Typical SCSI Bus Configuration Using the UC5602

UC5602

A Look at the Response of a SCSI-2 Cable

Figure 1 shows a single line of a SCSI cable. The driver

is an open colletor type which when asserted pulls low,

and when negated the termination resistance serves as

the pull-up.

Figure 2 shows a worst case scenario of mid cable de-

assertion with a close proximity receiver. The voltage

Driver Output Low Voltage

=

Current from Receiving Terminator

=

Cable Characteristic Impedance

=

110

In the pursuit of higher data rates, sampling could occur

during this step portion, therefore it is important to ensure

that the step is as high as possible to get the most noise

margin. For this reason the UC5602 is trimmed so that

max current spec of 22.4mA. The Termination impedance

is initially trimmed on the IC to 110 ohms typical, then the

regulator voltage is trimmed for the highest output cur-

rent to within 22.4mA.

Figure 1. A Single Line of a SCSI Cable

Figure 2. A Typical Response of a SCSI Cable

UDG-94054

UDG-94055

UDG-94053

4