UCC5621

UCC5621 provides 27 lines of active termination for a SCSI (Small Computer Systems Interface) parallel bus. The SCSI standard recommends active termination at both ends of the cable.

The UCC5621 is ideal for high performance 5V SCSI systems. During disconnect the supply current is typically only 100mA, which makes the IC attractive for lower powered systems.

The UCC5621 features a split reverse disconnect allowing the user to control termination lines 10 to 27 with disconnect one, DISCNCT1, and control terminiation lines 1 to 9 with disconnect two, DISCNCT2.

The UCC5621 is designed with a low channel capacitance of 2.5pF, which eliminates effects on signal integrity from disconnected terminators at interim points on the bus.

The power amplifier output stage allows the UCC5621 to source full termination current and sink active negation current when all termination lines are actively negated.

The UCC5621, as with all Unitrode terminators, is completely hot pluggable and appears as high impedance at the teminating channels with VTRMPWR = 0V or open.

Internal circuit trimming is utilized, first to trim the 110W 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.