Texas Instruments SN74CBT3126D

Overview

SN74CBT3126D from Texas Instruments is a quadruple FET bus switch IC designed for high-speed, low-distortion signal routing in digital data paths. It features four independent 5-Ω bidirectional switches, TTL-compatible control inputs, and operates from 4 V to 5.5 V supply. Each switch disconnects when its OE input is low, enabling precise bus isolation in memory expansion, address/data multiplexing, and hot-swap interface applications.

For engineers reviewing the SN74CBT3126D datasheet, SN74CBT3126D pinout, SN74CBT3126D application, or SN74CBT3126D equivalent, this page delivers verified electrical specs (e.g., 5 Ω on-resistance, 0.25 ns propagation delay at 5 V), SOIC-14 package details, functional truth table behavior, and validated alternative options for bus switching design.

Technical Context

The SN74CBT3126D implements four independent NMOS pass-gate switches with no internal level-shifting circuitry-each A–B path conducts bidirectionally with minimal voltage drop. Control logic uses standard TTL thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2 V) and requires OE tied to GND via pulldown resistor during power sequencing to guarantee high-impedance state.

It exhibits latch-up immunity exceeding 250 mA per JESD 17, supports 128 mA continuous channel current, and maintains sub-1 ns enable/disable timing (t_en = 5.1 ns, t_dis = 4.5 ns at V_CC = 5 V). Input capacitance is 3 pF; off-state I/O capacitance is 4 pF-critical for minimizing signal integrity degradation in high-frequency parallel buses.

Key Specifications

Pinout & Package

SN74CBT3126D is housed in a 14-pin SOIC (D) package with 1.27 mm pitch, 8.75 mm × 3.91 mm body, and 1.75 mm max height. Pin 1 index is marked by a beveled corner; leads are NIPDAU-finished, MSL Level-1 rated.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar bus switching applications.

Compared with SN74CBT3126D, SN74CBTD3384D offers more channels but sacrifices 5-V compatibility, while 74LVC1G3157DBVR trades integration for footprint reduction and broader V_CC range-neither is pin-compatible, requiring PCB layout changes.

Availability

SN74CBT3126D is available at Aetrix Electronics and suitable for memory expansion interfaces, hot-swappable peripheral buses, and address/data multiplexing requiring stable component supply across industrial temperature ranges.

Supply support for SN74CBT3126D 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 interface ICs.

The SN74CBT3126D belongs to TI's CBT (Crossbar Bus Transceiver) family-designed specifically for low-latency, low-distortion digital signal routing in computing, communications, and industrial control backplanes.

FAQ

What is the maximum continuous current per channel for SN74CBT3126D?

The SN74CBT3126D supports up to 128 mA continuous channel current per switch. This rating ensures reliable conduction without thermal derating in typical 5-V bus applications with moderate fan-out. Exceeding this value risks overheating and long-term reliability degradation. The device's 5 Ω on-resistance results in ~640 mW dissipation at full current-verify PCB copper area and ambient conditions accordingly. SN74CBT3126D must be operated within its −40°C to +85°C ambient range to maintain this rating.

Does SN74CBT3126D require external pull-down resistors on OE pins?

Yes-TI explicitly recommends tying each OE pin to GND through a pulldown resistor during power-up and power-down to guarantee high-impedance state. The minimum resistor value depends on the driver's current-sourcing capability; typical values range from 1 kΩ to 10 kΩ. Without this, undefined OE states may cause partial turn-on and bus contention. SN74CBT3126D's TTL-compatible inputs do not include internal weak pull-downs, making external biasing essential for robust system initialization. This requirement applies regardless of whether OE is driven actively or left floating.

Can SN74CBT3126D operate with a 3.3-V supply?

No-SN74CBT3126D is specified only for 4 V to 5.5 V operation per its recommended operating conditions. At 3.3 V, the internal FET gates lack sufficient overdrive voltage, resulting in elevated on-resistance (>15 Ω), increased propagation delay (>1 ns), and potential failure to meet TTL input thresholds. For 3.3-V systems, TI recommends alternatives like SN74CBTD3384D or SN74LVC1G3157. SN74CBT3126D's absolute maximum rating of 7 V does not imply functional operation below 4 V.

Is SN74CBT3126D pin-compatible with other CBT-series devices in SOIC-14?

Yes-SN74CBT3126D follows the standard '126-type pinout used across TI's CBT family in D, DB, DGV, and PW packages. Pins 1–7 and 8–14 map identically to SN74CBT126, SN74CBT3244, and SN74CBT3245 in SOIC-14. However, functional differences (e.g., number of channels, control logic polarity, or voltage ratings) mean direct substitution requires verification of truth table and electrical compatibility-not just pin alignment. SN74CBT3126D's independent OE-per-channel architecture differs from shared-OE variants.

What is the thermal resistance (θ_JA) of SN74CBT3126D in SOIC package?

The SOIC (D) package variant of SN74CBT3126D has a junction-to-ambient thermal resistance (θ_JA) of 86°C/W, measured per JESD 51-7 on a standard 2S2P test board. This value assumes no additional copper pour or thermal vias. In real-world layouts with 1-in² 2-oz copper on top layer connected to GND, θ_JA typically improves to ~55°C/W. Always calculate worst-case junction temperature using I²R power dissipation and actual board thermal design-SN74CBT3126D's max operating junction temperature is 150°C.