TC74VHCT138AFTEL

Overview

The TC74VHCT138AFTEL is a CMOS 3-to-8 line decoder manufactured by Toshiba Semiconductor and Storage. It operates within a supply voltage range of 4.5 V to 5.5 V and supports an operating temperature from -40°C to 85°C. The device features a typical propagation delay of 7.6 ns at 5 V, with balanced low-to-high and high-to-low delays. Quiescent current is limited to a maximum of 4 μA at 25°C. Input levels are compatible with TTL outputs, allowing for level conversion between 3.3 V and 5 V systems.

Feature Summary

• Provides power-down protection on all inputs and outputs to prevent device destruction during mismatched supply conditions.
• Features three enable inputs (G1, 2AG, 2BG) designed to facilitate cascade connections and memory address decoding.
• Maintains balanced propagation delays between low-to-high and high-to-low transitions.

Applications

• Memory system address decoding
• Interfacing 3.3 V logic to 5 V systems
• Cascade connection of multiple decoders

Procurement Notes

Verify the specific package suffix matches the required form factor, as the AF designation corresponds to the TSSOP-16 package. Confirm that the ordering suffix aligns with the reel or cut tape requirements specified by the distributor. Ensure the component meets RoHS compliance standards relevant to the target market before finalizing procurement orders.

Selection Notes

Select this component when a VHCT series decoder is required for 5 V applications needing TTL-compatible input thresholds. It serves as a direct pin-and-function replacement for other 74-series 138 types such as AC, HC, F, ALS, and LS variants. Consider the 7.6 ns propagation speed and low static power consumption for general electronics and industrial equipment designs.

Part Context

This part belongs to the TC74VHCT138 family, which includes variants in SOP, SOL, and VSSOP packages. The 'AF' suffix specifically denotes the TSSOP-16 plastic package with a 0.65 mm pitch. The device utilizes silicon gate C2MOS technology to achieve high-speed operation comparable to Bipolar Schottky TTL while maintaining standard CMOS power efficiency.

Replacement Considerations

The datasheet confirms pin and function compatibility with the 74AC/HC/F/ALS/LS 138 type decoders. Verify that the substitute device supports the same 4.5 V to 5.5 V operating voltage range and TTL-compatible input thresholds to ensure seamless integration without circuit modification.

FAQ

How does the device handle input voltages when the supply voltage is zero?

Input protection circuits allow 0 to 5.5 V to be applied to the pins even if the supply voltage is 0 V, preventing device destruction due to hot board insertion or battery backup scenarios.

What is the mechanism for inhibiting the decoding function?

Decoding is inhibited and all outputs go high if the G1 input is held low or if either of the 2AG or 2BG inputs is held high.