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Current Limit and Thermal Shutdown
Protection
DESCRIPTION
UCC5620 provides 27 lines of active termination for a SCSI (Small Com-
puter Systems Interface) parallel bus. The SCSI standard recommends
active termination at both ends of the cable.
The UCC5620 is ideal for high performance 5V SCSI systems. During
disconnect the supply current is typically only 100碌A(chǔ), which makes the IC
attractive for lower powered systems.
The UCC5620 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 UCC5620 to source full ter-
mination current and sink active negation current when all termination
lines are actively negated.
The UCC5620, 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
SCSI operation.
Other features include thermal shutdown and current limit. This device is
offered in low thermal resistance versions of the industry standard 36-Pin
Wide Body QSOP (MWP) and 48-Pin LQFP (FQP).
Consult QSOP-36 or LQFP-48 packaging diagram for exact dimensions.
BLOCK DIAGRAM
Circuit Design Patented
UDG-96109
SLUS287A - OCTOBER 1999
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