DS21T07

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FUNCTIONAL DESCRIPTION

The DS21T07 consists of a bandgap reference, buffer amplifier, and nine termination resistors (Figure 1).

The bandgap reference circuit produces a precise 2.55V level which is fed to a buffer amplifier. The

buffer produces a 2.85V level and is capable of sourcing at least 24 mA into each of the termination

resistors when the signal line is low (active). When the driver for a given signal line turns off, the

terminator will pull the signal line to 2.85V (quiescent state). To handle actively negated SCSI signals,

quiescent state, the regulator will consume about 5 mA. When the DS21T07 is put into power-down

will isolate the DS21T07 from the signal lines and effectively remove it from the circuit. The power-

pin should be left open circuited. When installed on disk drives or RAID system components, the

DS21T07 will not affect the SCSI bus during a hot plug operation.

To ensure proper operation, both the TERMPWR1 and TERMPWR2 pins must be connected to the SCSI

bus TERMPWR line and both the VREF1 and VREF2 pins must be tied together externally. Each

DS21T07 requires a 4.7 µF capacitor connected between the VREF pins and ground. Figure 2 details a

typical SCSI bus configuration. In an 8-bit wide SCSI bus arrangement, two DS21T07’s would be needed

at each end of the SCSI cable in order to terminate the 18 active signal lines. In a 16-bit wide SCSI bus

arrangement, three DS21T07’s would be needed at each end of the SCSI cable in order to terminate the

27 active signal lines.

DS21T16 BLOCK DIAGRAM Figure 1