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Texas Instruments SN74ALS518DW
- Part No.:
- SN74ALS518DW
- Manufacturer:
- Texas Instruments
- Category:
- Comparators
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS518DW.pdf
- Description:
- IC COMPARATOR IDENTITY 8B 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,420
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Product details
Overview
SN74ALS518DW from Texas Instruments is an 8-bit identity comparator IC with open-collector P = Q output, 20-kΩ internal pullup resistors on Q inputs, and operation over 0°C to 70°C. It compares two 8-bit binary or BCD words and supports analog or switch data interfaces in industrial control logic and digital test equipment.
For engineers reviewing the SN74ALS518DW datasheet, SN74ALS518DW pinout, SN74ALS518DW application, or SN74ALS518DW equivalent, this device is selected for precise word-equality detection where open-collector drive, input pullup convenience, and ALS-family speed-power tradeoffs are required in legacy TTL-compatible systems.
Technical Context
The SN74ALS518DW implements a combinatorial identity comparison function across eight parallel bit pairs (P₀–P₇ and Q₀–Q₇), with active-low enable (G) controlling output assertion. Its open-collector P = Q output allows wired-OR bus interfacing and level translation.
Internal 20-kΩ pullup resistors on all Q inputs simplify connection to mechanical switches or analog voltage sources, eliminating external biasing. Propagation delays range from 3 ns to 33 ns depending on signal path and load conditions, consistent with Advanced Low-Power Schottky (ALS) TTL performance.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | 8-bit identity comparator with P = Q open-collector output |
| Supply Voltage | 4.5 V to 5.5 V - compatible with standard 5 V TTL rails |
| Input Pullup | 20 kΩ on all Q inputs - enables direct switch/analog interface without external resistors |
| Output Drive | Open-collector, IOL = 24 mA - supports wired-OR busing and mixed-voltage signaling |
| Propagation Delay | tPHL/tPLH = 3–33 ns - ALS-speed timing for high-throughput digital comparison |
| Operating Temperature | 0°C to 70°C - commercial-grade reliability for embedded control and instrumentation |
| Logic Family | Advanced Low-Power Schottky (ALS) TTL - lower power than standard LS, faster than S-series |
Pinout & Package
SN74ALS518DW is housed in a 20-pin SOIC (DW) package, 7.5 mm wide, with 1.27 mm pitch and 2.65 mm max height. Pin 1 is located at the top-left corner with notch or dot marking.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | G (Enable) | Active-low global enable; output asserted only when G = L |
| 2–9, 11–18 | P₀–P₇, Q₀–Q₇ | Two 8-bit parallel data inputs; Q pins have internal 20-kΩ pullups |
| 10 | GND | Ground reference for logic and power |
| 20 | VCC | Positive supply (4.5–5.5 V); powers internal ALS circuitry |
| 19 | P = Q | Open-collector output; sinks current when P equals Q and G = L |
Key Features
| Feature | Design Value |
|---|---|
| Open-collector output | Enables wired-OR bus architectures and flexible level-shifting without external components |
| Integrated Q-input pullups | 20-kΩ resistors eliminate need for external biasing when interfacing switches or analog sources |
| ALS TTL compatibility | Direct drop-in replacement for 74LS518/74S518 in existing designs with improved speed/power ratio |
| 8-bit parallel comparison | Single-cycle equality detection across full byte - no clock or state machine required |
| Commercial temperature range | Validated operation from 0°C to 70°C ensures stability in office, lab, and factory-floor environments |
Applications
| Digital Test Equipment | Industrial PLC I/O Modules |
|---|---|
Use Scenario: Detecting exact match between reference and measured 8-bit sensor codes in automated calibration fixtures. IC Role / Device Role / Timing Role: Combinatorial comparator asserting P = Q to trigger pass/fail latch or LED indicator. Use Value: Eliminates microcontroller polling overhead; provides deterministic sub-33 ns response for real-time go/no-go decisions. |
Use Scenario: Validating address/data handshake between backplane bus and modular I/O expansion cards. IC Role / Device Role / Timing Role: Identity check on 8-bit command/address fields before enabling peripheral decode logic. Use Value: Prevents spurious module activation using hardware-level comparison-no firmware dependency or latency. |
| Legacy TTL System Upgrades | Programmable Logic Debug Interfaces |
Use Scenario: Replacing obsolete 74S518 in vintage minicomputer memory parity or instruction decode paths. IC Role / Device Role / Timing Role: Pin-compatible ALS upgrade delivering same function with 30% lower power and 2× speed margin. Use Value: Extends service life of aging systems without PCB redesign or timing revalidation. |
Use Scenario: Monitoring FPGA configuration bus activity to verify correct bitstream loading via known sync patterns. IC Role / Device Role / Timing Role: Comparing captured 8-bit bus snapshots against expected signature values during JTAG debug sessions. Use Value: Provides hardware-assisted visibility into configuration integrity-no logic analyzer required for basic validation. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 8-bit identity comparator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS520DW | Totem-pole P = Q output; same 20-kΩ Q-input pullups; identical pinout and timing | Requires external pullup for wired-OR; not suitable where bus arbitration or level translation is needed | Select when driving CMOS loads directly or when sourcing capability is preferred over sinking flexibility |
| SN74ALS521DW | No internal Q-input pullups; totem-pole P = Q output; otherwise identical timing and pinout | Requires external biasing for switch/analog Q inputs; better for fully buffered digital-only systems | Select when Q inputs are driven by clean logic signals and open-collector functionality is unnecessary |
Compared with SN74ALS520DW and SN74ALS521DW, the SN74ALS518DW uniquely combines open-collector output with integrated Q-input pullups-enabling direct switch interfacing and multi-drop bus use without added components, making it optimal for cost-sensitive, mixed-signal legacy upgrades.
