DS21T09

The DS21T09 is intended for one-chip Plug and Play (PnP) SCSI termination. Plug and Play SCSIrequires the exit-point terminator on computer motherboards or host bus adapters to automatically switchoff if an external device is connected to the system. The DS21T09 satisfies this requirement by offeringthe engineer a choice ofonboard current sensing circuitry or onboard ground detect circuitry. If anexternal device is connected, the DS21T09 will automatically be isolated from the SCSI bus therebymaintaining proper system termination.

The DS21T09 integrates a low drop-out regulator, 18 precisely switched 110Ω termination resistors, andbus termination sensors into a 28-pin, 300-mil SOIC package. Active termination provides: greaterimmunity to voltage drops on the TERMPWR (TERMination PoWeR) line, enhanced high-level noiseimmunity, intrinsic TERMPWR decoupling, and very low quiescent current consumption. The DS21T09contains an output port that can control the power-down pin of additional terminators (DS21T07) forWide SCSI applications.