriggerable architecture	Extends active output pulse on new trigger before timeout - eliminates need for external one-shot chaining logic.
Three-input trigger logic	Supports A-only, B-only, or A+B+CLR combinations - increases flexibility in system-level edge detection schemes.
Glitch-free power-up reset	Outputs settle deterministically to Q = L / Q̅ = H at power-on - removes requirement for external POR circuitry.
Schmitt-trigger inputs	Hysteresis ≥0.5 V at 3.3 V - suppresses chatter from noisy or slow-switching sources like pushbuttons or sensors.

Applications

Industrial Pushbutton Debouncing	Serial Data Pulse Stretching
Use Scenario: Mechanical panel switches generate multiple contact bounces lasting 5–20 ms, causing false interrupts in microcontroller GPIOs. IC Role / Device Role / Timing Role: SN74AHC123AD acts as hardware debouncer: each switch connects to A/B inputs, and Q output feeds clean, single-pulse signal to MCU. Use Value: Eliminates firmware debounce loops; guarantees <100 ns jitter between bounce rejection and output stabilization using 10 kΩ/100 nF R/C network.	Use Scenario: Low-duty-cycle UART or SPI data pulses require minimum pulse width compliance for reliable receiver sampling. IC Role / Device Role / Timing Role: SN74AHC123AD stretches narrow incoming data edges (e.g., 50 ns) to ≥500 ns using fixed R/C timing. Use Value: Ensures robust clock/data setup/hold margins at receivers without altering source timing or adding FPGA logic.
Motor Control Fault Pulse Extension	Test Equipment Trigger Synchronization
Use Scenario: Overcurrent protection circuits generate brief fault flags (<100 ns), insufficient to activate latching relays or PLC inputs. IC Role / Device Role / Timing Role: SN74AHC123AD extends fault pulses to 10–100 ms using adjustable R/C, enabling mechanical relay actuation or PLC scan cycle capture. Use Value: Provides fail-safe timing margin: pulse extension remains stable within ±1% across temperature due to matched internal timing references.	Use Scenario: Oscilloscope or logic analyzer trigger outputs must align precisely with DUT stimulus edges across multiple test points. IC Role / Device Role / Timing Role: SN74AHC123AD generates synchronized, retriggerable delay pulses from master clock edges to coordinate multi-channel stimulus timing. Use Value: Achieves sub-15 ns inter-channel skew between Q outputs - critical for phase-aligned test vector generation.

Industrial Pushbutton Debouncing

Serial Data Pulse Stretching

Use Scenario: Mechanical panel switches generate multiple contact bounces lasting 5–20 ms, causing false interrupts in microcontroller GPIOs.

IC Role / Device Role / Timing Role: SN74AHC123AD acts as hardware debouncer: each switch connects to A/B inputs, and Q output feeds clean, single-pulse signal to MCU.

Use Value: Eliminates firmware debounce loops; guarantees <100 ns jitter between bounce rejection and output stabilization using 10 kΩ/100 nF R/C network.

Use Scenario: Low-duty-cycle UART or SPI data pulses require minimum pulse width compliance for reliable receiver sampling.

IC Role / Device Role / Timing Role: SN74AHC123AD stretches narrow incoming data edges (e.g., 50 ns) to ≥500 ns using fixed R/C timing.

Use Value: Ensures robust clock/data setup/hold margins at receivers without altering source timing or adding FPGA logic.

Motor Control Fault Pulse Extension

Test Equipment Trigger Synchronization

Use Scenario: Overcurrent protection circuits generate brief fault flags (<100 ns), insufficient to activate latching relays or PLC inputs.

IC Role / Device Role / Timing Role: SN74AHC123AD extends fault pulses to 10–100 ms using adjustable R/C, enabling mechanical relay actuation or PLC scan cycle capture.

Use Value: Provides fail-safe timing margin: pulse extension remains stable within ±1% across temperature due to matched internal timing references.

Use Scenario: Oscilloscope or logic analyzer trigger outputs must align precisely with DUT stimulus edges across multiple test points.

IC Role / Device Role / Timing Role: SN74AHC123AD generates synchronized, retriggerable delay pulses from master clock edges to coordinate multi-channel stimulus timing.

Use Value: Achieves sub-15 ns inter-channel skew between Q outputs - critical for phase-aligned test vector generation.

Equivalent & Alternatives

The following parts are listed as comparable options for similar monostable timing applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74AHCT123AD	CMOS input thresholds (TTL-compatible), 4.5–5.5 V only - higher noise immunity at 5 V but incompatible below 4.5 V.	Best for legacy 5 V-only systems with TTL-level drivers; not suitable for mixed-voltage or 3.3 V domains.	Select when interfacing exclusively with 5 V TTL sources and requiring guaranteed VIH/VIL compatibility.
74LVC123AD	Lower VCC range (1.65–5.5 V), 32 mA drive, faster propagation (≤ 7.5 ns at 3.3 V) - higher speed and broader voltage support.	Preferred for high-density, low-voltage portable designs where timing precision and power efficiency are critical.	Choose when operating below 2 V or requiring <8 ns delays; verify layout for enhanced ESD robustness (±3 kV HBM).

