Texas Instruments CD74HC238PW

Overview

CD74HC238PW from Texas Instruments is a high-speed CMOS 3-to-8 line decoder/demultiplexer with active-high outputs, 2 V to 6 V operation, -55°C to 125°C temperature range, typical 13 ns propagation delay at 5 V/15 pF, and three enable inputs (G2, G1, G0) for cascading. It serves as an address decoder in microcontroller memory expansion systems.

For engineers reviewing the CD74HC238PW datasheet, CD74HC238PW pinout, CD74HC238PW application, or CD74HC238PW equivalent, key selection criteria include output polarity (active-high), HC-series voltage flexibility, wide industrial temperature support, and TSSOP-16 package compatibility with high-density PCB layouts.

Technical Context

The CD74HC238PW implements a standard 3:8 binary decoder with address inputs A0–A2 and three independent strobe enables (G2 = active-high, G1/G0 = active-low). When any strobe is asserted, all eight Y0–Y7 outputs are forced low - unlike the '138 variant which forces outputs high.

Its logic function is defined by Table 7-2 in the TI datasheet: only one output goes high per unique 3-bit address when all enables are satisfied; all outputs remain low otherwise. The device uses silicon-gate CMOS technology, delivering rail-to-rail output swing and high noise immunity (30% of VCC at 5 V).

Key Specifications

Pinout & Package

TSSOP-16 package (5.00 mm × 4.40 mm body size), thin shrink small-outline package with gull-wing leads, RoHS-compliant, moisture sensitivity 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 CD74HC138PW, the CD74HC238PW provides native active-high outputs eliminating external inversion; versus SN74HC238PWR, it shares identical electrical behavior but differs only in orderable suffix and tape-and-reel configuration - both are functionally interchangeable in design.

Availability

CD74HC238PW is available at Aetrix Electronics and suitable for memory address decoding, peripheral I/O selection, industrial PLC expansion, and test equipment signal routing requiring stable component supply across extended temperature ranges.

Supply support for CD74HC238PW 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 company designing analog ICs, embedded processors, and logic devices for industrial, automotive, and communications markets.

The CD74HC238PW belongs to TI's HC-series high-speed CMOS logic family, engineered for low-power, wide-voltage-operation digital interfacing in ruggedized industrial control and instrumentation systems.

FAQ

What is the output behavior of CD74HC238PW when all enable inputs are asserted?

When G2 = high and G1 = G0 = low, the CD74HC238PW decodes the A2–A0 address: exactly one of Y0–Y7 goes high (active-high), while all others remain low. This differs from the CD74HC138PW, where the selected output goes low. The CD74HC238PW's active-high behavior simplifies driving loads that require positive-enable signals without external inverters.

Can CD74HC238PW operate reliably at 3.3 V supply voltage?

Yes, CD74HC238PW is fully specified for 2 V to 6 V operation. At V_CC = 3.3 V, its input thresholds (V_IL ≤ 0.99 V, V_IH ≥ 2.31 V) and output drive (≥ 3.1 V VOH at I_OH = –4 mA) ensure clean interfacing with 3.3 V microcontrollers and FPGAs. Propagation delay increases to ~18 ns, remaining well within most 25 MHz system timing budgets.

Is CD74HC238PW pin-compatible with CD74HC138PW?

Yes, CD74HC238PW and CD74HC138PW share identical TSSOP-16 pinout, package dimensions, and electrical specifications - except output polarity. Both use the same A0–A2, G2/G1/G0, Y0–Y7, VCC, and GND pin assignments. Functional substitution requires logic-level inversion in downstream circuitry or firmware to accommodate active-high vs. active-low outputs.

What is the maximum output sink current supported by CD74HC238PW?

The CD74HC238PW supports up to 4 mA sink current per output (I_OL) at V_CC = 4.5 V, with VOL ≤ 0.33 V. This is sufficient to drive standard LEDs (with series resistor), small-signal MOSFET gates, or TTL-compatible inputs. Exceeding 4 mA risks violating VOL spec or increasing propagation delay; for higher loads, buffer stages are recommended.

Does CD74HC238PW require external pull-up resistors on its outputs?

No, CD74HC238PW features push-pull (totem-pole) outputs and does not require external pull-ups. Its outputs actively drive high or low depending on decode state. Pull-ups would conflict with active-high drive and cause excessive current during Yx = high transitions. Only unused inputs (A0–A2, G2/G1/G0) must be tied to VCC or GND to prevent floating states.