Texas Instruments UCC5611DWPTR, UCC5611DWP Datasheet

The UCC5611 provides 18 line s of active termina tion for a SCSI (Small
Computer Systems Interface) parallel bus. The SCSI standard recom­mends active termination at both ends of the cable segment.

The UCC5611 is ideal for high performance 3.3V SCSI systems. The key
features co ntributing to such low operating voltage are the 0.1V drop out
regulator and the 2.75V reference. The reduced reference voltage was
necessary t o accommodate the lower termin ation current dictated in the
SCSI-3 specification. During disconnect the supply current is typically
only 1µA, which makes the IC attractive for battery powered systems.

The UCC5611 is designed with an ultra low channel capacitance of 1.8pF,
which elimi nat es effect s on s ign al integri ty from disconnected terminators
at interim points on the bus.

The UCC5611 can be programmed for ei ther a 110 ohm or 2.5k ohm ter­mination. Th e 110 ohm termination is used for standard SCSI bus lengths
and the 2. 5k ohm term ination is typical ly 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 high, and discon-

nected when low. When the

DISCNCT pin is driven through an
impedance between 80k and 150k, the 2.5k ohm termination is con­nected when the

DISCNCT pin is driven high, and disconnected when

driven low.

UCC5611

18-Line 3-5 Volt SCSI Active Terminator, Reverse Disconnect

FEATURES DESCRIPTION

BLOCK DIAGRAM

Circuit Design Patented

•

Complies with SCSI, SCSI-2, SCSI-3
and FAST-20 (Ultra) Standards

•

2.75V to 7V Operation

•

1.8pF Channel Capacitance during
Disconnect

•1µ

A Supply Current in Disconnect

Mode

•

110 Ohm/2.5k Programmable
Termination

•

Completely Meets SCSI Hot Plugging

•−

650mA 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

3/97

UDG-94131-1

UCC5611

The power ampl ifier output stage allows the UCC5611 to
source full termination current and sink active negation
current when all termination lines are actively negated.

The UCC5611 is pin for pin compatible with Unitrode’s
other 18 line SCSI terminators, except that

DISCNCT is
now active low, allowing lower capacitance and lower
voltage upgrades to existing systems. The UCC5611, as
with all Uni trode terminators, is completely hot pluggable
and appears as high impeda nce at the terminating c han­nels with V

TRMPWR

= 0V or open.

Internal circuit trimming is utilized, first to trim the 110

ohm terminati on impedan ce to a 7% tolera nce, and then
most importantly, to trim the output current to a 4% toler­ance, as close to the max SCSI-3 spec as possible,
which maxi mizes noise margin in FAST-20 SCSI opera­tion.

Other features include thermal shutdown and current
limit.

This device i s offered in low thermal resistance versions
of the ind ustry standard 28 pin wide body SOIC, 24 pin
wide body DIP and 28 pin PLCC.

ABSOLUTE MAXIMUM RATINGS

Termpwr Vo ltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7V

Signal Line Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . 0V to +7V

Regulator Output Current . . . . . . . . . . . . . . . . . . Self-regulating

Storage Temperature . . . . . . . . . . . . . . . . . . . −65°C to +150°C

Operating Temperature . . . . . . . . . . . . . . . . . −55°C to +150°C

Lead Temperature (Soldering, 10 Sec.). . . . . . . . . . . . . +300°C

RECOMMENDED OPERATING CONDITIONS

Termpwr Voltage . . . . . . . . . . . . . . . . . . . . . . . . 2.75V to 5.25V

Signal Line Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . 0V to +5V

Disconnect Input Voltage . . . . . . . . . . . . . . . . . . 0V to Termpwr

Description Continued

Unless otherwise sp ec ified all voltages are with respect to
Ground. Currents are positive into, negative out of the speci­fied terminal.
Consult Packaging Section of Unitrode Integrated Circuits dat­abook for thermal limitations and considerations of packages.

CONNECTION DIAGRAMS

PLCC-28 (Top View)
QP Package

* QP package pins 12 - 18 serve as both heatsink and signal
ground.

* DWP package pin 28 serves as signal ground; pins 7, 8, 9,
20, 21, 22 serve as heatsink/ground.

SOIC-28 (Top View)
DWP Package

Note: Drawings are not to scale.

DIL-24 (Top View)
N or J Package

2