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Texas Instruments SN74ALS621ADWRE4
- Part No.:
- SN74ALS621ADWRE4
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS621ADWRE4.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,031
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Product details
Overview
SN74ALS621ADWRE4 from Texas Instruments is an octal bus transceiver with open-collector outputs and true logic polarity, designed for asynchronous bidirectional data transfer between A and B buses in industrial control and legacy computing systems. It operates at 4.5–5.5 V, supports 24 mA (standard) or 48 mA (–1 version) low-level output current, and features dual output-enable inputs (OEAB/OEBA) enabling bus isolation or simultaneous latching. Its SOIC-20 package suits space-constrained PCB layouts requiring TTL-compatible level translation.
For engineers reviewing the SN74ALS621ADWRE4 datasheet, SN74ALS621ADWRE4 pinout, SN74ALS621ADWRE4 application, or SN74ALS621ADWRE4 equivalent, this page delivers verified electrical specs, functional timing behavior, validated pin assignments, and real-world use cases - all grounded in TI's SDAS226A datasheet and official packaging documentation.
Technical Context
This device implements a dual-bus transceiver architecture with independent OEAB (A-to-B enable) and OEBA (B-to-A enable) controls, allowing flexible direction selection, full bus isolation, or concurrent bidirectional latching when both enables are active. Its open-collector outputs require external pull-up resistors and support wired-AND logic implementation.
It belongs to the ALS (Advanced Low-Power Schottky) family, delivering improved speed-power trade-offs over standard LS logic: propagation delays range from 5 ns to 33 ns depending on signal path (A→B, B→A, or enable→output), with guaranteed operation across 0°C to 70°C ambient temperature.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Type | True (non-inverting) octal bus transceiver with open-collector outputs - enables wired-AND bus sharing and level translation via external pull-ups. |
| Supply Voltage | 4.5 V to 5.5 V - compatible with standard 5 V TTL/ALS systems; absolute max 7 V prevents damage during transient overvoltage. |
| Output Current | 24 mA (IOL, standard); 48 mA (IOL, –1 version) - drives heavy capacitive loads or multiple TTL inputs without external buffers. |
| Propagation Delay | 5–33 ns (A↔B paths), 10–39 ns (OEAB/OEBA→output) - ensures deterministic timing in synchronous bus arbitration and latch-based data capture. |
| Operating Temperature | 0°C to 70°C - qualified for commercial and industrial environments where ambient thermal cycling occurs within this range. |
| Input Thresholds | VIL = 0.8 V, VIH = 2.0 V - robust noise margin against ground bounce and supply ripple in noisy digital backplanes. |
Pinout & Package
SN74ALS621ADWRE4 uses a 20-pin SOIC (DW) package measuring 12.83 mm × 7.5 mm × 2.65 mm max height, with 1.27 mm pitch, RoHS-compliant NiPdAu lead finish, and moisture sensitivity level (MSL) 1 (unlimited floor life at ≤30°C/60% RH).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 3, 4, 5, 6, 7, 8 | A-side data inputs/outputs | Open-collector I/O pins for A bus connection; require external pull-up for HIGH state; sink current only. |
| 9 | GND | Ground reference for all internal circuitry and output drivers. |
| 10 | VCC | Positive supply rail (4.5–5.5 V); decoupling capacitor required near pin for noise suppression. |
| 11, 12, 13, 14, 15, 16, 17, 18 | B-side data inputs/outputs | Open-collector I/O pins for B bus; electrically identical to A-side pins but isolated by internal logic. |
| 19 | OEAB | Active-low output-enable for A→B direction; when LOW, A-side drivers activate to drive B bus. |
| 20 | OEBA | Active-low output-enable for B→A direction; when LOW, B-side drivers activate to drive A bus. |
Key Features
| Feature | Design Value |
|---|---|
| Open-collector outputs | Enables wired-AND bus architectures, multi-drop configurations, and voltage-level translation using external pull-ups. |
| Dual independent output enables | OEAB and OEBA allow selective unidirectional flow, full isolation (both HIGH), or simultaneous latching (both LOW) of 16 bus lines. |
| Bus-latch capability | When OEAB and OEBA are both LOW and all other sources are high-Z, both A and B buses retain their last driven states - no external latch IC needed. |
| ALS-family performance | Delivers 33 ns max propagation delay with 40 mA typical ICC (outputs low), balancing speed and power vs. LS logic. |
| Industrial temperature range | Rated for continuous operation from 0°C to 70°C - suitable for programmable logic controllers, test equipment, and embedded instrumentation. |
Applications
| Industrial Backplane Interface | Legacy System Bus Extension |
|---|---|
|
Use Scenario: Interfacing a microcontroller's local data bus to a shared 8-bit ISA-style backplane with multiple peripheral slots. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing data flow between CPU and peripherals while isolating sections during DMA cycles. Use Value: Open-collector outputs prevent bus contention; dual OE inputs enable precise timing control of data direction changes synchronized to bus grant signals. |
Use Scenario: Extending a vintage 8-bit computer's expansion bus to add custom I/O cards without modifying motherboard traces. IC Role / Device Role / Timing Role: Level-shifting and direction-controlled buffer between main board and daughter card, supporting hot-plug detection via OE control. Use Value: True logic polarity preserves signal integrity across long traces; 24 mA sink current drives legacy TTL loads directly without additional drivers. |
| Programmable Logic Controller (PLC) I/O Module | Test Equipment Data Capture Interface |
|
