SS8218
Ultra160 Multi-mode LVD/SE SCSI Terminator
Features
Auto-selectable multi-mode Single-Ended
or LVD Termination
Meets SCSI-1, SCSI-2, SCSI-3 SPI Ultra
(Fast-20), Ultra 2(SPI-2 LVD), Ultra160 (SPI-3
LVD) standards.
Supports active negation
3pF channel capacitance
Thermal protection
Hot-swap compatible
5% tolerance on SE and LVD termination
resistance
28 and 36 pin SSOP package
28 Pin SSOP: Pin Compatible with DS2119
36 Pin SSOP: Pin Compatible with DS2118,
LX5241 and UCC5630
General Description
The SS8218 Multi-mode LVD/SE SCSI terminator pro-
vides a smooth transition to the next generation of
the SCSI Parallel Interface (SPI-3). It automatically
senses the bus, via DIFFSENS, and switches the ter-
mination to either single-ended (SE) or low voltage
differential (LVD) SCSI, dependent on which type of
devices are connected to the bus. If the SS8218 de-
tects a HVD SCSI device, it switches to a high imped-
ance state. For a 16-bit Wide SCSI bus to be opera-
tional, three SS8218 terminators are needed.
The Multi-mode terminator contains all functions re-
quired to terminate and auto detect and switch modes
for SCSI Parallel Interface (SPI) bus architectures. For
the SE termination, one regulator and nine precision
110ohm resistors are used. For the LVD termination,
the SS8218 integrates 18 regulated supplies with nine
precision resistor strings.
Applications
Server and workstation
High-end PC
Industrial PC
Disk Array (RAID)
SCSI cable
Pin Configuration
VREF
NC
NC
R1+
VREF
R1+
R1-
R2+
R2-
NC/HS GND
R3+
R3-
R4+
R4-
R5+
R5-
DISCNCT
GND
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
TPWR
TPWR
R9-
NC/HS GND
R9+
R8-
R8+
NC/HS GND
R7-
R7+
R6-
R6+
DIFFB
DIFFSENSE
M/S
R1-
R2+
R2-
HS/GND
HS/GND
HS/GND
R3+
R3-
R4+
R4-
R5+
R5-
DISCNCT
GND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
TPWR
HVD
LVD
SE
R9-
R9+
R8-
R8+
HS/GND
HS/GND
HS/GND
R7-
R7+
R6-
R6+
DIFFB
DIFFSENSE
M/S
28Pin SSOP/TSSOP
36Pin SSOP
Rev.2.01 6/06/2003
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SS8218
Ordering Information
PART NUMBER
SS8218-S4TB
SS8218-S4TR
SS8218-S5TB
SS8218-S5TR
SS8218-D3TB
SS8218-D3TR
TEMP. RANGE
0ºC-70ºC
0ºC-70ºC
0ºC-70ºC
0ºC-70ºC
0ºC-70ºC
0ºC-70ºC
PIN-PACKAGE
SSOP-28 pin / Tube
SSOP-28 pin / Tape & Reel
SSOP-36 pin / Tube
SSOP-36 pin / Tape & Reel
TSSOP-28 pin / Tube
TSSOP-28 pin / Tape & Reel
FEATURE
DISCNCT does not disable VREF
DISCNCT does not disable VREF
DISCNCT does not disable VREF
DISCNCT does not disable VREF
DISCNCT does not disable VREF
DISCNCT does not disable VREF
Note:
DIFFSENSRefers to the SCSI bus signal.
DIFFSENSERefers to the SS8218 pin name and internal circuitry relating to differential sensing.
DIFFB
Refers
to the SS8218 pin name and internal circuitry relating to monitoring the DIFFSENS line.
Functional Description
The SS8218 is used in multi-mode active termination
applications, where single ended (SE) and low voltage
differential (LVD) devices might coexist. The LVD ter-
mination section consists of 18 source/sink amplifiers
(VTOP, VBOT), biasing circuitry and nine precision
resistor strings (RTOP, RMID, RBOT). The SE termi-
nation section consists of a 2.85V source/sink regula-
tor with 9 precision 110ohm resistor. The DIFFSENSE
section consists of a 1.3V, 5mA driver and a sensing
circuit (Figure 1)
DIFFSENS is used to identify which types of SCSI
devices are present on the bus. If the voltage on
DIFFSENS is between 0-0.5V the bus is single-ended;
if it is between 0.7-1.9V the bus is LVD; and if it is
greater than 2.4V, the bus is HVD.
The SS8218 DIFFB pin monitors the DIFFSENS line to
determine the proper operating mode of the device;
this mode is indicated by the SE/LVD/HVD outputs.
HVD Isolation Mode
The SS8218 identifies that there
is an HVD (high voltage differential) device on the
SCSI bus and isolates the termination pins from the
bus.
When DISCNCT is pulled high, the termination pins
are isolated from the SCSI bus, and the bus mode
indicators (SE/LVD/HVD) as well as VREF remains
active. During thermal shutdown, the termination pins
are isolated from the SCSI bus and VREF becomes
high impedance. The DIFFSENSE driver is shut down
during either of these two events.
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 by-
passed locally. A 2.2µF capacitor and a 0.01µF high
frequency capacitor is recommended between TPWR
and ground and placed as close as possible to the
SS8218. The 8218 should be placed as close as
possible to the SCSI connector to minimize signal and
power trace length, thereby resulting in less input ca-
pacitance and reflections which can degrade the bus
signals.
