18-Line SCSI Terminator (Reverse Disconnect)

UCC5617

FEATURES

•

Complies with SCSI, SCSI-2,

SCSI-3 and FAST-20 Standards

•

2pF Channel Capacitance

During Disconnect

•50

µA Supply Current in

Disconnect Mode

•

110

Ω Termination

•

SCSI Hot Plugging Compliant,

10nA Typical

•

+400mA Sinking Current for

Active Negation

•

−650mA Sourcing Current for

Termination

•

Trimmed Impedance to 5%

DESCRIPTION

The UCC5617 provides 18 lines of active termination for a SCSI (Small

Computers Systems Interface) parallel bus. The SCSI standard recommends

and Fast-20 (Ultra) requires active termination at both ends of the cable.

Pin for pin compatible with the UC5609, the UCC5617 is ideal for high perfor-

mance 5V SCSI systems, Termpwr 4.0V to 5.25V. During disconnect the sup-

ply current is only 50

µA typical, which makes the IC attractive for lower pow-

ered systems.

The UCC5617 is designed with a low channel capacitance of 2pF, which elim-

inates effects on signal integrity from disconnected terminators at interim

points on the bus.

The power amplifier output stage allows the UCC5617 to source full termina-

tion current and sink active negation current when all termination lines are

actively negated.

The UCC5617, as with all Unitrode terminators, is completely hot pluggable

and appears as high impedance at the ter minating channels with

TRMPWR=0V or open.

Internal circuit trimming is utilized, first to trim the 110

Ω impedance, and then

most importantly, to trim the output current as close to the maximum SCSI-3

specification as possible, which maximizes noise margin in fast SCSI opera-

tion.

Other features include thermal shutdown and current limit.

This device is offered in low thermal resistance versions of the industry stan-

dard 28 pin wide body SOIC, TSSOP and PLCC.

4/97

BLOCK DIAGRAM

UDG-96073

Circuit Design Patented