DS2109S

Overview

The DS2109S is a Plug and Play SCSI terminator integrated circuit manufactured by Analog Devices Inc./Maxim Integrated. It provides active termination for 18 signal lines in SCSI-1, Fast SCSI, and Ultra SCSI systems. The device integrates a low-dropout regulator, 18 precise switched 110 ohm termination resistors, and bus termination sensors within a 28-pin SOIC package. Operating conditions range from 0°C to +70°C with a supply voltage of 5V. Termination resistance tolerance is specified at 2%, and the power down capacitance is 3 pF.

Feature Summary

• Supports automatic exit-point termination isolation when external devices connect to the SCSI bus
• Integrates onboard current sensing and ground detect circuitry for bus status monitoring
• Provides active termination to enhance high-level noise immunity and reduce quiescent current consumption

Applications

• Host bus adapters requiring Plug and Play SCSI compliance
• Computer motherboards needing automatic SCSI bus termination management
• Wide SCSI configurations utilizing additional terminators like the DS21S07A

Procurement Notes

Verify component authenticity through authorized distributors or manufacturer channels. Confirm RoHS compliance status and lead times prior to ordering. Ensure storage conditions align with specified temperature ranges to maintain reliability. Review datasheet specifications for absolute maximum ratings to prevent damage during handling and installation.

Selection Notes

Select this component for systems requiring single-chip Plug and Play SCSI termination solutions. Consider the 28-pin SOIC package constraints and thermal requirements. Evaluate compatibility with existing SCSI controller chips and connector pinouts. Verify that the 110 ohm termination resistance meets system impedance matching needs.

Part Context

The DS2109 series belongs to the family of SCSI interface integrated circuits designed for parallel interface standards. It functions as an active terminator subsystem compatible with SCSI-1, Fast SCSI, and Ultra SCSI protocols. The device simplifies motherboard design by automating termination state changes based on bus connectivity.

Replacement Considerations

The DS2109 is functionally compatible with the DS21S07A. Designers may consider the DS21S07A for Wide SCSI applications where additional termination control is required via the PDO pin connection.