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Texas Instruments SN74LS645-1NSR
- Part No.:
- SN74LS645-1NSR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74LS645-1NSR.pdf
- Description:
- IC TXRX NON-INVERT 5.25V 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:4,050
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Product details
Overview
SN74LS645-1NSR from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for bidirectional data flow control in TTL-level digital systems. It features 8-bit non-inverting data paths, independent output-enable (OE) and direction (DIR) controls, and operates over 0°C to 70°C. Used in legacy industrial controllers and backplane interface modules where level-shifting and bus isolation are required.
For engineers reviewing the SN74LS645-1NSR datasheet, SN74LS645-1NSR pinout, SN74LS645-1NSR application, or SN74LS645-1NSR equivalent, key selection criteria include its 3-state output drive capability, DIR/OE dual-control logic, SOP-20 package compatibility with automated SMT assembly, and guaranteed DC electrical specs per SDLS189 (March 1988).
Technical Context
This device implements two independent 4-bit bidirectional buffers within a single 20-pin SOP package, each with separate DIR and OE inputs enabling flexible bus arbitration. Its TTL-compatible input thresholds (VIL = 0.8 V, VIH = 2.0 V) and output drive (IOH = –15 mA, IOL = 24 mA) ensure interoperability with standard LS-TTL logic families.
The 3-state outputs support high-impedance disconnection during bus contention or power-down sequences, while the DIR pin determines data flow direction per nibble - low for A-to-B, high for B-to-A - without internal latching or clocking.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | LS-TTL: ensures direct compatibility with 74LS-series systems without level translation. |
| Data Width | Octal (8-bit): supports full byte-wide parallel bus transfer between two subsystems. |
| Output Type | 3-state non-inverting: enables shared bus operation with multiple drivers via OE control. |
| Direction Control | DIR pin per 4-bit group: allows independent forward/reverse data routing for A/B ports. |
| Supply Voltage | VCC = 4.75–5.25 V: tight tolerance ensures stable operation under noisy industrial rail conditions. |
| Operating Temperature | 0°C to 70°C: validated for commercial-grade embedded equipment, not extended/military range. |
| Package | SOP-20 (NS): surface-mount, 0.300" wide body, RoHS-compliant NIPDAU finish, MSL Level-1. |
Pinout & Package
SOP-20 (NS) package: 0.300" wide body, 1.27 mm pitch, 2.65 mm max height, tape-and-reel delivery (2000 pcs/reel), Q1 pin-1 quadrant orientation.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR1) | Direction control - lower nibble | Low = A→B data flow; High = B→A; sets path direction independently of OE. |
| 2–5 (A0–A3) | Input/output port A - lower nibble | Bidirectional I/O pins tied to local subsystem; driven only when OE active and DIR set. |
| 6 (GND) | Ground reference | Primary signal return path; must be low-impedance connection to minimize noise coupling. |
| 7–10 (B0–B3) | Input/output port B - lower nibble | Bidirectional I/O pins tied to remote bus; function mirrors A0–A3 based on DIR1 state. |
| 11 (OE1) | Output enable - lower nibble | Active-low: disables both A0–A3 and B0–B3 outputs to high-impedance when high. |
| 12–15 (A4–A7) | Input/output port A - upper nibble | Second 4-bit bidirectional group, controlled by DIR2 (pin 19) and OE2 (pin 18). |
| 16 (VCC) | Positive supply | 5 V nominal power rail; requires local 0.1 µF ceramic decoupling adjacent to pin. |
| 17–20 (B4–B7) | Input/output port B - upper nibble | Second 4-bit bidirectional group, functionally identical to B0–B3 but controlled separately. |
| 18 (OE2) | Output enable - upper nibble | Active-low enable for A4–A7/B4–B7; allows independent gating of upper byte. |
| 19 (DIR2) | Direction control - upper nibble | Independent DIR signal for upper nibble; enables split-direction operation across byte boundary. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent 4-bit transceivers | Enables simultaneous or asymmetric data routing: e.g., A→B on lower nibble while B→A on upper nibble. |
| Separate DIR and OE per nibble | Permits fine-grained bus arbitration without external logic; eliminates need for discrete direction latches. |
| 3-state outputs with TTL drive strength | IOL = 24 mA / IOH = –15 mA supports direct driving of multiple LS-TTL inputs without buffers. |
| SOP-20 RoHS-compliant packaging | Surface-mount footprint compatible with standard 0.65 mm pitch reflow profiles; MSL Level-1 simplifies handling. |
| Validated commercial temperature range | 0°C to 70°C operation confirmed per SDLS189 test conditions; suitable for office/industrial enclosures. |
Applications
| Industrial PLC Backplanes | Legacy Test Equipment Interfaces |
|---|---|
Use Scenario: Bidirectional data exchange between CPU module and I/O expansion cards in modular programmable logic controllers. IC Role / Device Role / Timing Role: Bus transceiver isolating main processor bus from field-side peripherals while supporting hot-swap-safe 3-state disconnect. Use Value: Prevents bus contention during card insertion/removal and enables deterministic read/write cycles using DIR/OE sequencing. | Use Scenario: Interfacing microcontroller-based test fixtures with vintage DUTs requiring TTL-level parallel handshaking. IC Role / Device Role / Timing Role: Level-consistent bidirectional data bridge between modern controller and legacy instrument buses (e.g., IEEE-488 subsets). Use Value: Eliminates need for discrete inverters or translators; maintains signal integrity across 20 cm ribbon cable runs at ≤10 MHz. |
| Embedded Data Acquisition Systems | Repair & Calibration Bench Adapters |
