SN74ALS990DWR

Overview

The SN74ALS990DWR is an octal D-type transparent read-back latch from the Texas Instruments ALS logic family. It features eight independent latches with tri-state outputs and a dedicated read-back input for each bit, allowing data verification without disturbing stored values. The device operates within a supply voltage range of 4.5 V to 5.5 V and supports surface-mount installation in a 20-pin SOIC package. It is designed for high-speed digital applications requiring reliable data storage and monitoring capabilities.

Feature Summary

• Provides eight independent D-type transparent latches with simultaneous data capture on clock edge
• Includes dedicated read-back inputs for each bit to verify stored data without affecting latch state
• Features tri-state outputs controlled by an enable signal for bus-oriented system designs
• Supports standard TTL input levels compatible with ALS logic family requirements

Applications

• Data acquisition systems requiring real-time status verification
• Bus interface circuits with bidirectional data flow control
• Digital storage modules needing non-destructive data inspection
• Microprocessor-based systems utilizing parallel data latching

Procurement Notes

Verify component authenticity through authorized distributors or direct manufacturer channels. Confirm RoHS compliance status and lot traceability before procurement. Check for obsolescence notices as this part may be subject to lifecycle changes. Ensure packaging specifications match assembly requirements. Validate datasheet revisions to confirm parameter consistency with design specifications.

Selection Notes

Select this component when octal latching with read-back capability is required. Compare propagation delay and output drive strength against system timing constraints. Evaluate power consumption relative to other ALS series devices. Consider package availability and thermal characteristics for PCB layout. Verify compatibility with existing logic families in the design architecture.

Part Context

Part of the Texas Instruments SN74ALS990 series, which includes variants like SN74ALS990DW and SN74ALS996DW. The ALS series offers improved speed-power product compared to standard 74LS logic. This specific variant uses a 20-lead SOIC package suitable for surface mount technology applications.

Replacement Considerations

• SN74ALS990DW (same function, different package)
• SN74ALS996DW (similar octal latch but with edge-triggered operation instead of transparent)

FAQ

What is the difference between SN74ALS990 and SN74ALS996?

The SN74ALS990 is a transparent latch that passes data directly when enabled, while the SN74ALS996 is an edge-triggered latch that captures data only on clock transitions.

How does the read-back feature work?

Each latch has a dedicated read-back input that allows the stored data to be monitored externally without affecting the current state of the latch or its output drivers.