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Texas Instruments SN74ALS621A-1DW
- Part No.:
- SN74ALS621A-1DW
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS621A-1DW.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,863
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Product details
Overview
SN74ALS621A-1DW 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 TTL-level systems. It supports local bus-latch capability via dual output-enable (OEAB/OEBA) control, delivers 48 mA low-level output current (IOL), and operates across 0°C to 70°C in a 20-pin SOIC (DW) package - commonly used in industrial backplane interfaces and legacy system bus expansion.
For engineers reviewing the SN74ALS621A-1DW datasheet, SN74ALS621A-1DW pinout, SN74ALS621A-1DW application, or SN74ALS621A-1DW equivalent, key selection criteria include its open-collector drive strength (48 mA), dual-enable bus-latching behavior, 5 V supply compatibility, and SOIC-20 thermal and layout constraints for high-density PCBs.
Technical Context
This device implements a dual-bus transceiver architecture with independent OEAB (A-to-B enable) and OEBA (B-to-A enable) inputs, enabling flexible direction control and simultaneous bus isolation or latching. Its open-collector outputs require external pull-up resistors and support wired-AND logic, unlike 3-state variants.
Unlike SN74ALS620A (inverting) or SN74ALS623A (3-state true), the SN74ALS621A-1DW provides non-inverted data flow with higher sink current (48 mA vs. 24 mA standard), making it suitable for driving heavier loads such as LEDs, relays, or multiple TTL inputs without buffering.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Supply | 4.5 V to 5.5 V - compatible with standard 5 V TTL rails; operation outside this range risks damage or undefined behavior. |
| IOL Output Current | 48 mA (min) - enables direct drive of up to 12 standard TTL loads or moderate-current peripherals without external drivers. |
| VOH / VOL | VOH = 5.5 V (open), VOL ≤ 0.5 V at 48 mA - ensures robust low-state voltage margin under full load for reliable logic-low recognition. |
| Propagation Delay | tPLH/tPHL ≤ 33 ns (A↔B), tPLZ/tPZL ≤ 39 ns (enable → output) - supports bus timing in sub-30 MHz synchronous systems with margin. |
| Operating Temperature | 0°C to 70°C - rated for commercial/industrial ambient environments; not qualified for extended temperature or automotive use. |
| Input Voltage Limits | VI ≤ 7 V (absolute max); VIH ≥ 2 V, VIL ≤ 0.8 V - fully compatible with standard TTL input thresholds and overvoltage-tolerant design. |
Pinout & Package
SN74ALS621A-1DW uses a 20-pin SOIC (DW) package with 7.5 mm body width, 2.65 mm max height, and 1.27 mm lead pitch. Pin 1 is marked by a beveled corner or notch on the top surface.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (OEAB) | A-to-B output enable | Active-low control: pulls A bus data to B bus when low; high-impedance B outputs when high. |
| 2–9 (A1–A8) | A-side data inputs/outputs | Open-collector I/O pins; require external pull-ups; connect to source bus (e.g., CPU address/data lines). |
| 10 (GND) | Ground reference | Primary power return path; must be low-inductance connection to minimize noise coupling into bus signals. |
| 11–18 (B1–B8) | B-side data inputs/outputs | Open-collector I/O pins; electrically identical to A-side; interface with destination bus (e.g., peripheral module). |
| 19 (OEBA) | B-to-A output enable | Active-low control: enables B→A data flow; used with OEAB for bidirectional latching or isolation. |
| 20 (VCC) | Positive supply | 5 V nominal power rail; decoupling capacitor (0.1 µF ceramic) required within 1 cm of this pin. |
Key Features
| Feature | Design Value |
|---|---|
| Open-collector outputs | Enables wired-AND bus arbitration and level translation to higher voltages using external pull-ups. |
| Dual output-enable (OEAB/OEBA) | Allows independent control of A→B and B→A paths, supporting isolated bidirectional communication or bus-hold latching. |
| Local bus-latch capability | Simultaneous assertion of OEAB and OEBA holds both A and B bus states without external storage elements. |
| True logic polarity | Data passes unchanged (non-inverted) between buses - simplifies timing analysis and eliminates need for inversion compensation. |
| 48 mA sink current (-1 version) | Supports direct drive of legacy TTL loads, optocouplers, or small-signal relays without buffer stages. |
Applications
| Industrial Backplane Interface | Legacy System Bus Expansion |
|---|---|
Use Scenario: Interfacing microcontroller-based control modules to parallel I/O backplanes in programmable logic controllers (PLCs). IC Role / Device Role / Timing Role: Bidirectional data transceiver managing address/data handshaking between CPU and peripheral slots. Use Value: Open-collector outputs tolerate bus contention during hot-swap events; 48 mA drive ensures signal integrity across 30 cm ribbon cables. |
Use Scenario: Adding memory-mapped peripherals (e.g., EPROM, latch-based I/O) to vintage 8-bit computer architectures like Z80 or 6502 systems. IC Role / Device Role / Timing Role: Level-shifting and direction-controlled bus bridge between CPU data bus and peripheral address/data lines. Use Value: True logic polarity avoids added propagation delay from inverters; dual-OE allows precise cycle-by-cycle bus ownership control. |
| Wired-AND Control Bus | TTL Load Driving Interface |
Use Scenario: Implementing shared interrupt or reset signaling across multiple boards in a chassis-based instrumentation system. IC Role / Device Role / Timing Role: Wired-AND bus transceiver aggregating open-collector interrupt requests onto a common line. Use Value: Built-in open-collector structure eliminates need for discrete diodes or external pull-downs; reduces component count and board area. |
