Analog Devices Inc./Maxim Integrated DS2125+T&R

Overview

DS2125+T&R from Maxim Integrated is a multimode Ultra3 SCSI terminator supporting both low-voltage differential (LVD) and single-ended (SE) bus configurations. It provides auto-sensing termination for 15 signal line pairs, integrates dual reference regulators (1.25V for LVD, 2.85V for SE), and features thermal shutdown, ISO isolation control, and DIFFSENSE-driven mode selection - deployed in RAID systems, SCSI HBAs, and enterprise storage enclosures.

For engineers reviewing the DS2125+T&R datasheet, DS2125+T&R pinout, DS2125+T&R application, or DS2125+T&R equivalent, key selection considerations include its 48-pin LQFP package, automatic LVD/SE mode switching via DIFFSENSE voltage detection, 110Ω ±5% SE termination resistance, 100–110Ω differential-mode LVD impedance, and hot-plug compatibility with SCSI buses.

Technical Context

The DS2125+T&R implements trinary DIFFSENS decoding using two comparators and a NAND gate to distinguish SE (<0.6V), HVD (0.7–1.9V), and LVD (>2.15V) bus conditions. Its internal control logic dynamically selects between 1.25V and 2.85V VREF references and reconfigures precision resistor strings accordingly.

LVD termination uses laser-trimmed 15× resistor strings with current sources yielding 105Ω differential and 150Ω common-mode impedance; SE mode employs a 2.85V regulator and 15× 110Ω resistors, with Rp pins actively switched to ground. Thermal shutdown activates at 150°C with 10°C hysteresis.

Key Specifications

Pinout & Package

DS2125+T&R is housed in a 48-pin LQFP (7mm × 7mm, 0.5mm pitch) with exposed thermal pad connected internally to HS_GND pins. The package supports surface-mount assembly and requires local decoupling per TPWR (2.2µF + 0.01µF) and VREF (4.7µF + 0.1µF).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar SCSI termination applications.

Compared with DS2125+T&R, DS2124+T&R offers lower cost and simpler design for SE-only environments but sacrifices LVD compatibility, auto-sensing, and thermal protection; MAX3221ESE+ serves an entirely different interface standard and cannot substitute for SCSI termination.

Availability

DS2125+T&R is available at Aetrix Electronics and suitable for RAID systems, SCSI host bus adapter cards, and enterprise servers requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for DS2125+T&R 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

Maxim Integrated (now part of Analog Devices) is a U.S.-based semiconductor company specializing in high-performance analog, mixed-signal, and power management ICs for industrial, communications, and computing applications.

The DS2125+T&R belongs to Maxim's legacy Dallas Semiconductor SCSI interface product line, engineered specifically for multimode physical-layer termination in Ultra3-compliant storage subsystems.

FAQ

What is the primary function of the DS2125+T&R in a SCSI system?

The DS2125+T&R serves as an auto-sensing multimode terminator for Ultra3 SCSI buses, providing precise 15-line LVD or SE termination based on real-time DIFFSENSE voltage detection. It integrates dual reference regulators, thermal shutdown, and ISO-controlled isolation - enabling plug-and-play interoperability between legacy SE and modern LVD SCSI devices without manual configuration. Its role is strictly physical-layer signal integrity maintenance.

How does the DS2125+T&R determine whether to use LVD or SE termination mode?

The DS2125+T&R determines termination mode by monitoring the SCSI bus DIFFSENS line through its DIFF_CAP and DIFFSENSE circuitry. Using two internal comparators and a NAND gate, it detects trinary voltage levels: <0.6V (SE), 0.7–1.9V (HVD), or >2.15V (LVD). Based on this, the control logic selects either the 1.25V (LVD) or 2.85V (SE) VREF and configures the corresponding resistor network - all autonomously, with no external intervention required for the DS2125+T&R.

What are the critical decoupling requirements for the DS2125+T&R's TPWR and VREF pins?

The DS2125+T&R requires a 2.2µF bulk capacitor plus a 0.01µF high-frequency ceramic capacitor between TPWR and ground, placed adjacent to the device. For VREF, a minimum 4.7µF capacitor (plus optional 0.1µF ceramic) must connect to ground to maintain regulation stability under fast edge-rate conditions. These values are specified in the DS2125+T&R datasheet and are mandatory for proper LVD/SE reference accuracy and thermal performance.

Does the DS2125+T&R support hot-plug operation on live SCSI buses?

Yes, the DS2125+T&R supports SCSI bus hot-plug operation due to its ISO pin isolation control, 3pF low pin capacitance, and active DIFFSENSE driving capability. When inserted into a live bus, the DS2125+T&R senses DIFFSENS voltage within 1.25ms, configures termination mode, and avoids signal disruption. Thermal shutdown and fail-safe biasing further ensure robustness during transient insertion events - all confirmed in DS2125+T&R characterization data.

What is the purpose of the HS_GND pins on the DS2125+T&R package?

The HS_GND pins (Pins 4–9 and 28–33) are internally connected to the exposed thermal pad on the DS2125+T&R's 48-pin LQFP package. They serve as dedicated heat-sink ground terminals and must be soldered to a large PCB copper pour tied to system ground. This thermal path dissipates up to 2W of power at +70°C ambient and is essential for maintaining junction temperature below 150°C - a requirement explicitly stated in the DS2125+T&R absolute maximum ratings table.