DS21S07AS+T&R

Overview

The DS21S07AS+T&R is a monolithic SCSI terminator compliant with SCSI-1, Fast SCSI, and Ultra SCSI standards. It integrates a low-dropout voltage regulator and nine laser-trimmed 110Ω termination resistors with 2% tolerance. The device operates on a TERMPWR supply ranging from 4V to 5.5V within an operating temperature range of 0°C to +70°C. Packaged in a 16-pin SOIC (0.295" width), it provides active termination for nine signal lines, featuring intrinsic decoupling and hot-plug compatibility.

Feature Summary

• Integrates a bandgap reference and buffer amplifier to source at least 24mA per line when active and sink at least 200mA for actively negated signals.
• Includes a power-down mode that isolates termination resistors from the bus via an active-low control pin with an internal pullup resistor.
• Features on-board thermal shutdown circuitry to protect against overheating conditions.

Applications

• Terminating active signal lines at both ends of cable segments in SCSI systems with single-ended drivers.
• Integration into disk drives or RAID system components to ensure bus stability during hot plug operations.
• Providing enhanced noise immunity and reduced quiescent current consumption compared to passive terminators.

Procurement Notes

Verify component authenticity by checking for the lead-free marking suffix (+) and the top mark DS21T07S. Confirm the package type matches the 16-pin SOIC footprint and validate the manufacturing date code against the supplier's documentation. Ensure the ordering suffix T&R corresponds to the reel packaging format required for surface-mount assembly processes.

Selection Notes

Select this component for designs requiring compliance with SCSI-1, Fast SCSI, and Ultra SCSI specifications. It serves as a backward-compatible replacement for the DS2107 and DS2107A. Choose this part when active termination benefits, such as improved noise immunity and lower power consumption, are necessary for the specific bus architecture.

Part Context

This device belongs to the DS21S07A family of SCSI terminators manufactured by Analog Devices Inc./Maxim Integrated. The 'AS' designation indicates the 16-pin plastic SO package variant, while the '+T&R' suffix specifies the lead-free environmental status and tape-and-reel shipping configuration.

Replacement Considerations

The DS21S07A is backward compatible with the DS2107 and DS2107A. Designers replacing legacy parts should verify pin compatibility and ensure the new active termination requirements align with the existing bus design parameters.

FAQ

How does the device handle actively negated SCSI signals?

The internal buffer can sink at least 200mA to handle actively negated signals, ensuring the reference voltage (VREF) moves less than 60mV during these transitions.

What is the function of the PD pin?

The Power-Down (PD) pin is active-low. Tying it low activates power-down mode, isolating the termination resistors from the bus. Leaving it open-circuited activates the device due to an internal 50kΩ pullup resistor.

What external components are required for proper operation?

A 4.7µF capacitor must be connected between the VREF pins and ground. Additionally, either a 2.2µF or 4.7µF capacitor is recommended for decoupling the TERMPWR lines.