Use Scenario: Driving LED status indicators, relay coils, or opto-isolator inputs directly from a microcontroller's parallel port. IC Role / Device Role / Timing Role: High-current digital output buffer translating logic levels to load-compatible drive signals. Use Value: 48 mA per channel replaces discrete transistor drivers; SOIC-20 footprint fits compact control panel layouts. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS621ADW | Standard version with 24 mA IOL (vs. 48 mA in -1 variant); otherwise identical pinout, logic, and timing. | Suitable where load current ≤ 24 mA; lower power dissipation but insufficient for heavy TTL fanout or relay driving. | Select SN74ALS621ADW only if verified load requirements stay below 24 mA per channel. |
| SN74ALS623ADW | 3-state (not open-collector) outputs, true logic, 24 mA IOL; shares same pinout and control scheme but lacks wired-AND capability. | Used where bus isolation without pull-ups is preferred; incompatible with wired-AND or level translation applications. | Choose SN74ALS623ADW when clean 3-state isolation is needed and open-collector functionality is unnecessary. |
Compared with SN74ALS621ADW and SN74ALS623ADW, the SN74ALS621A-1DW uniquely combines open-collector drive with enhanced 48 mA sink capability - making it the only option among these three for direct high-current wired-AND bus interfacing.
Availability
SN74ALS621A-1DW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus expansion, wired-AND control buses, and TTL load driving applications requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS621A-1DW 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 broad industrial and automotive reach.
The SN74ALS621A-1DW belongs to TI's legacy ALS (Advanced Low-Power Schottky) logic family, engineered for high-speed, low-power TTL-compatible bus interfacing in industrial control and computing systems of the 1980s–1990s.
FAQ
What is the maximum sink current supported by SN74ALS621A-1DW?
The SN74ALS621A-1DW supports a minimum low-level output current (IOL) of 48 mA per channel under recommended operating conditions (VCC = 4.75 V to 5.25 V). This rating applies specifically to the "-1" version and exceeds the 24 mA capability of the standard SN74ALS621A. Exceeding 48 mA may cause VOL to rise above specification limits or induce thermal stress.
Does SN74ALS621A-1DW support bidirectional data flow without external logic?
Yes. The SN74ALS621A-1DW natively supports bidirectional data flow via two independent active-low enables: OEAB controls A→B transmission, and OEBA controls B→A transmission. With proper sequencing - e.g., OEAB low + OEBA high for A→B, or vice versa - the SN74ALS621A-1DW routes data in either direction without additional gates or controllers.
Can SN74ALS621A-1DW replace SN74ALS620A in an existing design?
No - SN74ALS621A-1DW cannot directly replace SN74ALS620A due to fundamental functional differences: SN74ALS620A has inverting logic and 3-state outputs, while SN74ALS621A-1DW has true (non-inverting) logic and open-collector outputs. Swapping them would invert data polarity and eliminate high-impedance tri-state behavior, likely causing system failure.
What pull-up resistor value is recommended for SN74ALS621A-1DW open-collector outputs?
A 1.0 kΩ to 2.2 kΩ pull-up resistor to 5 V is typically recommended for SN74ALS621A-1DW outputs. At 48 mA sink, a 1.0 kΩ resistor yields ~0.5 V VOL (within spec), while 2.2 kΩ improves noise immunity and reduces power consumption at the cost of slightly slower rise time - appropriate for bus speeds ≤ 10 MHz.
Is SN74ALS621A-1DW RoHS compliant and lead-free?
Yes. According to Texas Instruments' packaging documentation, SN74ALS621A-1DW carries NIPDAU (nickel-palladium-gold) lead finish and is RoHS compliant. It meets JEDEC Level-1 moisture sensitivity standards and is rated for peak reflow at 260°C, supporting standard lead-free PCB assembly processes.
SN74ALS621A-1DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tube
- 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
SN74ALS621A-1DW FAQ
1.How can I place an order for SN74ALS621A-1DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS621A-1DW 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 SN74ALS621A-1DW reliable?
The price and inventory of SN74ALS621A-1DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS621A-1DW is usually 5 days.
3.What payment methods are accepted for SN74ALS621A-1DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS621A-1DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS621A-1DW?
SN74ALS621A-1DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS621A-1DW 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 SN74ALS621A-1DW?
For technical support, including SN74ALS621A-1DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS621A-1DW requirements.
6.How does Aetrix verify that SN74ALS621A-1DW is sourced from the original manufacturer or authorized distributors?
All SN74ALS621A-1DW 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 SN74ALS621A-1DW meets industry standards.
7.What is the process for return or replacement of SN74ALS621A-1DW?
All SN74ALS621A-1DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS621A-1DW, 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 SN74ALS621A-1DW part is unused and in its original packaging.
Return procedure for SN74ALS621A-1DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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