TI UC5603J

The UC5603 provides 9 lines of active termination for a SCSI (Small Computers Systems Interface) parallel bus. The SCSI standard recommends active termination at both ends of the cable segment. The UC5603 provides a disconnect feature which, when opened or driven high, will disconnect all terminating resistors, and disables the regulator; greatly reducing standby power. The output channels remain high impedance even without Termpwr applied. A low channel capacitance of 6 pF allows units at interim points of the bus to have little to no effect on the signal integrity. Functionally the UC5603 is similar to its predecessor, the UC5601 − 18 line Active Terminator. Several electrical enhancements were incorporated in the UC5603, such as a sink/source regulator output stage to accommodate all signal lines at 5 V, while the regulator remains at its nominal value, reduced channel capacitance to 6 pF typical, and as with the UC5601, custom power packages are utilized to allow normal operation at full power conditions (1.2 watts). Internal circuit trimming is utilized, first to trim the impedance to a 3% tolerance, and then most importantly, to trim the output current to a 3% tolerance, as close to the max SCSI spec as possible, which maximizes noise margin in fast SCSI operation. Other features include negative clamping on all signal lines to protect external circuitry from latch-up, thermal shutdown and current limit. This device is offered in low thermal resistance versions of the industry standard 16 pin narrow body SOIC.

• Complies with SCSI, SCSI−2 and SPI−2 Standards
• 6-pF Channel Capacitance during Disconnect
• 100 μA Supply Current in Disconnect Mode
• Meets SCSI Hot Plugging
• -400-mA Sourcing Current for Termination
• +400-mA Sinking Current for Active Negation Drivers
• Logic Command Disconnects all Termination Lines
• Trimmed Termination Current to 3%
• Trimmed Impedance to 3%
• Negative Clamping on all Signal Lines
• Current Limit and Thermal Shutdown Protection