M74HC138B1R

Overview

The M74HC138B1R is a high-speed CMOS 3-to-8 line decoder manufactured by STMicroelectronics using silicon gate C2MOS technology. It features three binary select inputs (A, B, and C) that determine which of the eight low-active outputs goes low when enabled. The device includes three enable inputs: one high-active (G1) and two low-active (G2A, G2B). Functional operation requires G1 to be high while G2A and G2B are low; otherwise, all outputs remain high. It operates within a supply voltage range of 2V to 6V and supports an operating temperature from -55°C to +125°C.

Feature Summary

• High-speed decoding with balanced propagation delays for address decoding applications
• Three enable inputs facilitate cascade connection and memory system expansion
• Low power dissipation with symmetrical output impedance characteristics
• Input protection circuits against static discharge and transient excess voltage

Applications

• Address decoders for memory systems
• Data routing in high-performance storage systems
• Cascaded multi-line decoding configurations

Procurement Notes

Verify component authenticity through authorized distribution channels. Confirm package integrity upon receipt as the DIP-16 tube packaging may be subject to handling variations. Ensure environmental compliance documentation matches project requirements. Cross-reference datasheet revisions to confirm electrical specifications align with current design constraints before finalizing procurement orders.

Selection Notes

Select this component for designs requiring wide voltage operation between 2V and 6V. Verify that the required propagation delay fits within the system timing budget, noting typical values vary with supply voltage. Ensure the application utilizes low-active outputs compatible with downstream logic levels. Consider thermal derating if operating near maximum ambient temperatures or power dissipation limits.

Part Context

This part belongs to the M74HC138 series of 3-to-8 line decoders. It is pin and function compatible with standard 74 series 138 devices. The B1R suffix indicates the specific DIP-16 tube packaging variant. It is designed for general-purpose digital logic applications requiring efficient address decoding capabilities within standard industrial temperature ranges.

Replacement Considerations

Direct substitutes include CD74HC138E from Texas Instruments and SN74HC138N from Texas Instruments. These alternatives maintain functional compatibility but require verification of mechanical dimensions and specific electrical parameter tolerances against the original design specifications.