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Texas Instruments SN74ALS645A-1NSR
- Part No.:
- SN74ALS645A-1NSR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74ALS645A-1NSR.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:1,378
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Product details
Overview
SN74ALS645A-1NSR from Texas Instruments is an octal bidirectional bus transceiver with 3-state outputs in a 20-pin SOP package, designed for asynchronous two-way data communication between A and B buses. It features direction control (DIR), output enable (OE), ±48 mA low-level output drive (IOL), 0°C to 70°C operating range, and TTL-compatible logic levels. It is used in legacy industrial backplane interfaces requiring robust bus isolation and level translation.
For engineers reviewing the SN74ALS645A-1NSR datasheet, SN74ALS645A-1NSR pinout, SN74ALS645A-1NSR application, or SN74ALS645A-1NSR equivalent, this page delivers verified electrical specs, validated pin functions, confirmed package dimensions (SOP-20, 7.6 mm × 12.8 mm), and real-world use cases in bus arbitration, memory expansion, and microcontroller peripheral interfacing.
Technical Context
The SN74ALS645A-1NSR implements true bipolar ALS logic with dual-bus bidirectional data flow controlled by DIR and OE inputs. Its 3-state outputs provide high-impedance isolation when OE is high, enabling multi-drop bus sharing without contention.
It operates strictly within 4.5 V–5.5 V supply range and supports fast propagation delays: tPLH/tPHL ≤ 10 ns (CL = 50 pF), tPZH/tPLZ ≤ 20 ns, and tPHZ/tPLZ ≤ 15 ns - all specified at commercial temperature range and compatible with standard TTL load conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - ensures compatibility with 5 V TTL systems and tolerates typical rail droop in industrial power supplies. |
| IOL (max) | 48 mA - enables direct driving of multiple TTL loads or termination resistors without external buffers. |
| tPLH / tPHL | ≤10 ns - supports bus transfer rates up to ~100 MHz in short-trace, low-capacitance configurations. |
| VOH / VOL | VOH ≥ 2.4 V (IOH = –12 mA), VOL ≤ 0.5 V (IOL = 48 mA) - guarantees noise margins >0.4 V under full drive conditions. |
| Operating Temp | 0°C to 70°C - qualified for commercial-grade embedded control, instrumentation, and legacy computing applications. |
| Package | SOP-20 (NS), 7.6 mm × 12.8 mm body, 1.27 mm pitch - surface-mount compatible with standard reflow profiles (MSL Level-1). |
Pinout & Package
SOP-20 (NS) package: 7.6 mm × 12.8 mm body, 1.27 mm lead pitch, 2.65 mm max height, RoHS-compliant NiPdAu lead finish, MSL Level-1-260°C-UNLIM.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Low = B→A data transfer; High = A→B data transfer; TTL-compatible threshold (VIL ≤ 0.8 V, VIH ≥ 2 V). |
| 2–9 (A1–A8) | Port A I/O Terminals | Bidirectional data lines connected to one bus segment; 3-state when OE = high or DIR conflict disabled. |
| 10 (GND) | Ground Reference | Primary signal return path; requires low-inductance connection to minimize ground bounce during 48 mA switching. |
| 11–18 (B1–B8) | Port B I/O Terminals | Bidirectional data lines connected to second bus segment; electrically identical to A-port pins. |
| 19 (OE) | Output Enable Input | Low = transceiver active; High = all A/B pins in high-impedance state; critical for bus arbitration timing. |
| 20 (VCC) | Power Supply | +5 V supply input; requires local 0.1 µF ceramic decoupling adjacent to pin for stable 48 mA transient response. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional Data Flow | Single DIR pin selects A→B or B→A path - eliminates need for separate transmit/receive ICs in space-constrained backplanes. |
| Enhanced Drive Strength | 48 mA IOL (–1 version only) - sustains signal integrity across longer traces or higher fan-out (up to 10+ TTL loads) without buffering. |
| True 3-State Isolation | OE-controlled high-impedance mode with <1 µA leakage - prevents bus contention during CPU reset, DMA handshaking, or hot-swap events. |
| ALS Logic Family | Lower power than standard TTL (ICC ≤ 58 mA active, ≤ 63 mA disabled) with improved speed-power product vs. 74LS. |
Applications
| Industrial Backplane Interface | Microcontroller Peripheral Expansion |
|---|---|
|
Use Scenario: Isolating and translating data between CPU local bus and modular I/O carrier board in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing address/data multiplexing and direction arbitration under microcontroller control. Use Value: Enables shared 8-bit data path between CPU and up to four I/O modules using single OE/DIR control, reducing PCB layer count and connector pin count. |
Use Scenario: Extending GPIO count of an 8-bit MCU via parallel peripheral interface (e.g., LCD controller, SRAM, keypad matrix). IC Role / Device Role / Timing Role: Level-translating and direction-controlled data conduit between MCU port and external memory-mapped device. Use Value: Provides 48 mA drive to overcome trace capacitance and pull-up requirements of legacy peripherals, eliminating discrete buffer stages. |
| Legacy Memory Subsystem | Test Equipment Bus Arbitration |
|
Use Scenario: Interfacing Z80 or 8085-based CPU with dual-port static RAM or EPROM banks in vintage computer restoration. IC Role / Device Role / Timing Role: Synchronizing read/write strobes and data direction between processor and memory using OE-gated 3-state control. Use Value: Matches original system timing (tPLH ≤ 10 ns) while supporting modern 5 V supply stability and thermal margin. |
Use Scenario: Managing shared GPIB or IEEE-488 bus access among multiple instruments in automated test racks. IC Role / Device Role / Timing Role: Enabling/disabling instrument data drivers on command bus to prevent signal collisions during talker/listener handshaking. Use Value: 3-state isolation ensures <1 µA off-state leakage - critical for maintaining bus DC bias integrity across 10+ daisy-chained devices. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bidirectional bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS645AN | PDIP-20 package (13.97 mm width), through-hole mounting, same electrical specs and -1 drive strength. | Suitable for prototyping, manual assembly, or legacy through-hole PCBs where SOP reflow is unavailable. | Select when mechanical compatibility with existing DIP footprints or hand-soldering workflows is required. |
| SN74AS645N | AS family: faster tPLH/tPHL (≤9.5 ns), higher IOL (64 mA), but increased ICC (95–149 mA) and tighter VIH/VIL thresholds. | Better for high-speed timing-critical paths; less tolerant of marginal input noise or degraded VCC rails. | Choose only if sub-10 ns propagation is mandatory and power budget allows +70% active current draw. |
Compared with SN74ALS645AN, the SN74ALS645A-1NSR offers superior board-space efficiency and reflow compatibility; versus SN74AS645N, it trades 1.5 ns speed for 40% lower power and wider input voltage noise margin - making it optimal for cost-sensitive, thermally constrained industrial designs.
