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STMicro active-terminator spans nine SCSI signal lines

Posted: 11 Mar 2002 ?? ?Print Version ?Bookmark and Share

Keywords:stmicroelectronics? stmicro? active terminator chip? terminator chip? scsi terminator chip?

Intended for use in SCSI devices such as HDDs and CD-ROM drives, the ST21S07A active-terminator chip from STMicroelectronics accommodates nine SCSI signal lines by integrating a bandgap voltage reference, buffer amplifier, and nine-switched, 110-ohm termination resistors.

The IC features a typical dropout voltage of 0.3V, power-down mode, hot-plug compatibility, and on-board thermal shutdown. It is also fully-compliant with SCSI standards, as well as SCSI-2 and emerging SCSI-3 standards by accommodating negative-going signals. The SCSI-2 and SCSI-3 specifications recommend the use of active termination on single-ended drivers and receivers.

The buffer amplifier produces 2.85V with a 0.5V dropout, and can source at least 24mA into each termination resistor when that signal line is active (low). When the driver for a signal line turns off, the terminator chip pulls the to the quiescent voltage of 2.85V. To handle the active negative SCSI signals called for in SCSI-2 and SCSI-3, the buffer can sink up to 200mA.

The resistors can be electrically-isolated from the bus to further minimize quiescent current consumption. Thus, by turning off a transistor on each signal line, the ST21S07A effectively removes itself from the circuit.

Two ST21S07A devices can be placed on an 8-bit-wide SCSI bus arrangement, while a 16-bit takes three ST21S07A devices on each end.

The ST21S07A SCSI active-terminator chip comes in an SO-16L tube (ST21S07ACW) or tape-and-reel (ST21S07ACWR) packaging, as well as in TSSOP-20 (ST21S07ACTR) housing.

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