My Inquiry
My Account
Texas Instruments SN74LS645N
- Part No.:
- SN74LS645N
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS645N.pdf
- Description:
- IC TXRX NON-INVERT 5.25V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:211
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SN74LS645N 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 mA output drive, and uses standard PDIP-20 packaging.
For engineers reviewing the SN74LS645N datasheet, SN74LS645N pinout, SN74LS645N application, or SN74LS645N equivalent, this page delivers verified functional identity, confirmed pin roles, real-world timing and drive specifications, and validated alternatives for legacy TTL bus interface design and system-level compatibility assessment.
Technical Context
The SN74LS645N implements dual 8-bit bidirectional data paths controlled by separate DIR (direction) and OE (output enable) inputs. Its TTL-compatible inputs accept standard logic thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V), and outputs deliver guaranteed high/low voltage levels (VOH ≥ 2.7 V, VOL ≤ 0.5 V) under full load.
Propagation delay is specified at tPLH/tPHL ≤ 25 ns (max) across temperature and supply conditions, and it draws ICC ≤ 34 mA typical at VCC = 5 V. The device lacks internal bus-hold or slew-rate control - external termination or layout care is required for noise-sensitive applications.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | LS-TTL - ensures compatibility with legacy 74LS-series systems and predictable DC noise margins. |
| Function | Octal 3-state bidirectional bus transceiver - enables controlled data transfer between two 8-bit buses using DIR/OE logic. |
| Supply Voltage | VCC = 4.75 V to 5.25 V - requires tightly regulated 5 V rail; no wide-VCC operation supported. |
| Output Drive | ±20 mA per output - sufficient to drive multiple TTL inputs or short PCB traces without buffering. |
| Propagation Delay | tPD ≤ 25 ns (max) - defines maximum clock-to-data latency in synchronous bus handshaking. |
| Operating Temperature | 0°C to +70°C - commercial-grade rating; not qualified for extended industrial or automotive ranges. |
| Package | PDIP-20 (N) - through-hole mounting compatible with legacy prototyping and repair workflows. |
Pinout & Package
SN74LS645N is housed in a 20-pin plastic dual in-line package (PDIP), 0.300-inch body width, with standard 0.100-inch pin spacing. Pin 1 is located at the top-left corner marked by a notch or dot.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction control input | High = A→B data flow; Low = B→A; determines signal path polarity for all 8 channels. |
| 2–9 (A1–A8) | Bus A data terminals | Connect to first 8-bit data bus; function as inputs or outputs depending on DIR state. |
| 10 (GND) | Ground reference | Primary return path for all logic and output currents; must be low-impedance. |
| 11–18 (B1–B8) | Bus B data terminals | Connect to second 8-bit data bus; mirror A-side behavior under DIR control. |
| 19 (OE) | Output enable input | Low = outputs active; High = all outputs in high-impedance state - essential for bus sharing. |
| 20 (VCC) | Positive supply | 5 V nominal power source; decoupling capacitor (0.1 µF) required near pin for noise suppression. |
Key Features
| Feature | Design Value |
|---|---|
| Independent DIR and OE controls | Enables precise timing separation: direction can be set before enabling outputs, avoiding bus contention. |
| 3-state outputs with TTL-compatible levels | Guarantees VOH ≥ 2.7 V and VOL ≤ 0.5 V into 400 Ω loads - interoperable with standard LS-TTL inputs. |
| High sink/source capability | Drives up to 20 mA per output - supports fan-out of 20 LS-TTL loads without external buffers. |
| Matched propagation delays | tPLH and tPHL both ≤ 25 ns - ensures symmetrical timing for bidirectional data integrity. |
| Standard PDIP-20 footprint | Direct replacement for legacy 74LS640/645 sockets; compatible with manual soldering and wave-solder processes. |
Applications
| Industrial Control Backplane | Legacy Computer Memory Expansion |
|---|---|
Use Scenario: Isolating CPU address/data buses from peripheral modules in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus isolation element synchronized to control strobes; DIR set by module select, OE gated by chip enable. Use Value: Prevents bus contention during hot-swap of I/O cards while maintaining deterministic 25 ns data turnaround. |
Use Scenario: Extending memory-mapped I/O space in 8-bit microcomputer systems (e.g., Z80 or 8085-based). IC Role / Device Role / Timing Role: Data path translator between processor bus and expansion slot; DIR fixed for memory read/write direction. Use Value: Enables 8-bit parallel data transfer at full system clock speed without added wait states. |
| Test Equipment Bus Interface | Instrumentation Data Acquisition Hub |
Use Scenario: Interfacing digital pattern generators with DUT boards requiring bidirectional stimulus/response routing. IC Role / Device Role / Timing Role: Reconfigurable data conduit; DIR toggled per test phase, OE used for bus release between sequences. Use Value: Eliminates need for discrete directional switches or multiplexers in automated test fixtures. |
Use Scenario: Aggregating sensor data streams from multiple 8-bit ADCs onto a shared microcontroller bus. IC Role / Device Role / Timing Role: Time-multiplexed bus concentrator; OE sequenced per ADC channel, DIR held constant. Use Value: Reduces microcontroller pin count and simplifies PCB routing versus individual parallel connections. |
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 OE control only; no dedicated DIR pin - direction managed via external logic or bus arbitration. | Requires additional gate logic to replicate DIR functionality; less flexible for dynamic bidirectional switching. | Preferred when direction is static or externally controlled; lower gate count but reduced runtime flexibility. |
| SN74ALS645N | Advanced LS variant: 2× faster (tPD ≤ 12 ns), lower ICC (≤ 22 mA), same pinout and logic behavior. | Drop-in timing upgrade for performance-critical paths; maintains identical interface and layout. | Recommended for new designs needing improved speed/power; fully backward-compatible with SN74LS645N layouts. |
Compared with SN74LS645N, SN74LS245N reduces control complexity at the cost of runtime direction agility, while SN74ALS645N delivers measurable timing and power advantages without altering board design or firmware logic.
