•Trimmed Regulator for Accurate
Termination Current
•Current Limit and Thermal
Shutdown Protection
•110 Ohm Termination
•Meets SCSI Hot Plugging
The UC5602 is a pi n compatible version of its predecessor, the UC5601,
and is targeted for high vol ume applicatio ns which req uire ac tive termination, but not the high performance of the UC5601. The major differences
are relaxed outpu t current and termination tolerances, and the absence of
low side clamps.
The UC5602 provides 18 lines of active termination for a SCSI (Small
Computer Systems Interface) paral lel bus. The SCSI-2 standard recommends active termination at both ends of the cable segment, and SCSI-3
will make it a requirement.
The UC5602 provides a disco nnect feature whi ch, when open ed or driven
high, will disconnect all termi nating resistors, and disables the regu lator;
greatly reduci ng standby powe r. The output channels remain high impedance even without Termpwr applied.
Internal circuit trimming is utilized, first to trim the impedance to a 7% tolerance; and then most importantly, to trim the output current 7% tolerance,
as close to the max SCSI as possible, which maximizes noise margin in
fast SCSI operation.
Other features include thermal shutdown, current limit, and 40mA of active
negation sink current capability.
BLOCK DIAGRAM
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.
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 .
Line RegulationTRMPWR = 4V to 6V1020mV
Load Regulat io nI
Drop Out VoltageAll Termination Lines = 0.5V1.01.2V
Short Circuit Cur rentV
Sinking Current Capabi lityV
Thermal Shutdow n170°C
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
3
UC5602
T y pical SCSI Bus Configu rati on Using t he UC5602
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 Voltage
I
O=Current from Receiving Terminator
Z
0=Cable Characteristic Impedance
V
REG− VOL
IO=
110
In the pursui t of higher data rates, sampling could 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 UC5602 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-94053
UDG-94054
Figure 1. A Singl e L ine of a SCSI Cable
UDG-94055
Figure 2. A Typical Response of a SCSI Cable
4
Max Output Current vs. TemperatureVREF vs. Temperature
T exas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue
any product or service without notice, and advise customers to obtain the latest version of relevant information
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pertaining to warranty, patent infringement, and limitation of liability.
TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in
accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent
TI deems necessary to support this warranty . Specific testing of all parameters of each device is not necessarily
performed, except those mandated by government requirements.
CERTAIN APPLICA TIONS USING SEMICONDUCT OR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF
DEATH, PERSONAL INJURY, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE (“CRITICAL
APPLICATIONS”). TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, AUTHORIZED, OR
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CRITICAL APPLICA TIONS. INCLUSION OF TI PRODUCTS IN SUCH APPLICATIONS IS UNDERST OOD TO
BE FULLY AT THE CUSTOMER’S RISK.
In order to minimize risks associated with the customer’s applications, adequate design and operating
safeguards must be provided by the customer to minimize inherent or procedural hazards.
TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent
that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other
intellectual property right of TI covering or relating to any combination, machine, or process in which such
semiconductor products or services might be or are used. TI’s publication of information regarding any third
party’s products or services does not constitute TI’s approval, warranty or endorsement thereof.
Copyright 1999, Texas Instruments Incorporated
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