My Inquiry
My Account
Texas Instruments SN74ALS688DWR
- Part No.:
- SN74ALS688DWR
- Manufacturer:
- Texas Instruments
- Category:
- Comparators
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS688DWR.pdf
- Description:
- IC COMPARATOR IDENTITY 8B 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,253
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SN74ALS688DWR from Texas Instruments is an 8-bit identity comparator IC with totem-pole outputs, designed for digital logic systems requiring precise word-equality detection between two parallel 8-bit binary or BCD inputs (P₀–P₇ and Q₀–Q₇). It operates at 4.5–5.5 V, delivers 24 mA low-level output drive, supports 0°C to 70°C industrial temperature range, and features active-low enable (G) controlling the P = Q output state. It is used in address decoding, memory mapping, and bus arbitration circuits.
For engineers reviewing the SN74ALS688DWR datasheet, SN74ALS688DWR pinout, SN74ALS688DWR application, or SN74ALS688DWR equivalent, key selection considerations include its 20-pin SOIC-DW package, 12 ns maximum propagation delay (tPHL/tPLH) at 5 V/50 pF, totem-pole output architecture, and compatibility with ALS logic family voltage thresholds and drive strength.
Technical Context
The SN74ALS688DWR implements a combinatorial equality comparison function across eight parallel bit pairs using TTL-compatible ALS (Advanced Low-Power Schottky) circuitry. Its internal logic evaluates all eight P/Q bit pairs simultaneously and asserts the active-high P = Q output only when all bits match and the G input is low.
It requires no external timing or clocking-operation is purely level-sensitive and asynchronous. The device exhibits defined VIH/VIL thresholds (2.0 V/0.8 V), guaranteed VOL ≤ 0.4 V at IOL = 12 mA, and VOH ≥ 2.4 V at IOH = –1 mA, ensuring robust noise margins and interoperability within mixed-ALS logic systems.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | 8-bit parallel identity comparator with single P = Q output |
| Supply Voltage | 4.5 V to 5.5 V - compatible with standard 5 V TTL/ALS rail |
| Propagation Delay | Max 12 ns (tPLH/tPHL) at VCC = 5 V, CL = 50 pF - enables high-speed bus comparison |
| Output Drive | 24 mA sink capability (IOL) - sufficient to directly drive multiple TTL inputs or small LEDs |
| Input Thresholds | VIH = 2.0 V min, VIL = 0.8 V max - ensures reliable recognition of ALS/TTL logic levels |
| Operating Temperature | 0°C to 70°C - qualified for commercial/industrial ambient environments |
| Package | 20-pin SOIC (DW) - surface-mount, RoHS-compliant, tape-and-reel (2000 pcs) |
Pinout & Package
SN74ALS688DWR is housed in a 20-pin SOIC (DW) package, 7.5 mm wide, 12.8 mm long, 2.65 mm max height, with 1.27 mm pitch, RoHS-compliant NiPdAu lead finish, and moisture sensitivity level 1 (unlimited floor life at ≤30°C/60% RH).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G) | Active-low enable input | When high, forces P = Q output low regardless of P/Q data; enables comparison when low |
| 2–9 (P₀–P₇) | First 8-bit operand inputs | Parallel data inputs for word P; must be driven to valid TTL/ALS logic levels |
| 10 (GND) | Ground reference | Primary power return path; requires low-impedance PCB connection |
| 11–18 (Q₀–Q₇) | Second 8-bit operand inputs | Parallel data inputs for word Q; matched pin order to P inputs for layout symmetry |
| 19 (P = Q) | Equality output | Active-high totem-pole output asserting logic high only when G = L and all Pᵢ = Qᵢ |
| 20 (VCC) | Positive supply | 5 V nominal supply; requires local 0.1 µF bypass capacitor near pin |
Key Features
| Feature | Design Value |
|---|---|
| Totem-pole output structure | Eliminates need for external pull-up resistors; provides fast, low-impedance high/low switching |
| ALS logic family compatibility | Guaranteed VIH/VIL, drive strength, and propagation delay matching other 74ALS devices |
| Simultaneous 8-bit comparison | Single-cycle equality decision without pipelining or clocking overhead |
