DS2105Z Maxim Integrated, DS2105Z Datasheet - Page 2

• Manufacturer Part Number: DS2105Z
• Description: SCSI Interface IC
• Manufacturer: Maxim Integrated
• Series: DS2105r

Specifications of DS2105Z

• Part # Aliases: 90-2105Z-000

FUNCTIONAL DESCRIPTION
The DS2105 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 pro-
duces 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, the buffer can sink 200 mA, and V
move less than 60 mV. When all lines settle in the quies-
cent state, the regulator will consume about 5 mA.
When the DS2105 is put into power–down mode by
bringing PD low, the power–down circuitry will turn off
the transistors on each signal line. This will isolate the
DS2105 from the signal lines and effectively remove it
DS2105 BLOCK DIAGRAM Figure 1
DS2105
022698 2/7
TERMPWR1
TERMPWR2
GND
PD
REFERENCE
BANDGAP
50K ohm
REF
will
CIRCUITRY
POWER
DOWN
from the circuit. The power–down pin (PD) has an inter-
nal 50K pull–up resistor. To place the DS2105 into an
active state, the PD pin should be left open circuited.
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 DS2105 requires
a 4.7 F 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 DS2105’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 DS2105’s would be needed at each end of
the SCSI cable in order to terminate the 27 active signal
lines.
110 ohms
110 ohms
110 ohms
110 ohms
110 ohms
110 ohms
110 ohms
110 ohms
110 ohms
VREF1
VREF2
R1
R3
R2
R4
R5
R6
R7
R8
R9