DS2107A
SCSI Terminator
DS2107A
022698 1/7
FEATURES
Fully compliant with SCSI and SCSI-2 standards
Backward compatible to the DS2107S
Provides active termination for 9 signal lines
Laser-trimmed 110 ohm termination resistors have
1% tolerance
Low dropout voltage
Power-down mode isolates termination resistors from
the bus
Handles actively negated SCSI signals
Onboard thermal shutdown circuitry
16-pin plastic SOIC (DS2107AS) and 20-pin plastic
thin SSOP (DS2107AE)
PIN ASSIGNMENT
7
1
2
3
4
5
6
7
8
9
DS2107AS 16-Pin SOIC (300 mil)
TERMPWR1
R1
R2
R3
R4
R5
VREF1
GND
PD
VREF2
NC
R9
R8
R7
R6
TERMPWR2
1
2
3
4
5
6
8
9
DS2107AE 20-Pin TSSOP (173 mil)
TERMPWR1
R1
R2
R3
R4
R5
VREF1
GND
PD
VREF2
NC
R9
R8
R7
R6
TERMPWR2
HSGND
HSGND
HSGND
HSGND
10
11
12
13
14
15
16
17
18
19
20
11
12
13
14
15
16
10
ACTUAL FOOTPRINT SIZE
.41"
.41"
.27"
.26"
DS2107AS
DS2107AE
DESCRIPTION
The SCSI-2 standard recommends the use of active ter-
minations at both ends of every cable segment in a
SCSI system with single-ended drivers and receivers.
The DS2107A SCSI Terminator, which is fully compliant
with the standard, enables the designer to gain the
benefits of active termination: 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. The DS2107A integrates a regulator and
nine precise switched 110 ohm termination resistors
into a monolithic IC.
DS2107A
022698 2/7
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
F and 4. 7
F 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
GND
TERMPWR1
TERMPWR2
PD
Power
Down
Circuitry
50K Ohm
Bandgap
Reference
110 Ohms
R1
R2
R3
R4
R5
R6
R7
R8
R9
VREF1
VREF2
110 Ohms
110 Ohms
110 Ohms
110 Ohms
110 Ohms
110 Ohms
110 Ohms
110 Ohms
DS2107A
022698 3/7
TYPICAL SCSI BUS CONFIGURATION Figure 2
Termination Power Line
SCSI
Bus
Transceiver
SCSI
Bus
Transceiver
SCSI
Bus
Transceiver
SCSI
Bus
Transceiver
DS2107A
TERMPWR1
TERMPWR2
VREF1
VREF2
GND
R1
R2
R9
DS2107A
R8
TERMPWR1
TERMPWR2
VREF1
VREF2
GND
R1
R9
SCSI
Cable
C3
C1
C2
+
+
C3
+
C1
C2
+
NOTES:
1. C1 = 0.1
F ceramic
C2 = 4.7
F tantalum
C3 = 2.2
F tantalum or 4.7
F aluminum
2. If the DS2107A 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.
DS2107A
022698 4/7
PIN DESCRIPTION Table 1
DS2107AE
PIN
DS2107AS
PIN
SYMBOL
DESCRIPTION
1
1
TERMPWR1
Termination Power 1. Should be connected to the SCSI
TERMPWR line. Must be decoupled with either a 2.2
F or 4.7
F.
See Figure 2.
3
2
R1
Signal Termination 1. 110 ohm termination.
4
3
R2
Signal Termination 2. 110 ohm termination.
5
4
R3
Signal Termination 3. 110 ohm termination.
6
5
R4
Signal Termination 4. 110 ohm termination.
7
6
R5
Signal Termination 5. 110 ohm termination.
9
7
VREF1
Reference Voltage 1. Must be externally connected directly to
the VREF2 pin. Must be decoupled with a 4.7
F and a 0.1
F as
shown in Figure 2.
10
8
GND
Ground. Signal ground; 0.0V.
11
9
TERMPWR2
Termination Power 2. Should be connected to the SCSI
TERMPWR line. Must be decoupled with either a 2.2
F or 4.7
F.
See Figure 2.
13
10
R6
Signal Termination 6. 110 ohm termination.
14
11
R7
Signal Termination 7. 110 ohm termination.
15
12
R8
Signal Termination 8. 110 ohm termination.
16
13
R9
Signal Termination 9. 110 ohm termination.
17
14
NC
No Connect. Do not connect any signal to this pin.
19
15
VREF2
Reference Voltage 2. Must be externally connected directly to
the VREF1 pin. Must be decoupled with a 4.7
F and a 0.1
F as
shown in Figure 2.
20
16
PD
Power Down. When tied low, the DS2107A enters a power-down
mode. Contains an internal 50K pull-up. Strap low to deactivate
the DS2107A, leave open circuited to activate the DS2107A.
2,8,12,18
N/A
HSGND
Heat Sink Ground. Internally connected to the mounting pad.
Should be either grounded or electrically isolated from other cir-
cuitry.
DS2107A
022698 5/7
ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground
-1.0V to +7.0V
Operating Temperature
0
C to +70
C
Storage Temperature
-55
C to 125
C
Soldering Temperature
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 maxi-
mum rating conditions for extended periods of time may affect reliability.
RECOMMENDED OPERATING CONDITIONS
(0
C to 70
C)
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
NOTES
TERMPWR Voltage
V
TP
4.00
5.25
V
PD Active
V
PDA
-0.3
0.8
V
PD Inactive
V
PDI
2.0
V
TP
+0.3
V
DC CHARACTERISTICS
(0
C to 70
C)
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
NOTES
TERMPWR Current
I
TP
I
TP
5
250
8
mA
mA
1,3
1,4
Power Down Current
I
PD
100
A
1,2,5
Termination Resistance
R
TERM
108
110
112
ohms
1,2
Die Thermal Shutdown
T
SD
150
C
1
Power Down Termination
Capacitance
C
PD
8.5
10
pF
1,2,5,6
PD Hysteresis
H
PD
280
mV
1
REGULATOR CHARACTERISTICS
(0
C to 70
C)
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
NOTES
Output Voltage
V
REF
2.79
2.85
2.91
V
1,2
Drop Out Voltage
V
DROP
0.75
1.0
V
3,6
Line Regulation
LI
REG
1.0
2.0
%
1,4,6
Load Regulation
LO
REG
1.3
3.0
%
1,2,6
Current Limit
I
LIM
300
350
400
mA
1
Sink Current
I
SINK
200
mA
1
NOTES:
1. 4.00V < TERMPWR < 5.25V.
2. 0.0V < signal lines < 3.0V.
3. All signal lines = 0.0V.
4. All signal lines open.
5. PD = 0.0V.
6. Guaranteed by design; not production tested.
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