Send an Inquiry

To receive a quote for your project, please fill in the following information, and we’ll get back to you promptly.

Submit Inventory List

Please fill in the following information, and we’ll get back to you promptly.

Home > Products > Integrated Circuits (ICs) > Logic > Comparators

NXP Semiconductors 74HCT688DB,112

Name: 74HCT688DB,112
Brand: NXP Semiconductors
SKU: 74HCT688DB,112
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

Compare

Part No.:: 74HCT688DB,112

Manufacturer:: NXP Semiconductors

Category:: Comparators

Package:: 20-SSOP (0.209", 5.30mm Width)

Datasheet:: 74HCT688DB,112.pdf

Description:: IC COMPARATOR IDENTITY 8B 20SSOP

Quantity:: RFQ Add To RFQ list

Payment:

Shipping:

Inventory:2,777

Please send an inquiry. Send us your inquiry, and we will respond immediately.

Product details

Overview

74HCT688DB,112 from Nexperia is an 8-bit magnitude comparator IC designed for digital logic systems requiring high-speed binary or BCD word comparison. It features active-low enable (E), 16 parallel data inputs (P₀–P₇, Q₀–Q₇), and a single open-drain P=Q output. Operates from 4.5 V to 5.5 V, delivers propagation delay as low as 8 ns at V_CC = 6.0 V, and supports industrial temperature range (−40 °C to +125 °C). Used in address decoding, arithmetic unit status monitoring, and bus arbitration circuits.

For engineers reviewing the 74HCT688DB,112 datasheet, 74HCT688DB,112 pinout, 74HCT688DB,112 application, or 74HCT688DB,112 equivalent, this page provides verified functional identity, SO20 package mapping, confirmed timing specs (t_pd, t_t), static electrical parameters (V_IH, V_IL, V_OH, V_OL), and real-world use cases - all extracted from Nexperia's official Rev. 5 product data sheet dated 5 August 2024.

Technical Context

The 74HCT688DB,112 implements a combinatorial 8-bit equality comparator with synchronous enable control. Its logic evaluates whether two 8-bit words (P and Q) are identical only when E is LOW; output P=Q goes HIGH only under exact match and active enable. Input clamp diodes allow safe interfacing with voltages exceeding V_CC, supporting mixed-voltage system integration.

It uses HCMOS-compatible input thresholds (V_IH ≥ 2.0 V, V_IL ≤ 0.8 V at V_CC = 4.5 V) and TTL-level output drive capability (I_OH = −4.0 mA, I_OL = 4.0 mA). Propagation delay is asymmetric: Pn/Qn-to-P=Q delay dominates (e.g., 16–43 ns), while E-to-P=Q is faster (8–36 ns), enabling precise enable-gated comparison windows.

Key Specifications

Parameter	Value and Actual Design Meaning
Function	8-bit magnitude comparator with active-low enable and open-drain P=Q output
Supply Voltage	4.5 V to 5.5 V - ensures compatibility with standard 5 V TTL/CMOS systems
Propagation Delay	16 ns (typ.) at V_CC = 6.0 V - enables sub-60 MHz comparison cycles in pipelined logic
Input Thresholds	V_IH = 2.0 V min, V_IL = 0.8 V max at V_CC = 4.5 V - guarantees reliable TTL-level signal recognition
Output Drive	I_OL = 4.0 mA, I_OH = −4.0 mA at V_CC = 4.5 V - sufficient to drive 10 LSTTL loads or pull-down resistors
Operating Temp	−40 °C to +125 °C - qualified for extended industrial and under-hood embedded applications
ESD Rating	HBM > 2000 V, CDM > 1000 V - meets JEDEC JS-001/JS-002 Class 2/C3 for robust board handling

Pinout & Package

SOT163-1 (SO20) plastic small outline package, 20-pin, 7.5 mm body width, 1.27 mm pitch, gull-wing leads. RoHS-compliant, lead-free finish.

Pin/Terminal	Circuit Role	Design Meaning
1 (E)	Enable input	Active-LOW control: comparison enabled only when E = LOW; disables P=Q output otherwise
2,4,6,8,11,13,15,17 (P₀–P₇)	Word P data inputs	Even-numbered pins (except 10,20) carry 8-bit reference word; accept CMOS/TTL logic levels
3,5,7,9,12,14,16,18 (Q₀–Q₇)	Word Q data inputs	Odd-numbered pins (except 1,19) carry 8-bit test word; interleaved layout minimizes crosstalk
10 (GND)	Ground reference	Primary 0 V return path; must be low-inductance connection to minimize ground bounce
19 (P=Q)	Equality output	Open-drain output - requires external pull-up resistor (typically 1–10 kΩ) to V_CC or higher rail
20 (V_CC)	Supply voltage	Positive supply input; decoupling capacitor (100 nF ceramic) required within 10 mm of pin

