dallas semiconductor DS2114 service manual
DS2114
DS2114
SCSI Terminator
FEATURES
• Fully compliant with SCSI, SCSI–2 and SCSI–3 stan-
dards
• Provides active termination for nine signal lines
• Laser–trimmed 110 ohms termination resistors have
2% tolerance
• Low dropout voltage regulator
• Fully supports actively negated SCSI signals
• Onboard thermal shutdown circuitry
• Narrow 16–pin plastic SOIC (DS2114Z)
PIN ASSIGNMENT
TERMPWR1
R1
R2
R3
R4
R5
VREF1
GND
DS2114Z 16–PIN SOIC (150 MIL)
16
15
14
13
12
11
10
9
NC
VREF2
R9
R8
R7
R6
NC
TERMPWR2
1
2
3
4
5
6
7
8
DESCRIPTION
The SCSI–2 and SCSI–3 standards recommend the
use of active terminations at both ends of every cable
segment in a SCSI system with single–ended drivers
and receivers. The DS2114 SCSI Terminator, which is
fully compliant with these standards, enables the designer to gain the benefits of active termination: greater
immunity to voltage drops on the TERMPWR (TERMination PoWeR) line, enhanced high–level noise im-
munity, intrinsic TERMPWR decoupling, and very low
quiescent current consumption. The DS21 14 integrates
a regulator and nine precise 110 ohms termination resistors into a monolithic IC. The DS2114 is intended for
cable end terminator assemblies and devices where the
terminators do not need to be isolated from the SCSI
bus.
070198 1/6
DS2114
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 produces 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 negated SCSI signals, the buffer can sink at least 200 mA
will move less than 60 mV . When all lines settle
and V
ref
in the quiescent state, the regulator will consume about
2.5 mA.
DS2114 BLOCK DIAGRAM Figure 1
TERMPWR1
TERMPWR2
BANDGAP
REFERENCE
+
–
GND
T o 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 DS21 14 requires
a 4.7 µF capacitor 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 DS21 14’ 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 DS21 14’s would be needed at each end of
the SCSI cable in order to terminate the 27 active signal
lines.
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
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VREF1
VREF2
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