The UCC5614 provides 9 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 UCC5614 is ideal for high performance 3.3V SCSI systems. The key

features contributing to such low operating voltage are the 0.1V drop out

regulator and the 2.7V reference. The reduced reference voltage was

necessary to accommodate the lower termination current dictated in the

SCSI-3 specification. During disconnect the supply current is typically

only 0.5

µA, which makes the IC attractive for battery powered systems.

The UCC5614 is designed with an ultra low channel capacitance of

1.8pF, which eliminates effects on signal integrity from disconnected ter-

minators at interim points on the bus.

The UCC5614 can be programmed for either a 110 ohm or 2.5k ohm ter-

mination. The 110 ohm termination is used for standard SCSI bus lengths

and the 2.5k ohm termination is typically used in short bus applications.

When driving the TTL compatible DISCNCT pin directly, the 110 ohm ter-

mination is connected when the DISCNCT pin is driven low, and discon-

nected when driven high. When the DISCNCT pin is driven through an

impedance between 80k and 150k, the 2.5k ohm termination is con-

nected when the DISCNCT pin is driven low, and disconnected when

driven high.

UCC5614

9-Line 3-5 Volt Low Capacitance SCSI Active Terminator

FEATURES

DESCRIPTION

BLOCK DIAGRAM

Circuit Design Patented

•

Complies with SCSI, SCSI-2 and

SCSI-3 Standards

•

2.7V to 7V Operation

•

1.8pF Channel Capacitance during

Disconnect

•

0.5

µA Supply Current in Disconnect

Mode

•

110 Ohm/2.5k Programmable

Termination

•

Completely Meets SCSI Hot Plugging

•

-400mA Sourcing Current for

Termination

•

+400mA Sinking Current for Active

Negation Drivers

•

Trimmed Termination Current to 4%

•

Trimmed Impedance to 7%

•

Current Limit and Thermal Shutdown

Protection

continued

12/94

UDG-94029-1