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Texas Instruments SN74ALS845DW
- Part No.:
- SN74ALS845DW
- Manufacturer:
- Texas Instruments
- Package:
- -
- Datasheet:
-
SN74ALS845DW.pdf
- Description:
- BUS DRIVER, ALS SERIES
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Product details
Overview
SN74ALS845DW from Texas Instruments is an 8-bit transparent D-type latch with three independent 3-state output-enable inputs (OE1, OE2, OE3), noninverting data path, and asynchronous preset/clear. It delivers ±48 mA low-level drive (IOL), 24 ns max tPHL, and operates at 4.5–5.5 V over 0°C to 70°C - designed for bus-holding I/O ports and bidirectional data buffering in legacy TTL systems.
For engineers reviewing the SN74ALS845DW datasheet, SN74ALS845DW pinout, SN74ALS845DW application, or SN74ALS845DW equivalent, key selection criteria include its bus-structured 24-pin SOIC-DW package, independent PRE/CLR control, high-impedance power-up state, and compatibility with ALS logic families requiring robust capacitive bus driving without external pull-ups.
Technical Context
This device implements eight edge-transparent latches with true (noninverting) D-to-Q propagation, where data passes through while LE is high and is latched on LE falling edge. PRE and CLR operate asynchronously and override clocked behavior - PRE low forces Q high, CLR low forces Q low, and simultaneous low prioritizes PRE.
All three output-enable inputs (OE1, OE2, OE3) are buffered and ORed internally to control 3-state output drivers; they do not affect latch storage or data entry timing. The outputs enter high-impedance state independently of LE, enabling dynamic bus arbitration and multi-drop bus sharing without disrupting internal register state.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - supports standard 5 V TTL bus operation with ±5% tolerance |
| IOL (max) | 48 mA - enables direct drive of heavily loaded buses without external buffers or pull-ups |
| tPHL (max) | 26 ns - ensures timing compliance in 12–16 MHz address/data strobe cycles |
| VIH / VIL | 2.0 V / 0.8 V - compatible with standard TTL input thresholds for seamless interfacing |
| Operating Temp | 0°C to 70°C - qualified for commercial-grade embedded and industrial control systems |
| ICC (disabled) | 25–42 mA - reduced quiescent current during 3-state mode improves system power efficiency |
| tsu / th | 10 ns / 5 ns - defines minimum D setup and hold relative to LE↓ for reliable latch capture |
Pinout & Package
SN74ALS845DW uses a 24-pin SOIC (Small-Outline Integrated Circuit) package with 300-mil body width and DW suffix per TI's packaging nomenclature. Pin spacing is 0.050″ (1.27 mm), and the package is surface-mount compatible with standard reflow profiles.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | OE1 | Output-enable input 1 - active-low; ORed with OE2/OE3 to control all 8 outputs |
| 2 | OE2 | Output-enable input 2 - active-low; enables shared bus control across multiple devices |
| 3 | 1D | Data input channel 1 - noninverting D input for first latch |
| 4 | 2D | Data input channel 2 - connects directly to second latch without inversion |
| 5 | 3D | Data input channel 3 - part of 8-bit parallel data path aligned with bus structure |
| 6 | 4D | Data input channel 4 - matches physical pin layout to simplify PCB routing |
| 7 | 5D | Data input channel 5 - maintains consistent signal integrity across all D lines |
| 8 | 6D | Data input channel 6 - supports wide-data-path implementations (e.g., 16-bit address latching) |
| 9 | 7D | Data input channel 7 - routed adjacent to 8D for differential pair or length-matching purposes |
| 10 | 8D | Data input channel 8 - completes full byte-wide input interface |
| 11 | CLR | Asynchronous clear - forces all Q outputs low regardless of LE or clock state |
| 12 | GND | Ground reference - dedicated return path for logic and output driver currents |
| 13 | VCC | Supply voltage - powers internal logic and high-current output stages |
| 14 | OE3 | Output-enable input 3 - third enable for fine-grained bus segment control |
| 15 | 1Q | Output channel 1 - true (noninverted) latched value of 1D, 3-state capable |
| 16 | 2Q | Output channel 2 - matches 2D timing and drive strength for synchronized bus loading |
| 17 | 3Q | Output channel 3 - maintains identical VOL/VOL specs as other Q pins under load |
