UCC5617
18-Line SCSI Terminator (Reverse Disconnect)
FEATURES
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Complies with SCSI, SCSI-2,
SCSI-3 and FAST-20 Standards
2pF Channel Capacitance
During Disconnect
50µA Supply Current in
Disconnect Mode
110Ω 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 50µA 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 110Ω 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.
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BLOCK DIAGRAM
UDG-96073
Circuit Design Patented
4/97
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