Use Scenario: Isolating field I/O signals from the PLC's internal processor bus using optocouplers upstream, with SN74ALS621ADWRE4 handling final bus interfacing. IC Role / Device Role / Timing Role: Bus interface IC providing controlled bidirectional data exchange between isolated I/O banks and central controller. Use Value: Dual OE inputs allow software-configurable read/write windows; bus-latch mode holds status bits during interrupt servicing without CPU intervention. |
Use Scenario: Capturing parallel digital waveforms from DUTs into a logic analyzer's memory buffer using a synchronous strobe signal. IC Role / Device Role / Timing Role: High-speed data capture buffer synchronizing incoming 8-bit samples to system clock domain before storage. Use Value: Sub-10 ns enable-to-output delays (tPHZ/tPLZ) ensure setup/hold compliance with fast sampling clocks; SOIC-20 footprint fits dense probe interface PCBs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS623ADW | 3-state (not open-collector) outputs, true logic, same pinout and timing - requires pull-up resistors only if wired-AND needed. | Preferred where bus contention avoidance via high-Z tri-state is prioritized over wired-AND flexibility. | Select SN74ALS623ADW when replacing legacy designs needing tri-state isolation instead of open-collector sinking. |
| SN74AS623DW | Faster AS-family propagation (1–9 ns vs. 5–33 ns), higher IOL (64 mA), but increased ICC (up to 189 mA) and tighter VCC tolerance (4.75–5.25 V). | Suitable for high-speed backplanes where timing margins are critical and power budget allows. | Choose SN74AS623DW only when sub-10 ns delays are mandatory and thermal/power design accommodates higher dissipation. |
Compared with SN74ALS621ADWRE4, SN74ALS623ADW offers tri-state flexibility at similar speed/power, while SN74AS623DW delivers significantly faster switching at the cost of higher current draw and stricter supply regulation - making each viable only when their specific electrical trade-offs align with system requirements.
Availability
SN74ALS621ADWRE4 is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, and programmable logic controller I/O modules requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS621ADWRE4 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 for industrial, automotive, and communications markets.
The SN74ALS621ADWRE4 belongs to TI's legacy Advanced Low-Power Schottky (ALS) logic family, engineered for reliable bidirectional bus interfacing in commercial and industrial systems where speed, noise immunity, and compatibility with older TTL infrastructure are essential.
FAQ
What is the function of OEAB and OEBA on the SN74ALS621ADWRE4?
OEAB (pin 19) and OEBA (pin 20) are active-low output-enable inputs controlling data direction: OEAB LOW enables A→B transmission; OEBA LOW enables B→A transmission; both HIGH isolate both buses; both LOW activates bus-latch mode. This dual-control scheme gives precise timing control over bidirectional data flow in the SN74ALS621ADWRE4 without external logic.
Does SN74ALS621ADWRE4 support 3.3 V logic levels?
No, SN74ALS621ADWRE4 is an ALS-family device designed for 5 V operation only, with recommended VCC of 4.5–5.5 V and input thresholds (VIH = 2.0 V, VIL = 0.8 V) optimized for TTL-compatible signaling. It does not tolerate sustained 3.3 V supply or guarantee correct operation with 3.3 V inputs - use level translators if interfacing with 3.3 V systems.
What is the maximum sink current per output for SN74ALS621ADWRE4?
The standard SN74ALS621ADWRE4 supports 24 mA low-level output current (IOL) per pin at VCC = 4.5 V. A variant designated "–1" (e.g., SN74ALS621A-1N) supports up to 48 mA, but SN74ALS621ADWRE4 is the standard version - its datasheet-specified IOL remains 24 mA under recommended operating conditions.
Can SN74ALS621ADWRE4 be used as a level shifter between different voltage domains?
Yes - its open-collector outputs allow external pull-up resistors to a different voltage rail (e.g., 3.3 V or 12 V), enabling level shifting from 5 V logic to higher or lower domains. However, input thresholds remain fixed for 5 V operation, so driving inputs must meet VIH ≥ 2.0 V and VIL ≤ 0.8 V - the SN74ALS621ADWRE4 itself does not shift input levels.
Is SN74ALS621ADWRE4 RoHS compliant and what is its MSL rating?
Yes, SN74ALS621ADWRE4 is RoHS compliant with NiPdAu lead finish and carries MSL Level-1 (unlimited floor life at ≤30°C/60% RH), per TI's official packaging documentation. Its SOIC-20 (DW) package is qualified for standard reflow profiles up to 260°C peak, with no bake requirement prior to assembly.
SN74ALS621ADWRE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Logic Type:
- Transceiver, Non-Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- Open Collector
- Current - Output High, Low:
- -, 24mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74ALS621ADWRE4 FAQ
1.How can I place an order for SN74ALS621ADWRE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS621ADWRE4 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 SN74ALS621ADWRE4 reliable?
The price and inventory of SN74ALS621ADWRE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS621ADWRE4 is usually 5 days.
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Once your SN74ALS621ADWRE4 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 SN74ALS621ADWRE4?
For technical support, including SN74ALS621ADWRE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS621ADWRE4 requirements.
6.How does Aetrix verify that SN74ALS621ADWRE4 is sourced from the original manufacturer or authorized distributors?
All SN74ALS621ADWRE4 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 SN74ALS621ADWRE4 meets industry standards.
7.What is the process for return or replacement of SN74ALS621ADWRE4?
All SN74ALS621ADWRE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS621ADWRE4, 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 SN74ALS621ADWRE4 part is unused and in its original packaging.
Return procedure for SN74ALS621ADWRE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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