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NXP Semiconductors 74HCT688D,652
- Part No.:
- 74HCT688D,652
- Manufacturer:
- NXP Semiconductors
- Category:
- Comparators
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
74HCT688D,652.pdf
- Description:
- IC COMPARATOR IDENTITY 8BIT 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:1,534
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Product details
Overview
74HCT688D,652 from Nexperia is an 8-bit magnitude comparator IC designed for digital logic systems requiring high-speed word equality detection. It compares two 8-bit binary or BCD words (P₀–P₇ and Q₀–Q₇), features active-low enable (E), delivers a single P = Q output, and operates at 4.5 V with 17 ns typical propagation delay (Pn/Qn to P = Q) at 25 °C - used in address decoding and data validation circuits.
For engineers reviewing the 74HCT688D,652 datasheet, 74HCT688D,652 pinout, 74HCT688D,652 application, or 74HCT688D,652 equivalent, this page provides verified functional role, validated timing parameters, confirmed package mapping (SO20), real-world cascading capability, and direct alternative options for 8-bit digital comparison tasks.
Technical Context
The 74HCT688D,652 implements combinational logic for exact 8-bit word matching using TTL-compatible input thresholds (VI = GND to 3 V). Its P = Q output asserts HIGH only when all eight bit pairs match and enable E is LOW - no internal latching or clocking is involved.
It supports cascading via the P = Q output driving the E input of a higher-order comparator, enabling multi-byte comparisons without external logic. The device belongs to the 74HCT family, ensuring compatibility with standard TTL signal levels while retaining CMOS power efficiency.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | 8-bit magnitude comparator with active-low enable and single P = Q output |
| Supply Voltage | 4.5 V to 5.5 V - compatible with standard 5 V TTL logic rails |
| tPHL/tPLH (Pn/Qn → P=Q) | 17 ns typical at VCC = 5 V, Tamb = 25 °C - defines max clock rate for synchronous compare chains |
| tPHL/tPLH (E → P=Q) | 12 ns typical at VCC = 5 V - enables fast enable-controlled comparison gating |
| Input Threshold | VIH = 2.0 V min, VIL = 0.8 V max - ensures reliable interfacing with legacy TTL outputs |
| Output Drive | Standard CMOS drive (±4 mA at VCC = 4.5 V) - directly fans out to ≥10 HCT inputs |
Pinout & Package
74HCT688D,652 is housed in a 20-pin small outline (SO) package (SO20), 7.5 mm body width, with 1.27 mm pitch and gull-wing leads. Pin 1 is marked by a bevelled corner or notch.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| E | Active-low enable input | Comparison enabled only when LOW; HIGH forces P = Q output LOW regardless of inputs |
| P₀–P₇ | First 8-bit word input (pins 2,4,6,8,11,13,15,17) | Even-numbered pins (except pin 10) accept first operand; TTL-compatible voltage thresholds |
| Q₀–Q₇ | Second 8-bit word input (pins 3,5,7,9,12,14,16,18) | Odd-numbered pins (except pin 10) accept second operand; interleaved layout aids PCB routing |
| P = Q | Equality output (pin 19) | Open-drain capable? No - push-pull CMOS output; asserts HIGH only on full 8-bit match + E = LOW |
| GND | Ground reference (pin 10) | Primary return path for all internal logic; must be low-impedance connection |
| VCC | Positive supply (pin 20) | 5 V nominal supply; decoupling capacitor (100 nF) required within 10 mm of pin 20 |
Key Features
| Feature | Design Value |
|---|---|
| 8-bit parallel comparison | Performs simultaneous evaluation of all eight bit pairs - eliminates sequential checking latency |
| TTL-compatible input levels | Accepts standard 5 V TTL outputs without level-shifting - simplifies integration into mixed-logic systems |
| Cascadable architecture | P = Q output drives E input of next-stage 74HCT688D,652 - enables 16-, 24-, or 32-bit comparisons with no glue logic |
| Low quiescent current | ICC < 4 µA at VCC = 5 V, Tamb = 25 °C - suitable for low-power control subsystems |
Applications
| Memory Address Decoding | Microprocessor Bus Monitoring |
|---|---|
Use Scenario: Detecting CPU access to specific memory-mapped I/O registers in an 8-bit microcontroller system. IC Role / Device Role / Timing Role: 74HCT688D,652 compares address bus bits A₀–A₇ against fixed decode pattern; asserts P = Q to enable peripheral chip select. Use Value: Enables deterministic, cycle-accurate peripheral selection with zero additional gate delay beyond propagation specs. | Use Scenario: Validating instruction fetch addresses during debug trace capture in embedded development tools. IC Role / Device Role / Timing Role: 74HCT688D,652 monitors lower byte of program counter; triggers logic analyzer trigger when matching predefined breakpoint address. Use Value: Provides sub-20 ns address match resolution - critical for capturing precise instruction execution windows. |
| Data Integrity Verification | Industrial Control Word Matching |
Use Scenario: Confirming correct loading of configuration words into FPGA configuration PROMs before initialization. IC Role / Device Role / Timing Role: 74HCT688D,652 compares expected header value (P) against read-back PROM data (Q); enables write-enable only on match. Use Value: Prevents misconfiguration due to bit errors or timing skew - leverages deterministic combinational logic, not state machines. | Use Scenario: Matching command words from PLC master to slave I/O modules in factory automation networks. IC Role / Device Role / Timing Role: 74HCT688D,652 validates 8-bit command opcode field in serially shifted control frames before executing actuator commands. Use Value: Ensures command fidelity in noise-prone industrial environments - uses robust TTL-level thresholds and fast response. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 8-bit magnitude comparison applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74HCT688N | DIP-20 package; identical AC/DC specs and pinout; same 74HCT family logic behavior | Through-hole mounting only; unsuitable for surface-mount production or space-constrained designs | Select when manual prototyping, breadboarding, or legacy through-hole assembly is required |
| 74HCT688PW,118 | TSSOP-20 package; same electrical specs; 4.4 mm width vs SO20's 7.5 mm; thermal resistance 120 K/W vs 100 K/W | Higher density layout possible; slightly reduced thermal margin under continuous operation | Select when board area is constrained and reflow soldering is available |
Compared with SN74HCT688N and 74HCT688PW,118, the 74HCT688D,652 offers optimal balance of surface-mount compatibility, thermal performance, and industry-standard SO20 footprint - making it preferred for automated SMT manufacturing and mid-power industrial control boards.
