5400 vs 7400 Series — What is the key difference between these classic TTL families?

Introduction / Context:
The 54xx and 74xx families are foundational TTL series seen in countless schematics and catalogs. Understanding their distinction helps engineers select parts that meet environmental constraints without over-specifying (and overspending) on ruggedized devices.

Given Data / Assumptions:

• 54xx parts were specified for military/extended temperature ranges and tighter reliability targets.
• 74xx parts were intended for commercial/consumer ranges with narrower environmental specs.
• Both families share the same basic logic functions (e.g., 5400/7400, 54138/74138).

Concept / Approach:
The standard distinction is environmental rating: 5400-series devices are military/extended versions with wider allowable supply and temperature ranges; 7400-series are commercial. The underlying logic function is equivalent; qualifications differ.

Step-by-Step Solution:
Identify environmental rating difference: 54xx (mil/extended) vs 74xx (commercial).Map to answer choices → option stating 5400 has wider ranges is correct.Reject statements about patent lineage or “improvements” that do not reflect the canonical spec difference.

Verification / Alternative check:
Cross-references show identical logic functions with distinct suffixes for temperature and qualification; data books explicitly separate 54xx (–55 °C to +125 °C typical) from 74xx (0 °C to +70 °C typical).

Why Other Options Are Wrong:

• a: “Require tighter” is misleading; 54xx tolerate a wider environmental range.
• c, d: Do not capture the key standardized environmental distinction.

Common Pitfalls:
Assuming 54xx are electrically different in logic function—function is the same, qualification differs.

Final Answer:
The 5400 series are military grade and allow for a wider range of supply voltages and temperatures.