NXP Semiconductors 74HCT688PW,112

Overview

74HCT688PW,112 from Nexperia is an 8-bit magnitude comparator IC that performs binary or BCD word comparison with active-low enable (E), 8-bit P and Q inputs, and single P = Q output. It operates at 4.5 V to 5.5 V, delivers 17 ns typical propagation delay (Pn/Qn to P = Q), and supports industrial temperature range (−40 °C to +125 °C). It is used in digital systems requiring equality detection between parallel data words, such as address decoding and arithmetic logic units.

For engineers reviewing the 74HCT688PW,112 datasheet, 74HCT688PW,112 pinout, 74HCT688PW,112 application, or 74HCT688PW,112 equivalent, key selection considerations include TTL-compatible input thresholds, standard-output drive capability, cascading support for multi-word comparison, and TSSOP-20 package constraints for high-density PCB layouts.

Technical Context

The 74HCT688PW,112 implements a combinatorial equality function across two 8-bit parallel inputs using CMOS logic with HCT-level input voltage compatibility (VIH = 2.0 V min, VIL = 0.8 V max at VCC = 4.5 V). Its enable input (E) gates the P = Q output, asserting HIGH only when E is LOW and all eight Pn/Qn bit pairs match.

Propagation delays are asymmetric: 12 ns typical (E to P = Q) is faster than 17 ns typical (Pn/Qn to P = Q), reflecting internal gating structure. Output transition time is 19 ns typical at CL = 50 pF, supporting reliable interfacing with downstream TTL or CMOS loads without external buffering.

Key Specifications

Pinout & Package

TSSOP-20 package: 20-pin thin shrink small outline package with 0.65 mm pitch, body width 4.4 mm, height 1.1 mm - optimized for automated SMT assembly and space-constrained PCBs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HCT688PW,112, the 74HCT688DB,118 offers identical functionality in a larger SOIC package, while the SN74LS688N trades CMOS efficiency for legacy TTL compatibility-making the 74HCT688PW,112 optimal for new designs prioritizing density, power, and noise margin.

Availability

74HCT688PW,112 is available at Aetrix Electronics and suitable for address decoding, bus arbitration, and industrial input validation requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for 74HCT688PW,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 high-volume, high-reliability discrete, logic, and power MOSFET solutions for automotive, industrial, and computing markets.

The 74HCT688PW,112 belongs to Nexperia's 74HCT logic family, engineered for TTL-compatible CMOS performance in cost-sensitive, high-reliability digital control and interface applications.

FAQ

What is the logic function implemented by the 74HCT688PW,112?

The 74HCT688PW,112 is an 8-bit magnitude comparator that outputs HIGH on the P = Q pin only when the enable (E) input is LOW and all eight corresponding bits of the P0–P7 and Q0–Q7 inputs are identical. It does not indicate greater-than or less-than relationships-only exact equality. This function is implemented in hardwired CMOS logic with no internal latching or clocking.

Does the 74HCT688PW,112 support BCD or binary comparison exclusively?

The 74HCT688PW,112 supports both binary and BCD comparison equally, as confirmed in the Philips/Nexperia datasheet General Description. Its logic evaluates bitwise identity without interpreting numeric weight or encoding-so it functions identically whether inputs represent unsigned binary integers or unpacked BCD digits. No configuration or mode selection is required.

What is the maximum operating frequency for reliable operation of the 74HCT688PW,112?

The 74HCT688PW,112 has no defined maximum clock frequency because it is a purely combinatorial device with no internal clock. Its usable toggle rate depends on propagation delay and system-level timing margins: with 17 ns typical Pn/Qn-to-P=Q delay and 19 ns typical output transition, it supports input update rates up to approximately 25 MHz in well-designed synchronous systems with adequate setup/hold margins.

Can multiple 74HCT688PW,112 devices be cascaded for comparing more than 8 bits?

Yes, the 74HCT688PW,112 supports cascading per the official application information: the P = Q output of a lower-order device connects to the E input of the next higher-order device. When all lower-order bytes match, the upstream P = Q enables the next stage to evaluate its own P/Q inputs-enabling seamless 16-bit, 24-bit, or wider comparisons without external logic.

Is the 74HCT688PW,112 pin-compatible with the 74HC688 variant?

Yes, the 74HCT688PW,112 is fully pin-compatible with the 74HC688 in the same TSSOP-20 package. Both share identical pinout, terminal functions, and DC/AC timing specifications except for input threshold voltages: the HCT version uses TTL-compatible thresholds (VIH ≥ 2.0 V), while HC requires CMOS thresholds (VIH ≥ 3.5 V at VCC = 5 V), making HCT preferable for mixed-logic interfacing.