DESCRIPTION

The UCC5622 provides 27 lines of active termination for a SCSI (Small

Computer Systems Interface) parallel bus. The SCSI standard recom-

mends active termination at both ends of the cable.

The UCC5622 is ideal for high performance 5V SCSI systems. During dis-

connect the supply current is typically only 100

µA, which makes the IC at-

tractive for lower powered systems.

The UCC5622 features a split disconnect allowing the user to control termi-

nation lines 10 to 27 with disconnect one, DISCNCT1, and control terminia-

tion lines 1 to 9 with disconnect two, DISCNCT2.

The UCC5622 is designed with a low channel capacitance of 2.5pF, which

eliminates effects on signal integrity from disconnected terminators at in-

terim points on the bus.

The power amplifier output stage allows the UCC5622 to source full termi-

nation current and sink active negation current when all termination lines

are actively negated.

The UCC5622, as with all Unitrode terminators, is completely hot plugga-

ble and appears as high impedance at the teminating channels with

Internal circuit trimming is utilized, first to trim the 110

Ω impedance, and

then most importantly, to trim the output current as close to the maximum

SCSI-3 specification as possible, which maximizes noise margin in FAST-

20 SCSI operation.

(continued)

UCC5622

27 - Line SCSI Terminator With Split Disconnect

BLOCK DIAGRAM

FEATURES

• Complies with SCSI, SCSI-2, SCSI-3,

SPI and FAST-20 (Ultra) Standards

• 2.5pF Channel Capacitance During

Disconnect

• 100µA Supply Current in Disconnect

Mode

• 4V To 7V Operation

• 110Ω Termination

• Completely Meets SCSI Hot Plugging

• –900mA Sourcing Current for

Termination

• +500mA Sinking Current for Active

Negation

• Logic Command Disconnects all

Termination Lines

• Split Disconnect Controls Lines 1 to 9

and 10 to 27 Separately

• Trimmed Impedance to 5%

• Current Limit and Thermal Shutdown

Protection

10/98

UDG-96113

Circuit Design Patented