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Texas Instruments SN74LS645NSR
- Part No.:
- SN74LS645NSR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74LS645NSR.pdf
- Description:
- IC TXRX NON-INVERT 5.25V 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:3,129
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Product details
Overview
SN74LS645NSR from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for bidirectional data flow control between two 8-bit buses in TTL-level systems. It features independent output-enable (OE) and direction (DIR) controls, operates at 0°C to 70°C, supports 20-pin SOP (NS) packaging, and is used in legacy industrial control backplanes and microprocessor system expansion interfaces.
For engineers reviewing the SN74LS645NSR datasheet, SN74LS645NSR pinout, SN74LS645NSR application, or SN74LS645NSR equivalent, this page delivers verified functional specifications, validated pin assignments, confirmed operating conditions, and real-world use context - all aligned with TI's SDLS189 production data sheet (Rev. March 1988).
Technical Context
The SN74LS645NSR implements dual 8-bit bidirectional bus interface logic using standard TTL circuitry. Its DIR input determines data flow direction (A-to-B or B-to-A), while OE independently places both A- and B-side outputs into high-impedance state. Propagation delay is specified at 22 ns max (tPLH/tPHL) under VCC = 5 V, TA = 25°C, and RL = 400 Ω.
It meets LS-TTL electrical compatibility: input thresholds are VIL ≤ 0.8 V and VIH ≥ 2.0 V; output drive capability is IOH = –15 mA and IOL = 24 mA at VCC = 5 V. The device lacks internal clamping diodes or ESD protection beyond standard LS process limits.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal bidirectional bus transceiver with 3-state outputs |
| Logic Family | LS-TTL - ensures compatibility with 74LS-series inputs/outputs and defined noise margins |
| Supply Voltage | VCC = 4.75 V to 5.25 V - requires regulated 5 V rail; no wide-VCC support |
| Propagation Delay | 22 ns max (A↔B path) - constrains maximum bus clock rate in synchronous designs |
| Output Drive | IOL = 24 mA / IOH = –15 mA - drives standard LS loads without external buffers |
| Operating Temperature | 0°C to 70°C - commercial-grade rating; not qualified for extended or military temperature ranges |
| Package | SOP-20 (NS) - surface-mount, 0.300" wide body, 12.0 mm × 7.5 mm footprint |
Pinout & Package
SOP-20 (NS) package: 20-pin small-outline plastic package with gull-wing leads, 1.27 mm pitch, 0.300" body width, and moisture sensitivity level (MSL) 1 (unlimited floor life at ≤30°C/60% RH).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction control input | High = A→B data flow; Low = B→A; must be stable before enabling outputs |
| 2–9 (A1–A8) | Bus A data terminals | Input when DIR = Low and OE = Low; output when DIR = High and OE = Low |
| 10 (GND) | Ground reference | Primary return path for all internal logic and output currents |
| 11–18 (B1–B8) | Bus B data terminals | Input when DIR = High and OE = Low; output when DIR = Low and OE = Low |
| 19 (OE) | Output-enable input | Low enables transceiver; High forces all A/B outputs into high-impedance state |
| 20 (VCC) | Positive supply | 5 V nominal; decoupling capacitor required within 1 cm of pin for noise immunity |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional data control | Single DIR pin selects A→B or B→A flow - eliminates need for separate transmit/receive buffers |
| Independent 3-state enable | OE pin disables both A and B ports simultaneously - supports bus arbitration and hot-swap isolation |
| LS-TTL compatible I/O | VIH/VIL, IOH/IOL, and timing match 74LS family - allows drop-in replacement in existing LS designs |
| 20-pin SOP packaging | NS package enables automated SMT assembly and fits standard 0.300"-width PCB footprints |
| Commercial temperature range | 0°C to 70°C operation - suitable for office, lab, and non-harsh industrial environments |
Applications
| Industrial Backplane Interface | Microprocessor System Expansion |
|---|---|
Use Scenario: Connecting CPU local bus to peripheral card slots in programmable logic controllers (PLCs). IC Role / Device Role / Timing Role: Bidirectional data bridge between 8-bit address/data multiplexed bus and isolated I/O module bus. Use Value: Enables shared bus architecture with direction-controlled data transfer and OE-based slot isolation during configuration. |
Use Scenario: Extending Z80 or 8085-based single-board computer memory or I/O space via expansion headers. IC Role / Device Role / Timing Role: Level-shifting and bus-driving transceiver between main CPU bus and add-on peripheral cards. Use Value: Provides LS-compatible drive strength and timing to maintain signal integrity across 150 mm backplane traces. |
| Legacy Test Equipment Data Path | Embedded Instrumentation Subsystem |
Use Scenario: Routing measurement data between ADC/DAC modules and controller bus in benchtop multimeters. IC Role / Device Role / Timing Role: Controlled-direction data conduit synchronized to system clock edges for deterministic sampling windows. Use Value: DIR and OE pins allow precise timing of data capture and hold phases without external latches. |
Use Scenario: Interfacing sensor front-end ASICs to host MCU in environmental monitoring nodes. IC Role / Device Role / Timing Role: Isolation buffer between mixed-voltage subsystems (e.g., 3.3 V sensor IC ↔ 5 V legacy controller). Use Value: 3-state outputs prevent bus contention during firmware updates or sensor calibration sequences. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS245N | Identical function and pinout; differs only in package (PDIP-20 vs SOP-20) and marking format | Same electrical behavior and timing; requires through-hole PCB layout instead of SMT | Select SN74LS245N only if PDIP mounting and manual assembly are preferred over automated SOP placement |
| SN74LS640NSR | Same package and pinout; differs in DIR logic polarity (active-low DIR on SN74LS640 vs active-high on SN74LS645) | Requires inverted direction control signal; otherwise identical bus loading and timing | Choose SN74LS640NSR only when system control logic naturally provides active-low DIR signals |
Compared with SN74LS245N and SN74LS640NSR, the SN74LS645NSR offers native SOP-20 surface-mount compatibility and active-high DIR polarity - simplifying control logic integration and enabling higher-density PCB layouts without requiring signal inversion or mechanical rework.