Availability
SN74ALS518DW is available at Aetrix Electronics and suitable for industrial control logic, digital test equipment, and legacy TTL system upgrades requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74ALS518DW 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, automotive, and communications reach.
The SN74ALS518DW belongs to TI's Advanced Low-Power Schottky (ALS) TTL logic family, designed for high-speed, low-power digital comparison in commercial-grade systems where compatibility with legacy 5 V TTL infrastructure is essential.
FAQ
What is the primary function of the SN74ALS518DW?
The SN74ALS518DW is an 8-bit identity comparator that outputs a logic-low signal on its open-collector P = Q pin when all eight corresponding P and Q input bits match and the G (enable) input is low. It performs this comparison combinatorially-no clock or internal state is involved-and is used for real-time word-equality detection in digital systems.
Does the SN74ALS518DW require external pullup resistors on its Q inputs?
No. The SN74ALS518DW integrates 20-kΩ pullup resistors on all Q₀–Q₇ inputs, allowing direct connection to mechanical switches, open-drain sources, or analog voltage thresholds without external components. This feature distinguishes it from SN74ALS521DW, which lacks internal Q-input pullups.
Can the SN74ALS518DW be used as a direct replacement for the 74LS518?
Yes-the SN74ALS518DW is pin-compatible and functionally equivalent to the 74LS518 but offers improved performance: typical propagation delay reduced from ~45 ns to 3–33 ns and power consumption lowered by ~30%. It maintains full 5 V TTL electrical compatibility and operates within the same 0°C to 70°C range.
What is the maximum sink current capability of the SN74ALS518DW P = Q output?
The SN74ALS518DW P = Q output can sink up to 24 mA while maintaining VOL ≤ 0.5 V at VCC = 4.5 V, per datasheet specifications. This allows direct driving of LEDs, relays (with flyback diode), or multiple TTL inputs in wired-OR configurations without additional buffer stages.
Is the SN74ALS518DW RoHS compliant?
Yes. The SN74ALS518DW is RoHS compliant, with NiPdAu (NIPDAU) lead finish and MSL Level-1 rating (unlimited floor life at ≤30°C/60% RH), per TI's official packaging addendum. It is suitable for modern lead-free reflow assembly processes with peak temperatures up to 260°C.
SN74ALS518DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Bulk
- Product Status:
- Active
- Type:
- Identity Comparator
- Number of Bits:
- 8
- Output:
- Active High
- Output Function:
- A=B
- Voltage - Supply:
- 4.5V ~ 5.5V
- Current - Output High, Low:
- 100µA, 24mA
- Max Propagation Delay @ V, Max CL:
- 33ns @ 5V, 50pF
- Current - Quiescent (Iq):
- -
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Supplier Device Package:
- 20-SOIC
- Mounting Type:
- Surface Mount
SN74ALS518DW FAQ
1.How can I place an order for SN74ALS518DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS518DW 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 SN74ALS518DW reliable?
The price and inventory of SN74ALS518DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS518DW is usually 5 days.
3.What payment methods are accepted for SN74ALS518DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS518DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS518DW?
SN74ALS518DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS518DW 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 SN74ALS518DW?
For technical support, including SN74ALS518DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS518DW requirements.
6.How does Aetrix verify that SN74ALS518DW is sourced from the original manufacturer or authorized distributors?
All SN74ALS518DW 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 SN74ALS518DW meets industry standards.
7.What is the process for return or replacement of SN74ALS518DW?
All SN74ALS518DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS518DW, 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 SN74ALS518DW part is unused and in its original packaging.
Return procedure for SN74ALS518DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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