Use Scenario: Connecting ADC/DAC modules to host microcontrollers in compact data loggers with space-constrained PCBs. IC Role / Device Role / Timing Role: Octal transceiver managing multiplexed sensor data lanes and control signals over shared trace bundles. Use Value: Reduces interconnect count by 50% vs. unidirectional buffers; DIR-controlled flow avoids software overhead of manual bus turnaround. | Use Scenario: Building field-service adapters that convert proprietary test head connectors to standard 20-pin IDC headers. IC Role / Device Role / Timing Role: Signal-conditioning transceiver ensuring clean TTL transitions across mismatched impedance paths in calibration jigs. Use Value: Provides robust 24 mA sink capability to drive long cables and multiple scope probe inputs simultaneously. |
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 | Single-direction DIR control (global), no per-nibble OE; PDIP-20 only. | Lacks independent nibble gating; requires external logic for split-byte arbitration. | Choose when system uses uniform direction per transaction and SOP packaging is not required. |
| SN74LS640NSR | Identical SOP-20 package and pinout; differs in DIR logic polarity (active-high vs. SN74LS645's active-low DIR). | Requires inverted DIR signal routing; otherwise drop-in replacement for same physical layout. | Choose when existing design already routes active-high direction control and board revision is constrained. |
Compared with SN74LS245N, SN74LS645-1NSR offers finer bus control granularity via dual DIR/OE pairs but at higher gate count cost; compared with SN74LS640NSR, it provides complementary direction logic enabling direct integration with active-low control buses without inverters.
Availability
SN74LS645-1NSR is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy test equipment interfaces, and embedded data acquisition systems requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS645-1NSR 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 founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74LS645-1NSR belongs to TI's legacy 74LS logic family, engineered for reliability in commercial-grade digital systems where predictable timing, noise immunity, and backward compatibility with 1970s–1990s TTL infrastructure are critical.
FAQ
What is the maximum clock/data rate supported by SN74LS645-1NSR?
The SN74LS645-1NSR is a static logic device with no internal clock; its usable data rate depends on external system timing. Per SDLS189, propagation delay (tPLH/tPHL) is 15 ns typical at VCC = 5 V, supporting reliable operation up to approximately 10 MHz in well-terminated, low-capacitance bus environments. SN74LS645-1NSR does not specify AC characteristics beyond DC and switching parameters.
Can SN74LS645-1NSR replace SN74LS640NSR in an existing design?
SN74LS645-1NSR can replace SN74LS640NSR only if the direction-control logic is inverted: SN74LS645-1NSR uses active-low DIR (low = A→B), whereas SN74LS640NSR uses active-high DIR. The pinout, package, and 3-state behavior are identical. SN74LS645-1NSR requires upstream signal inversion or redesign of DIR drive circuitry to maintain functional equivalence.
Does SN74LS645-1NSR support mixed-voltage interfacing (e.g., 3.3 V logic)?
No. SN74LS645-1NSR is strictly a 5 V TTL device with VIH = 2.0 V minimum and VIL = 0.8 V maximum. Driving its inputs from 3.3 V logic may result in marginal or unreliable recognition of HIGH states. SN74LS645-1NSR requires level-shifting circuitry (e.g., SN74LVC245) for safe interfacing with sub-5 V systems.
What is the recommended bypass capacitor for SN74LS645-1NSR?
A 0.1 µF ceramic capacitor placed as close as possible to the VCC (pin 16) and GND (pin 6) terminals is mandatory per SDLS189 guidelines. This minimizes supply rail noise induced by simultaneous output switching of all eight drivers. SN74LS645-1NSR exhibits high transient current demand during 3-state transitions, making localized decoupling essential for signal integrity.
Is SN74LS645-1NSR pin-compatible with newer CMOS equivalents like SN74HC245?
No. Although both are octal transceivers, SN74LS645-1NSR (SOP-20, LS-TTL) and SN74HC245 (SOIC-20, HC-CMOS) differ in pin function assignment: SN74HC245 uses a single DIR and single OE, while SN74LS645-1NSR has two DIR/OE pairs. Their electrical characteristics (voltage levels, drive strength, timing) are also incompatible without interface conditioning. SN74LS645-1NSR cannot be substituted directly.
SN74LS645-1NSR 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, 48mA
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SO
SN74LS645-1NSR FAQ
1.How can I place an order for SN74LS645-1NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS645-1NSR 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 SN74LS645-1NSR reliable?
The price and inventory of SN74LS645-1NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS645-1NSR is usually 5 days.
3.What payment methods are accepted for SN74LS645-1NSR?
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4.How is shipping managed for SN74LS645-1NSR?
SN74LS645-1NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS645-1NSR 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 SN74LS645-1NSR?
For technical support, including SN74LS645-1NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS645-1NSR requirements.
6.How does Aetrix verify that SN74LS645-1NSR is sourced from the original manufacturer or authorized distributors?
All SN74LS645-1NSR 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 SN74LS645-1NSR meets industry standards.
7.What is the process for return or replacement of SN74LS645-1NSR?
All SN74LS645-1NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS645-1NSR, 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 SN74LS645-1NSR part is unused and in its original packaging.
Return procedure for SN74LS645-1NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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