DS2109 Datasheet, PDF (1/10 Pages) Dallas Semiconductor – Plug and Play SCSI Terminator

DS2109
DS2109
Plug and Play SCSI Terminator
FEATURES
• Fully compliant with SCSI–1, 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
PDI
1
R1
2
R2
3
R3
4
R4
5
R5
6
HS–GND
7
HS–GND
8
PDO
9
R6
10
R7
11
R8
12
R9
13
TPWR
14
28
GND
27
R18
26
R17
25
R16
24
R15
23
R14
22
TCS
21
HS–GND
20
PDE
19
R13
18
R12
17
R11
16
R10
15
V_REF
DS2109, DS2109S 28–PIN SOIC (300 MIL)
DESCRIPTION
The DS2109 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 exter-
nal device is connected to the system. The DS2109 sat-
isfies 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 drop–out regulator, 18
precise switched 110 ohm termination resistors, and
bus termination sensors into a 28–pin 300 mil SOIC
package. Active termination provides: greater immu-
nity to voltage drops on the TERMPWR (TERMination
PoWeR) line, enhanced high–level noise immunity,
intrinsic TERMPWR decoupling, and very low quies-
cent current consumption. The DS2109 contains an
output port that can control the power down pin of addi-
tional terminators (DS21S07A) for Wide SCSI applica-
tions.
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