DALLAS DS2105

DS2105
DS2105
SCSI Terminator
FEATURES
• Fully
PIN ASSIGNMENT
compliant with SCSI–1, Fast SCSI and Ultra
TERMPWR1
1
16
PD
R1
2
15
VREF2
R2
3
14
R9
R3
4
13
R8
R4
5
12
R7
R5
6
11
R6
VREF1
7
10
NC
GND
8
9
SCSI
• Functionally compatible to the DS21S07A, targeted
for high volume applications
• Provides active termination for nine signal lines
• Laser–trimmed 110
ohm termination resistors have
5% tolerance
• Low dropout voltage
• Power–down
mode isolates termination resistors
from the bus
• Fully supports actively negated SCSI signals
• Onboard thermal shutdown circuitry
• 16–pin plastic SOIC (DS2105)
TERMPWR2
DS2105Z 16–PIN SOIC (150 MIL)
TERMPWR1
1
16
PD
R1
2
15
VREF2
R2
3
14
NC
R3
4
13
R9
R4
5
12
R8
R5
6
11
R7
VREF1
7
10
R6
GND
8
9
TERMPWR2
DS2105S 16–PIN SOIC (300 MIL)
DESCRIPTION
Fast SCSI and Ultra SCSI require the use of active terminations at both ends of every cable segment in a
SCSI system with single–ended 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 voltage drops on the TERMPWR (TERMination PoWeR)
line, enhanced high–level noise immunity, intrinsic
TERMPWR decoupling, and very low quiescent current
consumption. The DS2105, which integrates a regulator and nine precise switched 110 ohm termination resistors 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 termination but not the high performance of the DS21S07A.
The DS2105 is offered in both 300 mil and 150 mil SOIC
packages.
022698 1/7
DS2105
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 produces 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 VREF will
move less than 60 mV. When all lines settle in the quiescent state, the regulator will consume about 5 mA.
When the DS2105 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
DS2105 from the signal lines and effectively remove it
from the circuit. The power–down pin (PD) has an internal 50KΩ pull–up 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 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 DS2105’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 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
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
DS2105
TYPICAL SCSI BUS CONFIGURATION Figure 2
Termination Power Line
+
C2
DS2105
C1
+
TERMPWR1
TERMPWR2
VREF1
VREF2
GND
R1
SCSI
CABLE
R8 R9
SCSI
BUS
TRANSCEIVER
SCSI
BUS
TRANSCEIVER
DS2105
C1
+
TERMPWR1
TERMPWR2
VREF1
VREF2
GND
R1 R2
R9
SCSI
BUS
TRANSCEIVER
SCSI
BUS
TRANSCEIVER
NOTES:
1. C1 = 4.7 µF tantalum
C2 = 2.2 µF tantalum or 4.7 µF 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 µF recommended) can be added in parallel to C1 for applications using
fast rise/fall time drivers.
022698 3/7
DS2105
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 µF or 4.7 µF.
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
8
8
GND
9
9
TERMPWR2
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
16
16
PD
Power Down. When tied low, the DS2105 enters a power–down
mode. Contains an internal 50K pull–up. 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.
022698 4/7
Reference Voltage 1. Must be externally connected directly to
the VREF2 pin. Must be decoupled with a 4.7 µF capacitor 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 2.2 µF or 4.7 µF.
See Figure 2.
Reference Voltage 2. Must be externally connected directly to
the VREF1 pin. Must be decoupled with a 4.7 µF capacitor as
shown in Figure 2.
DS2105
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.
(0°C to 70°C)
RECOMMENDED OPERATING CONDITIONS
PARAMETER
SYMBOL
MIN
VTP
4.00
PD Active
VPDA
PD Inactive
VPDI
SYMBOL
MIN
TERMPWR Voltage
TYP
MAX
UNITS
5.25
V
–0.3
+0.8
V
2.0
VTP +0.3
V
TYP
MAX
UNITS
NOTES
5
250
8
mA
mA
1, 3
1, 4
µA
1, 2, 5
118
ohm
1, 2
°C
1
pF
1, 2, 5, 6
µA
1, 8
µA
1, 7
(0°C to 70°C)
DC CHARACTERISTICS
PARAMETER
NOTES
TERMPWR Current
ITP
ITP
Power Down Current
IPD
500
Termination Resistance
RTERM
Die Thermal Shutdown
TSD
150
Power Down Termination
Capacitance
CPD
3.0
Input Leakage High
IIH
Input Leakage Low
IIL
110
5.0
–1.0
1.0
(0°C to 70°C)
REGULATOR CHARACTERISTICS
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
NOTES
Output Voltage
VREF
2.7
2.85
3.0
V
1, 2
Drop Out Voltage
Output Current
VDROP
0.75
IOUT
1.0
V
3, 6
24.0
mA
9
Line Regulation
LIREG
1.0
2.0
%
1, 4
Load Regulation
LOREG
1.3
3.0
%
1, 2
mA
1
mA
1
Current Limit
ILIM
Sink Current
ISINK
350
200
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.
022698 5/7
DS2105
6. Guaranteed by design; not production tested.
7. R1 through R9 only.
8. R1 through R9 and PD.
9. VSIGNAL=0.2V.
DS2105Z SCSI TERMINATOR 16–PIN SOIC (150 MIL)
ÎÎ
ÎÎ
PKG
16–PIN
DIM
MIN
MAX
A IN.
MM
0.053
1.35
0.069
1.75
A1 IN.
MM
0.004
0.10
0.010
0.25
A2 IN.
MM
0.048
1.24
0.062
1.57
b IN.
MM
0.012
0.30
0.020
0.50
C IN
MM
0.007
0.17
0.011
0.28
D IN.
MM
0.386
9.80
0.393
9.98
e IN.
MM
0.050 BSC
1.27 BSC
E1 IN.
MM
0.150
3.81
0.158
4.01
H IN.
MM
0.230
5.84
0.244
6.20
L IN.
MM
0.016
0.40
0.050
0.89
0°
8°
Θ
022698 6/7
DS2105
DS2105S SCSI TERMINATOR 16–PIN SOIC (300 MIL)
The chamfer on the body is optional. If it is not present, a
terminal 1 identifier must be positioned so that 1/2 or
more of its area is contained in the hatched zone.
PKG
16–PIN
DIM
MIN
MAX
A IN.
MM
0.094
2.38
0.105
2.68
A1 IN.
MM
0.004
0.102
0.012
0.30
A2 IN.
MM
0.089
2.26
0.095
2.41
b IN.
MM
0.013
0.33
0.020
0.51
C IN
MM
0.009
0.229
0.013
0.33
D IN.
MM
0.398
10.11
0.412
10.46
e IN.
MM
0.050 BSC
1.27 BSC
E1 IN.
MM
0.290
7.37
0.300
7.62
H IN
MM
0.398
10.11
0.416
10.57
L IN
MM
0.016
0.40
0.040
1.02
0°
8°
Θ
022698 7/7