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9-Line 3-5 Volt SCSI Active Terminator, Reverse Disconnect (Rev. A)
Texas Instruments

The UCC5606 provides 9 lines of active termination for a small computer systems interface (SCSI) parallel bus. The SCSI standard recommends active termination at both ends of the cable segment. The UCC5606 is ideal for high performance 3.3-V SCSI systems. The key features contributing to such low operating voltage are the 0.1-V drop out regulator and the 2.7-V reference. During disconnect the supply current is typically only 0.5 ?A, which makes the device attractive for battery powered systems. The UCC5606 is designed with an ultra-low channel capacitance of 1.8 pF, which eliminates effects on signal integrity from disconnected terminators at interim points on the bus. The UCC5606 can be programmed for either a 110- or 2.5-k termination. The 110- termination is used for standard SCSI bus lengths and the 2.5-k termination is typically used in short bus applications. When driving the TTL compatible DISCNCT\ pin directly, the 110- termination is connected when the DISCNCT\ pin is driven high, and disconnected when low. When the DISCNCT\ pin is driven through an impedance between 80 k and 150 k, the 2.5-k 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 single-ended SCSI terminators, except that DISCNCT\ is now active low, allowing lower capacitance and lower voltage upgrades to existing systems. The UCC5606 is completely hot pluggable and appears as high impedance at the terminating channels with VTRMPWR = 0 V or open. Internal circuit trimming is utilized, first to trim the 110- termination impedance to a 7% tolerance, and then most importantly, to trim the output current to a 4% tolerance, as close to the maximum SCSI 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 16-pin narrow body SOIC, 16-pin N and 24-pin TSSOP.
Complies with SCSI, SCSI-2 and SPI-2 Standards 2.7-V to 5.25-V Operation 1.8-pF Channel Capacitance during Disconnect 0.5-?A Supply Current in Disconnect Mode 110-/2.5-k Programmable Termination Completely Meets SCSI Hot Plugging ?400-mA Sourcing Current for Termination +400-mA Sinking Current for Active Negation Drivers Trimmed Termination Current to 4% Trimmed Impedance to 7% Current Limit and Thermal Shutdown Protection

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