DS2106 Datasheet by Maxim Integrated

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DS2106
SCSI Terminator
DS2106
022698 1/6
FEATURES
Fully compliant with SCSI–1, Fast SCSI and
Ultra SCSI
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
PIN ASSIGNMENT
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
VREF
PD
R1
R2
R3
R4
R5
HS–GND
HS–GND
NC
R6
R7
R8
R9
TPWR
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.
fir
DS2106
022698 2/6
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
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 50K pull–up resistor. To place the DS2106 into an
active state, the PD pin should be left open circuited.
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).
DS2106 BLOCK DIAGRAM Figure 1
PD
POWER
DOWN
CIRCUIT-
RY
50K ohm
BANDGAP
REFERENCE R18
R17
R1
VREF
110 ohms
110 ohms
110 ohms
+
TPWR
ll [:lv 5+ {v
DS2106
022698 3/6
TYPICAL SCSI BUS CONFIGURATION Figure 2
Termination Power Line
SCSI
BUS
TRANSCEIVER
SCSI
BUS
TRANSCEIVER
SCSI
BUS
TRANSCEIVER
SCSI
BUS
TRANSCEIVER
DS2106
TPWR
GND
R1 R2R18
DS2106
R8
TPWR
VREF
GND
R1 R18
SCSI
CABLE
C1 +C1 +
+
C2 C3
VREF2
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.
DS2106
022698 4/6
PIN DESCRIPTION Table 1
PIN SYMBOL DESCRIPTION
1 PD Power Down. When tied low, the DS2106 enters power–down mode. Contains
an internal 50K pull–up. Strap low to deactivate the DS2106, leave open cir-
cuited to activate the DS2106.
2 –6, 10 –
13, 16 – 19,
23 – 27
R1...R13
R14...R18 Signal Termination 1. 110 Ohm termination. Connect to SCSI bus signal lines.
7, 8, 21 HS–GND Heat Sink Ground. Internally connected to the mounting pad. Should be either
grounded or electrically isolated from other circuitry.
14 TPWR Termination Power. Connect to the SCSI TERMPWR line. Bypass with a
2.2 µF cap.
15 VREF Reference Voltage. 2.85 volt reference; must be decoupled with a 4.7 µF
capacitor.
28 GND Ground. Signal ground; 0.0 volts.
9, 20, 22 NC No Connect. Do not connect to these pins.
DS2106
022698 5/6
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 VTP 4.00 5.25 V
PD Active VPDA –0.3 0.8 V
PD Inactive VPDI 2.0 VTP +0.3 V
DC CHARACTERISTICS (0°C to 70°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
TERMPWR Current ITP
ITP 10 500
14 mA 1, 3
1, 4
Power Down Current IPD 500 µA1, 2, 5
Termination Resistance RTERM 110 118 ohm 1, 2
Die Thermal Shutdown TSD150 °C 1
Power Down Termination
Capacitance CPD 3.0 5.0 pF 1, 2, 5, 6
Input Leakage High IIH –1.0 µA 1
Input Leakage Low IIL 1.0 µA1, 8
REGULATOR CHARACTERISTICS (0°C to 70°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Output Voltage VREF 2.7 2.85 3.0 V 1, 2
Drop Out Voltage VDROP 0.75 1.0 V 3, 6
Output Current IOUT 21.6 22.8 24.0 mA 9
Line Regulation LIREG 1.0 2.0 % 1, 4
Load Regulation LOREG 1.3 3.0 % 1, 2
Current Limit IL700 mA 1
Sink Current ISINK 400 mA 1
The chamfer on the body is optional. If it is not present, a termi-
nal 1 identifier must be positioned so that 1/2 or more of its area
is contained in the hatched zone.
DS2106
022698 6/6
NOTES:
1. 4.00V < TERMPWR < 5.50V.
2. 0.0V < signal lines < TERMPWR.
3. All signal lines = 0.0V.
4. All signal lines open.
5. Power down enabled; PD = 0.0V.
6. Guaranteed by design; not production tested.
7. R1 through R18 only.
8. R1 through R18 and PD.
9. VSIGNAL = 0.2V.
28–PIN SOIC (300 MIL)
PKG 28–PIN
DIM MIN MAX
A IN.
MM 0.094
2.39 0.105
2.67
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 0.698
17.73 0.712
18.08
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
Θ0°8°

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