Dallas DS2118M Ultra2 lvd/se scsi terminator Datasheet

DS2118M
Ultra2 LVD/SE SCSI Terminator
www.dalsemi.com
FEATURES
PIN ASSIGNMENT
Fully compliant with Ultra2 SCSI
Provides Multimode Low Voltage
Differential/Single-Ended (LVD/SE)
termination for 9 signal line pairs
Auto-selection of LVD or SE termination
5% tolerance on SE and LVD termination
resistance
Low power down capacitance of 3 pF
Onboard thermal shutdown circuitry
SCSI bus hot plug compatible
Fully supports actively negated SE SCSI
signals
VREF
NC
NC
R1P
R1N
R2P
R2N
HS GND
HS GND
HS GND
R3P
R3N
R4P
R4N
R5P
R5N
ISO
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
R9N
R9P
R8N
R8P
HS GND
HS GND
HS GND
R7N
R7P
R6N
R6P
DIFF_CAP
DIFFSENSE
MSTR/SLV
DS2118MB 36-Pin SSOP
DESCRIPTION
The DS2118M Ultra2 LVD/SE SCSI Terminator is both a Low Voltage Differential (LVD) and SingleEnded (SE) terminator. The multimode operation enables the designer to implement LVD in current
products while allowing the end-user SE backward compatibility with legacy devices. If the device is
connected in an LVD-only bus, the DS2118M will use LVD termination. If any SE devices are connected
to the bus, the DS2118M will use SE termination. This is accomplished automatically inside the part by
sensing the voltage on the SCSI bus DIFFSENS line.
For the LVD termination, the DS2118M integrates two regulated supplies with nine precision resistor
strings. For the SE termination, one regulator and nine precision 110-ohm resistors are used. Three
DS2118M terminators are needed for a Wide SCSI bus.
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DS2118M
REFERENCE DOCUMENTS
Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface (SPI)
Project: 0855-M, 1995
Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface 2 (SPI-2) Project: 1142-M, 1998
Available from:
American National Standards Institute (ANSI) Phone: (212) 642-4900
Global Engineering Documents 15 Inverness Way East; Englewood, CO 80112 Phone: (800) 854-7179
FUNCTIONAL DESCRIPTION
The DS2118M combines LVD and SE termination with DIFFSENS sourcing and detection. The LVD
termination section consists of two source/sink amplifiers (VTOP, VBOT), biasing circuitry and nine
precision resistor strings (RTOP, RMID, RBOT). The SE termination section consists of a 2.85V
source/sink regulator with 9 precision 110 Ohm resistors. The DIFFSENSE section consists of a 1.3V, 5
mA driver and a sensing circuit (Figure 1).
The DIFFSENSE circuitry decodes trinary logic. There will be one of three voltages on the SCSI control
line called DIFFSENS. Two comparators and a NAND gate determine if the voltage is below 0.6V, above
2.15V, or in between. That indicates the mode of the bus to be HVD, SE, or LVD, respectively.
The DS2118M’s DIFF_CAP pin monitors the DIFFSENS line to determine the proper operating mode of
the device; this mode is indicated by the SE/LVD/HVD outputs. The DIFFSENSE pin can also drive the
SCSI DIFFSENS line (when MSTR/SLV = 1) to determine the SCSI bus operating mode. The DS2118M
switches to the termination 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 laser trimmed resistor string with two amplifiers.
This configuration yields a 105Ω=differential and 150Ω=common mode impedance. A fail-safe bias of 112
mV 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 22 mA per line while keeping the voltage reference in regulation. The terminating resistors maintain
their 110Ω=value.
HVD Isolation Mode The DS2118M identifies that there is an HVD (high voltage differential) device on
the SCSI bus and isolates the termination pins from the bus.
When ISO is pulled high, the termination pins are isolated from the SCSI bus, Vref remains active, and
the bus mode indicators (SE/LVD/HVD) remain active. During thermal shutdown, the termination pins
are isolated from the SCSI bus, Vref becomes high impedance, and the bus mode indicators
(SE/LVD/HVD) remain active . The DIFFSENSE driver is shut down during either of these two events.
An internal pull-down resistor assures that the DS2118M will be terminating the bus if the ISO pin is left
floating.
To ensure proper operation, the TPWR pin should be connected to the SCSI bus TERMPWR line. As
with all analog circuitry, the TERMPWR and VDD 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 DS2118M. The DS2118M should be placed as close as possible to the SCSI connector
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DS2118M
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 (VREF) and
ground of each DS2118M. A high frequency cap (0.1 µF ceramic recommended) can also be placed on
the Vref pin in applications that use fast rise/fall time drivers. A typical SCSI bus configuration is shown
in Figure 2.
NOTE:
DIFFSENS – Refers to the SCSI bus signal.
DIFFSENSE – Refers to the DS2118M pin name and internal circuitry capable of driving the
DIFFSENS line.
DIFF_CAP - Refers to the DS2118M pin name and internal circuitry relating to monitoring the
DIFFSENS line.
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DS2118M
DS2118M BLOCK DIAGRAM Figure 1
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DS2118M
SCSI BUS CONFIGURATION Figure 2
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DS2118M
PIN DESCRIPTION Table 1
PIN
1
SYMBOL
VREF
2, 3
4-7, 11-16,
22-25, 29-32
8, 10, 26,
9, 28, 27
17
NC
RxP,
RxN
HS GND
18
19
20
21
33
34
35
36
DESCRIPTION
Reference Voltage. 2.85 volt reference; must be decoupled with a 4.7
µF cap.
