TI UC5612PWP

The UC5612 provides 9 active termination lines for the Small Computer System Interface (SCSI) parallel bus. The SCSI standard recommends active termination at both ends of a cable segment. The only functional difference between the UC5603 and UC5612 is the absence of a negative clamp on the UC5612's output lines. In terms of parameters, the UC5612 has impedance and current tolerances of 5%, while the UC5603 has tolerances of 3%. A custom power package is used, allowing normal operation at 2W full power.

The UC5612 provides a disconnect function which, when activated or driven high, disconnects all termination resistors, disables the regulator, and significantly reduces standby power consumption. The output channels remain in a high-impedance state even when TERMPWR is not applied. The low channel capacitance of 5pF ensures minimal to no impact on signal integrity at midpoints along the bus.

Internal circuit trimming is used first to trim impedance to a 5% tolerance, and more importantly, to trim output current to a 5% tolerance, as close as possible to the maximum SCSI specification. This maximizes noise margin in Fast SCSI operation. Additional features include thermal shutdown and current limiting.

The device is available in an industry-standard 16-pin narrow-body SOIC, 16-pin DIL, and a low thermal resistance version in 24-pin TSSOP.

• Compliant with SCSI, SCSI-2, and SPI-2 standards
• Disconnected channel capacitance: 5pF
• Meets SCSI hot-plug requirements
• Termination current source: -400mA
• Active negation sink current: +100mA
• 1V dropout regulator
• Logic high command disconnects all termination lines
• Disconnect mode supply current: 100μA
• Termination current regulated to 5%
• Impedance regulated to 5%
• Low thermal resistance surface mount package