Analog Devices Inc./Maxim Integrated DS21S07AE

Overview

DS21S07AE from Maxim Integrated is a 20-pin TSSOP SCSI active terminator IC designed for single-ended Fast and Ultra SCSI bus termination. It integrates a low-dropout 2.85V regulator, nine laser-trimmed 110Ω ±2% termination resistors, and power-down isolation logic. It operates from 4.0V–5.5V TERMPWR and delivers 24mA per line in active state, enabling robust termination in RAID controllers and hot-pluggable disk drives.

For engineers reviewing the DS21S07AE datasheet, DS21S07AE pinout, DS21S07AE application, or DS21S07AE equivalent, key selection considerations include its 20-pin TSSOP package, 2.85V regulated VREF output, 2.5mA quiescent current, thermal shutdown protection, and compatibility with actively negated SCSI signals.

Technical Context

The DS21S07AE implements a bandgap-referenced LDO regulator that generates a precise 2.85V (±2.5%) reference voltage to drive nine switched 110Ω termination resistors. Each resistor path supports ≥24mA sourcing and ≥200mA sinking to maintain signal integrity during active negation.

Its power-down circuitry disables all termination paths when PD is pulled low (≤0.8V), reducing current draw to ≤150µA and isolating the device electrically from the SCSI bus - critical for hot-plug operation without physical removal.

Key Specifications

Pinout & Package

DS21S07AE is housed in a 20-pin Thin Shrink Small Outline Package (TSSOP) with exposed thermal pad (HS-GND). The package measures 6.5mm × 4.4mm × 1.2mm (max) and supports reflow soldering per IPC/JEDEC J-STD-020.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS21S07AS, DS21S07AE offers superior thermal management via HS-GND pads and fits tighter layouts; compared with MAX3221E, it delivers purpose-built SCSI termination functionality with validated 110Ω matching and protocol-aware sink capability - neither alternative replicates its core active termination role.

Availability

DS21S07AE is available at Aetrix Electronics and suitable for RAID controller design, hot-pluggable storage modules, SCSI tape library interfaces, and legacy industrial control backplanes requiring stable component supply and long-term obsolescence mitigation.

Supply support for DS21S07AE 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 DS21S07AE belongs to Maxim's legacy SCSI interface product line, engineered specifically to replace passive and discrete active terminators in high-reliability storage subsystems operating under Fast and Ultra SCSI protocols.

FAQ

What is the primary function of the DS21S07AE in a SCSI system?

The DS21S07AE serves as an active SCSI terminator, providing regulated 2.85V bias and precise 110Ω line matching for nine signal lines. It replaces passive terminators to improve noise immunity, reduce TERMPWR voltage droop, and support Fast/Ultra SCSI data rates up to 40MB/s. Its integrated LDO and laser-trimmed resistors ensure compliance with SCSI-1, Fast SCSI, and Ultra SCSI standards.

How does the DS21S07AE handle hot-plug operations on a live SCSI bus?

The DS21S07AE supports hot-plug via its active-low PD (power-down) pin. When PD is pulled low (≤0.8V), the device disables all termination paths, reducing current draw to ≤150µA and electrically isolating itself from the SCSI bus. With an internal 50kΩ pullup resistor, DS21S07AE defaults to active state when PD is left open - enabling seamless insertion/removal without bus reset or manual intervention.

What external components are required for proper DS21S07AE operation?

The DS21S07AE requires two external capacitors: a 4.7µF tantalum capacitor between VREF1 and VREF2 (pins 9 and 19) for reference stability, and either a 2.2µF or 4.7µF capacitor on each TERMPWR pin (1 and 11) for supply decoupling. A 0.1µF high-frequency bypass capacitor may be added in parallel to the VREF capacitor for fast-rise-time driver applications, per Maxim's recommendation.

Is the DS21S07AE pin-compatible with earlier Maxim SCSI terminators?

Yes, the DS21S07AE is backward compatible with DS2107 and DS2107A in functional behavior and signal pin mapping (R1–R9, VREF1/VREF2, TERMPWR1/TERMPWR2, GND, PD). However, its 20-pin TSSOP package adds HS-GND pins (2,8,12,18) and an NC pin (17) not present in the older 16-pin SO packages - PCB layout must accommodate these differences even though core functionality remains identical.

What is the role of the HS-GND pins on the DS21S07AE?

The HS-GND pins (2, 8, 12, 18) connect internally to the exposed thermal pad of the DS21S07AE's TSSOP package. They must be either solidly grounded to dissipate heat during sustained 200mA sink operation or electrically isolated if thermal management is handled externally. Unlike signal GND (pin 10), HS-GND is dedicated solely to thermal conduction and should not carry signal return currents to avoid noise coupling.