鈥?/div>
Reverse Disconnect
Complies with SCSI, SCSI-2
and SPI-2 Standards
5pF Channel Capacitance
during Disconnect
Hot Plugging Capability
鈭?00mA
Sourcing Current for
Termination
+100mA Sinking Current for
Active Negation
1V Dropout Voltage Regulator
100碌A(chǔ) Supply Current in
Disconnect Mode
Trimmed Termination Current
to 5%
Trimmed Impedance to 5%
Low Thermal Resistance
Surface Mount Packages
DESCRIPTION
The UC5605 provides 9 lines of active termination for a SCSI (Small Computer
Systems Interface) parallel bus. The SCSI standard recommends active termi-
nation at both ends of the cable segment.
The only functional differences between the UC5603 and UC5605 is the ab-
sence of the negative clamps on the output lines and the disconnect input must
be at a logic-low for the terminating resistors to be disconnected. Parametri-
cally, the UC5605 has a 5% tolerance on impedance and current compared to
a 3% tolerance on the UC5603. Custom power packages are utilized to allow
normal operation at full power (2 Watts).
The UC5605 provides a disconnect feature which, when driven low, discon-
nects all terminating resistors, disables the regulator and greatly reduces
standby power consumption. The output channels remain high impedance even
without Termpwr applied. A low channel capacitance of 5pF allows interim
points of the bus to have little to no effect on the signal integrity.
Internal circuit trimming is utilized, first to trim the impedance to a 5% tolerance,
and then most importantly, to trim the output current to a 5% tolerance, as close
to the maximum SCSI specification as possible. This maximizes the noise mar-
gin in fast SCSI operation. Other features include thermal shutdown and cur-
rent limit.
This device is offered in low thermal resistance versions of the industry stand-
ard 16 pin narrow body SOIC, 16 pin ZIP (zig-zag in line package) and 24 pin
TSSOP.
BLOCK DIAGRAM
UDG-94122
Circuit Design Patented
3/97
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