UCC5621
DESCRIPTION
UCC5621 provides 27 lines of active termination for a SCSI (Small Computer Systems Interface) parallel bus. The SCSI standard recommends active termination at both ends of the cable.
The UCC5621 is ideal for high performance 5V SCSI systems. During disconnect the supply current is typically only 100µA, which makes the IC attractive for lower powered systems.
The UCC5621 features a split reverse disconnect allowing the user to control termination lines 10 to 27 with disconnect one, DISCNCT1
, and control
terminiation lines 1 to 9 with disconnect two, DISCNCT2
.
The UCC5621 is designed with a low channel capacitance of 2.5pF, which
eliminates effects on signal integrity from disconnected terminators at interim points on the bus.
The power amplifier output stage allows the UCC5621 to source full termination current and sink active negation current when all termination lines
are actively negated.
The UCC5621, as with all Unitrode terminators, is completely hot pluggable and appears as high impedance at the teminating channels with
V
TRMPWR = 0V or open.
Internal circuit trimming is utilized, first to trim the 110Ω impedance, and
then most importantly, to trim the output current as close to the maximum
SCSI-3 specification as possible, which maximizes noise margin in FAST20 SCSI operation.
(continued)
27 - Line SCSI Terminator With Split Reverse Disconnect
BLOCK DIAGRAM
FEATURES
• Complies with SCSI, SCSI-2, SCSI-3,
SPI and FAST-20 (Ultra) Standards
• 2.5pF Channel Capacitance During
Disconnect
• 100µA Supply Current in Disconnect
Mode
• 4V To 7V Operation
• 110Ω Termination
• Completely Meets SCSI Hot Plugging
• –900mA Sourcing Current for
Termination
• +500mA Sinking Current for Active
Negation
• Logic Command Disconnects all
Termination Lines
• Split Reverse Controls Lines 1 to 9
and 10 to 27 Separately
• Trimmed Impedance to 5%
• Current Limit and Thermal Shutdown
Protection
10/98
UDG-96111
Circuit Design Patented
2
UCC5621
ABSOLUTE MAXIMUM RATINGS
TRMPWR Voltage................................+7V
Signal Line Voltage ..........................0Vto+7V
Regulator Output Current ..........................1.5A
Storage Temperature ...................-65°C to +150°C
Junction Temperature...................-55°C to +150°C
Lead Temperature (Soldering, 10 Sec.).............+300°C
Currents are positive into, negative out of the specified terminal.
Consult Packaging Section of Databook for thermal limitations
and considerations of packages.
CONNECTION DIAGRAM
QSOP-44 (Top View)
MWP Package
ELECTRICAL CHARACTERISTICS Unless otherwise stated, these specifications apply for T
A
= 0°C to 70°C,
TRMPWR = 4.75V, DISCNCT1 = DSCNCT2 = 4.75V, TA=TJ.
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Supply Current Section
TRMPWR Supply Current All Termination Lines = Open 1 2 mA
All Termination Lines = 0.2V 630 650 mA
Power Down Mode DISCNCT1
= DSCNCT2 = 0V 100 200 µA
Other features include thermal shutdown and current
limit. This device is offered in low thermal resistance versions of the industry standard 44 pin wide body QSOP
(MWP) and 48 pin LQFP. Consult QSOP-44 and FQP-48
Packaging Diagrams for exact dimensions.
DESCRIPTION (cont.)
LQFP-48 (Top View)
FQP Package
3
UCC5621
ELECTRICAL CHARACTERISTICS
Unless otherwise stated, these specifications apply for TA= 0°C to 70°C,
TRMPWR = 4.75V, DISCNCT1 = DSCNCT2 = 4.75V, TA=TJ.
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Output Section (Termination Lines)
Termination Impedance (Note 3) 104.5 110 115.5 Ω
Output High Voltage (Note 1) 2.6 2.8 3.0 V
Max Output Current V
LINE
= 0.2V, TJ =25°C
-
22.1-23.3-24 mA
V
LINE
= 0.2V
-
20.7-23.3-24 mA
V
LINE
= 0.2V, TRMPWR = 4V, TJ= 25°C (Note 1)
-
21
-
23
-
24 mA
V
LINE
= 0.2V, TRMPWR = 4V (Note 1)
-
20
-
23
-
24 mA
V
LINE
= 0.5V
-
22.4 mA
Output Leakage DISCNCT1 = DISCNCT2 = 0V, TRMPWR = 0V to 5.25V 10 400 nA
Output Capacitance DISCNCT1
= DISCNCT2 = 0V (Note 2) 2.5 4 pF
Regulator Section
Regulator Output Voltage 2.6 2.8 3.0 V
Drop Out Voltage All Termination Lines = 0.2V 0.4 0.8 V
Short Circuit Current V
REG
=0V
-
650-900 –1300 mA
Sinking Current Capability V
REG
= 3.5V 300 500 900 mA
Thermal Shutdown 170 °C
Thermal Shutdown Hysteresis 10 °C
Disconnect Section
Disconnect Threshold DISCNCT1
Controls Lines 10 to 27 0.8 1.5 2.0 V
Input Current DISCNCT1
DISCNCT1 = 0V –10 –30 µA
Disconnect Threshold DISCNCT2 Controls Lines 1 to 9 0.8 1.5 2 V
Input Current DISCNCT2 DISCNCT2 = 0V –10 –30 µA
Note 1: Measuring each termination line while other 26 are low (0.2V).
Note 2: Guaranteed by design. Not 100% tested in production.
Note 3: Testedby measuring I
OUT
with V
OUT
= 0.2V and V
OUT
with no load, then calculate:
Z
VNL V
IatV
OUT
OUT
=
−
.. ..02
02
DISCNCT1: Disconnect one controls termination lines
L10 – L27. Taking this pin low causes termination lines
L10 – L27 to become high impedence, taking this pin
high or leaving it open allows the channels to provide
normal termination.
DISCNCT2
: Disconnect two controls termination lines
L1 – L9. Taking this pin low causes termination lines L1 –
L9 to become high impedence. Taking this pin high or
leaving it open allows the channels to provide normal terminiation. Taking both disconnect pins low will put the
chip in to sleep mode where it will be in low-power mode.
GND: Ground reference for the IC.
L1 - L27: 110Ω termination channels.
REG: Output of the internal 2.7V regulator.
TRMPWR: Power for the IC.
PIN DESCRIPTIONS
4
UCC5621
Figure 1. Typical Wide SCSI Bus Configuration Using the UCC5621
UDG-98168
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