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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

R1+

VREF

R1+

R1-

R2+

R2-

NC/HS GND

R3+

R3-

R4+

R4-

R5+

R5-

DISCNCT

GND

TPWR

R9-

NC/HS GND

R9+

R8-

R8+

NC/HS GND

R7-

R7+

R6-

R6+

DIFFB

DIFFSENSE

M/S

R1-

R2+

R2-

HS/GND

R3+

R3-

R4+

R4-

R5+

R5-

DISCNCT

GND

TPWR

HVD

LVD

R9-

R9+

R8-

R8+

HS/GND

R7-

R7+

R6-

R6+

DIFFB

DIFFSENSE

M/S

28Pin SSOP/TSSOP

36Pin SSOP

Rev.2.01 6/06/2003

www.SiliconStandard.com

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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

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

Note:

DIFFSENSRefers to the SCSI bus signal.

DIFFSENSERefers 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

110 Ohms

CONTROL

LOGIC

DIFFB

R1-

R9-

110 Ohms

REFERENCE

GENERATION

VTOP1

RTOP1

R1-

RTOP9

R1-

R9-

RMID1

R1+

RMID9

R1+

R9+

RBOT1

RBOT9

VBOT1

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

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

VREF

DIFFB

VREF

4.7µF

2.2µF

TPWR

M/S

DISCNCT

DATA LINES (9)

4.7µF

TPWR

M/S

DISCNCT

2.2µF

SS8218

VREF

DIFFB

VREF

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

tpwr (SE)

tpwr (LVD)

amb

MIN

4.0

2.9

-0.3

2.0

TYP

MAX

5.5

+0.8

tpwr

+0.3

UNITS

°C

Electrical Characteristics

Unless otherwise specified, these specifications apply over the operating ambient temperature range of

0°C≤T

≤

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

tpmr

seor

lvdor

hvdor

dso

dsh

dsl

M/S=1; I

= 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

out

= 2.4 volts;SE/LVD/HVD Pins only

out

=0.4 volts;SE/LVD/HVD Pins only

-1.0

4.0

-0.3

0.7

2.4

1.2

0.5

1.9

tpwr

+0.3

1.4

200

µA

SYMBOL

Rdm

Rcm

Vdm

Vcm

Cout

Rse

Vref

Iose

REG

LIM

SINK

Condition

MIN

100

TYP

105

150

112

1.25

MAX

110

190

125

1.375

115.5

2.93

25.4

2.5

3.5

UNITS

Ohms

Volts

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

Rev.2.01 6/06/2003

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