Texas Instruments SN74CBTLV3857DWE4

Overview

SN74CBTLV3857DWE4 from Texas Instruments is a 10-bit FET bus switch optimized for 3.3-V SSTL_2 DDR SDRAM data paths, featuring 7–13 Ω on-state resistance, rail-to-rail switching, and integrated 10-kΩ B-port pulldowns. It replaces series termination resistors in DDR memory interfaces and supports partial-power-down via Ioff.

For engineers reviewing the SN74CBTLV3857DWE4 datasheet, SN74CBTLV3857DWE4 pinout, SN74CBTLV3857DWE4 application, or SN74CBTLV3857DWE4 equivalent, key selection criteria include OE input compatibility with SSTL_2 logic levels (VREF ±350 mV), 0.25-ns propagation delay, and SOIC-24 package thermal performance (θJA = 46°C/W).

Technical Context

This device implements a flow-through architecture with 10 independent bidirectional FET switches, each controlled by a single active-low OE signal referenced to VREF (0.38 × VCC). Its internal pulldown network on the B port and 50-kΩ pullup on OE eliminate external biasing components in DDR-SDRAM stub-bus topologies.

The switch operates across 3.0–3.6 V VCC with guaranteed rail-to-rail signal handling and Ioff protection that blocks backflow current during partial power-down-critical for mixed-voltage DDR systems where memory controllers and SDRAM operate at different supply domains.

Key Specifications

Pinout & Package

SN74CBTLV3857DWE4 is housed in a 24-pin SOIC (DW) package with 0.75-mm lead pitch and standard JEDEC MS-013 outline. The pinout follows a flow-through layout with A1–A10 and B1–B10 aligned on opposite sides, OE and VREF centrally located, and dedicated VCC/GND pins for low-noise switching.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74CBTLV3857DWE4, SN74CBT3244DW lacks VREF-referenced OE and Ioff, limiting DDR use; SN74LVC1G3157DBVR offers lower ron but cannot replace a 10-bit parallel switch without 10x duplication and external biasing-making SN74CBTLV3857DWE4 uniquely suited for compact, standards-compliant DDR interconnects.

Availability

SN74CBTLV3857DWE4 is available at Aetrix Electronics and suitable for DDR SDRAM memory interfaces, FPGA-to-SDRAM bridging, and embedded memory buffering requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for SN74CBTLV3857DWE4 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-speed interface and memory subsystem design.

The SN74CBTLV3857DWE4 belongs to TI's CBTLV (CrossBar TTL) logic family, engineered specifically for low-skew, low-resistance signal routing in DDR memory systems and high-speed digital interconnects.

FAQ

What is the function of the VREF pin on the SN74CBTLV3857DWE4?

The VREF pin on the SN74CBTLV3857DWE4 sets the reference voltage (0.38 × VCC) for the OE input threshold, ensuring precise SSTL_2 compatibility. It allows the OE signal to be recognized correctly at AC high/low levels of VREF ±350 mV, matching DDR memory controller output specifications. This eliminates the need for external level-shifting circuitry when interfacing with SSTL_2 drivers. The SN74CBTLV3857DWE4 relies on this pin to maintain timing accuracy and noise immunity in high-speed DDR data paths.

Does the SN74CBTLV3857DWE4 support partial-power-down operation?

Yes, the SN74CBTLV3857DWE4 supports partial-power-down operation via its Ioff feature. When VCC is powered down while other system rails remain active, the Ioff circuitry blocks reverse current flow through the switch, preventing damage and maintaining isolation. This capability is critical in DDR systems where memory controllers and SDRAM may operate on independent power domains. The SN74CBTLV3857DWE4 meets JESD 78 Class II latch-up requirements (>100 mA), confirming robustness during transitional power states.

What is the typical on-state resistance (ron) of the SN74CBTLV3857DWE4 and why does it matter?

The typical on-state resistance (ron) of the SN74CBTLV3857DWE4 is 7–13 Ω, measured at VCC = 3 V and VI = 1.25 V with 24 mA test current. This low, tightly controlled resistance allows the device to replace discrete 25–33 Ω series termination resistors in SSTL_2 DDR data paths, reducing component count and PCB area while maintaining impedance matching. The SN74CBTLV3857DWE4's ron specification directly enables clean signal edges and minimized reflections at 200 Mbit/s DDR data rates.

Can the SN74CBTLV3857DWE4 be used with DDR2 or DDR3 memory standards?

No, the SN74CBTLV3857DWE4 is specifically designed for 200 Mbit/s DDR SDRAM (original DDR) applications and is not characterized for DDR2 or DDR3 signaling. Its timing parameters-including 0.25 ns propagation delay and OE response times-are optimized for DDR-SDRAM's 2.5 V/2.6 V VDDQ and SSTL_2 I/O standards. DDR2/DDR3 require stricter jitter, slew rate, and voltage tolerance specs not validated for the SN74CBTLV3857DWE4. For newer DDR generations, TI recommends purpose-built switches like the SN74AVC series. The SN74CBTLV3857DWE4 remains appropriate only for legacy DDR-SDRAM designs.

How are the internal pulldown resistors configured on the SN74CBTLV3857DWE4?

The SN74CBTLV3857DWE4 integrates 10-kΩ pulldown resistors to ground on all B-port pins (B1–B10), ensuring defined logic-low states when the switch is disabled or SDRAM is unconnected. These resistors eliminate the need for external biasing components in DDR stub-bus configurations, simplifying layout and improving reliability. They are always active-regardless of OE state-and do not interfere with signal transmission when the switch is enabled. This design choice directly supports the SN74CBTLV3857DWE4's role in DDR memory interfaces where bus contention and floating nodes must be avoided.