鈥?/div>
Current Limit and Thermal Shutdown
Protection
DESCRIPTION
The UCC5622 provides 27 lines of active termination for a SCSI (Small
Computer Systems Interface) parallel bus. The SCSI standard recom-
mends active termination at both ends of the cable.
The UCC5622 is ideal for high performance 5V SCSI systems. During dis-
connect the supply current is typically only 100碌A(chǔ), which makes the IC at-
tractive for lower powered systems.
The UCC5622 features a split disconnect allowing the user to control termi-
nation lines 10 to 27 with disconnect one, DISCNCT1, and control terminia-
tion lines 1 to 9 with disconnect two, DISCNCT2.
The UCC5622 is designed with a low channel capacitance of 2.5pF, which
eliminates effects on signal integrity from disconnected terminators at in-
terim points on the bus.
The power amplifier output stage allows the UCC5622 to source full termi-
nation current and sink active negation current when all termination lines
are actively negated.
The UCC5622, as with all Unitrode terminators, is completely hot plugga-
ble and appears as high impedance at the teminating channels with
V
TRMPWR
= 0V or open.
Internal circuit trimming is utilized, first to trim the 110鈩?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-
20 SCSI operation.
(continued)
BLOCK DIAGRAM
Circuit Design Patented
UDG-96113
10/98
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