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090199

FEATURES

Fully compliant with Ultra2, Ultra3, and
Ultra 160/m 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

PIN ASSIGNMENT

DESCRIPTION

The DS2117M Ultra3 LVD/SE SCSI Terminator is both a Low Voltage Differential (LVD) and Single-
Ended (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 DS2117M will use LVD termination. If any SE devices are connected
to the bus, the DS2117M 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 DS2117M integrates two current sources with nine precision resistor
strings. For the SE termination, one regulator and nine precision 110-ohm resistors are used. Three
DS2117M terminators are needed for a wide SCSI bus.

DS2117M

Ultra3 LVD/SE SCSI Terminator

www.dalsemi.com

34
33

31
30
29
28
27
26
25
24

LVD
SE
R9N

R8N

R8P

HS GND
HS GND
HS GND

R7N
R7P
R6N

R9P

R1P

R1N

R2N

HS GND
HS GND

R3P

R3N

R4P

R4N

R2P

DS2117MB 36-Pin SSOP

VREF

TPWR
HVD

HS GND

2
3

5
6
7
8
9

10
11
12
13

15
16
17
18

22
21
20
19

R5P

R5N

ISO

GND

DIFF_CAP
DIFFSENSE
MSTR/SLV

R6P

DS2117M

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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
Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface 3 (SPI-3) Project: 1302-D, 1999
Small Computer Systems Interface (SCSI-3) SCSI Parallel Interface 4 (SPI-4) Project: 1365-D, xxxx

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 DS2117 combines LVD and SE termination with DIFFSENSE sourcing and detection.

A bandgap reference is fed into two amplifiers, which creates a 1.25V reference voltage and a 2.85V
reference voltage. The control logic determines which of these references will be applied to the
termination resistors. If the SCSI bus is in LVD mode, then the 1.25V reference will be used. If the SCSI
bus is in SE mode, then the 2.85V reference will be used. That same control logic will switch in/out
parallel resistors to change the total termination resistance accordingly. Finally, in SE mode the Rp pins
will be switched to ground.

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 DS2117M'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 DS2117M
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 current
sources. This configuration yields a 105

=differential and 150

=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 110

=value.

HVD Isolation Mode The DS2117M 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 is grounded, and the
bus mode indicators (SE/LVD/HVD) remain active. During thermal shutdown, the termination pins are
isolated from the SCSI bus, Vref is grounded, and the bus mode indicators (SE/LVD/HVD) remain
active. The

DIFFSENSE

driver is shut down during either of these two events.

DS2117M

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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

�

F capacitor

and a 0.01

�

F high frequency capacitor is recommended between TPWR and ground and placed as close

as possible to the DS2117M. The DS2117M should be placed as close as possible to the SCSI 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

�

F capacitor is required between the Vref pin (VREF) and

ground of each DS2117M. A high frequency cap (0.1

�

F 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.

DIFFSENS noise filtering The DS2117M incorporates a digital filter to remove high frequency
transients on the DIFFSENS control line, thereby eliminating erroneous switching between modes. This
filter eliminates the need for the external capacitor and resistor, which heretofore performed this function.
The external filter may be used in addition to the digital filter if the DS2117M and DS2118M are to be
used interchangeably.

NOTE:

DIFFSENS � Refers to the SCSI bus signal.
DIFFSENSE � Refers to the DS2117M pin name and internal circuitry capable of driving the

DIFFSENS line.

DIFF_CAP - Refers to the DS2117M pin name and internal circuitry relating to monitoring the

DIFFSENS line.

DS2117M

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PIN DESCRIPTION Table 1

PIN

SYMBOL

DESCRIPTION

VREF

Reference Voltage. 2.85 volt reference in SE mode and 1.25 volt
reference in LVD mode; must be decoupled with a 4.7 �F cap.

2, 3

No Connect. Do not connect these pins.

4-7, 11-16,

22-25, 29-32

RxP

RxN

Signal Termination. Connect to SCSI bus signal lines.

8, 10, 26,

9, 28, 27

HS GND

Heat Sink Ground. Internally connected to the mounting pad. Should
be grounded.

ISO

Isolation. When pulled high, the DS2117M isolates its bus pins (RxP,
RxN) 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 �F capacitor for
DIFFSENSE filter. Input to detect the type of device (differential or
single-ended) on the SCSI bus.

Single-ended. SE output of DIFFSENSE receiver; output high
indicates SE bus operation.

LVD

Low Voltage Differential. LVD output of DIFFSENSE receiver;
output high indicates LVD bus operation.

HVD

High Voltage Differential. HVD output of DIFFSENSE receiver;
output high indicates HVD bus operation or thermal shutdown.

TPWR

Termination Power. Connect to the SCSI TERMPWR line and
decouple with 2.2 �F capacitor.

RECOMMENDED OPERATING CONDITIONS

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

Termpower Voltage

SE mode
LVD mode

tpwr

(SE)

tpwr

(LVD)

4.0
2.7

5.5
5.5

V
V

Logic 0

-0.3

+0.8

Logic 1

2.0

tpwr

+ 0.3

Operating Temperature

amb

�C

DS2117M

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SINGLE ENDED CHARACTERISTICS

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

SE Termination Resistance

Rse

104.5

110

115.5

Ohms

SE Voltage Reference

Vref

2.7

3.0

Volts

SE Output Current

lose

25.4

Output Capacitance

Cout

LOW VOLTAGE DIFFERENTIAL CHARACTERISTICS

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

Differential Mode
Termination Resistance

Rdm

100

110

Ohms

Common Mode
Termination Resistance

Rcm

110

190

Ohms

Differential Mode Bias

Vdm

100

125

Common Mode Bias

Vcm

1.125

1.375

DC CHARACTERISTICS

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

Termpower Current

tpmr

Input Leakage High

-1.0

�A

Input Leakage Low

1.0

�A

Output Current High

-1.0

5, 7

Output Current Low

4.0

6, 7

DIFFSENS SE
Operating Range

seor

-0.3

0.5

DIFFSENS LVD
Operating Range

lvdor

0.7

1.9

DIFFSENS HVD
Operating Range

hvdor

2.4

tpwr

+ 0.3

DIFFSENSE Driver
Output Voltage

dso

1.2

1.4

8, 9

DIFFSENSE Driver
Source Current

dsh

8, 10, 12

DIFFSENSE Driver
Sink Current

dsl

200

�A

8, 11

Thermal Shutdown

150

�C

DS2117M

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DS2117M 36-PIN SSOP PACKAGE

CSP option - mechanical drawing

Please check the following web location for latest information on our Chip Scale Package (a.k.a
"solder bump") "http://www.dalsemi.com/DocControl/Chips/index.html"

DIM

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 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.

DIMENSIONS ARE IN MILLIMETERS

Part Number DS2117M