The UCC5606 provides 9 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 segment.
The UCC5606 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 1μA, which makes the IC attractive for battery powered systems.
The UCC5606 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 UCC5606 can be programmed for either a 110 ohm or 2.5k ohm termination. 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 termination is connected when the DISCNCT pin is driven high, and disconnected when low. When the DISCNCT pin is driven through an impedance between 80k and 150k, the 2.5k ohm termination is connected when the DISCNCT pin is driven high, and disconnected when driven low.
The power amplifier output stage allows the UCC5606 to source full termination current and sink active negation current when all termination lines are actively negated.
The UCC5606 is pin for pin compatible with Unitrode’s other 9 line SCSI terminators, except that DISCNCT is now active low, allowing lower capacitance and lower voltage upgrades to existing systems. The UCC5606, as with all Unitrode terminators, is completely hot pluggable and appears as high impedance at the terminating channels with VTRMPWR = 0V or open.
TI UCC5606DP/81217