DS21T05 Dallas Semiconducotr, DS21T05 Datasheet

DS21T05

Manufacturer Part Number

DS21T05

Description

SCSI Terminator

Manufacturer

Dallas Semiconducotr

Datasheet

1.DS21T05.pdf (7 pages)

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DS21T05

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FEATURES

DESCRIPTION

Fast SCSI and Ultra SCSI require the use of active terminations at both ends of every cable segment in a

SCSI system with single-ended drivers and receivers. The DS21T05 SCSI Terminator, which is fully

compliant with these standards, enables the designer to gain the benefits of active termination: greater

immunity to voltage drops on the TERMPWR (TERMination PoWeR) line, enhanced high-level noise

immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS21T05,

which integrates a regulator and nine precise-switched, 110-ohm termination resistors into a monolithic

IC, is a functionally compatible version of the DS21T07. With relaxed output current and termination

tolerances, the DS21T05 is intended for high volume applications which require active termination but

not the high performance of the DS21T07.

FUNCTIONAL DESCRIPTION

The DS21T05 consists of a bandgap reference, buffer amplifier, and nine termination resistors (Figure 1).

The bandgap reference circuit produces a precise 2.55V level which is fed to a buffer amplifier. The

buffer produces a 2.85V level and is capable of sourcing at least 24 mA into each of the termination

resistors when the signal line is low (active). When the driver for a given signal line turns off, the

terminator will pull the signal line to 2.85V (quiescent state). To handle actively negated SCSI signals,

www.dalsemi.com

Fully compliant with SCSI-1, Fast SCSI and

Ultra SCSI

Functionally compatible to the DS21T07,

targeted for high volume applications

Provides active termination for nine signal

lines

Laser-trimmed 110-ohm termination resistors

have 5% tolerance

Low dropout voltage

Power-down mode isolates termination

resistors from the bus

SCSI bus hot-plug compatible

Fully supports actively negated SCSI signals

Onboard thermal shutdown circuitry

16-pin plastic narrow SOIC

1 of 7

TERMPWR1

PIN ASSIGNMENT

VREF1

GND

VREF1

DS21T05S 16-Pin SOIC (300-mil)

GND

DS21T05Z 16-Pin SOIC (150-mil)

SCSI Terminator

VREF2

TERMPWR2

VREF2

TERMPWR2

DS21T05

112099

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