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PDF DS21T09S Data sheet ( Hoja de datos )
| Número de pieza | DS21T09S | |
| Descripción | Plug and Play SCSI Terminator | |
| Fabricantes | Dallas Semiconducotr | |
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DS21T09
Plug and Play SCSI Terminator
FEATURES
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
HS-GND
PDO
R6
R7
R8
R9
TPWR
7
8
9
10
11
12
13
14
22 TCS
21 HS-GND
20 PDE
19 R13
18 R12
17 R11
16 R10
15 VREF
DS21T09S 28-Pin SOIC (300-mil)
DESCRIPTION
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 110Ω=termination 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
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112099
1 page  
DS21T09
BUS GROUND SENSING
If internal and external SCSI devices are connected to the SCSI bus, the DS21T09 will disconnect from
the SCSI bus according to the circuit in Figure 3. To utilize this automatic disconnect method of bus
sensing, configure the DS21T09 as shown in Figure 4. The PDI (Power Down Internal) pin should be
connected to pin 22 of the internal SCSI connector, and the PDE (Power Down External) connected to
pin 36 of the external SCSI connector.
BUS GROUND SENSING CIRCUIT Figure 3
BUS GROUND DETECT CONFIGURATION Figure 4
5 of 10
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| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet DS21T09S.PDF ] | |
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