DS2107A Ver la hoja de datos (PDF) - Dallas Semiconductor -> Maxim Integrated
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DS2107A Datasheet PDF : 7 Pages
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DS2107A
FUNCTIONAL DESCRIPTION
The DS2107A 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. When all lines
settle in the quiescent state, the regulator will consume
about 5 mA. When the DS2107A is put into power-
down mode by bringing PD low, the power-down circuit-
ry will turn off the transistors on each signal line. This will
isolate the DS2107A from the signal lines and effective-
ly remove it from the circuit. The power-down pin (PD)
has an internal 50K ohm pull-up resistor. To place the
DS2107A 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 DS2107A re-
quires parallel 0.1 µF and 4. 7 µF capacitors connected
between the VREF pins and ground. Figure 2 details a
typical SCSI bus configuration. In an 8-bit wide SCSI
bus arrangement (“A” Cable), two DS2107A’s would be
needed at each end of the SCSI cable in order to termi-
nate the 18 active signal lines. In a 16-bit wide SCSI bus
arrangement (“P” Cable), three DS2107A’s would be
needed at each end of the SCSI cable in order to termi-
nate the 27 active signal lines.
DS2107A BLOCK DIAGRAM Figure 1
PD
TERMPWR1
TERMPWR2
50K Ohm
Power
Down
Circuitry
Bandgap
Reference
GND
110 Ohms
R1
110 Ohms
R2
110 Ohms
R3
110 Ohms
R4
110 Ohms
R5
110 Ohms
R6
110 Ohms
R7
110 Ohms
R8
110 Ohms
R9
VREF1
VREF2
022698 2/7
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