Texas Instruments CD74HCT137E

Overview

CD74HCT137E from Texas Instruments is a high-speed CMOS 3-to-8 line decoder/demultiplexer with address latches, designed for memory address decoding and data routing in industrial control and instrumentation systems. It features active-low outputs, dual output enables (OE0, OE1), latch enable (LE), three binary select inputs (A0–A2), and operates over -55°C to +125°C at 4.5V–5.5V.

For engineers reviewing the CD74HCT137E datasheet, CD74HCT137E pinout, CD74HCT137E application, or CD74HCT137E equivalent, this page delivers verified electrical specs, truth-table behavior, latch-controlled output isolation, LSTTL-compatible input thresholds, and cascading support via dual enables - all critical for deterministic address decoding in harsh-environment embedded designs.

Technical Context

The CD74HCT137E implements a 3-bit binary latch followed by an active-low 1-of-8 decoder. Inputs A0–A2 are latched on LE high, freezing output states independent of subsequent address changes - enabling stable bus selection during dynamic addressing. Output enable logic (OE0 and OE1) allows hierarchical cascading: one enable serves as demultiplexed data input while the other remains asserted.

Its HCT logic family ensures direct compatibility with LSTTL inputs (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and CMOS-level outputs (VOH ≥ 4.4 V, VOL ≤ 0.1 V at VCC = 4.5 V). Propagation delay is 16 ns typical (A→Y, CL = 15 pF, VCC = 5 V), with balanced tPLH/tPHL and transition times under 22 ns, supporting reliable timing in synchronous digital subsystems.

Key Specifications

Pinout & Package

CD74HCT137E is supplied in a 16-lead plastic dual in-line package (PDIP), with 0.3-inch body width and standard through-hole footprint. Pin 1 is located at the top-left corner when viewed from the top with notch or dot orientation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-to-8 decoder with latch applications.

Compared with CD74HCT137E, CD74HC137E offers wider voltage range but lacks native TTL compatibility, while CD74HCT237E retains identical timing and robustness but reverses output polarity - making it ideal for drop-in reuse in existing '237-based designs without logic inversion.

Availability

CD74HCT137E is available at Aetrix Electronics and suitable for industrial control systems, automotive ECUs, and test instrumentation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HCT137E includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and logic solutions, with decades of heritage in high-reliability logic families.

The CD74HCT137E belongs to TI's High-Speed CMOS Logic portfolio, engineered for deterministic address decoding and data routing in mission-critical industrial, aerospace, and automotive systems where latch stability and wide temperature operation are essential.

FAQ

What is the maximum clock frequency supported by CD74HCT137E?

The CD74HCT137E does not operate on a clock signal - it is combinational logic with latched inputs. Its usable switching rate depends on propagation delay (16 ns typical) and system setup/hold timing. For reliable operation with 15 pF loads, maximum toggle frequency is approximately 30 MHz, assuming clean edges and proper decoupling. Always verify timing margins using the device's truth table and worst-case delays from the datasheet for CD74HCT137E.

Does CD74HCT137E require external pull-up resistors on its outputs?

No, CD74HCT137E features totem-pole CMOS outputs capable of actively driving both high and low states. Its outputs source up to 4 mA and sink up to 4 mA under standard conditions (VCC = 4.5 V), eliminating the need for external pull-ups. Pull-ups should only be added if interfacing with open-drain inputs or if additional drive strength is required beyond the device's rated capability for CD74HCT137E.

How does the latch enable (LE) pin affect output behavior in CD74HCT137E?

When LE is high, the CD74HCT137E latches the current values of A0–A2, freezing the decoded output state regardless of further changes to the address lines. When LE is low, outputs track A0–A2 in real time (transparent mode). This latch function prevents glitches during address bus transitions and is essential for stable chip-select generation in microprocessor systems using CD74HCT137E.

Can CD74HCT137E be used in place of a 74LS138 in existing designs?

Yes - CD74HCT137E is pin-compatible and functionally equivalent to the 74LS138, with identical pinout, active-low outputs, and dual-enable architecture. Its LSTTL-compatible inputs (VIH ≥ 2.0 V, VIL ≤ 0.8 V) ensure direct substitution without level shifting. However, note that CD74HCT137E has faster propagation (16 ns vs. ~24 ns for LS138) and lower power consumption, which may affect timing closure in legacy designs originally timed for LS propagation.

What is the purpose of the two output enable inputs (OE0 and OE1) in CD74HCT137E?

In CD74HCT137E, both OE0 and OE1 must be low for any output to be active. This dual-enable structure simplifies cascading: one enable (e.g., OE0) can serve as a global master enable, while the other (OE1) accepts demultiplexed data - allowing the CD74HCT137E to function as either a decoder or a 1-of-8 demultiplexer. This eliminates external AND gates and reduces component count in multi-stage decoding architectures.