Availability
74HCT688D,652 is available at Aetrix Electronics and suitable for memory decoding, bus monitoring, data verification, and industrial control applications requiring stable component supply, long-term lifecycle support, and consistent parametric performance across temperature ranges.
Supply support for 74HCT688D,652 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
Nexperia is a global leader in discrete, logic, and PowerMOS semiconductors, spun off from NXP's Standard Products division in 2017, with focus on automotive, industrial, computing, and consumer markets.
The 74HCT688D,652 belongs to Nexperia's 74HCT logic family - engineered for seamless interoperability with legacy TTL systems while delivering CMOS efficiency and reliability in industrial-grade packages.
FAQ
What is the function of the E pin on the 74HCT688D,652?
The E pin on the 74HCT688D,652 is an active-low enable input. When E is HIGH, the P = Q output is forced LOW regardless of the P and Q word values. Only when E is LOW does the device perform the 8-bit comparison and assert P = Q HIGH upon full match. This allows precise timing control over comparison activation in synchronous systems.
Does the 74HCT688D,652 support BCD comparison?
Yes, the 74HCT688D,652 supports both binary and BCD word comparison. Its logic performs bitwise equality evaluation - identical functionality applies to BCD-encoded digits since each 4-bit group is compared as raw binary. No internal encoding conversion is performed; users must ensure proper BCD formatting on P and Q inputs prior to assertion of E.
Can multiple 74HCT688D,652 devices be cascaded for wider comparisons?
Yes, the 74HCT688D,652 supports cascading: the P = Q output of a lower-order device connects to the E input of the next higher-order device. For example, two 74HCT688D,652 units can compare 16-bit words - the MSB comparator enables only when LSBs match. This hierarchical structure requires no external gates and preserves propagation timing predictability.
What is the maximum operating temperature range for the 74HCT688D,652?
The 74HCT688D,652 is specified for operation from −40 °C to +125 °C. Its AC and DC characteristics - including propagation delays, input thresholds, and output drive - are guaranteed across this full industrial temperature range, making it suitable for under-hood automotive modules and factory-floor controllers.
Is the 74HCT688D,652 pin-compatible with older 74LS688 devices?
No, the 74HCT688D,652 is not pin-compatible with 74LS688. While both are 8-bit comparators with similar logic functions, the 74LS688 uses a 24-pin package and different pin assignments (e.g., separate P>Q and P<Q outputs). The 74HCT688D,652 uses a 20-pin SO package with only P = Q output and shares pinout with other 74HCT688 variants - not with LS-series predecessors.
74HCT688D,652 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- NXP Semiconductors
- Series:
- 74HCT
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Type:
- Identity Comparator
- Number of Bits:
- 8
- Output:
- Active Low
- Output Function:
- A=B
- Voltage - Supply:
- 4.5V ~ 5.5V
- Current - Output High, Low:
- 4mA, 4mA
- Max Propagation Delay @ V, Max CL:
- 34ns @ 4.5V, 50pF
- Current - Quiescent (Iq):
- 8 µA
- Operating Temperature:
- -40°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Supplier Device Package:
- 20-SO
- Mounting Type:
- Surface Mount
74HCT688D,652 FAQ
1.How can I place an order for 74HCT688D,652 through Aetrix?
Please submit a Request for Quotation (RFQ) for 74HCT688D,652 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 74HCT688D,652 reliable?
The price and inventory of 74HCT688D,652 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 74HCT688D,652 is usually 5 days.
3.What payment methods are accepted for 74HCT688D,652?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 74HCT688D,652 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 74HCT688D,652?
74HCT688D,652 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 74HCT688D,652 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 74HCT688D,652?
For technical support, including 74HCT688D,652 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 74HCT688D,652 requirements.
6.How does Aetrix verify that 74HCT688D,652 is sourced from the original manufacturer or authorized distributors?
All 74HCT688D,652 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 74HCT688D,652 meets industry standards.
7.What is the process for return or replacement of 74HCT688D,652?
All 74HCT688D,652 units undergo pre-shipment inspection (PSI). If there is an issue with 74HCT688D,652, 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 74HCT688D,652 part is unused and in its original packaging.
Return procedure for 74HCT688D,652:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
74HCT688D,652 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
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