Availability
SN74LS645N is available at Aetrix Electronics and suitable for industrial control backplanes, legacy computer memory expansion, test equipment bus interfaces, and instrumentation data acquisition hubs requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS645N 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 SN74LS645N belongs to TI's classic 74LS logic family, engineered for reliable, low-cost bidirectional bus interfacing in commercial-grade digital systems from the 1970s onward.
FAQ
What is the primary function of the SN74LS645N in a digital system?
The SN74LS645N serves as an octal 3-state bidirectional bus transceiver, enabling controlled data exchange between two 8-bit buses. Its DIR input selects transmission direction (A→B or B→A), while OE places outputs in high-impedance state to prevent bus conflicts. This makes SN74LS645N ideal for memory-mapped I/O, backplane interconnects, and modular system architectures where bus sharing is required.
Can SN74LS645N operate with a 3.3 V supply?
No, SN74LS645N is strictly a 5 V TTL device with VCC specification of 4.75 V to 5.25 V. It does not support 3.3 V operation, and applying 3.3 V will result in undefined logic levels, marginal noise immunity, and potential failure to meet output drive or timing specs. For 3.3 V systems, consider modern alternatives like SN74LVC245A or level-shifting solutions alongside SN74LS645N.
How does the SN74LS645N differ from SN74LS245N?
SN74LS645N provides independent DIR and OE inputs for full bidirectional control, whereas SN74LS245N uses a single OE input and relies on external logic to manage direction. SN74LS645N thus offers greater flexibility in dynamic bus arbitration scenarios. Both share identical PDIP-20 packaging and 5 V operation, but SN74LS645N's dual-control architecture eliminates need for supplemental gates when direction must change rapidly - a key distinction in real-time SN74LS645N deployments.
Is SN74LS645N RoHS compliant?
Yes, SN74LS645N is RoHS compliant, as confirmed by Texas Instruments' packaging documentation. It uses NiPdAu (NIPDAU) lead finish and meets EU Directive 2011/65/EU requirements. The "Yes" RoHS flag appears in TI's official packaging addendum for orderable part number SN74LS645N, and no exemptions apply. This compliance applies to current production lots supplied by Aetrix Electronics.
What is the maximum capacitive load SN74LS645N can drive reliably?
SN74LS645N is characterized for loads up to 400 Ω (equivalent to ~15 pF at 5 V with typical trace capacitance), with guaranteed VOH ≥ 2.7 V and VOL ≤ 0.5 V. Driving >50 pF may degrade edge rates and increase propagation delay beyond the 25 ns max spec. For longer traces or higher fan-out, use series termination or buffer stages - SN74LS645N itself does not include slew-rate control or transmission-line optimization.
SN74LS645N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- 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:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74LS645N FAQ
1.How can I place an order for SN74LS645N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS645N 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 SN74LS645N reliable?
The price and inventory of SN74LS645N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS645N is usually 5 days.
3.What payment methods are accepted for SN74LS645N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS645N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS645N?
SN74LS645N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS645N 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 SN74LS645N?
For technical support, including SN74LS645N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS645N requirements.
6.How does Aetrix verify that SN74LS645N is sourced from the original manufacturer or authorized distributors?
All SN74LS645N 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 SN74LS645N meets industry standards.
7.What is the process for return or replacement of SN74LS645N?
All SN74LS645N units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS645N, 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 SN74LS645N part is unused and in its original packaging.
Return procedure for SN74LS645N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SN74LS645N Tags
-
SN74LVC1G17DBVR
Texas Instruments
-
SN74LVC1G07DCKR
Texas Instruments
-
SN74LVC1G17DCKR
Texas Instruments
-
SN74LVC1G07DBVR
Texas Instruments
-
SN74LVC1G125DCKR
Texas Instruments
-
SN74AHCT1G126DBVR
Texas Instruments
-
SN74LVC1G125DBVR
Texas Instruments
-
SN74AHCT1G125DBVR
Texas Instruments
-
SN74LVC2G17DBVR
Texas Instruments
-
SN74LVC2G07DCKR
Texas Instruments
-
SN74LVC1G34DCKR
Texas Instruments
-
SN74LVC2G17DCKR
Texas Instruments
Tech Hub
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…
Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…
An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…
Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…
Jumper cables guide covering safe connection order, red and black clamp placement, final ground connection, cable gauge, length, clamp quality, copper vs CCA cables, jump starter comparison and battery…
