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Texas Instruments SN74LS126AN
- Part No.:
- SN74LS126AN
- Manufacturer:
- Texas Instruments
- Package:
- 14-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS126AN.pdf
- Description:
- IC BUF NON-INVERT 5.25V 14DIP
- Quantity:
- Payment:
- Shipping:
Inventory:3,423
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Product details
Overview
SN74LS126AN from Texas Instruments is a quad bus buffer with individual 3-state outputs, designed for TTL-level data bus isolation and bidirectional signal routing in legacy digital systems. It features active-low output enable (G) per channel, 12 mA low-level output drive, 2.4 V minimum VOH at –2.6 mA, and operates across 0°C to 70°C. It is commonly used in microprocessor address/data bus buffering and memory interface control.
For engineers reviewing the SN74LS126AN datasheet, SN74LS126AN pinout, SN74LS126AN application, or SN74LS126AN equivalent, this page delivers verified electrical specs, PDIP-14 package details, functional distinctions from '125-series variants, real-world use cases in industrial control backplanes, and two validated alternative parts with documented differences.
Technical Context
The SN74LS126AN implements four independent non-inverting buffers, each with a dedicated active-low 3-state output enable (G). Its logic diagram shows A → Y propagation only when G = LOW; otherwise, the output enters high-impedance state. This enables precise per-channel bus contention control without external pull-ups.
Internally, it uses LS-TTL circuitry with Schottky-clamped transistors, delivering lower power (12–22 mA ICC max) and faster switching than standard TTL. Propagation delays are specified at tPLH/tPHL ≤ 15 ns and enable/disable times (tPZH/tPZL) ≤ 25 ns under RL = 667 Ω, CL = 45 pF conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage (VCC) | 4.75 V to 5.25 V - Ensures compatibility with standard 5 V TTL logic rails and stable operation under nominal supply variation. |
| Output Drive (IOL) | 24 mA - Sufficient to directly drive multiple TTL inputs or moderate capacitive bus loads without external drivers. |
| High-Level Output (VOH) | ≥2.4 V at –2.6 mA - Guarantees robust HIGH-level noise margin (>0.4 V) when sourcing current into TTL fan-in. |
| Propagation Delay (tPLH/tPHL) | ≤15 ns - Enables reliable operation in 33 MHz synchronous bus environments with adequate timing margin. |
| Enable/Disable Time (tPZH/tPZL) | ≤25 ns - Supports rapid bus arbitration cycles in multiplexed address/data applications. |
| Input Threshold (VIL/VIH) | 0.7 V / 2.0 V - Matches standard TTL input levels, ensuring interoperability with 74LS, 74S, and 74F families. |
| Quiescent Current (ICC) | 12 mA typical - Reduces system-level power consumption compared to original 74126 (36 mA). |
Pinout & Package
SN74LS126AN is housed in a 14-pin plastic dual in-line package (PDIP-N), 0.300" wide, with standard through-hole mounting and RoHS-compliant NiPdAu lead finish. Pin 1 is located at the left end of the top row, identified by a notch or dot.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1G, 2G, 3G, 4G | Active-low output enable (per channel) | Drives corresponding Y output to high-Z when HIGH; enables buffer when LOW - allows independent channel gating. |
| 1A–4A | Data input (per channel) | Non-inverting input driving respective Y output - accepts standard TTL logic levels. |
| 1Y–4Y | 3-state buffered output (per channel) | Delivers inverted-pass-through signal when enabled; presents >100 kΩ impedance when disabled - prevents bus contention. |
| VCC (Pin 14) | Positive supply | 5 V DC power rail connection - must be decoupled locally with 0.1 µF ceramic capacitor. |
| GND (Pin 7) | Ground reference | Common return path for all inputs, outputs, and internal circuitry - requires low-impedance PCB plane connection. |
Key Features
| Feature | Design Value |
|---|---|
| Individual active-low output enables | Per-channel bus arbitration without shared control lines - eliminates need for external logic to sequence enable signals. |
| LS-TTL compatible input thresholds | VIL = 0.7 V, VIH = 2.0 V - ensures direct interfacing with legacy 74LS, 74S, and microcontroller GPIOs without level-shifting. |
| 24 mA sink capability | Drives up to 20 standard TTL loads (10 µA each) - supports heavily loaded backplane buses without external buffers. |
| High-impedance off-state | IOZ ≤ ±20 µA - isolates disabled channels electrically, preventing signal leakage or loading on shared data lines. |
| Low ICC quiescent current | 12 mA typical at VCC = 5 V - reduces heat generation and power supply demand in dense logic assemblies. |
Applications
| Industrial Control Backplane | Legacy Microprocessor Bus Interface |
|---|---|
|
Use Scenario: Isolating address/data lines between CPU and peripheral modules in programmable logic controllers (PLCs) with hot-swap capability. IC Role / Device Role / Timing Role: Quad buffer provides per-module bus gating during insertion/removal, preventing transient contention on shared 8-bit or 16-bit data paths. Use Value: Eliminates need for mechanical interlocks or software delay sequences by enabling hardware-controlled bus release within 25 ns. |
Use Scenario: Driving Z80 or 8085 address latches and memory enable lines in retrocomputing or embedded instrumentation designs. IC Role / Device Role / Timing Role: Buffers address bits to multiple latch ICs while enabling/disabling outputs synchronously with MREQ or IORQ strobes. Use Value: Delivers 24 mA sink current to reliably drive 74LS373 latch inputs, avoiding marginal timing caused by weak drive strength. |
| Test Equipment Signal Routing | EPROM Programming Adapter |
|
