DS2107A
DS2107A
SCSI Terminator
FEATURES
PIN ASSIGNMENT
TERMPWR1
R1
R2
R3
R4
R5
VREF1
GND
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
PD
VREF2
NC
R9
R8
R7
R6
TERMPWR2
•
Fully compliant with SCSI and SCSI-2 standards
•
Backward compatible to the DS2107S
•
Provides active termination for 9 signal lines
•
Laser-trimmed
1% tolerance
110 ohm termination resistors have
•
Low dropout voltage
•
Power-down mode isolates termination resistors from
the bus
DS2107AS 16-Pin SOIC (300 mil)
TERMPWR1
HS–GND
R1
R2
R3
R4
R5
HS–GND
VREF1
GND
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
PD
VREF2
HS–GND
NC
R9
R8
R7
R6
HS–GND
TERMPWR2
•
Handles actively negated SCSI signals
•
Onboard thermal shutdown circuitry
•
16-pin plastic SOIC (DS2107AS) and 20-pin plastic
thin SSOP (DS2107AE)
DS2107AE 20-Pin TSSOP (173 mil)
ACTUAL FOOTPRINT SIZE
.41”
.26”
.41”
.27”
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.
022698 1/7
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
110 Ohms
R1
110 Ohms
R2
Bandgap
Reference
110 Ohms
R3
110 Ohms
R4
110 Ohms
R5
110 Ohms
R6
GND
110 Ohms
R7
110 Ohms
R8
110 Ohms
R9
VREF1
VREF2
022698 2/7
DS2107A
TYPICAL SCSI BUS CONFIGURATION
Figure 2
Termination Power Line
+
C3
DS2107A
TERMPWR1
TERMPWR2
VREF1
VREF2
GND
R1
SCSI
Cable
R8 R9
C3
+
DS2107A
TERMPWR1
TERMPWR2
VREF1
VREF2
GND
R1 R2
C1
C2
+
C1
C2
+
R9
SCSI
Bus
Transceiver
SCSI
Bus
Transceiver
SCSI
Bus
Transceiver
SCSI
Bus
Transceiver
NOTES:
1. C1 = 0.1µF ceramic
C2 = 4.7µF tantalum
C3 = 2.2
µF
tantalum or 4.7
µF
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.
022698 3/7
DS2107A
PIN DESCRIPTION
Table 1
DS2107AE
PIN
1
DS2107AS
PIN
1
SYMBOL
TERMPWR1
DESCRIPTION
Termination Power 1.
Should be connected to the SCSI
TERMPWR line. Must be decoupled with either a 2.2µF or 4.7µF.
See Figure 2.
Signal Termination 1.
110 ohm termination.
Signal Termination 2.
110 ohm termination.
Signal Termination 3.
110 ohm termination.
Signal Termination 4.
110 ohm termination.
Signal Termination 5.
110 ohm termination.
Reference Voltage 1.
Must be externally connected directly to
the VREF2 pin. Must be decoupled with a 4.7µF and a 0.1µF as
shown in Figure 2.
Ground.
Signal ground; 0.0V.
Termination Power 2.
Should be connected to the SCSI
TERMPWR line. Must be decoupled with either a 2.2µF or 4.7µF.
See Figure 2.
Signal Termination 6.
110 ohm termination.
Signal Termination 7.
110 ohm termination.
Signal Termination 8.
110 ohm termination.
Signal Termination 9.
110 ohm termination.
No Connect.
Do not connect any signal to this pin.
Reference Voltage 2.
Must be externally connected directly to
the VREF1 pin. Must be decoupled with a 4.7µF and a 0.1µF as
shown in Figure 2.
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.
Heat Sink Ground.
Internally connected to the mounting pad.
Should be either grounded or electrically isolated from other cir-
cuitry.
3
4
5
6
7
9
2
3
4
5
6
7
R1
R2
R3
R4
R5
VREF1
10
11
8
9
GND
TERMPWR2
13
14
15
16
17
19
10
11
12
13
14
15
R6
R7
R8
R9
NC
VREF2
20
16
PD
2,8,12,18
N/A
HS–GND
022698 4/7
DS2107A
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 maxi-
mum 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
PD Hysteresis
SYMBOL
I
TP
I
TP
I
PD
R
TERM
T
SD
C
PD
H
PD
108
MIN
TYP
5
100
110
150
8.5
280
10
112
MAX
250
8
UNITS
mA
mA
µA
ohms
°C
pF
mV
(0
°
C to 70
°
C)
NOTES
1,3
1,4
1,2,5
1,2
1
1,2,5,6
1
REGULATOR CHARACTERISTICS
PARAMETER
Output Voltage
Drop Out Voltage
Line Regulation
Load Regulation
Current Limit
Sink Current
SYMBOL
V
REF
V
DROP
LI
REG
LO
REG
I
LIM
I
SINK
300
MIN
2.79
TYP
2.85
0.75
1.0
1.3
350
200
MAX
2.91
1.0
2.0
3.0
400
UNITS
V
V
%
%
mA
mA
(0
°
C to 70
°
C)
NOTES
1,2
3,6
1,4,6
1,2,6
1
1
NOTES:
1.
2.
3.
4.
5.
6.
4.00V < TERMPWR < 5.25V.
0.0V < signal lines < 3.0V.
All signal lines = 0.0V.
All signal lines open.
PD = 0.0V.
Guaranteed by design; not production tested.
022698 5/7
京公网安备 11010802033920号
EEWORLD