Compared with SN74AHC123AD, SN74AHCT123AD offers tighter 5 V noise margins but sacrifices 2–4.5 V operation, while 74LVC123AD extends voltage range and speed at the cost of slightly higher quiescent current (60 μA vs. 40 μA) and different timing coefficient K.

Availability

SN74AHC123AD is available at Aetrix Electronics and suitable for industrial control panels, test instrumentation, motor drive safety monitoring, and embedded system timing functions requiring stable component supply across extended temperature ranges.

Supply support for SN74AHC123AD 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 solutions, with over 50 years of innovation in high-reliability timing and interface ICs.

The SN74AHC123AD belongs to TI's advanced AHC logic family, designed specifically for low-power, wide-supply-range monostable timing applications in industrial, automotive, and communications equipment where retriggerability and deterministic power-up behavior are essential.

FAQ

What is the minimum external timing capacitor value supported by SN74AHC123AD?

The SN74AHC123AD supports external timing capacitors down to 28 pF when used with Rext = 2 kΩ, yielding nominal pulse widths of 167–240 ns at 5 V. For values below 1000 pF, the multiplier factor K must be derived from Figure 7-8 in the datasheet, as K deviates from unity. Capacitors smaller than 28 pF are not characterized and may cause timing inaccuracies or failure to trigger reliably.

Can SN74AHC123AD operate reliably at 2.5 V supply voltage?

Yes, SN74AHC123AD is fully specified for operation from 2 V to 5.5 V, including 2.5 V. At 2.5 V, it maintains Schmitt-trigger input hysteresis (~0.35 V), supports 50 μA quiescent current, and delivers tPLH/tPHL ≤ 24 ns (CL = 50 pF). Output drive drops to ±4 mA, which remains sufficient for driving CMOS loads or small-signal transistors in low-voltage systems.

How does the retriggering mechanism work in SN74AHC123AD?

SN74AHC123AD allows retriggering during an active output pulse: a new valid edge on A or B input (per configured mode) restarts the timing cycle from zero, extending total pulse width. Minimum retrigger interval tMIR ≈ 0.3 × tw ensures reliable recognition. This behavior eliminates need for cascaded monostables or external logic to achieve long, variable-duration pulses.

Is SN74AHC123AD pin-compatible with older SN74LS123?

No, SN74AHC123AD is not pin-compatible with SN74LS123. While both are dual monostables, SN74LS123 uses 16-pin PDIP with different pin assignments (e.g., separate R/C pins per channel but no dedicated CLR per channel), lacks Schmitt inputs, and operates only at 5 V. SN74AHC123AD uses SOIC-16 with distinct pinout (e.g., shared VCC/GND, dual CLR inputs), requiring PCB redesign for replacement.

What is the maximum recommended external timing resistor value for SN74AHC123AD?

The datasheet specifies Rext up to 10 kΩ for stable operation with Cext ≥ 0.01 μF, yielding pulse widths up to 110 μs (CL = 50 pF). Higher values increase sensitivity to leakage and noise; TI does not characterize Rext beyond 10 kΩ. For pulses >1 ms, use Cext = 0.1 μF with Rext = 10 kΩ - verified to deliver 0.9–1.1 ms with ±1% variation between channels in same SN74AHC123AD package.

SN74AHC123AD Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74AHC

Package/Case:: 16-SOIC (0.154", 3.90mm Width)

Packaging:: Bulk

Product Status:: Obsolete

Logic Type:: Monostable

Independent Circuits:: 2

Schmitt Trigger Input:: Yes

Propagation Delay:: 7.5 ns

Current - Output High, Low:: 8mA, 8mA

Voltage - Supply:: 2 V ~ 5.5 V

Operating Temperature:: -40°C ~ 85°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 16-SOIC

SN74AHC123AD FAQ

1.How can I place an order for SN74AHC123AD through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74AHC123AD 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 SN74AHC123AD reliable?

The price and inventory of SN74AHC123AD are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AHC123AD is usually 5 days.

3.What payment methods are accepted for SN74AHC123AD?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AHC123AD transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SN74AHC123AD?

SN74AHC123AD orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SN74AHC123AD 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 SN74AHC123AD?

For technical support, including SN74AHC123AD datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AHC123AD requirements.

6.How does Aetrix verify that SN74AHC123AD is sourced from the original manufacturer or authorized distributors?

All SN74AHC123AD 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 SN74AHC123AD meets industry standards.

7.What is the process for return or replacement of SN74AHC123AD?

All SN74AHC123AD units undergo pre-shipment inspection (PSI). If there is an issue with SN74AHC123AD, 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 SN74AHC123AD part is unused and in its original packaging.

Return procedure for SN74AHC123AD:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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