| Enable-controlled operation | G input allows dynamic activation/deactivation of comparison logic to reduce system power or avoid spurious outputs |
| Industrial temperature rating | Validated operation from 0°C to 70°C ensures reliability in non-military embedded control applications |
Applications
| Memory Address Decoding | Bus Arbitration Logic |
|---|---|
Use Scenario: Detecting exact match between CPU address bus and peripheral chip-select address range. IC Role / Device Role / Timing Role: Identity comparator generating chip-select strobe when address equals configured base address. Use Value: Enables deterministic, zero-latency peripheral selection without microcontroller intervention or additional logic gates. | Use Scenario: Resolving contention among multiple masters sharing a common data bus. IC Role / Device Role / Timing Role: Comparing master ID registers to grant bus access only when requesting master matches current owner. Use Value: Provides hardware-level arbitration with sub-15 ns decision latency, eliminating software polling delays. |
| ROM/RAM Content Verification | Digital Test Equipment Pattern Matching |
Use Scenario: Validating integrity of stored firmware by comparing read-back data against known golden pattern. IC Role / Device Role / Timing Role: Real-time byte-by-byte equality checker during memory dump or burn-in test sequences. Use Value: Delivers immediate pass/fail indication per 8-bit word without CPU involvement or DMA overhead. | Use Scenario: Embedded logic analyzer detecting specific instruction or data patterns in real-time signal streams. IC Role / Device Role / Timing Role: Parallel pattern matcher triggering capture on occurrence of predefined 8-bit signature. Use Value: Achieves deterministic trigger response with fixed 12 ns worst-case latency, independent of processor load. |
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 |
|---|---|---|---|
| SN74LS688N | Lower drive (8 mA IOL), slower propagation (20 ns max), LS-family thresholds (VIH = 2.0 V, VIL = 0.8 V same), PDIP only | Compatible in logic function but unsuitable for high-speed or high-fanout designs requiring ALS performance | Select when cost or legacy through-hole assembly outweighs speed and drive requirements |
| SN74F688N | Fast TTL variant: 10 ns max delay, 20 mA IOL, higher ICC (28 mA), tighter VIH/VIL (2.0 V/0.8 V), PDIP only | Higher speed than SN74ALS688DWR but greater power consumption and no SOIC option | Select when sub-12 ns latency is critical and surface-mount is not required |
Compared with SN74LS688N and SN74F688N, the SN74ALS688DWR offers optimal balance of speed (12 ns), drive strength (24 mA), low power (19 mA ICC), and modern SOIC packaging-making it preferred for new industrial control and instrumentation designs where board space and thermal efficiency matter.
Availability
SN74ALS688DWR is available at Aetrix Electronics and suitable for memory address decoding, bus arbitration logic, ROM/RAM content verification, and digital test equipment pattern matching requiring stable component supply and long-term industrial availability.
Supply support for SN74ALS688DWR 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 SN74ALS688DWR belongs to TI's legacy 74ALS logic family, engineered for high-speed, low-power digital system interfacing in commercial and industrial applications where reliability and pin-compatible upgrade paths from earlier 74LS devices are essential.
FAQ
What is the primary function of the SN74ALS688DWR?
The SN74ALS688DWR is an 8-bit identity comparator that outputs a high signal on its P = Q pin only when all eight corresponding bits of two parallel input words (P₀–P₇ and Q₀–Q₇) match exactly and the active-low enable (G) input is asserted low. It performs this comparison asynchronously with no clock required, making it ideal for real-time digital logic decisions in address decoding and bus control systems. The SN74ALS688DWR uses ALS technology to deliver faster switching and lower power than standard LS variants.
Does the SN74ALS688DWR require external pull-up resistors on its P = Q output?
