DS2109
The DS2109 consists of 3 major functional blocks,
Figure 2:
•
Voltage reference, terminating resistors, and isolation
switches
•
Bus current sensing circuitry
•
Bus ground sensing circuity
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
PDI
BUS GROUND
SENSING
CIRCUITRY
DISABLE
DISABLE
BUS CURRENT
SENSING
CIRCUITRY
TCS
PDE
PDO
POWER
DOWN
BUFFER
BANDGAP
REFERENCE
+
110 OHMS
R14
–
110 OHMS
R18
110 OHMS
R1
V
REF
022698 3/10
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