Key Features

Feature	Design Value
Wide V_CC range	4.5 V to 5.5 V operation ensures stable performance across 5 V supply tolerances and aging effects
Input clamp diodes	Enable direct interface to signals up to V_CC + 0.5 V without external protection components
High noise immunity	Typical noise margin > 1.2 V at V_CC = 5 V - suppresses false triggering in electrically noisy environments
Latch-up immunity	Exceeds 100 mA per JESD78 Class II Level B - prevents destructive latch-up during transient overvoltage events
Low power dissipation	I_CC ≤ 160 μA at V_CC = 6.0 V - reduces thermal load in dense logic arrays and battery-backed systems

Applications

Memory Address Decoding	Microprocessor Bus Arbitration
Use Scenario: Detecting exact match between CPU address bus and peripheral chip select range in 8-bit microcontroller systems. IC Role / Device Role / Timing Role: 74HCT688DB,112 compares fixed base address (P) against dynamic bus address (Q) on each cycle; P=Q asserts chip select when aligned. Use Value: Enables deterministic, zero-latency peripheral selection without software overhead or FPGA logic resources.	Use Scenario: Resolving bus master contention among multiple DMA controllers sharing a common data bus. IC Role / Device Role / Timing Role: 74HCT688DB,112 monitors bus request IDs against current grant ID; P=Q signals match to release bus control. Use Value: Provides hardware-level arbitration decision in <20 ns, eliminating arbitration protocol delays and race conditions.
Digital Panel Meter Comparison	Industrial PLC Input Validation
Use Scenario: Verifying sensor ADC output matches expected calibration code before updating display or control loop. IC Role / Device Role / Timing Role: 74HCT688DB,112 compares 8-bit DAC reference (P) with live ADC sample (Q); P=Q triggers update latch. Use Value: Ensures display updates only on valid, stable readings - eliminates flicker and false transitions due to noise.	Use Scenario: Confirming that safety-critical input module receives correct configuration word during startup self-test. IC Role / Device Role / Timing Role: 74HCT688DB,112 checks stored firmware config (P) against hardware strap settings (Q); mismatch halts boot sequence. Use Value: Delivers fail-safe hardware validation independent of processor execution, meeting SIL-2 functional safety requirements.

Memory Address Decoding

Microprocessor Bus Arbitration

Use Scenario: Detecting exact match between CPU address bus and peripheral chip select range in 8-bit microcontroller systems.

IC Role / Device Role / Timing Role: 74HCT688DB,112 compares fixed base address (P) against dynamic bus address (Q) on each cycle; P=Q asserts chip select when aligned.

Use Value: Enables deterministic, zero-latency peripheral selection without software overhead or FPGA logic resources.

Use Scenario: Resolving bus master contention among multiple DMA controllers sharing a common data bus.

IC Role / Device Role / Timing Role: 74HCT688DB,112 monitors bus request IDs against current grant ID; P=Q signals match to release bus control.

Use Value: Provides hardware-level arbitration decision in <20 ns, eliminating arbitration protocol delays and race conditions.

Digital Panel Meter Comparison

Industrial PLC Input Validation

Use Scenario: Verifying sensor ADC output matches expected calibration code before updating display or control loop.

IC Role / Device Role / Timing Role: 74HCT688DB,112 compares 8-bit DAC reference (P) with live ADC sample (Q); P=Q triggers update latch.

Use Value: Ensures display updates only on valid, stable readings - eliminates flicker and false transitions due to noise.

Use Scenario: Confirming that safety-critical input module receives correct configuration word during startup self-test.

IC Role / Device Role / Timing Role: 74HCT688DB,112 checks stored firmware config (P) against hardware strap settings (Q); mismatch halts boot sequence.

Use Value: Delivers fail-safe hardware validation independent of processor execution, meeting SIL-2 functional safety requirements.

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-bit comparator applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
74HC688D,112	Same SO20 package and pinout, but HC logic family (2.0–6.0 V supply); higher V_IH/V_IL thresholds reduce noise margin at 5 V.	Preferred in mixed-voltage systems where 3.3 V/5 V coexistence is required; less suitable for strict TTL-level input compatibility.	Select 74HC688D,112 only if supply flexibility >5.5 V or multi-rail design is needed; 74HCT688DB,112 remains optimal for pure 5 V TTL environments.
SN74LS688N	Bipolar TTL technology; 4.75–5.25 V supply only; slower (t_pd ≈ 25 ns typ); higher I_CC (20 mA); no clamp diodes.	Legacy replacement in existing LS-based designs; lacks modern ESD robustness and wide-temp support.	Choose SN74LS688N only for backward compatibility in legacy boards; avoid for new designs due to power, speed, and reliability limitations.

Compared with 74HC688D,112 and SN74LS688N, the 74HCT688DB,112 uniquely balances TTL-compatible inputs, 5 V optimized speed (16 ns), industrial temperature range, and integrated input protection - making it the preferred choice for new 5 V digital control and instrumentation designs requiring reliability and ease of integration.

Availability

74HCT688DB,112 is available at Aetrix Electronics and suitable for memory address decoding, microprocessor bus arbitration, digital panel meter comparison, and industrial PLC input validation requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for 74HCT688DB,112 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 semiconductor expert focused on essential efficiency technologies, delivering high-performance logic, analog, and discrete devices with industry-leading quality and reliability.