No, the SN74ALS688DWR does not require external pull-up resistors because it features a totem-pole output stage on the P = Q pin. This internal push-pull driver actively sources current when outputting high and sinks current when outputting low, enabling direct interface with TTL/ALS inputs without additional components. This design reduces board space, simplifies layout, and improves switching speed compared to open-collector alternatives. The SN74ALS688DWR's totem-pole output is fully specified for 24 mA sink and 2.6 mA source capability under recommended operating conditions.
What are the absolute maximum ratings for the SN74ALS688DWR?
The absolute maximum ratings for the SN74ALS688DWR are: supply voltage (VCC) up to 7 V, input voltage (VI) up to 7 V, operating free-air temperature range of 0°C to 70°C, and storage temperature from –65°C to 150°C. Exceeding any of these limits may cause permanent damage. These are stress ratings only; functional operation is guaranteed only within the recommended operating conditions (VCC = 4.5–5.5 V, TA = 0°C to 70°C). The SN74ALS688DWR must never be operated continuously at absolute maximum values, as reliability degradation can occur even if parameters appear nominal.
Can the SN74ALS688DWR operate with a 3.3 V supply?
No, the SN74ALS688DWR is not rated for 3.3 V operation. Its recommended supply voltage is strictly 4.5 V to 5.5 V, and absolute maximum VCC is 7 V. At 3.3 V, the internal ALS circuitry will not meet VIH/VIL thresholds, propagation delay specs, or output drive guarantees-the device may fail to recognize valid logic highs or produce weak outputs. For 3.3 V systems, consider modern CMOS comparators like the CD74HC688 or SN74LV688. The SN74ALS688DWR is designed exclusively for 5 V TTL/ALS environments.
Is the SN74ALS688DWR pin-compatible with the SN74LS688?
Yes, the SN74ALS688DWR is pin-compatible with the SN74LS688 in the same package type (e.g., SOIC-DW or PDIP-N), sharing identical pin count, pinout order, and terminal functions-including G (enable), P₀–P₇, Q₀–Q₇, P = Q, VCC, and GND. However, due to differences in ALS vs. LS electrical characteristics (e.g., higher drive, faster speed, lower ICC), direct substitution requires verification of timing margins and fanout loading in the target circuit. The SN74ALS688DWR is a functional and physical drop-in replacement for SN74LS688 in SOIC-DW form factor.
SN74ALS688DWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Type:
- Identity Comparator
- Number of Bits:
- 8
- Output:
- Active Low
- Output Function:
- A=B
- Voltage - Supply:
- 4.5V ~ 5.5V
- Current - Output High, Low:
- 2.6mA, 24mA
- Max Propagation Delay @ V, Max CL:
- 20ns @ 5V, 50pF
- Current - Quiescent (Iq):
- -
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Supplier Device Package:
- 20-SOIC
- Mounting Type:
- Surface Mount
SN74ALS688DWR FAQ
1.How can I place an order for SN74ALS688DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS688DWR 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 SN74ALS688DWR reliable?
The price and inventory of SN74ALS688DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS688DWR is usually 5 days.
3.What payment methods are accepted for SN74ALS688DWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS688DWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS688DWR?
SN74ALS688DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS688DWR 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 SN74ALS688DWR?
For technical support, including SN74ALS688DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS688DWR requirements.
6.How does Aetrix verify that SN74ALS688DWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS688DWR 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 SN74ALS688DWR meets industry standards.
7.What is the process for return or replacement of SN74ALS688DWR?
All SN74ALS688DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS688DWR, 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 SN74ALS688DWR part is unused and in its original packaging.
Return procedure for SN74ALS688DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SN74ALS688DWR Tags
-
SN74HC688PWR
Texas Instruments
-
74HC85PW,118
Nexperia USA Inc.
-
74HC688D,653
Nexperia USA Inc.
-
SN74F521DWR
Texas Instruments
-
CD74HCT688M96
Texas Instruments
-
SN74F521N
Texas Instruments
-
CD4585BE
Texas Instruments
-
SN74HC688DWR
Texas Instruments
-
SN74LS85DR
Texas Instruments
-
CD74HC85E
Texas Instruments
-
MC14585BDR2G
onsemi
-
SN74HC688N
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…
