DS21T09S+

DS21T09S+ Datasheet

DS21T09 Plug and Play SCSI Terminator

Part	Datasheet
DS21T09S+	DS21T09S+ (pdf)

Related Parts	Information
DS21T09S	DS21T09S
DS21T09S/T&R	DS21T09S/T&R

PDF Datasheet Preview
DS21T09 Plug and Play SCSI Terminator Fully compliant with SCSI-1, Fast SCSI and Ultra SCSI Compatible with Plug and Play SCSI Profile Functional drop in replacement for the DS2109 Complementary part to DS21T07 for wide SCSI 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 PDI 1 28 GND R1 2 R2 3 R3 4 R4 5 R5 6 27 R18 26 R17 25 R16 24 R15 23 R14 HS-GND 7 HS-GND 8 PDO 9 R6 10 R7 11 R8 12 R9 13 TPWR 14 22 TCS 21 HS-GND 20 PDE 19 R13 18 R12 17 R11 16 R10 15 VREF DS21T09S 28-Pin SOIC 300-mil The DS21T09 is intended for one-chip Plug and Play PnP SCSI termination. Plug and Play SCSI requires the exit-point terminator on computer motherboards or host bus adapters to automatically switch off if an external device is connected to the system. The DS21T09 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 DS21T09 will automatically be isolated from the SCSI bus thereby maintaining proper system termination. The DS21T09 integrates a low drop-out regulator, 18 precisely switched resistors, and bus termination sensors into a 28-pin, 300-mil SOIC package. Active termination provides greater immunity to voltage drops on the TERMPWR TERMination PoWeR line, enhanced high-level noise immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS21T09 contains an output port that can control the power-down pin of additional terminators DS21T07 for Wide SCSI applications. REFERENCE DOCUMENTS SCSI-2 X3.131-1994 SCSI-3 Parallel Interface X3T10/855D Available from Global Engineering Documents 15 Inverness Way East Englewood, CO 80112-5704 Phone 800 854-7179, 303 792-2181 Fax 303 792-2192 1 of 10 112099 PnP SCSI Specification PnP ISA Specification PnP BIOS Specification PnP Option ROM Specification Available from Plug and Play forum on CompuServe Go plugplay . DS21T09 FUNCTIONAL DESCRIPTION The DS21T09 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 DS21T09 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 DS21T07. DS21T09 APPLICATION ENVIRONMENT Figure 1 2 of 10 The DS21T09 consists of three major functional blocks, Figure 2: DS21T09 • Voltage reference, terminating resistors, and isolation switches • Bus current sensing circuitry • Bus ground sensing circuitry When the Bus Ground Sensing Circuitry or Bus Current Sensing Circuitry determines that the SCSI bus is properly terminated without the DS21T09, the power-down buffer isolates the resistors from the SCSI bus and disables the power amp, thereby placing the DS21T09 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 DS21T07 SCSI terminator for Wide SCSI configurations, Figure DS21T09 BLOCK DIAGRAM Figure 2 3 of 10 DS21T09 DETAILED PIN DESCRIPTION Table 1 PIN 1 2-6, 10-13, 16-19, 24-27 7, 8, 21 HS-GND TPWR VREF FCN I T P O P O I

PDF Datasheet Preview

DS21T09 Plug and Play SCSI Terminator

Fully compliant with SCSI-1, Fast SCSI and Ultra SCSI Compatible with Plug and Play SCSI Profile Functional drop in replacement for the DS2109 Complementary part to DS21T07 for wide SCSI 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

PDI 1
28 GND

R1 2 R2 3 R3 4

R4 5 R5 6
27 R18 26 R17 25 R16 24 R15 23 R14

HS-GND 7 HS-GND 8

PDO 9 R6 10 R7 11 R8 12 R9 13

TPWR 14
22 TCS 21 HS-GND 20 PDE 19 R13 18 R12 17 R11 16 R10 15 VREF

DS21T09S 28-Pin SOIC 300-mil

The DS21T09 is intended for one-chip Plug and Play PnP SCSI termination. Plug and Play SCSI requires the exit-point terminator on computer motherboards or host bus adapters to automatically switch off if an external device is connected to the system. The DS21T09 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 DS21T09 will automatically be isolated from the SCSI bus thereby maintaining proper system termination.

The DS21T09 integrates a low drop-out regulator, 18 precisely switched resistors, and bus termination sensors into a 28-pin, 300-mil SOIC package. Active termination provides greater immunity to voltage drops on the TERMPWR TERMination PoWeR line, enhanced high-level noise immunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS21T09 contains an output port that can control the power-down pin of additional terminators DS21T07 for Wide SCSI applications.

REFERENCE DOCUMENTS

SCSI-2 X3.131-1994 SCSI-3 Parallel Interface X3T10/855D Available from Global Engineering Documents 15 Inverness Way East Englewood, CO 80112-5704 Phone 800 854-7179, 303 792-2181 Fax 303 792-2192
1 of 10
112099

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

DS21T09

FUNCTIONAL DESCRIPTION

The DS21T09 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 DS21T09 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 DS21T07.

DS21T09 APPLICATION ENVIRONMENT Figure 1
2 of 10

The DS21T09 consists of three major functional blocks, Figure 2:

DS21T09
• Voltage reference, terminating resistors, and isolation switches
• Bus current sensing circuitry
• Bus ground sensing circuitry

When the Bus Ground Sensing Circuitry or Bus Current Sensing Circuitry determines that the SCSI bus is properly terminated without the DS21T09, the power-down buffer isolates the resistors from the SCSI bus and disables the power amp, thereby placing the DS21T09 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 DS21T07 SCSI terminator for Wide SCSI configurations, Figure

DS21T09 BLOCK DIAGRAM Figure 2
3 of 10

DS21T09

DETAILED PIN DESCRIPTION Table 1

PIN 1
2-6, 10-13, 16-19, 24-27 7, 8, 21

HS-GND

TPWR VREF

FCN I T

P O P O I

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Datasheet ID: DS21T09S+ 647169