My Inquiry
My Account
Texas Instruments SN74ALS645AN
- Part No.:
- SN74ALS645AN
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74ALS645AN.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:633
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SN74ALS645AN from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for asynchronous bidirectional data transfer between A and B buses in TTL-compatible systems. It features direction control (DIR), output enable (OE), ±24 mA low-level drive capability, 0°C to 70°C operating range, and standard 20-pin PDIP (N) package.
For engineers reviewing the SN74ALS645AN datasheet, SN74ALS645AN pinout, SN74ALS645AN application, or SN74ALS645AN equivalent, this device supports legacy industrial backplane interfaces, microprocessor address/data bus isolation, and legacy test equipment I/O expansion where ALS logic speed and drive strength are required.
Technical Context
The SN74ALS645AN implements true TTL-compatible logic with active-low 3-state control via OE and unidirectional data flow selection via DIR. Its propagation delays are specified at 3–10 ns (tPLH/tPHL) under 50 pF load, with guaranteed VOL ≤ 0.4 V at IOL = 24 mA and VOH ≥ 2.4 V at IOH = –12 mA.
It operates strictly within 4.5–5.5 V supply range and is characterized only for commercial temperature (0°C to 70°C); no military-grade (-55°C to 125°C) or -1 enhanced-drive variant is associated with the SN74ALS645AN ordering code.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | ALS (Advanced Low-Power Schottky) - ensures TTL compatibility with lower power than standard LS, suitable for legacy board upgrades. |
| Supply Voltage | 4.5 V to 5.5 V - requires stable +5 V rail; not tolerant of undervoltage or overvoltage beyond absolute max of 7 V. |
| Output Drive | IOL = 24 mA (max), IOH = –12 mA (max) - sufficient to drive 10 LS-TTL loads or terminate short stubs on parallel buses. |
| Propagation Delay | tPLH/tPHL ≤ 10 ns @ CL = 50 pF - enables reliable operation up to ~50 MHz bus toggle rates in point-to-point configurations. |
| Operating Temperature | 0°C to 70°C - qualified for commercial/industrial ambient environments, not extended or military grade. |
| Package Type | 20-pin PDIP (N) - through-hole mounting; 300-mil width; RoHS-compliant NiPdAu lead finish. |
Pinout & Package
SN74ALS645AN uses a 20-pin plastic dual in-line package (PDIP-N) with standard 0.3-inch body width and 0.1-inch pin pitch. Pin 1 is located at the top-left corner when viewed from the top with notch or dot orientation.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Low = B→A data flow; High = A→B data flow; TTL-compatible threshold (VIL ≤ 0.8 V, VIH ≥ 2 V). |
| 2–9 (A1–A8) | Port A I/O Terminals | Bidirectional data lines tied to A bus; high-impedance when OE = High or device powered down. |
| 10 (GND) | Ground Reference | Primary signal and power return path; must be low-inductance connection for noise immunity. |
| 11 (VCC) | Positive Supply | +5 V DC supply pin; requires local 0.1 µF ceramic decoupling adjacent to pin. |
| 12–19 (B1–B8) | Port B I/O Terminals | Bidirectional data lines tied to B bus; electrically identical to A-side pins in 3-state behavior. |
| 20 (OE) | Output Enable Input | Active-Low control: OE = Low enables transceiver; OE = High places all A/B pins in high-impedance state. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional Data Flow | Single DIR pin selects A→B or B→A path without external logic, reducing PCB routing complexity in bus arbitration designs. |
| True 3-State Outputs | OE-controlled high-impedance state isolates both A and B buses simultaneously, enabling multi-drop bus sharing without contention. |
| TTL-Compatible Interface | VIL/VIL thresholds and VOH/VOL levels match standard TTL, allowing direct replacement of SN74LS645 or SN74S645 in existing designs. |
| ALS Logic Performance | Combines LS-speed propagation (≤10 ns) with reduced power consumption versus standard LS, improving thermal margin in dense layouts. |
Applications
| Industrial Backplane Interface | Microprocessor Bus Isolation |
|---|---|
Use Scenario: Interfacing legacy PLC I/O modules across a 20-slot passive backplane using shared address/data lines. IC Role / Device Role / Timing Role: SN74ALS645AN acts as a direction-controlled bus repeater, isolating master CPU from peripheral slots during write cycles and enabling slot-to-slot diagnostics. Use Value: Prevents bus contention during hot-swap events and supports deterministic timing with sub-10 ns propagation, critical for cycle-accurate I/O scanning. | Use Scenario: Separating Z80 or 8086 CPU address/data bus from memory and peripheral controllers on a single-board computer. IC Role / Device Role / Timing Role: SN74ALS645AN serves as a bidirectional bus transceiver, controlled by CPU RD/WR and DTACK signals to gate data flow between CPU and peripherals. Use Value: Enables clean bus segmentation without added glue logic; 24 mA drive sustains signal integrity across 15 cm traces on double-layer PCBs. |
| Legacy Test Equipment I/O Expansion | Parallel Port Signal Conditioning |