Availability
SN74LS645NSR is available at Aetrix Electronics and suitable for industrial backplane interfaces, microprocessor system expansion, legacy test equipment data paths, and embedded instrumentation subsystems requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS645NSR 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 SN74LS645NSR belongs to TI's legacy 74LS logic family, engineered for reliable 5 V TTL bus interfacing in cost-sensitive, non-high-speed digital systems where proven robustness outweighs advanced feature sets.
FAQ
What is the primary function of the SN74LS645NSR?
The SN74LS645NSR is an octal bidirectional bus transceiver with 3-state outputs. It enables controlled data flow between two 8-bit buses - either A-to-B or B-to-A - using DIR and OE inputs. Its LS-TTL compatibility, 22 ns propagation delay, and SOP-20 packaging make it suitable for legacy industrial and microprocessor expansion applications where deterministic bus control is required. The SN74LS645NSR remains fully specified per TI's SDLS189 datasheet.
Does the SN74LS645NSR support 3.3 V operation?
No, the SN74LS645NSR is strictly a 5 V device with VCC specification of 4.75 V to 5.25 V. It does not support 3.3 V supply or tolerate 3.3 V logic inputs reliably due to LS-TTL input threshold requirements (VIH ≥ 2.0 V, VIL ≤ 0.8 V). Using it with 3.3 V systems risks undefined operation or excessive input current. For mixed-voltage designs, level-shifting circuitry or a 3.3 V–compatible transceiver such as SN74LVC245A is required alongside the SN74LS645NSR.
What is the pinout compatibility between SN74LS645NSR and SN74LS245?
The SN74LS645NSR and SN74LS245 share identical pin functions and ordering across all 20 pins, including DIR, OE, A1–A8, B1–B8, VCC, and GND. The only physical difference is package type: SN74LS645NSR uses SOP-20 (NS), while SN74LS245 is commonly offered in PDIP-20 (N) or SOIC-20 (DW). Electrical timing, drive strength, and logic behavior are functionally equivalent - making SN74LS245N a direct functional alternative when through-hole mounting is acceptable.
How does SN74LS645NSR differ from SN74LS640NSR?
The SN74LS645NSR and SN74LS640NSR are pin-compatible octal transceivers in SOP-20 packages, but differ in DIR input polarity: SN74LS645NSR uses active-high DIR (High = A→B), whereas SN74LS640NSR uses active-low DIR (Low = A→B). All other parameters - propagation delay, drive strength, supply range, and OE behavior - are identical. This polarity difference requires corresponding adjustment in control logic; no other hardware or timing changes are needed when substituting SN74LS645NSR for SN74LS640NSR.
Is SN74LS645NSR RoHS compliant?
Yes, SN74LS645NSR is RoHS compliant, as confirmed by TI's packaging documentation: lead finish is NiPdAu (NIPDAU), and the part carries "Yes" in the RoHS column of the official Package Option Addendum. It meets EU Directive 2011/65/EU requirements for restricted substances and is suitable for environmentally regulated commercial electronics manufacturing. The SN74LS645NSR also complies with TI's MSL Level-1 rating for unlimited floor life under standard handling conditions.
SN74LS645NSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- 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:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SO
SN74LS645NSR FAQ
1.How can I place an order for SN74LS645NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS645NSR 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 SN74LS645NSR reliable?
The price and inventory of SN74LS645NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS645NSR is usually 5 days.
3.What payment methods are accepted for SN74LS645NSR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS645NSR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS645NSR?
SN74LS645NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS645NSR 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 SN74LS645NSR?
For technical support, including SN74LS645NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS645NSR requirements.
6.How does Aetrix verify that SN74LS645NSR is sourced from the original manufacturer or authorized distributors?
All SN74LS645NSR 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 SN74LS645NSR meets industry standards.
7.What is the process for return or replacement of SN74LS645NSR?
All SN74LS645NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS645NSR, 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 SN74LS645NSR part is unused and in its original packaging.
Return procedure for SN74LS645NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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