DS2109S/T&R

DS2109S/T&R Datasheet

DS2109

Part	Datasheet
DS2109S/T&R	DS2109S/T&R (pdf)

Related Parts	Information
DS2109S	DS2109S

PDF Datasheet Preview
DS2109 DS2109 Plug and Play SCSI Terminator FEATURES • Fully compliant with Fast SCSI and Ultra SCSI • Compatible with Plug and Play SCSI Profile • Functionally compatible with DS21S07A • Provides active termination for 18 signal lines • 2% tolerance on termination resistors and voltage regulator • Bus termination sensing • Low power down capacitance of 3 pF • Onboard thermal shutdown circuitry PIN ASSIGNMENT TPWR VREF DS2109, DS2109S SOIC 300 MIL DESCRIPTION The DS2109 is intended for one chip Plug and Play PnP SCSI termination. Plug and Play SCSI requires the terminator on computer motherboards or host bus adapters to automatically switch off if an external device is connected to the system. The DS2109 satisfies this requirement by offering the engineer a choice of onboard current sensing circuitry or onboard ground detect circuitry. If an external device is connected, the DS2109 will automatically be isolated from the SCSI bus thereby maintaining proper system termination. The DS2109 integrates a low regulator, 18 precise switched 110 ohm termination resistors, and bus termination sensors into a 300 mil SOIC package. Active termination provides greater immunity to voltage drops on the TERMPWR TERMination PoWeR line, enhanced noise immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS2109 contains an output port that can control the power down pin of additional terminators DS21S07A for Wide SCSI applications. 022698 1/10 DS2109 REFERENCE DOCUMENTS Parallel Interface X3T10/855D Available from Global Engineering Documents 15 Inverness Way East Englewood, CO Phone 800 Fax 303 PnP SCSI Specification PnP ISA Specification PnP BIOS Specification PnP Option ROM Specification Available from Plug and Play forum on CompuServe Go plugplay . FUNCTIONAL DESCRIPTION The DS2109 is designed to be a single chip termination subsystem for use in PnP SCSI systems, Figure When embedded on a host bus adapter or motherboard, the DS2109 can automatically sense the termination status of the SCSI bus and attach or isolate its resistors as needed to maintain proper bus termination. External and internal active termination can be provided by the DS21S07A. DS2109 APPLICATION ENVIRONMENT Figure 1 DS2109 AUTOMATIC TERMINATOR HOST SCSI PROTOCOL CHIP SCSI PERIPHERAL DEVICES PERIPHERAL SUBSYSTEM EXTERNAL TERMINATOR TWO DS21S07A HIGH DENSITY CONNECTORS SCSI EXTERNAL CABLE SCSI INTERNAL CABLES INTERNAL TERMINATOR TWO DS21S07A 022698 2/10 DS2109 The DS2109 consists of 3 major functional blocks, Figure 2: • Voltage reference, terminating resistors, and isolation switches • Bus current sensing circuitry • Bus ground sensing circuity When the Bus Ground Sensing Circuitry or Bus Current Sensing Circuitry determine that the SCSI bus is prop- erly terminated without the DS2109, the power down buffer isolates the resistors from the SCSI bus and disables the power amp, thereby placing the DS2109 in a low power mode the bus sensing circuitry always stays active . The PDO Power Down Output pin can be connected to the pin of a DS21S07A SCSI terminator for Wide SCSI configurations, Figure DS2109 BLOCK DIAGRAM Figure 2 PDI PDE BUS GROUND SENSING CIRCUITRY DISABLE

PDF Datasheet Preview

DS2109

DS2109 Plug and Play SCSI Terminator

FEATURES
• Fully compliant with Fast SCSI and Ultra

SCSI
• Compatible with Plug and Play SCSI Profile
• Functionally compatible with DS21S07A
• Provides active termination for 18 signal lines
• 2% tolerance on termination resistors and voltage
regulator
• Bus termination sensing
• Low power down capacitance of 3 pF
• Onboard thermal shutdown circuitry

PIN ASSIGNMENT

TPWR

VREF

DS2109, DS2109S SOIC 300 MIL

DESCRIPTION The DS2109 is intended for one chip Plug and Play PnP SCSI termination. Plug and Play SCSI requires the terminator on computer motherboards or host bus adapters to automatically switch off if an external device is connected to the system. The DS2109 satisfies this requirement by offering the engineer a choice of onboard current sensing circuitry or onboard ground detect circuitry. If an external device is connected, the DS2109 will automatically be isolated from the SCSI bus thereby maintaining proper system termination.

The DS2109 integrates a low regulator, 18 precise switched 110 ohm termination resistors, and bus termination sensors into a 300 mil SOIC package. Active termination provides greater immunity to voltage drops on the TERMPWR TERMination PoWeR line, enhanced noise immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS2109 contains an output port that can control the power down pin of additional terminators DS21S07A for Wide SCSI applications.
022698 1/10

DS2109

REFERENCE DOCUMENTS Parallel Interface X3T10/855D Available from Global Engineering Documents 15 Inverness Way East Englewood, CO Phone 800 Fax 303

PnP SCSI Specification PnP ISA Specification PnP BIOS Specification PnP Option ROM Specification Available from Plug and Play forum on CompuServe Go plugplay .

FUNCTIONAL DESCRIPTION The DS2109 is designed to be a single chip termination subsystem for use in PnP SCSI systems, Figure When embedded on a host bus adapter or motherboard, the DS2109 can automatically sense the termination status of the SCSI bus and attach or isolate its resistors as needed to maintain proper bus termination. External and internal active termination can be provided by the DS21S07A.

DS2109 APPLICATION ENVIRONMENT Figure 1

DS2109 AUTOMATIC TERMINATOR

HOST SCSI PROTOCOL CHIP

SCSI PERIPHERAL

DEVICES

PERIPHERAL SUBSYSTEM

EXTERNAL TERMINATOR TWO DS21S07A

HIGH DENSITY CONNECTORS

SCSI EXTERNAL CABLE

SCSI INTERNAL CABLES

INTERNAL TERMINATOR TWO DS21S07A
022698 2/10

DS2109

The DS2109 consists of 3 major functional blocks, Figure 2:
• Voltage reference, terminating resistors, and isolation
switches
• Bus current sensing circuitry
• Bus ground sensing circuity

When the Bus Ground Sensing Circuitry or Bus Current Sensing Circuitry determine that the SCSI bus is prop-
erly terminated without the DS2109, the power down buffer isolates the resistors from the SCSI bus and disables the power amp, thereby placing the DS2109 in a low power mode the bus sensing circuitry always stays active . The PDO Power Down Output pin can be connected to the pin of a DS21S07A SCSI terminator for Wide SCSI configurations, Figure

DS2109 BLOCK DIAGRAM Figure 2

PDI PDE

BUS GROUND SENSING CIRCUITRY

DISABLE

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Datasheet ID: DS2109S/T&R 647167