Analog Devices Inc./Maxim Integrated DS2119M

Overview

DS2119M from Maxim Integrated is an Ultra3 multimode SCSI terminator supporting both low-voltage differential (LVD) and single-ended (SE) bus configurations, with automatic mode detection via DIFFSENSE voltage sensing, 110Ω SE termination resistance, 105Ω differential impedance in LVD mode, and HVD isolation capability. It enables backward-compatible SCSI-3/4 bus termination in storage subsystems and server backplanes.

For engineers reviewing the DS2119M datasheet, DS2119M pinout, DS2119M application, or DS2119M equivalent, key selection criteria include its trinary DIFFSENS decoding (SE/LVD/HVD), thermal shutdown protection, 3pF output capacitance, autoselecting termination logic, and TSSOP-28 package compatibility with wide SCSI bus layouts.

Technical Context

The DS2119M implements trinary-mode SCSI bus detection using two comparators and a NAND gate to interpret DIFFSENS voltage levels: <0.6V (SE), 0.7–1.9V (LVD), or >2.4V (HVD). Its internal bandgap reference generates 1.25V for LVD and 2.85V for SE termination regulation.

In LVD mode, it delivers 105Ω differential and 150Ω common-mode termination using laser-trimmed resistor strings and dual current sources; in SE mode, it provides active 110Ω termination with 2.85V quiescent bias and 22mA sink capability per line, while ISO=1 isolates termination pins during HVD detection or thermal shutdown.

Key Specifications

Pinout & Package

DS2119M is housed in a 28-pin TSSOP (0.173") package with exposed heat-sink ground pad (pins 6 and 22). Pin functions are validated per Maxim DS2119M datasheet Rev 010406.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS2119M, DS2118M offers lower cost but no SE support or HVD isolation, making it unsuitable for mixed-mode environments; MAX3219E belongs to a different interface standard entirely and cannot substitute for SCSI termination.

Availability

DS2119M is available at Aetrix Electronics and suitable for SCSI server backplanes, industrial RAID controllers, hot-swap storage chassis, and embedded SCSI boot modules requiring stable component supply and long-term lifecycle support.

Supply support for DS2119M 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) designs precision analog, mixed-signal, and power management ICs for industrial, computing, and communications applications.

The DS2119M belongs to Maxim's SCSI interface product line, engineered specifically to resolve multimode termination challenges in evolving parallel SCSI architectures from SPI-2 through Ultra320.

FAQ

What is the primary function of the DS2119M in a SCSI system?

The DS2119M serves as an intelligent multimode terminator for Ultra3 SCSI buses, automatically selecting between low-voltage differential (LVD) and single-ended (SE) termination based on real-time DIFFSENSE voltage detection. It also provides HVD isolation and thermal shutdown protection. The DS2119M ensures signal integrity across mixed-device SCSI environments without manual configuration or external mode-selection circuitry.

How does the DS2119M detect and respond to HVD devices on the SCSI bus?

The DS2119M monitors the DIFFSENS line and identifies HVD presence when the voltage exceeds 2.4V. Upon detection, it asserts the ISO pin internally, isolating all RxP/RxN termination pins from the SCSI bus while maintaining VREF activity. This prevents potential damage or interference between incompatible HVD and LVD/SE circuitry. The DS2119M datasheet confirms this behavior is intrinsic to the DS2119M's design and requires no external intervention.

What decoupling capacitors are required for proper operation of the DS2119M?

The DS2119M requires three critical decoupling capacitors: a 4.7µF capacitor between VREF (Pin 1) and GND, a 2.2µF capacitor plus a 0.01µF ceramic capacitor between TPWR (Pins 27/28) and GND, and a 0.1µF capacitor on DIFF_CAP (Pin 17). These values are specified in the DS2119M datasheet Rev 010406 and are essential for stable reference regulation, TERMPWR filtering, and DIFFSENS noise immunity.

Can the DS2119M be used in a purely single-ended SCSI-2 system?

Yes, the DS2119M fully supports actively negated SE SCSI signals and provides precise 110Ω termination with 2.85V quiescent bias. It meets SCSI-2/3 SE specifications and maintains 22mA sink capability per line while limiting reference voltage shift to under 100mV. The DS2119M operates reliably in pure SE systems and is explicitly qualified for 0°C to +70°C ambient conditions per its ordering information.

What is the purpose of the MSTR/SLV pin on the DS2119M?

The MSTR/SLV pin (Pin 15) configures the DS2119M as either a master or slave terminator on the SCSI bus. When pulled high, it enables the internal DIFFSENSE driver (Pin 16) to actively drive the SCSI DIFFSENS line, allowing the DS2119M to assert bus mode. When low, the DS2119M operates as a non-controlling terminator that only senses DIFFSENS. This function is defined in the DS2119M pin description and functional block diagram.