How to find the right Digital Multiplexers AI guide
Written by an AI model from its trained knowledge.
What the AI looks for in Digital Multiplexers
- Logic family and supply voltage
- Match the family to the system: HC for CMOS at 2 to 6 V, HCT for TTL-level inputs on 5 V, LVC/LVT-type for 3.3 V, legacy LS only to repair old TTL gear. The wrong family gives marginal logic thresholds or won't run at all at your supply voltage.
- Function and input count
- 8:1 (151-type), dual 4:1 (153-type) or quad 2:1 (157/158-type); check whether the output is true or inverted. Part numbers within a family differ in topology and output polarity. Small differences in the number change the function.
- Output type
- Choose a tri-state output version (for example, 251/253/257-type) if the output shares a bus with other drivers. Standard push-pull outputs fight each other and can be damaged when tied to a shared bus.
- Propagation delay
- Compare datasheet propagation delay at your actual supply voltage when timing margins are tight. Delay grows as supply voltage drops and differs a lot between families.
- Bus-specific multiplexers
- For I2C devices with conflicting addresses, use a dedicated I2C switch or mux (TCA9548A-type), not a generic logic mux. I2C is bidirectional and open-drain, and a one-way logic mux cannot pass it correctly.
Brands that matter
- Texas Instruments: Very broad 74-series mux catalog across HC, HCT, LV, LVC and the TCA954x I2C switches.
- Nexperia: Major 74HC/HCT/LVC logic supplier with consistent datasheets.
- onsemi: 74-series and MC-series logic multiplexers.
- Diodes Incorporated: 74-series logic, including low-voltage variants.
- STMicroelectronics: 74-series CMOS logic, including multiplexers.
What to avoid
- Mixing 3.3 V and 5 V logic without checking input thresholds and input tolerance.
- Using a digital logic mux to switch analog, audio or bidirectional signals.
- Leaving unused select or data inputs floating on CMOS parts.
- Using legacy LS TTL in new 3.3 V designs.
Questions
What is the difference between HC and HCT versions?
Both are CMOS. HCT has TTL-compatible input thresholds and is meant for 5 V systems driven by TTL-level outputs. HC uses CMOS thresholds and runs over a wider supply range.