Texas Instruments CD74AC138PWR

Overview

CD74AC138PWR from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in TSSOP-16 package, operating from 1.5 V to 5.5 V with ±24 mA output drive, balanced propagation delays (as low as 2.8 ns at 5 V), and three enable inputs (G1, G2A, G2B) for cascading in memory decoding systems.

For engineers reviewing the CD74AC138PWR datasheet, CD74AC138PWR pinout, CD74AC138PWR application, or CD74AC138PWR equivalent, this device supports high-speed address decoding in industrial controllers, FPGA I/O expansion, and multi-channel data routing where low-power CMOS logic with noise immunity and latch-up resistance is required.

Technical Context

The CD74AC138PWR implements positive-logic 3-to-8 decoding with active-low outputs and three independent strobe inputs-G1 (active-high), G2A and G2B (both active-low)-requiring all three enables to be asserted for valid output selection. Its function table defines eight mutually exclusive active-low outputs (Y0–Y7) based on binary inputs A, B, C.

It uses SCR-latchup-resistant CMOS process technology, achieves ±2 kV HBM ESD protection, and maintains balanced tPLH/tPHL across supply voltages (1.5 V, 3.3 V, 5 V), enabling stable timing in mixed-voltage systems without skew-induced glitches.

Key Specifications

Pinout & Package

TSSOP-16 (PW) package: 5.00 mm × 6.4 mm body size, 1.2 mm max height, lead pitch 0.65 mm, exposed pad not present (unlike WQFN variants).

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74AC138PWR, SN74AC138PWR trades extended temperature and ESD robustness for lower cost, while 74LVC138PW,118 offers faster typical delay at 3.3 V but sacrifices supply flexibility and ruggedness-making CD74AC138PWR the sole choice for mixed-voltage, high-reliability industrial deployments.

Availability

CD74AC138PWR is available at Aetrix Electronics and suitable for industrial PLCs, FPGA I/O expansion, automotive body control modules, and automated test equipment requiring stable component supply across extended temperature and voltage ranges.

Supply support for CD74AC138PWR 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 CD74AC138PWR belongs to TI's AC-series advanced CMOS logic family, designed specifically for high-speed memory decoding and data-routing applications demanding short propagation delays, wide supply tolerance, and latch-up immunity.

FAQ

What is the maximum operating frequency supported by CD74AC138PWR?

The CD74AC138PWR does not specify a maximum clock frequency because it is a combinational logic device-not clocked. Its usable speed is determined by propagation delay: at 5 V, tPD is 2.8 ns (min) to 10 ns (max), supporting reliable operation in address decode paths up to ~100 MHz effective toggle rate. System-level timing must account for worst-case delay plus setup/hold margins of downstream devices. The CD74AC138PWR itself imposes no inherent frequency ceiling beyond its specified switching characteristics.

Does CD74AC138PWR have 3-state outputs?

No, CD74AC138PWR does not feature 3-state outputs. Its eight outputs (Y0–Y7) are push-pull and always driven-either HIGH or LOW-based on input and enable conditions. When disabled (any enable inactive), all outputs go HIGH. It lacks output-enable (OE) pins or high-impedance states. For bus-oriented applications requiring tri-state capability, consider alternatives like CD74AC238PWR or dedicated bus transceivers instead of CD74AC138PWR.

Can CD74AC138PWR operate at 1.8 V supply voltage?

Yes, CD74AC138PWR is fully specified for operation at 1.8 V, as it falls within its guaranteed 1.5 V to 5.5 V supply range. At 1.8 V, VIH is 1.2 V (min), VIL is 0.6 V (max), and propagation delay increases to 138 ns (max) per datasheet Section 4.6. All DC and AC parameters-including noise immunity (30% of VCC = 0.54 V), output drive, and ESD rating-remain valid at 1.8 V, making CD74AC138PWR suitable for mixed-voltage systems interfacing with 1.8 V microcontrollers.

How are the enable inputs G2A and G2B used together in CD74AC138PWR?

In CD74AC138PWR, G2A and G2B are both active-low enables that must be held LOW simultaneously-along with G1 HIGH-for any output to activate. This 3-input AND logic (G1 ∧ ¬G2A ∧ ¬G2B) allows hierarchical control: G2A may connect to a system-level chip-select, while G2B links to a board-level enable, preventing spurious decoding during power-up or reset. Their separate pins simplify PCB routing in multi-device decode trees and avoid single-point failure modes that would occur with a merged enable signal.

Is thermal pad soldering required for CD74AC138PWR in TSSOP-16 package?

No, thermal pad soldering is not required for CD74AC138PWR because the TSSOP-16 (PW) package does not include an exposed thermal pad-unlike the WQFN (BQB) variant. The PW package relies on standard lead-frame conduction and PCB copper pour for thermal management. Its RθJA is 126.2 °C/W (per Section 4.4), and no thermal pad connection or via implementation is needed. Always verify land pattern against TI's PW0016A mechanical drawing, not WQFN guidelines, when designing the CD74AC138PWR footprint.