The TC74HCT138AFN is a high-speed CMOS 3-to-8 Line Decoder/Demultiplexer manufactured by Toshiba Semiconductor and Storage. This device accepts three binary weighted inputs (A0, A1, A2) and, depending upon the state of these inputs, provides one of eight mutually exclusive outputs (O0 to O7) that is active LOW. The TC74HCT138AFN features three enable inputs (E1, E2, and E3). The device is enabled when E1 is HIGH and E2 and E3 are LOW.

Applications

• Memory address decoding
• Data routing
• Output enabling
• Logic function generation
• Microprocessor systems

Features

• High Speed: tpd = 16 ns (typ.) at VCC = 5V.
• Low Power Dissipation: ICC = 4 μA (max) at Ta = 25°C.
• TTL Input Compatibility: VIH = 2.0 V (min), VIL = 0.8 V (max).
• Output Drive Capability: 10 LSTTL Loads.
• Symmetrical Output Impedance: |IOH| = IOL = 4 mA (min).
• Wide Operating Voltage Range: VCC = 4.5 V to 5.5 V.
• Three Enable Inputs to Simplify Cascading

Benefits

• Simplified memory address decoding for efficient memory management.
• Flexible data routing capabilities.
• Enables output control for selective activation of downstream circuits.
• Facilitates the generation of custom logic functions.
• Easy integration with microprocessor-based systems due to TTL input compatibility.
• Cascading capability allows expansion to larger decoding schemes.

Additional Details

The TC74HCT138AFN operates with a supply voltage between 4.5V and 5.5V. The device comes in a DIP (Dual In-line Package), allowing for easy prototyping and through-hole mounting. Inputs are protected against static discharge. When enabled, the selected output goes LOW, while all other outputs remain HIGH. The enable inputs provide a convenient method for device selection and cascading multiple decoders for larger address spaces.

The operating temperature range is typically between -40°C and +85°C. It adheres to JEDEC standards for CMOS integrated circuits. Symmetrical output impedance minimizes signal distortion and propagation delays. Its TTL input compatibility enables direct interfacing with TTL logic levels. The use of three enable inputs provides a flexible means of controlling the device's operation and cascading it with other decoders to implement larger address decoding schemes. When all enable inputs are not properly asserted, all outputs are HIGH.