DS2106
DS2106
SCSI Terminator
FEATURES
PIN ASSIGNMENT
•
Fully
compliant with SCSI–1, Fast SCSI and
Ultra SCSI
PD
R1
R2
R3
R4
R5
HS–GND
HS–GND
NC
R6
R7
R8
R9
TPWR
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
GND
R18
R17
R16
R15
R14
NC
HS–GND
NC
R13
R12
R11
R10
V
REF
•
Functionally compatible with DS21S07A
•
Provides active termination for 18 signal lines
•
5%
tolerance on termination resistors and voltage
regulator
•
5% tolerance on termination current
•
Low power down capacitance of 3 pF
•
Onboard thermal shutdown circuitry
•
SCSI bus hot plug compatible
•
Fully supports actively negated SCSI signals
DS2106S 28–PIN SOIC (300 MIL)
DESCRIPTION
Fast SCSI and Ultra SCSI require the use of active ter-
minations at both ends of every cable segment in a
SCSI system with single–ended drivers and receivers.
Ultra SCSI requires support of active negation and hot
plugging. The DS2106 is fully compliant with these
standards.
The DS2106 integrates a low drop–out regulator and 18
precise switched 110 ohm termination resistors into a
28–pin 300 mil SOIC package.
Active termination provides: greater immunity to volt-
age drops on the TERMPWR (TERMination PoWeR)
line, enhanced high–level noise immunity, intrinsic
TERMPWR decoupling, and very low quiescent current
consumption. One DS2106 can be used to terminate
the Narrow SCSI bus, and a DS21S07A can be used
with a DS2106 for termination of a Wide SCSI bus.
022698 1/6
DS2106
REFERENCE DOCUMENTS
SCSI–2 (X3.131–1994)
SCSI–3 Parallel Interface (X3T10/855D)
SCSI–3 Fast–20 (X3T10/1071D)
Available from: Global Engineering Documents
15 Inverness Way East
Englewood, CO 80112–5704
Phone: (800) 854–7179,(303) 792–2181
Fax: (303) 792–2192
To ensure proper operation, the TPWR pin should be
connected to the SCSI bus TERMPWR line. As with all
analog circuitry, the TERMPWR lines should be
bypassed locally. A 2.2
µF
capacitor and a 0.01
µF
high
frequency capacitor is recommended between TPWR
and ground and placed as close as possible to the
DS2106. The DS2106 should be placed as close as
possible to the connector to minimize signal and power
trace length, thereby resulting in less input capacitance
and reflections which can degrade the bus signals.
To maintain the specified regulation, a 4.7
µF
capacitor
is required between the VREF pin and ground of each
DS2106. A high frequency cap (0.1
µF
ceramic recom-
mended) can also be placed on the VREF pin in applica-
tions that use fast rise/fall time drivers. Figure 2 details a
typical SCSI bus configuration. In an 8–bit data SCSI
bus (Narrow SCSI), one DS2106 is needed for proper
termination of the 18 active signal lines. One DS2106
and one DS21S07A can be used to terminate the 27
active signal lines in a 16–bit data SCSI bus (Wide
SCSI).
FUNCTION DESCRIPTION
The DS2106 is designed to be a single chip termination
subsystem for use in Narrow SCSI systems. The
DS2106 consists of a bandgap reference, buffer ampli-
fier, and 18 termination resistors (Figure 1). The voltage
regulator circuitry (bandgap reference and class AB
power amplifier) produces a precise laser trimmed 2.85
volt level and is capable of sourcing 24 mA into each of
the terminating resistors when the signal line is low
(active). When the external driver for a given signal line
turns off, the active terminator will pull that signal line to
2.85 volts (quiescent state). When used with an active
negation driver, the power amp can sink 22 mA per line
while keeping the voltage reference in regulation; the
terminating resistors maintain their 110 ohm value over
the entire voltage range. When all lines settle in the
quiescent state, the regulator will consume about
10 mA.
When the DS2106 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
DS2106 from the signal lines and effectively remove it
from the circuit. The power–down pin (PD) has an inter-
nal 50KΩ pull–up resistor. To place the DS2106 into an
active state, the PD pin should be left open circuited.
