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
UCC5611
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Supply Current Section
Termpwr Supply Current All termination lines = Open 1 2 mA
All termination lines = 0.2V 415 435 mA
Power Down Mode DISCNCT = 0V 0.5 5
µ
A
Output Section (110 ohms - Terminator Lines)
Terminator Impedance (Note 4) 102.3 110 117.7 Ohms
Output High Voltage TRMPWR = 3V (Note 1) 2.5 2.7 3.0 V
Max Output Cur r e nt V
LINE
= 0.2V, TJ = 25°C −22.1 −23 −24 mA
V
LINE
= 0.2V
−
21
−
23
−
24 mA
V
LINE
= 0.2V, TRMPWR = 3V, TJ = 25°C (Note 1)
−
20.2−23
−
24 mA
V
LINE
= 0.2V, TRMPWR = 3V (Note 1) −19 −23 −24 mA
V
LINE
= 0.5V −22.4 mA
Output Leakage
DISCNCT = 0V, TRMPWR = 0V to 5.25V 10 400 nA
Output Capacitance
DISCNCT = 0V, DWP Package (Note 2, 3) 1.8 2.5 pF
Output Section (2.5k ohms - Terminator Lines) (R
DISCNCT
= 80k ohms)
Terminator Impedance 22.53kΩ
Output High Voltage TRMPWR = 3V (Note 1) 2.5 2.7 3.0 V
Max Output Cur r e nt V
LINE
= 0.2V −0.7 −1 −1.4 mA
V
LINE
= 0.2V, TRMPWR = 3V (Note 1)
−
0.6
−
1
−
1.5 mA
Output Leakage
DISCNCT = 0V, TRMPWR = 0 to 5.25V 10 400 nA
Output Capacitance
DISCNCT = 0V, DWP Package (Note 2, 3) 1.8 2.5 pF
Regulator Section
Regulator Output Voltage 5.25V > TRMPWR > 3V 2.5 2.7 3.0 V
Drop Out Voltage All Termination Lines = 0.2V 0.1 0.2 V
Short Circuit Current V
REG
= 0V
−
450−650−800 mA
Sinking Current Capability V
REG
= 3V 200 400 800 mA
Thermal Shutdown (Note 2) 170 °C
Thermal Shutdown Hysteresis (Note 2) 10 °C
Disconnect Section
Disconnect Threshold R
DISCNCT
= 0 & 80k 0.8 1.5 2.0 V
Input Current
DISCNCT = 3.3V 30 50
µ
A
ELECTRICAL CHARACTERISTICS
Unless otherwise st at ed, th ese sp ecif icat io ns app ly for TA = 0°C to 70°C.
TRMPWR = 3.3V, DISCNCT = 3.3V, R
DISCNCT
= 0 ohms. TA = TJ.
Note 1: Measuring each termin ation line while ot he r 17 are low (0. 2V).
Note 2: Guaranteed by desig n. Not 100% tested in produc ti on .
Note 3: Output Capacitance is measured at 0.5V.
Note 4: Tested by measuring I
OUT
with V
OUT
= 0.2V and V
OUT
= V
REG
- 0.1V then calculating the impedanc e.
3
UCC5611
Figure 1: Typical SCSI Bus Configurations Utilizing A UCC5611 Device
APPLICATION INFORMATION
UDG-94132
UNITRODE CORPORATI ON
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. (603) 424- 24 10 • FAX (603) 424-3460
4
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