Analog Devices Inc./Maxim Integrated DS21T07E+

Overview

DS21T07E+ from Analog Devices (formerly Dallas Semiconductor) is a 20-pin TSSOP SCSI active terminator IC designed for Fast and Ultra SCSI bus termination. It integrates nine laser-trimmed 110 Ω ±2% termination resistors, a low-dropout 2.85 V reference regulator, power-down control (PD), and thermal shutdown. It supports hot-plug operation and isolates the bus in power-down mode, used in RAID controllers and SCSI backplanes.

For engineers reviewing the DS21T07E+ datasheet, DS21T07E+ pinout, DS21T07E+ application, or DS21T07E+ equivalent, key selection criteria include termination resistance tolerance (±2%), TERMPWR voltage range (4.0–5.5 V), quiescent current (5 mA typ), power-down leakage (<150 µA), and compatibility with actively negated SCSI signals requiring ≥200 mA sink capability.

Technical Context

The DS21T07E+ implements a bandgap-based 2.55 V reference buffered to 2.85 V output, capable of sourcing ≥24 mA per termination line and sinking ≥200 mA total for actively negated SCSI signaling. Its internal power-down circuitry disables all termination transistors when PD is pulled low, isolating the device electrically without physical removal.

It requires external 4.7 µF decoupling on VREF1/VREF2 (tied together), dual TERMPWR connections (TERMPWR1/TERMPWR2), and supports 8-bit (two devices) or 16-bit (three devices) SCSI bus configurations. Thermal shutdown activates at 150°C, and HS-GND pins are internally connected to the exposed thermal pad.

Key Specifications

Pinout & Package

DS21T07E+ is housed in a 20-pin Thin Shrink Small Outline Package (TSSOP) with 0.65 mm pitch, 6.4–6.9 mm body width, and an exposed thermal pad (HS-GND) for enhanced heat dissipation. Pin 17 is NC; pins 2, 8, 12, and 18 are HS-GND (internally tied to mounting pad).

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS21T07S+, the DS21T07E+ offers superior thermal management and space efficiency in modern high-density SCSI designs; compared with MAX489EPA+, it delivers purpose-built SCSI active termination with guaranteed 110 Ω ±2% matching and hot-plug isolation - features absent in generic transceivers.

Availability

DS21T07E+ is available at Aetrix Electronics and suitable for RAID controller backplanes, SCSI disk drive modules, and industrial SCSI I/O expansion chassis requiring stable component supply, long-lifecycle availability, and guaranteed traceable sourcing.

Supply support for DS21T07E+ 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

Analog Devices acquired Maxim Integrated, which previously acquired Dallas Semiconductor - a pioneer in precision analog and interface ICs since 1984.

The DS21T07E+ belongs to Dallas Semiconductor's SCSI Interface family, engineered specifically for robust, standards-compliant active termination in mission-critical storage subsystems.

FAQ

What is the primary function of the DS21T07E+ in a SCSI system?

The DS21T07E+ serves as an active SCSI terminator, providing nine precisely matched 110 Ω termination resistors referenced to a stable 2.85 V regulator output. It replaces passive termination networks to improve noise immunity, eliminate TERMPWR voltage drop sensitivity, and support hot-plug operation - all critical for Fast and Ultra SCSI compliance. The DS21T07E+ is explicitly designed for single-ended SCSI bus ends in storage and industrial systems.

How does the power-down (PD) pin operate on the DS21T07E+?

The PD pin on the DS21T07E+ has an internal 50 kΩ pullup resistor. Leaving PD open circuited activates the device; pulling PD low places the DS21T07E+ into power-down mode, turning off all termination transistors and isolating the IC electrically from the SCSI signal lines. This feature enables dynamic bus reconfiguration without physical removal - a key requirement for hot-plug SCSI peripherals. The DS21T07E+ draws less than 150 µA in this state.

What external components are required for proper DS21T07E+ operation?

The DS21T07E+ requires two external capacitors: a 4.7 µF tantalum capacitor between VREF1 and VREF2 (which must be tied together externally) and decoupling capacitors (2.2–4.7 µF) on TERMPWR1 and TERMPWR2. A 0.1 µF high-frequency bypass capacitor is recommended in parallel with the 4.7 µF VREF capacitor for fast-edge SCSI drivers. No additional resistors or regulators are needed - the DS21T07E+ integrates all core termination and regulation functions.

Can the DS21T07E+ be used in Wide SCSI (16-bit) systems?

Yes - the DS21T07E+ is designed for use in Wide SCSI systems. Since it terminates nine signal lines per device, three DS21T07E+ units are required at each end of a 16-bit Wide SCSI bus to terminate all 27 active signals (e.g., DATA[0:7], DATA[8:15], and control lines). All DS21T07E+ devices share common TERMPWR and VREF connections, and their PD pins may be controlled independently or in parallel depending on system architecture. Each DS21T07E+ operates identically in this configuration.

Does the DS21T07E+ support actively negated SCSI signals like BSY# or SEL#?

Yes - the DS21T07E+ is explicitly designed to support actively negated SCSI signals. Its regulator buffer can sink at least 200 mA total while maintaining VREF droop under 60 mV, ensuring reliable low-state assertion on signals such as BSY#, SEL#, ACK#, and REQ#. This capability is confirmed in the Functional Description and DC Characteristics tables of the official datasheet, distinguishing the DS21T07E+ from basic passive or non-sinking active terminators.