DS2106 BLOCK DIAGRAM
Figure 1
PD
TPWR
50K ohm
POWER
DOWN
CIRCUIT-
RY
110 ohms
BANDGAP
REFERENCE
+
R18
110 ohms
R17
–
110 ohms
R1
VREF
022698 2/6
DS2106
TYPICAL SCSI BUS CONFIGURATION
Figure 2
Termination Power Line
DS2106
TPWR
+
C2
C3
DS2106
TPWR
C1
+
VREF2
SCSI
CABLE
GND
R1
R8 R18
C1
+
VREF
GND
R1 R2
R18
SCSI
BUS
TRANSCEIVER
SCSI
BUS
TRANSCEIVER
SCSI
BUS
TRANSCEIVER
SCSI
BUS
TRANSCEIVER
NOTES:
1. C1 = 4.7
µF
tantalum
C2 = 2.2
µF
tantalum or 4.7
µF
aluminum
C3 = 0.01
µF
ceramic
2. If the DS2106 is to be embedded into a peripheral that will act as a target on a SCSI bus, it is recommended that
TERMPWR be derived from the SCSI cable, not generated locally. In this configuration, if a power failure occurs
in the peripheral, it will not affect the bus.
3. A high frequency bypass capacitor (0.1
µF
recommended) can be added in parallel to C1 for applications using
fast rise/fall time drivers.
022698 3/6
DS2106
PIN DESCRIPTION
Table 1
PIN
1
SYMBOL
PD
DESCRIPTION
Power Down.
When tied low, the DS2106 enters power–down mode. Contains
an internal 50KΩ pull–up. Strap low to deactivate the DS2106, leave open cir-
cuited to activate the DS2106.
Signal Termination 1.
110 Ohm termination. Connect to SCSI bus signal lines.
2 –6, 10 –
13, 16 – 19,
23 – 27
7, 8, 21
14
15
28
9, 20, 22
R1...R13
R14...R18
HS–GND
TPWR
VREF
GND
NC
Heat Sink Ground.
Internally connected to the mounting pad. Should be either
grounded or electrically isolated from other circuitry.
Termination Power.
Connect to the SCSI TERMPWR line. Bypass with a
2.2
µF
cap.
Reference Voltage.
2.85 volt reference; must be decoupled with a 4.7
µF
capacitor.
Ground.
Signal ground; 0.0 volts.
No Connect.
Do not connect to these pins.
022698 4/6
DS2106
ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground
Operating Temperature
Storage Temperature
Soldering Temperature
–1.0V to +7.0V
0°C to 70°C
–55°C to +125°C
260°C for 10 seconds
* This is a stress rating only and functional operation of the device at these or any other conditions above those
indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods of time may affect reliability.
RECOMMENDED OPERATING CONDITIONS
PARAMETER
TERMPWR Voltage
PD Active
PD Inactive
SYMBOL
V
TP
V
PDA
V
PDI
MIN
4.00
–0.3
2.0
TYP
MAX
5.25
0.8
V
TP
+0.3
UNITS
V
V
V
(0
°
C to 70
°
C)
NOTES
DC CHARACTERISTICS
PARAMETER
TERMPWR Current
Power Down Current
Termination Resistance
Die Thermal Shutdown
Power Down Termination
Capacitance
Input Leakage High
Input Leakage Low
SYMBOL
I
TP
I
TP
I
PD
R
TERM
TS
D
C
PD
I
IH
I
IL
–1.0
1.0
110
150
3.0
5.0
MIN
TYP
10
500
118
MAX
500
14
UNITS
mA
µA
ohm
°C
pF
µA
µA
(0
°
C to 70
°
C)
NOTES
1, 3
1, 4
1, 2, 5
1, 2
1
1, 2, 5, 6
1
1, 8
REGULATOR CHARACTERISTICS
PARAMETER
Output Voltage
Drop Out Voltage
Output Current
Line Regulation
Load Regulation
Current Limit
Sink Current
SYMBOL
V
REF
V
DROP
I
OUT
LI
REG
LO
REG
I
L
I
SINK
21.6
MIN
2.7
TYP
2.85
0.75
22.8
1.0
1.3
700
400
MAX
3.0
1.0
24.0
2.0
3.0
UNITS
V
V
mA
%
%
mA
mA
(0
°
C to 70
°
C)
NOTES
1, 2
3, 6
9
1, 4
1, 2
1
1
022698 5/6
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