The DIFFSENSE pin can drive the SCSI DIFFSENS
line (when M/S is pulled high) to determine the SCSI
bus operating mode. The SS8218 switches to the ter-
mination mode that is appropriate for the bus based on
the value of the DIFFSENS voltage. These modes are:
LVD mode
LVD termination is provided by a precision
resistor string with two amplifiers. This configuration
yields a 105Ω differential and 150Ω common mode
impedance. A fail safe bias of 112mV is maintained
when no drivers are connected to the SCSI bus.
SE mode
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 22mA
per line while keeping the voltage reference in regula-
tion. The terminating resistors maintain their 110Ω
value.
To maintain the specified regulation, a 4.7µF capacitor
is required between the VREF pin and ground of each
SS8218. A high frequency cap (0.1µF ceramic recom-
mended) can also be placed on the VREF pin in ap-
plications that use fast rise/fall time drivers. A typical
SCSI bus configuration is shown in Figure2.
An internal pull down resistor assures that the SS8218
will be terminating the bus if the DISCNCT pin is left
floating.
Rev.2.01 6/06/2003
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SS8218
Block Diagram
(Figure 1)
( 36pin SSOP only )
M/S
DIFFSENSE
SE LVD HVD
DISCNCT
THERMAL
SHUTDOWN
CIRCUITRY
DIFFSENSE
CIRCUITRY
VREF
VREF
110 Ohms
CONTROL
LOGIC
DIFFB
R1-
R9-
110 Ohms
REFERENCE
GENERATION
+
_
VTOP1
X9
RTOP1
R1-
RTOP9
R1-
R9-
R9-
RMID1
R1+
RMID9
R1+
R9+
R9+
RBOT1
+
_
RBOT9
VBOT1
X9
SE
GND
DRIV ER
Rev.2.01 6/06/2003
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SS8218
SCSI Bus Configuration
(Figure 2)
TERMPWR
2.2µF
TPWR
M/S
DISCNCT
CONTROL LINES (9)
TPWR
M/S
DISCNCT
TERMPWR
2.2µF
SS8218
SS8218
DIFFSENSE
VREF
DIFFB
20K
4.7µF
0.1µF
DIFFSENS
DIFFSENSE
DIFFB
VREF
20K
0.1µF
4.7µF
2.2µF
TPWR
M/S
DISCNCT
DATA LINES (9)
TPWR
M/S
DISCNCT
2.2µF
SS8218
SS8218
VREF
DIFFB
DIFFB
VREF
4.7µF
2.2µF
TPWR
M/S
DISCNCT
DATA LINES (9)
4.7µF
TPWR
M/S
DISCNCT
2.2µF
SS8218
SS8218
VREF
DIFFB
DIFFB
VREF
4.7µF
4.7µF
Rev.2.01 6/06/2003
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SS8218
Recommended Operating Conditions
PARAMETER
Termpower Voltage
Logic 0
Logic 1
Operating Temperature
SYMBOL
V
tpwr (SE)
V
tpwr (LVD)
V
il
V
ih
T
amb
MIN
4.0
2.9
-0.3
2.0
0
TYP
5
5
MAX
5.5
5.5
+0.8
V
tpwr
+0.3
70
UNITS
V
V
V
°C
Electrical Characteristics
Unless otherwise specified, these specifications apply over the operating ambient temperature range of
0°C≤T
A
≤
70°C.
≤
PARAMETER
LVD Terminator Section
Differential Mode Termination Resistance
Common Mode Termination Resistance
Differential Mode Bias
Common Mode Bias
Single Ended Terminator Section
Output Capacitance
SE Termination Resistance
SE Voltage Reference
SE output Current
Regulator Section
Line Regulation
Load Regulation
Current Limit
Sink Current
DC Section
Termpower Current
Input Leakage High
Input Leakage Low
Output Current High
Output Current Low
DIFFSENS Section
DIFFSENS SE Operating Range
DIFFSENS LVD Operating Range
DIFFSENS HVD Operating Range
DIFFSENSE Driver Output Voltage
DIFFSENSE Driver Source Current
DIFFSENSE Driver Sink Current
I
tpmr
I
ih
I
il
I
oh
I
ol
V
seor
V
lvdor
V
hvdor
V
dso
I
dsh
I
dsl
M/S=1; I
ds
= 0-5mA
M/S = 1; V
dso
=0V
M/S=1; V
dso
=2.75V
SE mode (No Load)
LVD mode (No Load)
-1.0
1.0
V
out
= 2.4 volts;SE/LVD/HVD Pins only
V
out
=0.4 volts;SE/LVD/HVD Pins only
-1.0
4.0
-0.3
0.7
2.4
1.2
5
20
0.5
1.9
V
tpwr
+0.3
1.4
15
200
4
20
mA
µA
µA
mA
mA
V
V
V
V
mA
µA
SYMBOL
Rdm
Rcm
Vdm
Vcm
Cout
Rse
Vref
Iose
LI
REG
LO
REG
I
LIM
I
SINK
Condition
MIN
100
TYP
105
150
112
1.25
MAX
110
190
125
1.375
3
115.5
2.93
25.4
2.5
3.5
UNITS
Ohms
Ohms
mV
V
pF
Ohms
Volts
mA
%
%
mA
mA
All lines Open
110
100
1.125
Note
Vline = 0-3.0 volts
Vline = 0.2 volts
104.5
2.79
110
2.85
1.0
1.3
350
200
Note:
Guaranteed by Design
.
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