DS2109

Plug and Play SCSI Terminator

DS2109

022698 1/10

FEATURES

SCSI

regulator

PIN ASSIGNMENT

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

PDI

R1

R2

R3

R4

R5

HS–GND

HS–GND

PDO

R6

R7

R8

R9

TPWR

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.