Standard TTL totem-pole output capability For a standard 74xx TTL gate with a totem-pole output, what is the typical maximum sink current (IOL(max)) in the LOW state?

Introduction / Context:
Designers often need to know how much current a logic output can safely sink or source while keeping valid logic levels. In standard TTL (74xx), the totem-pole configuration provides defined current capabilities that determine fan-out and LED/relay driving limits (with proper resistors).

Given Data / Assumptions:

• Standard TTL family (not LS/ALS) with totem-pole output stage.
• Asking for IOL(max): maximum current the output can sink while LOW.

Concept / Approach:

Standard TTL typically specifies IOL(max) ≈ 16 mA and IOH(max) ≈ –0.4 mA. These asymmetric limits reflect transistor configurations and ensure VOL and VOH remain within guaranteed levels under load. Newer LS/ALS have different limits, but the classic “standard TTL” figure is 16 mA for sinking in the LOW state.

Step-by-Step Solution:

Verification / Alternative check:

Consult legacy datasheets and textbooks; they consistently cite 16 mA sink capability for standard TTL. LS versions are lower (around 8 mA), reinforcing that 16 mA is the “standard TTL” figure.

Why Other Options Are Wrong:

• 20 mA: higher than typical standard TTL specification.
• 16 µA / 20 µA: off by three orders of magnitude; those currents are far too small.

Common Pitfalls:

• Confusing standard 74xx TTL with 74LSxx values (which differ).
• Assuming source current equals sink current; in TTL, sourcing is much smaller.

Final Answer:

16 mA