| 18 | 4Q | Output channel 4 - shares same 3-state transition times (tPZH/tPLZ) as all outputs |
| 19 | 5Q | Output channel 5 - enables interleaved read/write bus protocols via independent OE gating |
| 20 | 6Q | Output channel 6 - supports parity generation/checking when used with 7Q/8Q |
| 21 | 7Q | Output channel 7 - provides deterministic output impedance in high-Z state (IOZL/IOZH ≤ ±20 µA) |
| 22 | 8Q | Output channel 8 - final bit of byte-wide output; matches pinout symmetry of D inputs |
| 23 | PRE | Asynchronous preset - forces all Q outputs high independent of LE or data state |
| 24 | LE | Latch enable - high level enables transparency; falling edge captures D inputs into latches |
Key Features
| Feature | Design Value |
|---|---|
| Bus-structured pinout | Input (D) and output (Q) pins arranged in mirrored 1–8 order across two sides - minimizes trace crossovers and reduces PCB layer count |
| Independent PRE/CLR | Asynchronous set/reset allows initialization or fault recovery without waiting for LE timing or bus availability |
| Three OE inputs (OE1–OE3) | Enables hierarchical bus control - e.g., OE1 for main bus, OE2 for peripheral segment, OE3 for diagnostics |
| Power-up high-impedance | Outputs remain in Z-state at power-on reset - prevents bus contention during system boot or brownout |
| Buffered control inputs | Reduced DC loading on upstream drivers (IIH ≤ 20 µA, IIL ≤ −0.1 mA) extends fan-out capability |
| 48 mA IOL drive (−1 version) | Eliminates need for external bus drivers in high-capacitance backplanes (>100 pF/load) |
Applications
| Industrial PLC Backplane Interface | Legacy Computer Memory Address Latching |
|---|---|
Use Scenario: Isolating CPU address bus from modular I/O expansion slots in programmable logic controllers. IC Role / Device Role / Timing Role: Acts as address latch buffer between microprocessor and slot-select decoders; LE synchronized to ALE signal. Use Value: Prevents address glitches during slot insertion/removal by holding stable address values while OE controls bus access per module. |
Use Scenario: Capturing and holding 16-bit memory address lines in 1980s-era minicomputer systems using discrete TTL logic. IC Role / Device Role / Timing Role: Transparent latch for upper/lower address bytes; PRE/CLR used for memory reset sequences. Use Value: Enables single-cycle address setup with 10 ns tsu, supporting 8–10 MHz CPU clock domains without wait states. |
| Parallel Printer Port Data Register | Test Equipment Bus Arbitration Logic |
Use Scenario: Holding parallel data from host controller before strobing to thermal print head in dot-matrix printers. IC Role / Device Role / Timing Role: Output latch for 8-bit data bus; OE3 tied to BUSY handshake, PRE used for paper-out reset. Use Value: 48 mA drive ensures fast rise/fall on long ribbon cables (≤2 m), reducing print jitter and misalignment. |
Use Scenario: Managing shared GPIB or IEEE-488 bus access among multiple test instruments in automated rack systems. IC Role / Device Role / Timing Role: Bidirectional bus transceiver latch; OE1/OE2 coordinate talker/listener roles, LE timed to bus grant. Use Value: High-impedance isolation prevents signal corruption during bus handoff; tPZH < 11 ns ensures sub-100 ns arbitration latency. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 8-bit transparent latch applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74AS845N | Faster propagation (tPHL = 10 ns typ), higher ICC (60 mA), AS family speed grade - requires tighter VCC regulation (4.75–5.25 V). | Better suited for >20 MHz clock domains but less tolerant of noisy 5 V rails. | Select SN74AS845N only if timing margin is critical and power supply stability is guaranteed. |
| SN74LS373N | Lower drive (IOL = 24 mA), slower (tPHL = 35 ns max), no independent OE inputs - single OE pin controls all outputs. | Used in cost-sensitive, lower-speed designs where bus segmentation isn't required. | Choose SN74LS373N for legacy LS-based systems where board space or BOM cost outweighs performance needs. |
Compared with SN74AS845N and SN74LS373N, the SN74ALS845DW offers balanced speed-power trade-off (26 ns/48 mA), triple OE flexibility for modular bus control, and ALS-family noise immunity - making it optimal for mid-speed industrial backplanes where reliability and configurability matter more than raw speed.