Use Scenario: Adding isolated digital I/O channels to automated test systems using GPIB or ISA-bus host controllers. IC Role / Device Role / Timing Role: SN74ALS645AN buffers and direction-controls parallel data paths between host controller and DUT interface cards. Use Value: Provides galvanic isolation via high-Z state during configuration, and ALS speed supports 100 kSPS digital pattern generation. | Use Scenario: Converting PC parallel port signals to robust industrial voltage levels for driving relays, sensors, and optocouplers. IC Role / Device Role / Timing Role: SN74ALS645AN functions as a level-shifting transceiver, translating LPT port's weak open-collector outputs into full TTL swing with current gain. Use Value: Eliminates need for discrete transistor arrays; 24 mA sink capability directly drives 5 V relay coils without external drivers. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74AS645N | Faster propagation (≤9.5 ns), higher drive (IOL = 64 mA), but higher ICC (up to 149 mA) and AS-family input thresholds. | Better suited for high-speed backplanes requiring <8 ns timing margins; less compatible with marginal LS-TTL fanout. | Select SN74AS645N only if timing budget demands sub-9 ns delay and system power budget allows >2× ICC increase. |
| SN74ALS645A-1N | Same ALS family, but rated for IOL = 48 mA (at VCC = 4.75–5.25 V); otherwise identical pinout, timing, and logic behavior. | Required only when driving >10 LS-TTL loads or long unterminated traces (>20 cm) demanding extra sink current. | Choose SN74ALS645A-1N only if measured IOL requirement exceeds 24 mA; SN74ALS645AN remains optimal for standard TTL fanout. |
Compared with SN74AS645N and SN74ALS645A-1N, the SN74ALS645AN delivers balanced speed-power tradeoff for cost-sensitive industrial control boards, offering proven reliability in legacy deployments without over-specifying drive or speed.
Availability
SN74ALS645AN is available at Aetrix Electronics and suitable for industrial automation backplanes, microprocessor bus isolation, and legacy test equipment I/O expansion requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS645AN 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74ALS645AN belongs to TI's legacy TTL logic portfolio, specifically engineered for backward-compatible bus interfacing in systems where ALS speed, power efficiency, and pin-for-pin replaceability with LS-family devices are essential.
FAQ
What is the maximum recommended operating supply voltage for the SN74ALS645AN?
The SN74ALS645AN has a recommended operating supply voltage range of 4.5 V to 5.5 V. While its absolute maximum rating is 7 V, sustained operation above 5.5 V risks parametric shift or premature failure. The device is characterized and guaranteed only within the 4.5–5.5 V window, and all published timing and drive specifications assume VCC = 5 V nominal.
Does the SN74ALS645AN support bidirectional data flow without external logic?
Yes, the SN74ALS645AN supports fully bidirectional data flow using only its DIR input pin. When DIR = Low, data passes from B bus to A bus; when DIR = High, data flows from A bus to B bus. No additional gates or control circuitry are needed, making it ideal for simple bus arbitration in legacy microprocessor systems.
Can the SN74ALS645AN be used as a direct replacement for SN74LS645 in existing designs?
Yes, the SN74ALS645AN is pin-compatible and functionally equivalent to SN74LS645, with identical pinout, logic behavior, and 3-state control. It offers improved speed (≤10 ns vs. ≤15 ns) and lower power consumption, while maintaining TTL-compatible voltage thresholds - enabling drop-in upgrades without layout changes.
What is the purpose of the OE pin on the SN74ALS645AN, and how should it be driven?
The OE (Output Enable) pin on the SN74ALS645AN is an active-low control that places all A and B port pins into high-impedance state when asserted High. It must be driven to TTL logic Low (≤0.8 V) to enable data transmission, and can be tied to GND for permanent enable or controlled by a microcontroller GPIO for dynamic bus arbitration in the SN74ALS645AN.
Is the SN74ALS645AN rated for extended temperature operation?
No, the SN74ALS645AN is characterized only for the commercial temperature range of 0°C to 70°C. It is not rated for extended industrial (–40°C to 105°C) or military (–55°C to 125°C) operation. For wider temperature ranges, consider the SN54ALS645A (military) or verify qualification status of alternate packages through TI's official documentation.
SN74ALS645AN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- 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:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74ALS645AN FAQ
1.How can I place an order for SN74ALS645AN through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS645AN 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 SN74ALS645AN reliable?
The price and inventory of SN74ALS645AN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS645AN is usually 5 days.
3.What payment methods are accepted for SN74ALS645AN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS645AN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS645AN?
SN74ALS645AN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS645AN 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 SN74ALS645AN?
For technical support, including SN74ALS645AN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS645AN requirements.
6.How does Aetrix verify that SN74ALS645AN is sourced from the original manufacturer or authorized distributors?
All SN74ALS645AN 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 SN74ALS645AN meets industry standards.
7.What is the process for return or replacement of SN74ALS645AN?
All SN74ALS645AN units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS645AN, 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 SN74ALS645AN part is unused and in its original packaging.
Return procedure for SN74ALS645AN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SN74ALS645AN 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…
