TL2218-285_14 Datasheet, PDF (1/13 Pages) Texas Instruments – EXCALIBUR CURRENT-MODE SCSI TERMINATOR

ą
TL2218Ć285, TL2218Ć285Y
EXCALIBUR CURRENTĆMODE SCSI TERMINATOR
ą
SLVS072C − DECEMBER 1992 − REVISED OCTOBER 1995
available features
• Fully Integrated 9-Channel SCSI
Termination
• No External Components Required
• Maximum Allowed Current Applied at First
High-Level Step
• 6-pF Typical Power-Down Output
Capacitance
• Wide V_term^† (Termination Voltage)
Operating Range, 3.5 V to 5.5 V
• TTL-Compatible Disable Feature
• Compatible With Active Negation
• Thermal Regulation
PW PACKAGE
(TOP VIEW)
TERMPWR
1
20
NC
2
19
NC
3
18
D0
4
17
D1
5
16
D2
6
15
D3
7
14
D4
8
13
NC
9
12
GND
10
11
NC − No internal connection
TERMPWR
DISABLE
NC
D8
D7
NC
D6
D5
NC
GND
description
The TL2218-285 is a current-mode 9-channel monolithic terminator specially designed for single-ended
small-computer-systems-interface (SCSI) bus termination. A user-controlled disable function is provided to
reduce standby power. No impedance-matching resistors or other external components are required for its
operation as a complete terminator.
The device operates over a wide termination-voltage (V_term†) range of 3.5 V to 5.5 V, offering an extra 0.5 V of
operating range when compared to the minimum termination voltage of 4 V required by other integrated active
terminators. The TL2218-285 functions as a current-sourcing terminator and supplies a constant output current
of 23 mA into each asserted line. When a line is deasserted, the device senses the rising voltage level and begins
to function as a voltage source, supplying a fixed output voltage of 2.85 V. The TL2218-285 features
compatibility with active negation drivers and has a typical sink current capability of 20 mA.
The TL2218-285 is able to ensure that maximum current is applied at the first high-level step. This performance
means that the device should provide a first high-level step exceeding 2 V even at a 10-MHz rate. Therefore,
noise margins are improved considerably above those provided by resistive terminators.
A key difference between the TL2218-285 current-mode terminator and a Boulay terminator is that the
TL2218-285 does not incorporate a low dropout regulator to set the output voltage to 2.85 V. In contrast with
the Boulay termination concept, the accuracy of the 2.85 V is not critical with the current-mode method used
in the TL2218-285 because this voltage does not determine the driver current. Therefore, the primary device
specifications are not the same as with a voltage regulator but are more concerned with output current.
The DISABLE terminal is TTL compatible and must be taken low to shut down the outputs. The device is
normally active, even when DISABLE is left floating. In the disable mode, only the device startup circuits remain
active, thereby reducing the supply current to just 500 µA. Output capacitance in the shutdown mode is typically
6 pF.
The TL2218-285 has on-board thermal regulation and current limiting, thus eliminating the need for external
protection circuitry. A thermal regulation circuit that is designed to provide current limiting, rather than an actual
thermal shutdown, is included in the individual channels of the TL2218-285. When a system fault occurs that
leads to excessive power dissipation by the terminator, the thermal regulation circuit causes a reduction in the
asserted-line output current sufficient to maintain operation. This feature allows the bus to remain active during
a fault condition, which permits data transfer immediately upon removal of the fault. A terminator with thermal
shutdown does not allow for data transfer until sufficient cooling has occurred. Another advantage offered by
the TL2218-285 is a design that does not require costly laser trimming in the manufacturing process.
The TL2218-285 is characterized for operation over the virtual junction temperature range of 0°C to 125°C.
† _{This symbol is not presently listed within EIA/JEDEC standards for letter symbols.}
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
Copyright  1995, Texas Instruments Incorporated
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
• POST OFFICE BOX 1443 HOUSTON, TEXAS
77251−1443
8−1