Availability
SN74ALS845DW is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy computer memory subsystems, parallel printer interfaces, and test equipment bus arbitration requiring stable component supply and long-term obsolescence support.
Supply support for SN74ALS845DW 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 with broad industrial and automotive reach.
The SN74ALS845DW belongs to TI's 74ALS advanced low-power Schottky logic family, engineered for high-speed, low-noise bus interfacing in commercial-temperature embedded systems where TTL compatibility and robust drive capability are essential.
FAQ
What is the function of the LE pin on the SN74ALS845DW?
The LE (Latch Enable) pin on the SN74ALS845DW controls transparency: when high, data passes directly from D inputs to Q outputs; on the falling edge, it captures and holds the current D values. This enables synchronous latching without a clock signal, making the SN74ALS845DW ideal for address/data strobe applications where edge-triggered capture is required.
Does the SN74ALS845DW support hot-swap or live-insertion on a powered bus?
The SN74ALS845DW supports controlled bus insertion via its power-up high-impedance state and buffered OE inputs - outputs remain in high-Z until OE is asserted, preventing contention. However, it lacks explicit hot-swap protection circuitry (e.g., slew-rate limiting or undervoltage lockout), so system-level current limiting and sequencing are recommended when inserting the SN74ALS845DW into an active bus.
How does the SN74ALS845DW differ from the SN74ALS845NT?
The SN74ALS845DW and SN74ALS845NT share identical electrical specifications and logic functionality, differing only in package: SN74ALS845DW uses a 24-pin SOIC (DW), while SN74ALS845NT uses a 24-pin PDIP (NT). Both are obsolete per TI's status, but the DW variant offers surface-mount compatibility and smaller footprint - critical for space-constrained industrial PCBs where the SN74ALS845DW replaces through-hole designs.
Can PRE and CLR be used simultaneously on the SN74ALS845DW?
Yes - when both PRE and CLR are low on the SN74ALS845DW, the outputs follow the preset condition (Q = high), as specified in the function table. This priority behavior allows deterministic initialization: asserting both signals guarantees known high outputs, useful for system reset sequences where undefined states must be avoided before software takes control of the SN74ALS845DW.
What is the maximum capacitive load the SN74ALS845DW can drive reliably?
The SN74ALS845DW is characterized for CL = 50 pF in switching tests, but its 48 mA IOL and 0.5 V VOL (at 48 mA) support reliable operation into ≥100 pF loads typical of long backplane traces or daisy-chained peripherals. For loads exceeding 150 pF, derating VCC to 5.25 V and verifying tPLH/tPHL margins against system timing budgets is recommended - a practice confirmed in SN74ALS845DW application notes for bus-hold configurations.
SN74ALS845DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- -
- Number of Elements:
- -
- Number of Bits per Element:
- -
- Input Type:
- -
- Output Type:
- -
- Current - Output High, Low:
- -
- Voltage - Supply:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
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SN74ALS845DW FAQ
1.How can I place an order for SN74ALS845DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS845DW 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 SN74ALS845DW reliable?
The price and inventory of SN74ALS845DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS845DW is usually 5 days.
3.What payment methods are accepted for SN74ALS845DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS845DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS845DW?
SN74ALS845DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS845DW 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 SN74ALS845DW?
For technical support, including SN74ALS845DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS845DW requirements.
6.How does Aetrix verify that SN74ALS845DW is sourced from the original manufacturer or authorized distributors?
All SN74ALS845DW 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 SN74ALS845DW meets industry standards.
7.What is the process for return or replacement of SN74ALS845DW?
All SN74ALS845DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS845DW, 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 SN74ALS845DW part is unused and in its original packaging.
Return procedure for SN74ALS845DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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