DS2109

022698 3/10

The DS2109 consists of 3 major functional blocks,

Figure 2:

switches

When the Bus Ground Sensing Circuitry or Bus Current

Sensing Circuitry determine that the SCSI bus is prop-

erly terminated without the DS2109, the power down

buffer isolates the resistors from the SCSI bus and dis-

ables the power amp, thereby placing the DS2109 in a

low power mode (the bus sensing circuitry always stays

active). The PDO (Power Down Output) pin can be con-

nected to the pin of a DS21S07A SCSI terminator for

Wide SCSI configurations, Figure 8.

DS2109 BLOCK DIAGRAM Figure 2

+

–

TCS

R14

R18

R1

110 OHMS

110 OHMS

110 OHMS

BANDGAP

REFERENCE

POWER

DOWN

BUFFER

BUS CURRENT

SENSING

CIRCUITRY

BUS GROUND

SENSING

CIRCUITRY

PDI

PDE

PDO

DISABLE

DISABLE