DS21S07A Dallas Semiconductor, DS21S07A Datasheet

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DS21S07A

Manufacturer Part Number
DS21S07A
Description
SCSI Terminator
Manufacturer
Dallas Semiconductor
Datasheet

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FEATURES
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.
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
Plug and Play SCSI Terminator
PIN ASSIGNMENT
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.
HS–GND
HS–GND
TPWR
DS2109, DS2109S 28–PIN SOIC (300 MIL)
PDO
PDI
R1
R2
R3
R4
R5
R6
R7
R8
R9
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
GND
R18
R17
R16
R15
R14
TCS
HS–GND
PDE
R13
R12
R11
R10
V
DS2109
REF
022698 1/10
DS2109

Related parts for DS21S07A

DS21S07A Summary of contents

Page 1

... 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. 022698 1/10 DS2109 ...

Page 2

... When embedded on a host bus adapter or mother- board, the DS2109 can automatically sense the ter- mination 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. SCSI EXTERNAL CABLE SCSI INTERNAL CABLES ...

Page 3

... DS2109 in a low power mode (the bus sensing circuitry always stays active). The PDO (Power Down Output) pin can be con- nected to the pin of a DS21S07A SCSI terminator for Wide SCSI configurations, Figure 8. BUS CURRENT ...

Page 4

... P Heat Sink Ground. Internally connected to the mounting pad. Should be either grounded or electronically isolated from other circuitry. 9 PDO O Power Down Output. Connect to DS21S07A for Wide SCSI applica- tions, see Figure 8. 14 TPWR P Termination Power. Connect to the SCSI TERMPWR line. Bypass with a 2.2 F capacitor, see Figures 4 and 6. ...

Page 5

BUS GROUND SENSING CIRCUIT Figure 3 PDI PDE BUS GROUND DETECT CONFIGURATION Figure 4 INTERNAL SCSI CONNECTOR 22 26 2.2 F DS2109 PDI TPWR DISABLE TERMPWR 38 GND 36 PDE V REF 4.7 F DS2109 022698 5/10 ...

Page 6

DS2109 BUS CURRENT SENSING The DS2109 has the capability to use current sensing to determine if the SCSI bus is over– or under–terminated. A series 1 ohm resistor between pads R14 and TCS is inserted into the SCSI bus (preferably ...

Page 7

BUS CURRENT SENSE CONFIGURATION Figure 6 INTERNAL SCSI CONNECTOR 26 TERMPWR DS2109 R1 TPWR 2.2 F R13 R15 V REF R18 TCS 4.7 F R14 GND BUS CURRENT SENSE TIMING DIAGRAM Figure 7 TCS COMPARATORS LATCH –RST ...

Page 8

... TERMPWR1 REF2 REF1 GND 8 9 TERMPWR2 DS21S07A 16–PIN SOIC (300 MIL) 4.7 F 022698 8/10 DS2109 ISOLATED I > 32 mA? FROM SCSI BUS? BUS No Isolated No Connected No Connected No Connected Yes Isolated Yes Isolated Yes Isolated Yes Isolated TERMINATION POWER LINE PDI 1 28 GND R18 R2 ...

Page 9

ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground Operating Temperature Storage Temperature Soldering Temperature * This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the ...

Page 10

DS2109 NOTES: 1. PDI, PDE, TCS 2. 4.00V < TERMPWR < 5.25V. 3. 0.0V < signal lines < 3.0V. 4. All signal lines = 0.0V. 5. All signal lines open. 6. Power down enabled. 7. Guaranteed by design; not production ...

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