Texas Instruments SN74LV138ANS

Overview

SN74LV138ANS from Texas Instruments is a 3-line to 8-line decoder/demultiplexer IC operating from 2 V to 5.5 V, with 9.5 ns maximum propagation delay at 5 V, active-low G0/G1 and active-high G2 enable inputs, and Ioff support for partial-power-down mode. It selects one of eight active-low outputs (Y0–Y7) based on binary address inputs A0–A2 and enables memory decoding in microcontroller peripheral expansion.

For engineers reviewing the SN74LV138ANS datasheet, SN74LV138ANS pinout, SN74LV138ANS application, or SN74LV138ANS equivalent, key selection criteria include VCC range compatibility (2–5.5 V), output drive capability (±12 mA at 5 V), ground bounce (<0.8 V at 3.3 V), VOH undershoot (>2.3 V), and mixed-mode voltage interface support across all ports.

Technical Context

The SN74LV138ANS implements standard CMOS logic with balanced push-pull outputs and dedicated enable architecture: two active-low (G0, G1) and one active-high (G2) strobes allow hierarchical expansion without external inverters. Its functional mode table defines eight decoded outputs (Y0–Y7) as active-low, with all outputs high-impedance when any enable condition fails.

It features Ioff circuitry that disables outputs and limits leakage to 5 μA when VCC = 0 V, enabling safe back-drive prevention in partial-power-down systems. Input transition rate requirements (20 ns/V at 5 V) and input capacitance (2.1 pF at 3.3 V) are specified to ensure stable switching and minimize dynamic power consumption.

Key Specifications

Pinout & Package

SN74LV138ANS uses the SOIC-16 (D) package: 9.90 mm × 3.91 mm body, 1.27 mm lead pitch, gull-wing leads. Pin 1 is top-left corner (A0), pin 16 is top-right (VCC), with GND at pin 8 and thermal pad absent.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HC138PW and SN74LVC138APW, SN74LV138ANS uniquely bridges 2–5.5 V operation with Ioff protection and 9.5 ns speed-making it the only option supporting mixed-voltage industrial control, hot-plug expansion, and legacy 5 V peripheral interfacing without redesign.

Availability

SN74LV138ANS is available at Aetrix Electronics and suitable for memory address decoding, LED matrix control, 7-segment display multiplexing, and peripheral I/O expansion requiring stable component supply across automotive, industrial, and embedded computing programs.

Supply support for SN74LV138ANS 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 over 50 years of innovation in high-reliability logic families.

The SN74LV138ANS belongs to TI's LV (Low-Voltage) logic series, engineered for robust performance across wide supply ranges (2–5.5 V) in industrial automation, test equipment, and mixed-signal system interfaces.

FAQ

What is the maximum capacitive load the SN74LV138ANS can drive while maintaining datasheet timing specifications?

The SN74LV138ANS is characterized for loads up to 50 pF across all VCC conditions (2.5 V, 3.3 V, 5 V). At 50 pF and 5 V, propagation delay remains ≤11.5 ns. Driving larger loads increases tpd nonlinearly and may cause overshoot/undershoot beyond VOLP/VOHV limits. For reliable operation, keep total trace + input capacitance ≤50 pF; if exceeded, add series termination or buffer stages.

Does the SN74LV138ANS support partial-power-down mode, and how does it behave when VCC = 0 V?

Yes, the SN74LV138ANS supports partial-power-down via its Ioff circuitry. When VCC = 0 V, all outputs enter high-impedance state and leakage current per pin is ≤5 μA - preventing back-current flow from live inputs or outputs into the unpowered device. This behavior is confirmed in Section 6.5 Electrical Characteristics and Section 8.3.3 of the SN74LV138ANS datasheet.

Can the SN74LV138ANS interface directly between a 5 V microcontroller and a 3.3 V FPGA without level shifters?

Yes, the SN74LV138ANS supports mixed-mode voltage operation: its inputs tolerate 0–5.5 V regardless of VCC setting. If powered at 3.3 V, it accepts 5 V logic highs from the MCU and outputs 3.3 V-compatible levels to the FPGA. No external level shifters are needed, provided output loading stays within ±12 mA and capacitive load ≤50 pF.

What is the purpose of the three enable inputs (G2, G0, G1) on the SN74LV138ANS, and how do they differ?

G2 is active-high; G0 and G1 are active-low. All three must be satisfied simultaneously for decoding: G2 = high AND G0 = low AND G1 = low. This asymmetric enable structure reduces external logic - e.g., a 24-line decoder needs zero inverters, while a 32-line version requires only one. The SN74LV138ANS datasheet Figure 8-1 and Function Table (Section 8.4) confirm this configuration.

Is the SN74LV138ANS pin-compatible with the older SN74LS138, and what design changes are required for replacement?

No, the SN74LV138ANS is not pin-compatible with SN74LS138. While both are 16-pin SOIC decoders, LS138 uses different enable polarity (all three enables active-low) and lacks Ioff. Replacing LS138 with SN74LV138ANS requires inverting G2 logic and verifying VCC compatibility (LS138 requires ≥4.75 V; SN74LV138ANS operates down to 2 V). The SN74LV138ANS pinout matches other LV/LVC138 variants, not LS-family.