DS2114

070198 2/6

FUNCTIONAL DESCRIPTION

The DS2114 consists of a bandgap reference, buffer

amplifier, and nine termination resistors (Figure 1). The

bandgap reference circuit produces a precise 2.55 volts

level which is fed to a buffer amplifier. The buffer pro-

duces a 2.85 volts 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 2.85 volts (quiescent state). To handle actively ne-

gated SCSI signals, the buffer can sink at least 200 mA

in the quiescent state, the regulator will consume about

2.5 mA.

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 DS2114 requires

a 4.7

µF capacitor connected between the VREF pins

and ground. Figure 2 details a typical SCSI bus configu-

ration. In an 8–bit wide SCSI bus arrangement (“A”

Cable), two DS2114’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 (“P”

Cable), three DS2114’s would be needed at each end of

the SCSI cable in order to terminate the 27 active signal

lines.

DS2114 BLOCK DIAGRAM Figure 1

GND

TERMPWR1

TERMPWR2

BANDGAP

REFERENCE

R1

R2

R3

R4

R5

R6

R7

R8

R9

VREF1

VREF2

+

–

110 ohms

110 ohms

110 ohms

110 ohms

110 ohms

110 ohms

110 ohms

110 ohms

110 ohms