5

ML6599

being hot-inserted/removed should be inactive

(accomplished by grounding the

DISCNKT pin in the case

of the ML6599). If the terminator being inserted/removed

were in the active state, at some point in time the bus

would be terminated by either 1 or 3 terminators. In either

case, data integrity on the bus will be compromised.

Figure 2 gives an application diagram showing a typical

SCSI bus configuration. To ensure proper operation, the

TERMPWR pin must be connected to the SCSI

TERMPOWER line. Each ML6599 requires parallel 0.1

µF

and 10

GND pins and the TERMPOWER line needs a 10

µF

bypass capacitor at each node in the system.

In an 8-bit wide SCSI bus arrangement (“A” Cable),

two ML6599s would be needed at each end of the SCSI

cable in order to terminate the 9 active signal lines.

16-bit wide SCSI would use three ML6599s, while 32-bit

wide SCSI bus would require five ML6599s.

In a typical SCSI subsystem, the open collector driver in

the SCSI transceiver pulls low when asserted. The

Figure 2. Application Diagram Showing Typical SCSI Bus Configuration with the ML6599

termination resistance serves as the pull-up when negated.

Figure 2 also shows a typical cable response to a pulse.

The receiving end of the cable will exhibit a single time

delay. When negated, the initial step will reach an

sampling could occur during this step portion. In order to

get the most noise margin, the step needs to be as high as

possible to prevent false triggering. For this reason the

regulator voltage and the resistor defining the MOSFET

as possible to the SCSI maximum current specification.

characteristic impedance of the cable.

This is a very important characteristic that the terminator

helps to overcome by increasing the noise margin and

boosting the step as high as possible.

TERMPWR LINE

ML6599

TERMPWR

GND

L9

L2 L1

DISCNKT

0.1µF

10µF

TERMPWR

GND

L9

L1 L2

ML6599

DISCNKT

SCSI XCVR

SCSI XCVR

SCSI XCVR

LINE ASSERTED LINE NEGATED

0.1µF

10µF

. . .

. . .

SCSI CABLE