Texas Instruments CD74HC688PWT

Overview

CD74HC688PWT from Texas Instruments is an 8-bit magnitude comparator IC designed for binary word comparison in digital logic systems. It operates from 2 V to 6 V, delivers propagation delay as low as 14 ns (at VCC = 4.5 V), supports –55°C to +125°C industrial/military temperature range, and features cascading capability via active-low Y output for multi-stage equality detection - used in address decoding and arithmetic unit control.

For engineers reviewing the CD74HC688PWT datasheet, CD74HC688PWT pinout, CD74HC688PWT application, or CD74HC688PWT equivalent, this page provides verified functional role, validated TSSOP-20 pin mapping, confirmed HC-series electrical specs (VIH/VIL, VOH/VOL, ICC), thermal metrics (RθJA = 131.8°C/W), and two technically documented alternative parts with explicit functional and application differences.

Technical Context

The CD74HC688PWT implements a fully combinatorial 8-bit equality comparison function with three-input enable logic (A/B inputs + active-high E). Its output Y goes low only when all eight A_n/B_n bit pairs match *and* E is high - enabling daisy-chained configurations where Y drives the E input of the next comparator in sequence.

It uses standard CMOS silicon process with rail-to-rail output swing, exhibits balanced t_PLH/t_PHL (≤43 ns max at VCC = 6 V), and maintains stable VIH/VIL thresholds across supply voltage (e.g., VIH = 4.2 V min at VCC = 6 V), ensuring reliable interfacing with mixed-voltage logic families.

Key Specifications

Pinout & Package

TSSOP-20 package (PW), 6.50 mm × 4.40 mm body size, 1.2 mm max height, 0.65 mm lead pitch, RoHS-compliant NiPdAu finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC688PWT, CD74HCT688PWR offers tighter input threshold compatibility with TTL but sacrifices supply flexibility, while SN74LS688N delivers pin-equivalent TTL behavior at significantly higher power and lower speed - making CD74HC688PWT the optimal choice for modern low-voltage, low-power, wide-temperature applications.

Availability

CD74HC688PWT is available at Aetrix Electronics and suitable for industrial control systems, aerospace avionics interfaces, and military-grade computing modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC688PWT 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 specializing in analog, embedded processing, and logic solutions, with over 50 years of innovation in high-reliability logic ICs.

The CD74HC688PWT belongs to TI's High-Speed CMOS (HC) logic family, engineered for low-power, wide-voltage, and extended-temperature operation in mission-critical digital systems where timing precision and robustness are essential.

FAQ

What is the function of the E pin on the CD74HC688PWT?

The E (Enable) pin on the CD74HC688PWT is an active-high control input that determines whether the comparator evaluates the A and B inputs. When E is low, the Y output remains high regardless of A/B values; only when E is high does Y go low upon A = B match. This enables precise cascading in multi-word comparisons and selective activation in shared-bus systems. The CD74HC688PWT's E pin has standard CMOS input thresholds and draws <1 μA leakage current.

Can CD74HC688PWT operate at 3.3 V supply voltage?

Yes, CD74HC688PWT is fully specified for 2 V to 6 V operation, including 3.3 V nominal systems. At VCC = 3.3 V, it maintains VIH ≥ 2.31 V, VIL ≤ 0.99 V, tPD ≤ 22 ns (typical), and ICC ≤ 80 μA (25°C), making it suitable for direct interface with 3.3 V microcontrollers and FPGAs without level translation. All AC/DC parameters in the official TI datasheet SCHS196E are validated across this full range.

Is CD74HC688PWT pin-compatible with CD74HCT688PWR?

Yes, CD74HC688PWT and CD74HCT688PWR share identical TSSOP-20 pinout, footprint, and terminal functions - both have E on pin 1, A0–A7/B0–B7 on pins 2–9 and 11–18, Y on pin 19, and GND/VCC on pins 10/20. However, they differ electrically: CD74HC688PWT supports 2–6 V with CMOS input thresholds, while CD74HCT688PWR is limited to 4.5–5.5 V with TTL-compatible inputs. Swapping requires verifying supply and driver compatibility.

What is the maximum operating temperature for CD74HC688PWT?

The CD74HC688PWT is rated for continuous operation from –55°C to +125°C, per TI's official datasheet SCHS196E. This extended temperature range is achieved through qualified silicon process and packaging (TSSOP-PW), and is validated with full electrical testing across the range - including propagation delay, VOH/VOL, and ICC limits. It meets MIL-PRF-38535 requirements for Class B devices and is widely deployed in engine control units and satellite subsystems.

Does CD74HC688PWT require external pull-up resistors on the Y output?

No, CD74HC688PWT features a totem-pole (push-pull) output stage on Y - not open-drain - so no external pull-up resistor is required. The Y pin actively drives high (VOH ≥ 4.4 V at VCC = 4.5 V, IOH = –20 μA) and low (VOL ≤ 0.4 V at VCC = 4.5 V, IOL = 4 mA). This simplifies board design and ensures fast, clean transitions without RC delays. The CD74HC688PWT's output structure is explicitly defined in the Functional Diagram and Electrical Characteristics tables of SCHS196E.