UC5601
SCSI Active Terminator
FEATURES DESCRIPTION
• Complies with SCSI, SCSI-2
Standards
• 10pF Channel Capacitance During
Disconnect
• Active Termination for 18 Lines
• Logic Command Disconnects all
Termination Lines
• Low Supply Current in Disconnect
Mode
The UC5601 provides precision resistive pull-up to a 2.9V reference for all
18 lines in a Small Computer Systems Interface (SCSI) bus cable. The
SCSI-2 standard recommends active termination at both ends of every cable segment utilizing single ended drivers and receivers.
Internal circuit trimming is utilized, first to reduce resistor tolerances to ±3%
and then to adjust the regulator’s output voltage to insure termination current accuracy of ±3%.
The UC5601 provi des a disconnect feature which, upon a logic command,
disconnects all terminating resistors, and turns off the regulator; greatly reducing standby power.
• Trimmed Regulator for Accurate
Termination Current
• Current Limit and Thermal
Shutdown Protection
• 110 Ohm Termination
• Meets SCSI Hot Plugging
BLOCK DIAGRAM
Other features include negative clamping on all signal lines, 20mA of active
negation sink current capability, regulator current limiting, and thermal shutdown protection.
This device is offered in low thermal re sistance versions of the industry
standard 28 pin wide body SOIC and PLCC, as well as a 24 pin DIL plastic
package.
10/94
UDG-94060
Circuit Design Patented
UC5601
ABSOLUTE MAXIMUM RATINGS
Termpwr Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7V
Signal Line Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . 0V to +7V
Regulator Output Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1A
Storage Temperature . . . . . . . . . . . . . . . . . . . −−65°C to +150°C
Operating Tem perat ure . . . . . . . . . . . . . . . . . −−55°C to +150°C
Lead Temperat ure (Solde ring, 10 Sec.). . . . . . . . . . . . . +300°C
Unless otherwise specified all volta ges are with respect to
Ground. Cur ren ts are po sitive into, negative out of the specified terminal.
Consult Packaging Section of Unitr ode Int egr ated Circ uits databook for thermal limitations and consider ations of pack ages .
RECOMMENDED OPERATING CONDITIONS
Termpwr Voltage . . . . . . . . . . . . . . . . . . . . . . . . . 4.0V to 5.25V
Signal Line Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . 0V to +3V
Disconnect Input Voltage . . . . . . . . . . . . . . . . . . 0V to Te rmpwr
SOIC-28 (Top View)
DWP Package
CONNECTION DIAGRAMS
PLCC-28 (Top View)
QP Package
* QP package pins 12 - 18 serve as both hea tsink and sign al
ground.
DIL-24 (Top View)
N or J Package
* DWP package pin 28 serves as signal ground ; pins 7, 8, 9,
20, 21, 22 serve as heatsink/ground.
Note: Drawings are not to scale.
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ELECTRICAL CHARACTERISTICS Unless otherwise stated, these specifications apply for TA = 0°C to 70°C.
TRMPWR = 4.75V, DISCNCT = 0V. T
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Supply Cur rent Sect ion
Termpwr Supply Current All termination lines = Op en 17 25 mA
Power Down Mode DISCNCT = Open 100 150 µA
Output Secti on (T erm inat i on Lines )
Termination Im peda nce ∆I
Output High Voltage V
Max Output Current V
Output Clamp Level I
Output Leakage
Output Capacit anc e DISCNCT = Open (Note 2) 10 12 pF
Regul ator Secti o n
Regulator Output Voltage 2.8 2.9 3.0 V
Line Regulation TRMPWR = 4V to 6V 10 20 mV
Load Regulat io n I
Drop Out Voltage All Termination Lines = 0.5 V 1.0 1.2 V
Short Circuit Cur rent V
Current Sink Capability V
Thermal Shutdow n 170 °C
Disconnect Section
Disconnect Threshold 1.3 1.5 1.7 V
Threshold Hys teres is 100 160 250 mV
Input Current DISCNCT = 0V 10 15 µA
Note 1: Measuring each term ination l ine while other 17 are low (0.5V).
Note 2: Guaranteed by design. Not 100% tested in production.
A = TJ.
All termination lines = 0.5 V 400 430 mA
LINE = -5mA to -15mA 107 110 113 Ω
TRMPWR = 4V (Note 1) 2.65 2.9 V
LINE = 0.5V -21.1 -21.7 -22.4 mA
V
LINE = 0.5V, TRMPWR = 4V (No te 1) -19.8 -21.7 -22.4 mA
LINE = -30mA -0.2 -0.05 0.1 V
TRMPWR = 0V to 5.25V
DISCNCT = 4V
REG = 0V
TRMPWR = 0V to 5.25V, REG = Open
LINE = 0V to 5.25V
V
REG = 0 to -400mA 20 50 mV
REG = 0V -450 -650 -850 mA
REG = 3.5V 8 20 25 mA
V
LINE = 0 to 4V 10 400 nA
V
LINE = 5.25V 100 µA
10 400 nA
UC5601
THERMAL DATA
QP package: (see packaging section of UICC data book for more details on thermal performance)
Thermal Resistance Junction to Leads, θjL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15°C/W
Thermal Resistance Junction to Ambient, θja. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30°-40°C/W
DWP package:
Thermal Resistance Junction to Leads, θjL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18°C/W
Thermal Resistance Junction to Ambient, θja. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33°-43°C/W
J package:
Thermal Resistance Junction to Leads, θjL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40°C/W
Thermal Resistance Junction to Ambient, θja. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75°-85°C/W
N package:
Thermal Resistance Junction to Leads, θjL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50°C/W
Thermal Resistance Junction to Ambient, θja. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95°-105°C/W
Note: The above n u mb ers for θjL are maximums for the limit ing ther ma l resistanc e of the packa ge in a standa rd mounting conf igu-
θ
ration. The
numbers assume no ambient airflow .
ja numbers are meant to be guidelines for the thermal per fo rmanc e of the device/pc -bo ard system . All of the abov e
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UC5601
T y pical SCSI Bus Configu rati on Using t he UC5601
A Look at the Respo nse o f a SCSI-2 Cabl e
Figure 1 shows a single line of a SCSI cable. The driver
is an open colletor type which when asserted pulls low,
and when negated the termination resistance serves as
the pull -up.
Figure 2 shows a worst case scenario of mid cable deassertion with a close proximity receiver. The voltage
V
STEP is defined as:
V
STEP = VOL +IO Z0
VOL = Driver Output Low V oltage
I
O = Current from Receiving Terminator
Z
0 = Cable Characteristic Impedance
REG − VOL
V
IO =
110
In the pursu it of h igher data rates, sampling culd occur
during this step portion, therefore it is important to ensure
that the step is as high as possible to get the most noise
margin. For this re ason the UC5601 is trimmed so that
the output current (I
O) is as close as possible to the SCSI
max current spec of 22.4mA. The Termination impedance
is initially trimmed on the IC to 110 ohms typical, then the
regulator voltage is trimmed for the highest output current to within 22.4mA.
UDG-94061
UDG-94062
Figure 1. A Singl e L ine of a SCSI Cable
UDG-94063
Figure 2. A Typical Response of a SCSI Cable
UNITRODE INTEGRATED CIRCUITS
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TEL. (603) 424-2410 • FAX (603) 424 3460
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