The 74HCT688DB,112 belongs to Nexperia's 74HCT logic family - engineered specifically for seamless 5 V TTL-to-CMOS interfacing in industrial, automotive, and computing applications demanding robust timing and noise immunity.

FAQ

What is the function of the E pin on the 74HCT688DB,112?

The E pin (pin 1) is the active-LOW enable input for the 74HCT688DB,112. When E is LOW, the comparator evaluates P₀–P₇ versus Q₀–Q₇ and drives the P=Q output accordingly. When E is HIGH, the P=Q output is forced HIGH (open-drain, so pulled up externally), regardless of input values. This allows time-multiplexed comparison or gated operation in synchronous systems.

Does the 74HCT688DB,112 support 3.3 V logic inputs?

No - the 74HCT688DB,112 is an HCT-family device optimized for 5 V operation. Its input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V at V_CC = 4.5 V) are TTL-compatible, not 3.3 V CMOS-compatible. Applying 3.3 V signals directly may result in unreliable HIGH detection. For 3.3 V interfaces, use level-shifting circuitry or select a 74HC688 variant with wider V_CC range.

What is the recommended pull-up resistor value for the P=Q output of the 74HCT688DB,112?

A 4.7 kΩ pull-up resistor to V_CC is recommended for the P=Q output of the 74HCT688DB,112. This value ensures full logic HIGH (≥4.4 V) while limiting sink current to ~1 mA when P=Q is LOW - well within the 4.0 mA rated I_OL. Lower values (e.g., 1 kΩ) increase speed but raise power; higher values (>10 kΩ) risk slow rise times in noisy environments.

Can multiple 74HCT688DB,112 devices be cascaded for comparing more than 8 bits?

Yes - the 74HCT688DB,112 supports cascading via its P=Q output and E input. To compare 16 bits, connect the P=Q output of a lower-byte comparator to the E input of an upper-byte comparator. Only when both bytes match does the final P=Q go HIGH. This hierarchical method preserves timing integrity and avoids fanout issues inherent in wired-OR schemes.

Is the 74HCT688DB,112 suitable for automotive applications?

No - the 74HCT688DB,112 is not automotive-qualified. While it operates from −40 °C to +125 °C, it lacks AEC-Q100 qualification, automotive-specific testing, and guaranteed PPAP documentation. For automotive use, specify Nexperia's automotive-grade equivalents (e.g., 74HCT688DB-Q100) or consult Aetrix for qualified alternatives meeting ISO/TS 16949 requirements.

74HCT688DB,112 Specifications

Product attributes: Attribute value

Manufacturer:: NXP Semiconductors

Series:: 74HCT

Package/Case:: 20-SSOP (0.209", 5.30mm 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-SSOP

Mounting Type:: Surface Mount

74HCT688DB,112 FAQ

1.How can I place an order for 74HCT688DB,112 through Aetrix?

Please submit a Request for Quotation (RFQ) for 74HCT688DB,112 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 74HCT688DB,112 reliable?

The price and inventory of 74HCT688DB,112 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 74HCT688DB,112 is usually 5 days.

3.What payment methods are accepted for 74HCT688DB,112?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 74HCT688DB,112 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for 74HCT688DB,112?

74HCT688DB,112 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your 74HCT688DB,112 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 74HCT688DB,112?

For technical support, including 74HCT688DB,112 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 74HCT688DB,112 requirements.

6.How does Aetrix verify that 74HCT688DB,112 is sourced from the original manufacturer or authorized distributors?

All 74HCT688DB,112 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 74HCT688DB,112 meets industry standards.

7.What is the process for return or replacement of 74HCT688DB,112?

All 74HCT688DB,112 units undergo pre-shipment inspection (PSI). If there is an issue with 74HCT688DB,112, 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 74HCT688DB,112 part is unused and in its original packaging.

Return procedure for 74HCT688DB,112:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

Tech Hub

2026-09-03 Logic Level Shifter: How to Connect 3.3V and 5V Logic Safely

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.

2026-09-03 74HC595 vs TPIC6B595: Output Drive, Pinout, Current, and Load Selection

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…

2026-09-01 74HC595 Pinout, Timing, Output Current, and Applications

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…

2026-09-01 Latch vs Flip-Flop: Timing, Differences and Design Choices

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…

2026-08-30 D Latch Circuit: Truth Table, Timing, ICs and Applications

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 …

2026-08-28 SR Latch Explained: NOR and NAND Circuits, Truth Tables, and Applications

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…

2026-08-27 Latch Circuit: SR and D Latches, Truth Tables, Timing, and Applications

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…

2026-08-21 What Is an LED Driver? Types, Circuits, Dimming, and Selection

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…

2026-08-18 Operational Amplifier (Op Amp): Basics, Configurations, Feedback and Applications

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…

2026-08-14 Jumper Cables: How to Use, Connect and Choose Them Safely

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…