Texas Instruments SN74HC138PWT

Overview

SN74HC138PWT from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in TSSOP-16 package, operating from 2 V to 6 V supply, delivering 15 ns typical propagation delay at 6 V, ±4-mA output drive at 5 V, and active-low outputs for memory decoding and LED matrix column selection.

For engineers reviewing the SN74HC138PWT datasheet, SN74HC138PWT pinout, SN74HC138PWT application, or SN74HC138PWT equivalent, key selection criteria include enable-input logic configuration (G1 high-active, G2A/G2B low-active), output drive capability under 5-V operation, thermal resistance (RθJA = 141.6 °C/W), and compatibility with HC-family logic level thresholds.

Technical Context

The SN74HC138PWT implements combinational 3-to-8 decoding using CMOS technology with balanced output drive and no internal latching. Its three binary select inputs (A, B, C) and three enable terminals (G1, G2A, G2B) allow cascading into larger decoders without external inverters - e.g., a 24-line decoder requires zero external gates.

Propagation delay is supply-voltage dependent: 15 ns (typ) at VCC = 6 V, 38 ns (max) over full temperature range, with output transition time as low as 6 ns (typ). All outputs are active-low and mutually exclusive - only one Yx line goes LOW per valid input combination when enables are asserted.

Key Specifications

Pinout & Package

TSSOP-16 package (5.00 mm × 4.40 mm body size), 0.65-mm lead pitch, RoHS-compliant, moisture sensitivity level (MSL) Level-1 (unlimited floor life at ≤30 °C/60% RH).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT138PW and 74LV138PW, SN74HC138PWT provides the broadest supply range (2–6 V), best noise immunity at 5 V, and lowest quiescent current - making it optimal for cost-sensitive, multi-rail industrial controls where reliability outweighs marginal speed gains.

Availability

SN74HC138PWT is available at Aetrix Electronics and suitable for industrial memory decoding, LED matrix display control, factory automation I/O expansion, and white goods user interface applications requiring stable component supply and long-term manufacturability support.

Supply support for SN74HC138PWT 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 expertise in high-reliability logic families and industrial-grade qualification.

The SN74HC138PWT belongs to TI's 74HC high-speed CMOS logic product line, engineered for low-power, high-noise-immunity decoding in memory systems, programmable logic interfaces, and real-time control applications.

FAQ

What is the maximum operating supply voltage for SN74HC138PWT?

The absolute maximum supply voltage for SN74HC138PWT is 7 V, but the recommended operating range is 2 V to 6 V per TI's SCLS107G datasheet. Operation above 6 V risks exceeding absolute maximum ratings and may cause permanent damage or parametric shift. For reliable long-term use, maintain VCC ≤ 6 V.

Does SN74HC138PWT support cascading with other decoders?

Yes, SN74HC138PWT supports seamless cascading using its three enable inputs: G1 (active-high), G2A and G2B (both active-low). For example, two SN74HC138PWT devices can implement a 4-to-16 decoder - one handles address bits A0–A2 and enables the second via Y0–Y3, eliminating external gates.

Can SN74HC138PWT directly drive LEDs in a multiplexed display?

Yes, SN74HC138PWT can directly sink up to 4 mA per output at 5 V, sufficient for low-current indicator LEDs or column-driving in 8×8 LED matrices. Its active-low outputs align with common-cathode configurations, and 15-ns propagation ensures precise timing alignment with row-scanning drivers like SN74HC595B.

What is the thermal resistance (RθJA) of SN74HC138PWT in its TSSOP package?

The junction-to-ambient thermal resistance (RθJA) for SN74HC138PWT in the TSSOP-16 package is 141.6 °C/W, as specified in Section 6.4 of the TI datasheet. This value assumes standard JEDEC 2-layer board conditions; actual thermal performance improves with copper pour and thermal vias beneath the exposed pad (if present) - though PW package lacks thermal pad.

Is SN74HC138PWT pin-compatible with SN74HCT138PW?

Yes, SN74HC138PWT and SN74HCT138PW share identical TSSOP-16 pinout, package dimensions, and function table. The only difference is input threshold compatibility: SN74HCT138PW accepts TTL-level inputs (VIH ≥ 2 V), while SN74HC138PWT requires CMOS-level inputs (VIH ≥ 3.15 V at 4.5 V). Both are drop-in replacements in layout.