No Connect. Do not connect these pins.
Signal Termination. Connect to SCSI bus signal lines.
Heat Sink Ground. Internally connected to the mounting pad. Should
be grounded.
ISO
Isolation. When pulled high, the DS2118M isolates it’s bus pins (RxP,
FxP) from the SCSI bus.
GND
Ground. Signal ground; 0.0 volts.
MSTR/SLV Master/slave. Mode select for the non-controlling terminator. When
pulled high (MSTR), the DIFFSENSE driver is enabled.
DIFFSENSE DIFFSENSE. Output to drive the SCSI bus DIFFSENS line.
DIFF_CAP DIFFSENSE CAPACITOR. Connect 0.1 µF capacitor for
DIFFSENSE filter. Input to detect the type of device (differential or
single-ended) on the SCSI bus.
SE
Single-ended. SE output of DIFFSENSE receiver; indicates SE bus
operation.
LVD
Low Voltage Differential. LVD output of DIFFSENSE receiver;
indicates LVD bus operation.
HVD
High Voltage Differential. HVD output of DIFFSENSE receiver;
indicates HVD bus operation or thermal shutdown.
TPWR
Termination Power. Connect to the SCSI TERMPWR line and
decouple with 2.2 µF capacitor.
RECOMMENDED OPERATING CONDITIONS
PARAMETER
Termpower Voltage
Logic 0
Logic 1
Operating Temperature
SYMBOL
MIN
Vtpwr
Vil
Vih
Vamb
4.0
-0.3
2.0
0
TYP
MAX
UNITS
5.50
+0.8
Vtpwr + 0.3
70
V
V
V
°C
NOTES
SINGLE ENDED CHARACTERISTICS
PARAMETER
SE Termination Resistance
SE Voltage Reference
SE Output Current
Output Capacitance
SYMBOL
Rse
MIN
104.5
Vref
lose
2.79
Cout
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TYP
110
MAX
115.5
UNITS
Ohms
2.93
25.4
Volts
mA
3
pF
NOTES
Vline=03.0 volts
Vline =
0.2 volts
guaranteed
by design
DS2118M
LOW VOLTAGE DIFFERENTIAL CHARACTERISTICS
PARAMETER
SYMBOL
MIN
MAX
UNITS
Rdm
100
110
Ohms
Rcm
110
190
Ohms
Differential Mode Bias
Vdm
100
125
mV
Common Mode Bias
Vcm
1.125
1.375
V
SYMBOL
MIN
MAX
UNITS
Differential Mode
Termination Resistance
Common Mode
Termination Resistance
TYP
NOTES
All lines
open
DC CHARACTERISTICS
PARAMETER
Termpower Current
Itpmr
Input Leakage High
Input Leakage Low
Iih
Iil
TYP
35
mA
-1.0
1.0
µA
µA
Output Current High
Ioh
-1.0
mA
Output Current Low
Iol
4.0
mA
Vseor
-0.3
0.5
V
Vlvdor
0.7
1.9
V
Vhvdor
2.4
Vtpwr
+ 0.3
V
DIFFSENSE Driver
Output Voltage
Vdso
1.2
1.4
V
DIFFSENSE Driver
Source Current
Idsh
15
mA
DIFFSENSE Driver
Sink Current
Idsl
200
µA
MAX
2.0
3.0
UNITS
%
%
mA
mA
DIFFSENS SE
Operating Range
DIFFSENS LVD
Operating Range
DIFFSENS HVD
Operating Range
5
20
REGULATOR CHARACTERISTICS
PARAMETER
Line Regulation
Load Regulation
Current Limit
Sink Current
SYMBOL
LIREG
LOREG
ILIM
ISINK
NOTES
All lines
open
VOUT = 2.4
volts;
SE/LVD/
HVD
pins only
VOUT = 0.4
volts;
SE/LVD/
HVD
pins only
MSTR/
SLV=1;
Ids=0-5 mA
MSTR/
SLV=1;
Vdso=0V
MSTR/
SLV=1;
Vdso=2.75V
(0°C to 70°C)
MIN
200
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TYP
1.0
1.3
350
NOTES
DS2118M
DS2118M 36-PIN SSOP PACKAGE
DIMENSIONS D AND E1 INCLUDE MOLD MISMATCH, BUT DO NOT
INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD
FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.254
MM PER SIDE.
SECTION A-A DIMENSIONS APPLY TO THE FLAT SECTION OF THE
LEAD BETWEEN 0.13 TO 0.25 MM FROM THE LEAD TIP.
THE CHAMFER ON THE BODY IS OPTIONAL. IF IT IS NOT PRESENT,
A VISUAL INDEX FEATURE MUST BE LOCATED WITHIN THE
CROSS-HATCHED AREA.
DIM
A
A1
b
c
D
E
E1
e
h
L
MIN
MAX
2.44
2.64
0.12
0.29
0.43
0.23
0.32
15.20 15.54
10.11 10.52
7.40
7.60
0.80 BSC
0.25
0.71
0.51
1.02
DIMENSIONS ARE IN MILLIMETERS
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