STMicroelectronics M74HCT138RM13TR

Overview

M74HCT138RM13TR from STMicroelectronics is a high-speed CMOS 3-to-8 line decoder with inverting outputs, designed for address decoding in memory systems and digital logic control. It features propagation delay of 16 ns (typ.) at V_CC = 4.5 V, quiescent supply current ≤4 µA at 25°C, and TTL-compatible input thresholds (V_IH ≥ 2.0 V, V_IL ≤ 0.8 V). Its three enable inputs (G1, G2A, G2B) support cascaded decoding in multi-chip architectures.

For engineers reviewing the M74HCT138RM13TR datasheet, M74HCT138RM13TR pinout, M74HCT138RM13TR application, or M74HCT138RM13TR equivalent, key selection criteria include guaranteed 4 mA output drive strength, symmetrical t_PLH/t_PHL delays, TSSOP-16 package compatibility, and operation across –55°C to +125°C industrial temperature range.

Technical Context

The M74HCT138 implements active-low 3-bit binary decoding: when enabled (G1 = HIGH, G2A = G2B = LOW), exactly one of eight outputs (Y0–Y7) goes LOW based on A/B/C inputs; all outputs remain HIGH otherwise. Enable logic supports hierarchical address decoding without external gating.

It uses silicon gate C2MOS technology, delivering TTL-compatible input levels while maintaining CMOS low-power advantages. Input protection circuits guard against ESD and transient overvoltage, and output impedance is balanced (|I_OH| = I_OL ≥ 4 mA) to ensure clean signal transitions under load.

Key Specifications

Pinout & Package

TSSOP-16 package: 4.9 mm × 6.4 mm body, 0.65 mm pitch, 1.2 mm max height, lead-free and RoHS-compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT138DR and 74VHC138M, the M74HCT138RM13TR uniquely combines TSSOP-16 space savings, full –55°C to +125°C qualification, and 16 ns propagation delay-making it optimal for compact, ruggedized embedded controllers.

Availability

M74HCT138RM13TR is available at Aetrix Electronics and suitable for memory address decoding, peripheral select logic, LED multiplexing, and industrial safety interlock systems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for M74HCT138RM13TR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, digital, and mixed-signal ICs for automotive, industrial, and consumer markets.

The M74HCT138 belongs to ST's high-speed HCMOS logic family, engineered specifically for pin-compatible upgrades of legacy 74LS devices while delivering CMOS power efficiency and enhanced noise immunity.

FAQ

Is M74HCT138RM13TR compatible with 5 V TTL logic outputs?

Yes. Its input voltage thresholds (V_IH ≥ 2.0 V, V_IL ≤ 0.8 V) match standard TTL levels, and it draws negligible input current (<±1 µA), allowing direct connection to 74LS and 74F series outputs without level-shifting or pull-up resistors.

What is the maximum capacitive load this decoder can drive reliably?

The M74HCT138RM13TR is characterized for CL = 50 pF in AC testing. With 4 mA output drive and 16 ns typical t_PD, it reliably drives up to 3–4 standard 74HCT inputs (≈30 pF total) or a single 50 pF transmission line stub without signal integrity degradation.

Does this device require external pull-up resistors on its outputs?

No. The outputs are active-pull-down (open-drain equivalent) with complementary CMOS totem-pole structure. They actively drive LOW (sink 4 mA) and HIGH (source 4 mA), eliminating need for external pull-ups in standard wired-OR or chip-select configurations.

Can M74HCT138RM13TR operate from a 3.3 V supply?

No. Its recommended V_CC range is strictly 4.5 V to 5.5 V. At 3.3 V, input thresholds become undefined, propagation delays increase unpredictably (>100 ns), and output drive falls below specification-operation outside this range is not guaranteed or characterized.