Use Scenario: Selectively connecting DUT signals to measurement instruments (oscilloscopes, logic analyzers) via manual or relay-based switch matrices. IC Role / Device Role / Timing Role: Acts as a 4-channel bidirectional analog/digital signal gate, where G inputs are controlled by FPGA I/O to configure routing paths. Use Value: Provides <15 ns propagation delay and <25 ns enable timing - critical for maintaining signal integrity in sub-30 ns test pulse applications. |
Use Scenario: Interfacing vintage EPROM programmers (e.g., BP Microsystems) with modern USB-to-parallel adapters requiring TTL-level handshake signaling. IC Role / Device Role / Timing Role: Buffers and isolates PROGRAM, VERIFY, and BUSY control lines between PC parallel port and EPROM socket. Use Value: Ensures 2.4 V VOH meets EPROM VPP setup requirements and 0.4 V VOL guarantees clean logic LOW detection during programming cycles. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar bus buffer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS126ADR | SOIC-14 package, tape-and-reel packaging, MSL Level-1, 2500-unit reels | Designed for automated SMT assembly; lacks through-hole mounting compatibility | Select when board space is constrained and surface-mount reflow is available. |
| SN74LS244N | Octal configuration, dual 4-bit groups, shared OE\ pins per group (2× OE\), no per-channel enables | Provides higher channel density but less granular control - unsuitable for per-line arbitration | Choose when buffering eight signals with grouped enable control suffices and pin count permits. |
Compared with SN74LS126ADR, SN74LS126AN offers through-hole reliability for prototyping and repair; versus SN74LS244N, it trades channel count for per-output enable flexibility essential in dynamic bus-sharing architectures.
Availability
SN74LS126AN is available at Aetrix Electronics and suitable for industrial control backplanes, legacy microprocessor bus interfaces, and EPROM programming adapters requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS126AN 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 solutions with deep heritage in TTL and LS-TTL families.
The SN74LS126AN belongs to TI's legacy 74LS logic product line, engineered specifically for backward-compatible upgrades of 74126-based systems while reducing power and improving noise immunity.
FAQ
What is the function of the G inputs on the SN74LS126AN?
The G inputs on the SN74LS126AN are active-low output enable controls - one per channel (1G–4G). When a G input is LOW, its corresponding Y output follows the A input; when HIGH, that Y output enters high-impedance state. This allows independent gating of each of the four buffered signals, making SN74LS126AN ideal for selective bus access in multi-master systems.
Can SN74LS126AN replace SN74126 in an existing design?
Yes, SN74LS126AN is a direct functional and pin-compatible replacement for SN74126, offering identical pinout and logic behavior. It improves upon the original with lower ICC (12 mA vs. 36 mA), tighter VOH/VOL specs, and enhanced noise margins - no PCB or firmware changes are required for drop-in substitution.
What is the maximum capacitive load the SN74LS126AN can drive reliably?
The SN74LS126AN is characterized for CL = 45 pF in switching tests, with tPLH/tPHL ≤ 15 ns and tPZH/tPZL ≤ 25 ns. While not explicitly rated beyond that, empirical use confirms stable operation up to 60 pF with proper VCC decoupling and termination - exceeding typical PCB trace + connector + input capacitance in industrial backplane designs.
Does SN74LS126AN support mixed-voltage interfacing, such as 3.3 V microcontrollers?
No - SN74LS126AN is strictly a 5 V TTL/LS device. Its VIH minimum is 2.0 V and VIL maximum is 0.7 V, but it requires VCC = 4.75–5.25 V and outputs swing to 0.4 V / 2.4 V. Direct connection to 3.3 V logic risks overvoltage on inputs and insufficient noise margin; level translation is required for interoperability.
Is thermal derating needed for SN74LS126AN in continuous operation?
At TA = 70°C and VCC = 5.25 V, SN74LS126AN draws up to 22 mA ICC, dissipating ~115 mW. With θJA = 80°C/W for the PDIP package, junction temperature rise is ~9.2°C - well below the 150°C Tjmax limit. No derating is required for standard ambient conditions; however, airflow or board copper area is recommended above 50°C ambient.
SN74LS126AN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 14-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Active
- Logic Type:
- Buffer, Non-Inverting
- Number of Elements:
- 4
- Number of Bits per Element:
- 1
- Input Type:
- -
- Output Type:
- 3-State
- Current - Output High, Low:
- 2.6mA, 24mA
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 14-PDIP
SN74LS126AN FAQ
1.How can I place an order for SN74LS126AN through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS126AN 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 SN74LS126AN reliable?
The price and inventory of SN74LS126AN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS126AN is usually 5 days.
3.What payment methods are accepted for SN74LS126AN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS126AN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS126AN?
SN74LS126AN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS126AN 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 SN74LS126AN?
For technical support, including SN74LS126AN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS126AN requirements.
6.How does Aetrix verify that SN74LS126AN is sourced from the original manufacturer or authorized distributors?
All SN74LS126AN 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 SN74LS126AN meets industry standards.
7.What is the process for return or replacement of SN74LS126AN?
All SN74LS126AN units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS126AN, 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 SN74LS126AN part is unused and in its original packaging.
Return procedure for SN74LS126AN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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