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112099

FEATURES

Fully compliant with SCSI, SCSI-2 and SCSI-

3 standards

Conforms to EIA RS-485 standard

Provides differential termination for 9 pairs of

signal lines

Operates with SCSI signal voltages of -7 to

+12 Volts

Laser-trimmed 330 and 150-ohm termination

resistors have ±5% tolerance over full

temperature range

Switchable power-down mode

Low power down capacitance of 6 pF

24-pin plastic SOIC (DS2108S)

PIN ASSIGNMENT

DESCRIPTION

The DS2108 SCSI Terminator has been specifically designed for High Voltage Differential (HVD) SCSI

systems requiring switchable termination. The DS2108 integrates eighteen 330-ohm and nine 150-ohm

precise switched termination resistors into a monolithic IC. The surface mount SOIC package saves board

space over conventional resistor SIPs. The termination resistors can be isolated from the SCSI bus under

software or hardware control. While in the powered down mode, the DS2108 isolates the nine terminator

blocks from the bus while adding only 6 pF capacitance to each signal line of the SCSI bus.

FUNCTIONAL DESCRIPTION

The DS2108 consists of power-down circuitry, eighteen 330-ohm and nine 150-ohm termination resistors

(Figure 1). The DS2108 can be removed from the circuit by bringing the power down pin (PD) low. The

power down capacitance on the terminating resistors is 6 pF, well below the SCSI-3 allotment of 25 pF.

The DS2108 supports SCSI signal voltages of -7 to +12 volts when powered on or off. When all lines

settle into the quiescent state (no signal transitions), 56 mA is typically consumed.

Only 1 mA is

typically consumed in the powered down mode.

DS2108

Differential SCSI Switchable Terminator

www.dalsemi.com

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24

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PD

GND

R1P

R3P

R4P

R5P

R6P

R7P

R8P

R9P

GND

R2P

TPWR

R1N

R2N

R4N

R5N

R6N

R7N

R8N

R9N

TPWR

NC

R3N

DS2108S 24-Pin SOIC (300-mil)