/home/web/htmldatasheet/html/maxim/170429
DS2105
SCSI Terminator
DS2105
022698 1/7
FEATURES
Fully compliant with SCSI1, Fast SCSI and Ultra
SCSI
Functionally compatible to the DS21S07A, targeted
for high volume applications
Provides active termination for nine signal lines
Lasertrimmed 110 ohm termination resistors have
5% tolerance
Low dropout voltage
Powerdown mode isolates termination resistors
from the bus
Fully supports actively negated SCSI signals
Onboard thermal shutdown circuitry
16pin plastic SOIC (DS2105)
PIN ASSIGNMENT
1
2
3
4
5
6
7
8
9
DS2105Z 16PIN SOIC (150 MIL)
TERMPWR1
R1
R2
R3
R4
R5
VREF1
GND
PD
VREF2
R9
R8
R7
R6
NC
TERMPWR2
11
12
13
14
15
16
10
1
2
3
4
5
6
7
8
9
DS2105S 16PIN SOIC (300 MIL)
TERMPWR1
R1
R2
R3
R4
R5
VREF1
GND
PD
VREF2
NC
R9
R8
R7
R6
TERMPWR2
11
12
13
14
15
16
10
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 singleended drivers and receivers.
The DS2105 SCSI Terminator, which is fully compliant
with these standards, enables the designer to gain the
benefits of active termination: greater immunity to volt-
age drops on the TERMPWR (TERMination PoWeR)
line, enhanced highlevel noise immunity, intrinsic
TERMPWR decoupling, and very low quiescent current
consumption. The DS2105, which integrates a regula-
tor and nine precise switched 110 ohm termination re-
sistors into a monolithic IC, is a functionally compatible
version of the DS21S07A. With relaxed output current
and termination tolerances, the DS2105 is intended for
high volume applications which require active termina-
tion but not the high performance of the DS21S07A.
The DS2105 is offered in both 300 mil and 150 mil SOIC
packages.
DS2105
022698 2/7
FUNCTIONAL DESCRIPTION
The DS2105 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, and V
REF
will
move less than 60 mV. When all lines settle in the quies-
cent state, the regulator will consume about 5 mA.
When the DS2105 is put into powerdown mode by
bringing PD low, the powerdown circuitry will turn off
the transistors on each signal line. This will isolate the
DS2105 from the signal lines and effectively remove it
from the circuit. The powerdown pin (PD) has an inter-
nal 50K
pullup resistor. To place the DS2105 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 DS2105 requires
a 4.7
F capacitor connected between the VREF pins
and ground. Figure 2 details a typical SCSI bus configu-
ration. In an 8bit wide SCSI bus arrangement ("A"
Cable), two DS2105's would be needed at each end of
the SCSI cable in order to terminate the 18 active signal
lines. In a 16bit wide SCSI bus arrangement ("P"
Cable), three DS2105's would be needed at each end of
the SCSI cable in order to terminate the 27 active signal
lines.
DS2105 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
DS2105
022698 3/7
TYPICAL SCSI BUS CONFIGURATION Figure 2
Termination Power Line
SCSI
BUS
TRANSCEIVER
SCSI
BUS
TRANSCEIVER
SCSI
BUS
TRANSCEIVER
SCSI
BUS
TRANSCEIVER
DS2105
TERMPWR1
TERMPWR2
VREF1
VREF2
GND
R1
R2
R9
DS2105
R8
TERMPWR1
TERMPWR2
VREF1
VREF2
GND
R1
R9
SCSI
CABLE
C1
+
C1
+
+
C2
NOTES:
1. C1 = 4.7
F tantalum
C2 = 2.2
F tantalum or 4.7
F aluminum
2. If the DS2105 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
F recommended) can be added in parallel to C1 for applications using
fast rise/fall time drivers.
DS2105
022698 4/7
PIN DESCRIPTION Table 1
DS2105S
PIN
DS2105Z
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.
2
2
R1
Signal Termination 1. 110 ohm termination.
3
3
R2
Signal Termination 2. 110 ohm termination.
4
4
R3
Signal Termination 3. 110 ohm termination.
5
5
R4
Signal Termination 4. 110 ohm termination.
6
6
R5
Signal Termination 5. 110 ohm termination.
7
7
VREF1
Reference Voltage 1. Must be externally connected directly to
the VREF2 pin. Must be decoupled with a 4.7
F capacitor as
shown in Figure 2.
8
8
GND
Ground. Signal ground; 0.0V.
9
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.
10
11
R6
Signal Termination 6. 110 ohm termination.
11
12
R7
Signal Termination 7. 110 ohm termination.
12
13
R8
Signal Termination 8. 110 ohm termination.
13
14
R9
Signal Termination 9. 110 ohm termination.
15
15
VREF2
Reference Voltage 2. Must be externally connected directly to
the VREF1 pin. Must be decoupled with a 4.7
F capacitor as
shown in Figure 2.
16
16
PD
Power Down. When tied low, the DS2105 enters a powerdown
mode. Contains an internal 50K pullup. Strap low to deactivate
the DS2105, leave open circuited to activate the DS2105.
14
10
NC
No Connect. Do not connect any signal to this pin.
DS2105
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 maximum 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
500
A
1, 2, 5
Termination Resistance
R
TERM
110
118
ohm
1, 2
Die Thermal Shutdown
T
SD
150
C
1
Power Down Termination
Capacitance
C
PD
3.0
5.0
pF
1, 2, 5, 6
Input Leakage High
I
IH
1.0
A
1, 8
Input Leakage Low
I
IL
1.0
A
1, 7
REGULATOR CHARACTERISTICS
(0
C to 70
C)
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
NOTES
Output Voltage
V
REF
2.7
2.85
3.0
V
1, 2
Drop Out Voltage
V
DROP
0.75
1.0
V
3, 6
PDF 
ZIP