Texas Instruments SN74AHCT138QPWRQ1

Overview

SN74AHCT138QPWRQ1 from Texas Instruments is an automotive-grade 3-line to 8-line decoder/demultiplexer in TSSOP-16 package, featuring TTL-compatible inputs, three enable inputs (G1 active-high, G2A/G2B active-low), propagation delays as low as 6.6 ns at 5 V, and operation across −40°C to +125°C for memory decoding and data-routing in ADAS domain controllers.

For engineers reviewing the SN74AHCT138QPWRQ1 datasheet, SN74AHCT138QPWRQ1 pinout, SN74AHCT138QPWRQ1 application, or SN74AHCT138QPWRQ1 equivalent, key selection considerations include automotive AEC-Q100 qualification, 5-V supply compatibility, cascading support via dual active-low enables, and output drive capability of ±8 mA at V_CC = 5 V.

Technical Context

This decoder implements positive-logic binary decoding with three select inputs (A, B, C) and three independent enables-G1 (active-high), G2A and G2B (both active-low)-enabling flexible cascading without external inverters. Its EPIC CMOS process ensures TTL-level input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2 V) while maintaining CMOS output swing.

Functional modes are fully defined by the truth table: all outputs remain high when any enable is inactive; only one Y_n goes low (active-low outputs) when all enables are asserted and a unique 3-bit select code is applied. No latching or internal state retention is present-it is purely combinational.

Key Specifications

Pinout & Package

TSSOP-16 (PW) package: 5.00 mm × 6.4 mm body, 1.2 mm max height, gull-wing leads, RoHS-compliant NiPdAu finish, MSL Level-1 (260°C peak reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV138AQPWRQ1 and MC74VHC138DT, the SN74AHCT138QPWRQ1 uniquely delivers guaranteed TTL compatibility, AEC-Q100 Grade 1 operation, and sub-7-ns enable-path delay - making it the sole choice for timing-critical automotive memory decode where legacy 5-V signaling coexists with modern microcontrollers.

Availability

SN74AHCT138QPWRQ1 is available at Aetrix Electronics and suitable for automotive ECUs, ADAS sensor hubs, digital instrument clusters, and body control modules requiring stable component supply across extended product lifecycles.

Supply support for SN74AHCT138QPWRQ1 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and automotive ICs with global manufacturing and quality certification infrastructure.

The SN74AHCT138QPWRQ1 belongs to TI's automotive logic portfolio, designed specifically to replace discrete gate solutions in high-reliability vehicle subsystems where timing precision, voltage compatibility, and AEC-Q100 compliance are mandatory.

FAQ

What is the maximum clock frequency supported by SN74AHCT138QPWRQ1?

The SN74AHCT138QPWRQ1 is a combinational decoder-not a clocked device-so it has no clock input or maximum clock frequency specification. Its usable switching rate is determined by propagation delay and load capacitance: with CL = 15 pF and V_CC = 5 V, t_PD ≤ 10.5 ns supports reliable operation up to approximately 50 MHz for address/data strobe edges. System-level timing must account for worst-case skew across all eight outputs.

Can SN74AHCT138QPWRQ1 drive LEDs directly?

Yes, SN74AHCT138QPWRQ1 can drive LEDs directly in active-low configuration: each Y_n output sinks up to 8 mA at V_OL ≤ 0.5 V (I_OL = 8 mA), sufficient for low-current indicator LEDs with appropriate series resistors. For higher-brightness or multiplexed displays, verify total package current limits (±75 mA continuous through V_CC/GND) and thermal rise in the TSSOP package under sustained load.

Is SN74AHCT138QPWRQ1 pin-compatible with SN74LS138?

Yes, SN74AHCT138QPWRQ1 is pin-compatible with SN74LS138 in the same TSSOP-16 (PW) package: identical pin numbering, function mapping (A–C, G1/G2A/G2B, Y0–Y7, V_CC, GND), and footprint. However, SN74AHCT138QPWRQ1 uses CMOS output stages (push-pull, not open-collector) and requires proper termination of unused inputs to V_CC or GND-unlike LS TTL which tolerates floating inputs.

Does SN74AHCT138QPWRQ1 support hot insertion or live swapping?

No, SN74AHCT138QPWRQ1 does not support hot insertion. Its absolute maximum ratings specify V_CC must be established before applying input signals, and simultaneous application of inputs during power ramp-up may cause latch-up or excessive ICC. Automotive systems using this device require controlled power sequencing-V_CC stable prior to enabling address/control buses.

What is the recommended bypass capacitor for SN74AHCT138QPWRQ1?

Texas Instruments recommends a 0.1 µF ceramic capacitor placed as close as possible (≤3 mm) to the V_CC (Pin 16) and GND (Pin 8) pins of SN74AHCT138QPWRQ1. For improved broadband noise suppression, a parallel 1 µF X7R ceramic capacitor may be added nearby. The capacitor must be mounted directly on the top layer with short, wide traces and multiple vias to the internal ground plane to minimize inductance.