UCC5611 Datasheet, PDF (1/5 Pages) Texas Instruments – 18-Line 3-5 Volt SCSI Active Terminator, Reverse Disconnect

UCC5611
18-Line 3-5 Volt SCSI Active Terminator, Reverse Disconnect
FEATURES
• Complies with SCSI, SCSI-2, SCSI-3
and FAST-20 (Ultra) Standards
• 2.75V to 7V Operation
• 1.8pF Channel Capacitance during
Disconnect
• 1µA Supply Current in Disconnect
Mode
• 110 Ohm/2.5k Programmable
Termination
• Completely Meets SCSI Hot Plugging
• −650mA 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
BLOCK DIAGRAM
DESCRIPTION
The UCC5611 provides 18 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 segment.
The UCC5611 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 2.75V 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 1µA, which makes the IC attractive for battery powered systems.
The UCC5611 is designed with an ultra low channel capacitance of 1.8pF,
which eliminates effects on signal integrity from disconnected terminators
at interim points on the bus.
The UCC5611 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 high, and discon-
nected when low. 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 high, and disconnected when
driven low.
continued
3/97
Circuit Design Patented
UDG-94131-1