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

Overview

DS2125/T&R from Maxim Integrated (formerly Dallas Semiconductor) is a multimode Ultra3 SCSI 15-line terminator supporting both low-voltage differential (LVD) and single-ended (SE) bus configurations. It auto-selects termination mode via DIFFSENSE voltage sensing, delivers 100–110Ω LVD differential impedance and 104.5–115.5Ω SE resistance with ±5% tolerance, and integrates thermal shutdown and hot-plug compatibility for RAID systems and SCSI HBAs.

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 automatic LVD/SE mode switching, 3pF power-down capacitance, dual VREF regulation (1.25V in LVD / 2.85V in SE), ISO-controlled bus isolation, and 48-pin LQFP package with HS_GND thermal pad.

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 (2.4–VTPWR+0.3V) bus conditions. Its control logic dynamically selects between 1.25V and 2.85V reference voltages and reconfigures precision resistor strings accordingly.

LVD termination uses two current sources with laser-trimmed 15-resistor strings yielding 105Ω differential and 150Ω common-mode impedance; SE mode employs a 2.85V regulator driving 15×110Ω resistors with active ground-switching on RP pins and -22.4mA termination current at 0.5V signal level.

Key Specifications

Pinout & Package

The DS2125/T&R is housed in a 48-pin LQFP (1.4mm height) with exposed thermal pad connected internally to HS_GND pins. The package supports automated tape-and-reel handling and RoHS compliance (lead-free marking "+" on top).

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS2125/T&R, DS2124 offers compact SE-only termination but no multimode flexibility, while MAX3202E provides LVD/SE support in smaller footprint yet demands additional external components for full Ultra3 compliance-making DS2125/T&R the only single-chip solution with integrated DIFFSENSE drive, thermal shutdown, and auto-mode switching.

Availability

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

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 (acquired Dallas Semiconductor in 2011) is a U.S.-based analog and mixed-signal semiconductor company specializing in high-reliability interface, power, and timing solutions.

The DS2125/T&R belongs to Maxim's legacy SCSI interface product line, designed specifically to simplify termination design in mixed-generation parallel SCSI storage systems while meeting Ultra3 specification requirements.

FAQ

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

The DS2125/T&R serves as an intelligent multimode terminator for Ultra3 SCSI buses, automatically selecting between low-voltage differential (LVD) and single-ended (SE) termination based on the DIFFSENS line voltage. It ensures proper impedance matching across 15 signal line pairs, maintains fail-safe bias levels, and supports hot-plug operations without manual configuration-critical for reliable data transfer in mixed-device storage environments where DS2125/T&R operates as the sole termination IC per bus segment.

How does the DS2125/T&R detect whether the SCSI bus is operating in LVD or SE mode?

The DS2125/T&R detects bus mode through its DIFFSENSE and DIFF_CAP pins using trinary voltage window detection: SE mode is identified when DIFFSENS voltage is below 0.6V, HVD when between 0.7V–1.9V, and LVD when above 2.4V. This is implemented via two internal comparators and a NAND gate within DS2125/T&R, enabling autonomous mode switching without external microcontroller intervention or configuration registers.

What are the required external components for proper operation of the DS2125/T&R?

The DS2125/T&R requires three mandatory external components: a 2.2µF capacitor between TPWR and ground for power rail decoupling, a 4.7µF capacitor between VREF and ground to stabilize reference voltage regulation, and a 0.1µF capacitor between DIFF_CAP and ground to filter noise on the DIFFSENS sense line. These capacitors must be placed as close as possible to their respective pins to ensure signal integrity and thermal stability in DS2125/T&R applications.

Does the DS2125/T&R support hot-plug functionality, and how is it implemented?

Yes, the DS2125/T&R supports SCSI bus hot-plug via integrated thermal shutdown circuitry (triggering at 150°C with 10°C hysteresis) and ISO-controlled isolation. When ISO is pulled high or thermal shutdown activates, DS2125/T&R disconnects its RxP/RxN pins from the bus while maintaining VREF output, preventing signal disruption during live insertion or removal of SCSI peripherals-ensuring continuous operation of DS2125/T&R in mission-critical storage systems.

What is the significance 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 of the 48-pin LQFP package and serve as dedicated heat-sink ground connections. They must be soldered to a large PCB copper pour tied to system ground to dissipate up to 2W of power and maintain junction temperature below 150°C. Proper HS_GND layout is essential for DS2125/T&R reliability in high-density server and RAID applications where thermal management directly impacts termination accuracy and longevity.