TI UCC5610QP

The UCC5610 provides 18 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. The UCC5610 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 2.75-V reference. During disconnect the supply current is typically only 0.5 μA, which makes the IC attractive for battery powered systems. The UCC5610 is designed with an ultralow-channel capacitance of 1.8 pF, which eliminates effects on signal integrity from disconnected terminators at interim points on the bus. The UCC5610 can be programmed for either a 110-Ω or 2.5-kΩ termination. The 110-Ω termination is used for standard SCSI bus lengths and the 2.5-kΩ termination is typically used in short bus applications. When driving the TTL compatible DISCNCT pin directly, the 110-Ω termination is connected when the DISCNCT pin is driven low, and disconnected when driven high. When the DISCNCT pin is driven through an impedance between 80 kΩ and 150 kΩ, the 2.5-kΩ termination is connected when the DISCNCT pin is driven low, and disconnected when driven high. The power amplifier output stage allows the UCC5610 to source full termination current and sink active negation current when all termination lines are actively negated. The UCC5610 is pin for pin compatible with Unitrode’s other 18-line SCSI terminators, allowing lower capacitance and lower voltage upgrades to existing systems. The UCC5610, as with all Unitrode terminators, 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-Ω termination impedance to a 7% tolerance, and then most importantly, to trim the output current to a 4% tolerance, which maximizes noise margin. Other features include thermal shutdown and current limit. This device is offered in low thermal resistance versions of the industry standard 28-pin wide body SOIC and 28-pin PLCC.

• Complies With SPI-2 and SPI-3 Standards
• 2.75-V to 7-V Operation
• 1.8-pF Channel Capacitance during Disconnect
• 0.5-μA Supply Current in Disconnect Mode
• 110-Ω/2.5-kΩ Programmable Termination
• Completely Meets SCSI Hot Plugging
• -650-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