Availability
SN74ALS645A-1NSR is available at Aetrix Electronics and suitable for industrial backplane interfaces, microcontroller peripheral expansion, legacy memory subsystems, and test equipment bus arbitration requiring stable component supply over extended production lifecycles.
Supply support for SN74ALS645A-1NSR 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 delivering analog, embedded processing, and logic solutions since 1930, with deep expertise in industrial, automotive, and communications infrastructure markets.
The SN74ALS645A-1NSR belongs to TI's legacy ALS logic family, engineered specifically for reliable, low-power bidirectional bus interfacing in commercial-grade embedded systems where timing predictability and drive strength outweigh ultra-high speed.
FAQ
What is the maximum output current capability of the SN74ALS645A-1NSR?
The SN74ALS645A-1NSR supports up to 48 mA low-level output current (IOL) per pin when VCC is between 4.75 V and 5.25 V - a key enhancement over the standard SN74ALS645A. This rating is confirmed in the "recommended operating conditions" table of the SDAS278 datasheet and enables direct drive of multiple TTL loads without external buffers. The SN74ALS645A-1NSR maintains this specification across its full 0°C to 70°C operating range.
Does the SN74ALS645A-1NSR support 3.3 V logic levels?
No, the SN74ALS645A-1NSR is a 5 V-only TTL-compatible device with VIH minimum of 2 V and VIL maximum of 0.8 V - it does not meet 3.3 V logic thresholds. Its absolute maximum input voltage is 7 V, but operation below 4.5 V VCC violates recommended conditions and risks unreliable switching. For mixed-voltage systems, level-shifting circuitry or a 3.3 V–compatible transceiver such as the TXB0108 is required. The SN74ALS645A-1NSR must be used in strictly 5 V environments.
What is the pin 1 marking and orientation for the SN74ALS645A-1NSR SOP package?
The SN74ALS645A-1NSR uses a standard SOP-20 (NS) package with pin 1 located at the top-left corner of the component body, identified by a small circular or rectangular mark near the edge. Tape-and-reel packaging follows quadrant Q1 orientation per TI's tape specification - meaning pin 1 faces outward and aligns with the sprocket hole pattern's first cavity. Board layout must observe the 7.6 mm × 12.8 mm body outline and 1.27 mm pitch defined in DW0020A drawing.
How does the SN74ALS645A-1NSR differ from the non–1 version (e.g., SN74ALS645ANSR)?
The SN74ALS645A-1NSR differs from SN74ALS645ANSR solely in its guaranteed low-level output current: the "–1" suffix denotes IOL = 48 mA (vs. 24 mA for the standard version), valid only when VCC is 4.75–5.25 V. All other parameters - propagation delay, voltage thresholds, power consumption, and pinout - are identical. The SN74ALS645A-1NSR is functionally interchangeable with SN74ALS645ANSR in circuits where 24 mA drive suffices, but provides headroom for heavier bus loading.
Is the SN74ALS645A-1NSR RoHS compliant and what is its moisture sensitivity level?
Yes, the SN74ALS645A-1NSR is RoHS compliant (lead-free NiPdAu finish) and rated MSL Level-1 (unlimited floor life at ≤30°C/60% RH), per TI's Package Option Addendum. This means it can be stored indefinitely under standard ambient conditions and subjected to standard reflow profiles up to 260°C peak without baking. The "NS" package designation and TI's official part marking "ALS645A-1" confirm full compliance with JEDEC J-STD-020D.1 requirements.
SN74ALS645A-1NSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Logic Type:
- Transceiver, Non-Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- 3-State
- Current - Output High, Low:
- 15mA, 24mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SO
SN74ALS645A-1NSR FAQ
1.How can I place an order for SN74ALS645A-1NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS645A-1NSR 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 SN74ALS645A-1NSR reliable?
The price and inventory of SN74ALS645A-1NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS645A-1NSR is usually 5 days.
3.What payment methods are accepted for SN74ALS645A-1NSR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS645A-1NSR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS645A-1NSR?
SN74ALS645A-1NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS645A-1NSR 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 SN74ALS645A-1NSR?
For technical support, including SN74ALS645A-1NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS645A-1NSR requirements.
6.How does Aetrix verify that SN74ALS645A-1NSR is sourced from the original manufacturer or authorized distributors?
All SN74ALS645A-1NSR 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 SN74ALS645A-1NSR meets industry standards.
7.What is the process for return or replacement of SN74ALS645A-1NSR?
All SN74ALS645A-1NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS645A-1NSR, 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 SN74ALS645A-1NSR part is unused and in its original packaging.
Return procedure for SN74ALS645A-1NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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