Analog Devices Inc./Maxim Integrated DS21S07AS+T&R

Overview

DS21S07AS+T&R from Maxim Integrated is a 16-pin SOIC SCSI active terminator IC designed for single-ended Fast and Ultra SCSI bus termination. It integrates nine laser-trimmed 110Ω resistors (±2% tolerance), a low-dropout 2.85V regulator, and power-down isolation logic. It operates from 4.0–5.5V TERMPWR and delivers 24mA per line in active state, enabling robust termination in disk drive and RAID controller backplanes.

For engineers reviewing the DS21S07AS+T&R datasheet, DS21S07AS+T&R pinout, DS21S07AS+T&R application, or DS21S07AS+T&R equivalent, key selection criteria include its 110Ω ±2% termination accuracy, 2.5mA quiescent current, thermal shutdown at 150°C, hot-plug compatibility, and explicit support for actively negated SCSI signals - all critical for stable SCSI-1/Fast/Ultra system design.

Technical Context

The DS21S07AS+T&R implements a bandgap-referenced 2.85V regulator with ≤0.75V dropout and ±2% output regulation, feeding nine matched termination paths. Each R1–R9 pin sources 24mA when its associated SCSI signal is low and sinks up to 200mA during active negation while maintaining VREF deviation under 60mV.

Its power-down mode (PD pin active-low) disables all termination transistors using internal circuitry, reducing current to ≤150µA and isolating the device electrically from the bus without physical removal - essential for hot-swap-capable storage subsystems.

Key Specifications

Pinout & Package

DS21S07AS+T&R is housed in a 16-pin plastic SOIC (Small Outline Integrated Circuit) package, 300 mil width, with standard JEDEC MS-012AC footprint and gull-wing leads.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS21S07AE and DS2107A, the DS21S07AS+T&R offers the same SOIC footprint as DS2107A but adds full monolithic integration, power-down isolation, and thermal protection - making it the preferred choice for new designs requiring production-ready, drop-in-compatible SCSI termination.

Availability

DS21S07AS+T&R is available at Aetrix Electronics and suitable for RAID controller backplanes, disk drive internal termination, SCSI tape library interfaces, and legacy workstation expansion requiring stable component supply and long-term industrial availability.

Supply support for DS21S07AS+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 precision analog, mixed-signal, and power management ICs for industrial, communications, and computing applications.

The DS21S07AS+T&R belongs to Maxim's legacy SCSI interface product line, engineered specifically to replace discrete termination networks with a single-chip solution meeting ANSI SCSI-1/Fast/Ultra electrical specifications.

FAQ

What is the operating temperature range for the DS21S07AS+T&R?

The DS21S07AS+T&R is specified for operation from 0°C to +70°C ambient temperature. This commercial-grade range aligns with standard SCSI peripheral environments such as disk drives, RAID controllers, and tape libraries. The device includes on-die thermal shutdown that activates at 150°C to prevent damage during transient overload conditions. DS21S07AS+T&R maintains full electrical compliance across this entire range, including 110Ω ±2% termination resistance and 2.85V regulator accuracy.

How does the DS21S07AS+T&R achieve active termination without an external voltage reference?

The DS21S07AS+T&R integrates a precision bandgap reference and buffer amplifier to generate its own 2.85V termination voltage internally. This eliminates the need for an external 2.85V supply or voltage divider. The VREF1 and VREF2 pins must be tied together externally and decoupled with a 4.7µF capacitor to stabilize the regulator loop. DS21S07AS+T&R delivers this regulated voltage to all nine termination resistors, ensuring consistent high-level noise immunity and immunity to TERMPWR line sag - a key advantage over passive or semi-active solutions.

Can the DS21S07AS+T&R be used on a differential SCSI bus?

No, the DS21S07AS+T&R is designed exclusively for single-ended SCSI buses (SCSI-1, Fast SCSI, Ultra SCSI). It does not support differential signaling or LVD (Low-Voltage Differential) SCSI standards. Its 110Ω termination resistance, 2.85V regulation, and pinout are optimized for single-ended driver/receiver topologies. For differential SCSI, separate terminators such as the DS21S07D or DS21S087A are required. DS21S07AS+T&R must not be substituted in differential applications due to incompatible voltage levels and termination topology.

What is the purpose of the two TERMPWR pins (TERMPWR1 and TERMPWR2) on the DS21S07AS+T&R?

TERMPWR1 and TERMPWR2 provide redundant connections to the SCSI bus TERMPWR line, ensuring robust power delivery to the internal regulator and termination network. Both pins must be connected to the same TERMPWR source and individually decoupled (with ≥2.2µF capacitors) to minimize impedance and suppress high-frequency noise. This dual-input design meets SCSI specification requirements for active terminators and improves fault tolerance - if one connection experiences high impedance, the other maintains regulator operation. DS21S07AS+T&R relies on both pins for full compliance and stable 2.85V output.

Is the DS21S07AS+T&R pin-compatible with the older DS2107A terminator?

Yes, the DS21S07AS+T&R is pin-compatible with the DS2107A in the 16-pin SOIC package, sharing identical pin numbering and signal assignments for TERMPWR1, R1–R9, VREF1, GND, TERMPWR2, VREF2, and PD. However, DS21S07AS+T&R adds internal regulation and power-down logic absent in DS2107A, so external 2.85V supplies and discrete resistors are no longer needed. This makes DS21S07AS+T&R a direct functional upgrade - no PCB redesign required, but schematic updates eliminate supporting components.