Analog Devices Inc./Maxim Integrated DS21T07E

Overview

DS21T07E from Dallas Semiconductor (now Maxim Integrated) is a 20-pin TSSOP SCSI active terminator IC designed for Fast and Ultra SCSI single-ended bus termination. It integrates nine laser-trimmed 110 Ω termination resistors (±2% tolerance), a low-dropout 2.85 V reference regulator, power-down isolation, and thermal shutdown. It enables hot-plug–compatible, high-noise-immunity termination in RAID controllers and SCSI disk drives.

For engineers reviewing the DS21T07E datasheet, DS21T07E pinout, DS21T07E application, or DS21T07E equivalent, key selection criteria include TERMPWR voltage range (4.0–5.5 V), quiescent current (5 mA), termination resistance accuracy (108–112 Ω), 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. Its nine switched 110 Ω resistors are laser-trimmed for ±2% tolerance and isolated via a dedicated PD pin with internal 50 kΩ pullup.

It operates across 0°C to 70°C, requires external 4.7 µF decoupling on VREF1/VREF2, and mandates dual TERMPWR connections (TERMPWR1/TERMPWR2) tied to the SCSI bus TERMPWR line. Thermal shutdown activates at 150°C and is guaranteed by design.

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 exposed heat-sink ground pad (HS-GND pins at positions 2, 8, 12, 18).

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS21T07S, the DS21T07E offers identical functionality in a space-constrained 20-pin TSSOP, enabling higher-density layouts; MAX3221E is unrelated and unsuitable - true alternatives are limited to Dallas/Maxim's own DS21T07 variants due to proprietary termination architecture and SCSI compliance certification.

Availability

DS21T07E is available at Aetrix Electronics and suitable for RAID controller design, SCSI disk drive backplane integration, and legacy server storage expansion requiring stable component supply and long-term obsolescence management.

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

Dallas Semiconductor, now part of Maxim Integrated (acquired 2001), specialized in precision analog, timing, and interface ICs for industrial, computing, and communications systems.

The DS21T07E belongs to the DS21Txx SCSI Terminator product line, engineered specifically to replace discrete resistor networks and external regulators in Fast/Ultra SCSI systems while meeting strict SCSI-1, Fast SCSI, and Ultra SCSI compliance requirements.

FAQ

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

The DS21T07E serves as a monolithic active SCSI terminator, integrating nine 110 Ω laser-trimmed resistors, a 2.85 V reference regulator, and power-down isolation into a single 20-pin TSSOP IC. It replaces discrete resistor networks and external regulators to provide compliant termination for Fast and Ultra SCSI buses, ensuring signal integrity, noise immunity, and hot-plug safety. The DS21T07E is essential for proper bus operation in RAID controllers and SCSI peripheral interfaces.

How does the DS21T07E handle actively negated SCSI signals?

The DS21T07E handles actively negated SCSI signals by sinking up to 200 mA total while maintaining VREF droop under 60 mV - a requirement for SCSI differential and single-ended active negation protocols. Its buffer amplifier architecture ensures stable 2.85 V bias even during high-current sink events, preserving logic thresholds and preventing false state transitions. This capability is explicitly verified in the DS21T07E datasheet's DC characteristics table and functional description.

What external components are required for proper DS21T07E operation?

The DS21T07E requires two external capacitors: a 4.7 µF tantalum capacitor between VREF1 and GND (with VREF2 tied directly to VREF1), and either a 2.2 µF or 4.7 µF capacitor on each TERMPWR pin (TERMPWR1 and TERMPWR2). A 0.1 µF high-frequency bypass capacitor may be added in parallel with the 4.7 µF VREF capacitor for fast-edge applications. No external regulator or resistor network is needed - all termination and regulation functions are internal to the DS21T07E.

Can the DS21T07E be used in place of the DS2107 or DS21S07?

Yes, the DS21T07E is explicitly backward compatible with the DS2107 and DS21S07 per its official datasheet features list. While pinout differs (DS21T07E uses 20-pin TSSOP vs. older packages), it maintains identical electrical behavior, termination resistance, reference voltage, and functional interface. Migration requires PCB layout update but delivers improved accuracy (±2% vs. ±5%), lower quiescent current, and integrated thermal protection - all confirmed in DS21T07E documentation.

What is the role of the HS-GND pins on the DS21T07E?

The HS-GND pins (positions 2, 8, 12, 18) on the DS21T07E connect internally to the exposed thermal pad of the 20-pin TSSOP package. They serve dual purposes: thermal conduction to the PCB ground plane for reliable operation under sustained load, and EMI suppression by providing low-inductance grounding for high-frequency termination currents. Dallas Semiconductor specifies that HS-GND should be either grounded or electrically isolated - floating connections are not permitted for thermal or electrical stability.