UCC5614
9-Line 3-5 Volt Low Capacitance SCSI Active Terminator
FEATURES
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Complies with SCSI, SCSI-2 and
SCSI-3 Standards
2.7V to 7V Operation
1.8pF Channel Capacitance during
Disconnect
0.5µA Supply Current in Disconnect
Mode
110 Ohm/2.5k Programmable
Termination
Completely Meets SCSI Hot Plugging
-400mA Sourcing Current for
Termination
+400mA Sinking Current for Active
Negation Drivers
Trimmed Termination Current to 4%
Trimmed Impedance to 7%
Current Limit and Thermal Shutdown
Protection
DESCRIPTION
The UCC5614 provides 9 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 UCC5614 is ideal for high performance 3.3V SCSI systems. The key
features contributing to such low operating voltage are the 0.1V drop out
regulator and the 2.7V reference. The reduced reference voltage was
necessary to accommodate the lower termination current dictated in the
SCSI-3 specification. During disconnect the supply current is typically
only 0.5µA, which makes the IC attractive for battery powered systems.
The UCC5614 is designed with an ultra low channel capacitance of
1.8pF, which eliminates effects on signal integrity from disconnected ter-
minators at interim points on the bus.
The UCC5614 can be programmed for either a 110 ohm or 2.5k ohm ter-
mination. The 110 ohm termination is used for standard SCSI bus lengths
and the 2.5k ohm termination is typically used in short bus applications.
When driving the TTL compatible DISCNCT pin directly, the 110 ohm ter-
mination is connected when the DISCNCT pin is driven low, and discon-
nected when driven high. When the DISCNCT pin is driven through an
impedance between 80k and 150k, the 2.5k ohm termination is con-
nected when the DISCNCT pin is driven low, and disconnected when
driven high.
continued
BLOCK DIAGRAM
UDG-94029-1
Circuit Design Patented
12/94
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